Science Helpdesk


ESO 1. Science

Topic 1.  Vocabulary
GravityEvery object in the Universe exerts a force of attraction upon the objects around it. This force is known as gravity. The Earth is retained by the Sun because of the Sun's gravity; the Moon is retained by the Earth because of the Earth's gravity, etc.
BillionIn most English-speaking countries a billion equals one thousand million; you can write it as 109. Likewise, a trillion equals one million millions, and you can write it as 1012.
Light yearDistances in the Universe are huge, and so they are measured in huge units. A light year is a distance unit that equals about 9.5 trillion km. It is the distance covered by the light in one year.
Astronomical unitIt is another distance unit. It is the distance between the Sun and the Earth, and equals some 150 million km.
Topic 1.  Galaxies and Clusters

The Universe is about 14 billion years old, and is formed by more than 100 billion galaxies. A galaxy is a huge system of stars, interstellar gas and dust. Typical galaxies contain from ten million to one trillion stars, all orbiting a common centre of gravity. Some galaxies are elliptical shape, some are spiral, others are irregular. Galaxies are usually separated from others by distances on the order of millions of light years. Groups of galaxies gravitationally attracted between themselves are called galactic clusters.

The Solar System is located in the Milky Way galaxy, a spiral galaxy with a diameter estimated at about 100,000 light years, containing approximately 200 billion stars. The Milky Way belongs in a cluster of over 30 galaxies known as the Local Group. The galaxy of Andromeda is the nearest to the Milky Way and the biggest one in the Local Group.

The Solar System resides in one of the Milky Way's spiral arms, known as the Orion Arm, at about 27,000 light years from the galactic centre. Its speed is about 220 kilometres per second, and it completes one revolution every 226 million years.

Topic 1.  Stars

Stars are massive, glowing balls of hot gases, mostly hydrogen and helium. Some stars are alone in the sky (the Sun, the North Star), others have companions (Sirius, which is a binary star system, and Alpha Centauri, which is a ternary star system). The nearest star to the Sun is Alpha Centauri C or Proxima Centauri. The brightest star in the Northern hemisphere's night sky is Sirius.

Not all stars are the same: stars come in all sizes, brightnesses, temperatures and colours:

  • The colour of a star is due to its temperature. A blue or white star is hotter than a yellow star, which is hotter than a red star.
  • The brightness of a star depends on two factors: (a) its distance from us and (b) its luminosity: how much energy it puts out in a given time, which, in turn, depends on its size. Think on a street lamp, which puts out more light than a hand torch. That is, the street lamp is more luminous. But if that street lamp is 1 km away from you, it will not be as bright, because light intensity decreases with distance. In this case, a hand torch held 10 m away from you would be brighter than the street lamp. The same is true for stars.
Topic 1.  Constellations

Constellations are groups of stars visibly related to each other in a particular pattern. Some well known constellations contain familiar patterns of bright stars. Examples are Ursa Major (containing the Big Dipper or Plough), Orion (that resembles the figure of a hunter) and Cassiopeia (with the shape of a "W"). The stars of a constellation, although appearing to be very near, may be millions LY away one to another.

Topic 1.  The Solar System

The Solar System is the stellar system formed by the Sun and the group of celestial objects gravitationally bound to it:

  • the eight planets and their 162 known moons,
  • five dwarf planets and their six known moons, and
  • thousands of small solar system bodies (SSSB).

The Sun is the main component of the Solar System, a star that contains 99.9% of the Solar System's mass. The Sun releases enormous amounts of energy in the form of electromagnetic radiation, which includes visible radiation (light), ultraviolet radiation and infrared radiation.

The planets are the biggest objects orbiting the Sun. Their orbit is almost circular. In order of their distances from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The four inner planets are small and rocky planets; the four outer planets are gaseous giant planets with a small rocky core. All planets but the two first are orbited by natural satellites (usually called "moons"). The planets, with the exception of Earth, are named after gods and goddesses from Greco-Roman mythology. The following table shows some major magnitudes measured relative to the Earth:

Diameter (relative to the Earth)Mass (relative to the Earth)Distance to the Sun (in AU)Revolution period (in Earth's years)Rotation period (in Earth's days)Moons

The dwarf planets are also rocky objects orbiting the Sun, smaller than the planets, but bigger than asteroids. There are currently (20-sep-2008) five dwarf planets in the Solar System; the two best known of which are:

  • Ceres, formerly considered the Solar System's biggest asteroid;
  • Pluto, a trans-neptunian object formerly considered the Solar System's ninth planet;

The SSSBs comprise several types of celestial bodies, the best known of which are:

  • Asteroids = planetoids = minor planets. They're the smallest rocky bodies orbiting the Sun. Unlike planets and dwarf planets, they are not spherical, but irregularly shaped. Most of them occupy orbits between the ones of Mars and Jupiter, and make up the asteroid belt. The biggest asteroid is called Vesta.
  • Comets, very small icy trans-neptunian objects that orbit the Sun in very eccentric orbits. When a comet approaches the Sun, its icy surface begins to boil away, creating two long tails, one of gas and another of dust, which are often visible with the naked eye. Two well known comets are Halley and Hale-Bopp.
Presentation: Why the Moon?
Topic 2.  The International System of Units
[Source: Wikipedia]

The International System of Units (abbreviated SI from the French language name Système international d'unités) is the world's most widely used system of units. The SI was developed in 1960 and, with few exceptions, is used in every country in the world.

The SI base units for the seven primary quantities are:

Electric currentampereA
Amount of substancemolemol
Luminous intensitycandelacd

Symbols are written in lower case, except for symbols derived from the name of a person. For example, the unit of electric current is named after André-Marie Ampère, so its symbol is written "A", whereas the unit itself is written "ampere". The only exception is the litre, whose original symbol "l" is unsuitably similar to the numeral "1"; thus it is recommended that "L" be used instead.

Abbreviated symbols should not be pluralized: for example "25 kg", not "25 kgs".

Symbols do not have an appended period (.) unless at the end of a sentence.

A prefix may be added to units to produce a multiple of the original unit. All multiples are integer powers of ten. For example, kilo- denotes a multiple of a thousand and milli- denotes a multiple of a thousandth. The SI main prefixes are as follows:

Topic 2.  Quantities

Quantities are the measurable properties of the physical bodies. Some of the most important ones are the following:

MassIs the amount of matter in a body. Its unit in the SI is the kg.
VolumeTells how much space an object occupies. Its unit in the SI is the m3.
CapacityIs the amount of space that can be contained by a body. It is measured in L.
DensityExpresses how concentrated is the matter in a body, this is, how much matter is there in a given unit of volume in a body. It is always the same for the same type of substance, this is, it doesn't depend on the size of the object. Its unit in the SI is the kg/m3.
TemperatureIt is not a kind of energy but a measure of the amount of heat in a body. It depends on the movement of its particles: the quicker the movement, the higher the temperature. Its unit in the SI is the K, but is commonly expressed in °C or °F.
Topic 2.  Characteristics of Some of the Common Chemical Elements Found in the Earth's Crust
SymbolAtomic numberAtomic mass% in continental crustRequired for Life
Mind Map: Calcium
Topic 4.  The Water Cycle
What is it?

The water cycle, also known as the hydrological cycle, is the circulation of water between the different compartments or reservoirs of the Earth's Hydrosphere, involving changes in the physical state of water between liquid, solid, and gaseous phases. The water cycle is powered by the Sun's energy and the Earth's gravity.

The Earth's water cycle involves the following main physical processes:
EvaporationIs the transfer of water from bodies of surface water into the atmosphere. This transfer involves a change in the physical state of water from liquid to gaseous phases, powered mainly by the solar radiation. 90% of atmospheric water comes from evaporation.
EvapotranspirationIs the transfer of water from living beings into the atmosphere. This transfer involves a change in the physical state of water from liquid to gaseous phases, powered mainly by the solar radiation and the heat released by the metabolism of the living beings. 10% of atmospheric water comes from evapotranspiration.
CondensationIt takes place when water vapour in the air accumulates to form liquid water droplets in clouds and fog.
PrecipitationIs atmospheric moisture that has previously condensed (or solidified), falling to the surface of the Earth. This happens mostly as rainfall, but also as snow, hail, or fog.
Surface runoffIncludes the variety of ways by which land surface water moves down slope to the oceans: snowmelt runoff to streams, streamflow, riverflow… Water flowing in streams and rivers may be delayed for a time in lakes. Much of the precipitated water evaporates before reaching the ocean or infiltrates into the soil.
InfiltrationIs the transition of land surface water into the ground. The infiltration rate depends on soil or rock permeability. Infiltrated water may become part of the soil moisture or accumulate in aquifers: in this case it is called groundwater.
Groundwater flowIncludes the movement of groundwater in aquifers. Aquifers tend to move slowly, so the water may return as surface water (into rivers, lagoons, oceans or through springs) after thousands of years in some cases. Water returns to the land surface at lower elevation than where it infiltrated.
Absorption or drinkingAre the ways in which soil moisture or surface water is taken in by living beings.
Volume of water stored in the water cycle's reservoirs:
Volume (106 km3)Percent of total
Seas and oceans137097.25
Ice caps, glaciers and snow covers292
Soil moisture0.0650.005
Streams and rivers0.00170.0001
Living beings0.00060.00004
Average reservoir residence times:
Groundwater: deep10,000 years
Seas and oceans3,200 years
Groundwater: shallow100 to 200 years
Lakes50 to 100 years
Ice caps and glaciers20 to 100 years
Streams and rivers2 to 6 months
Seasonal snow covers2 to 6 months
Soil moisture1 to 2 months
Atmosphere9 days
Topic 5.  Rock Grains

Sedimentary rocks can be made up of clasts or detritus (rock grains) weathered from other rocks by river waters, wind, coastal sea waters, glaciers, living beings, etc. This kind of sedimentary rocks are called detrital rocks.

They're classified upon the grains that they are made up of. First up, grains may be all the same size, uniform, as in a sandstone, or different sizes, as in a conglomerate. Secondly, grains may be bigger or smaller. The following table shows roughly how rock grains are classified upon their size:

Clay< 0.004 mm
Silt< 0.06 mm
Sand< 2 mm
Gravel< 6 cm
Cobble< 25 cm
Boulders> 25 cm
Topic 5.  Mineral Lustre

The term lustre refers to the appearance of a mineral surface in reflected light. The main types of mineral lustre are the following:

VitreousTranslucentQuartz, Halite, Olivine
ResinousTranslucentYellow and red sphalerite varieties
GreasyVariableMilky quartz
SilkyVariableFibrous gypsum
PearlyPoorly translucentOrthoclase, Mica aggregates
Dull metallicOpaqueCinnabar aggregates
MetallicOpaquePyrite, Chalcopyrite, Magnetite
Topic 6.  Vocabulary
Levels of organization Matter in living beings is organized in a series of levels of increasing complexity, ranging from the atomic level to the multicellular level with tissues and organs. Only plants and animals reach the highest one, whereas bacteria stay at the unicellular level.
Bioelements The most abundant chemical elements in a livig being, which are not much the same ones that you can find in a rock. The top six are C, H, O, N, P, S, and they're called the primary bioelements.
Biomolecules The most abundant types of molecules in living beings are always the same ones, no matter if it is a bacterium or a human. They may be organic (with a skeleton of carbon atoms: carbohydrates, lipids, proteins, nucleic acids) or inorganic (without it: water, mineral salts).
Cell The basic unit of Life. If something is not made up of cells, then it is not a living being. Cells can reproduce and interact with their environment (exchanginng matter and energy, and being able to notice its features). All cells have a plasma membrane, some organelles and genetic material.
Prokaryotic / Eukaryotic Cells without a real nucleus (no nuclear membrane) are the first type. Cells with a real nucleus (genetic material enclosed in a nuclear membrane) are the second type. Bacteria and Archaea are prokayotes; Algae, Protozoa, Fungi, Plants and Animals are eukaryotes.
Tissues In multicellular beings there may be different types of cells, each type being specialized in an specific function, and having the specific shape that allows them to fulfill that function the best. Each of those types is called a cellular tissue; examples are the vascular tissue (plants) or the blood tissue (animals). One tissue may have several subtypes of cells (e.g. white blood cells and red blood cells).
Organs / Organ Systems There are some tasks in a multicellular being that must be achieved by cells of different kinds working together (such as pumping blood throughout the human body). In this case, cells of different tissues gather and make up an organ (epithelial, connective, muscle and adipose cells make up the heart). Several organs working together in a common general task make up an organ system (the heart and the blood vessels make up the circulatory system).
Autotrophs / Heterotrophs Or Producers and Consumers. The former don't feed off other living beings: they transform inorganic substances to produce the organic substances they need; plants and algae are autotrophs. The latter need to feed on other beings and then transform the organic substances they have eaten into their own organic substances (i.e.: your proteins come partly from the proteins in that beef-steak you ate yesterday); animals, fungi and protozoa are heterotrophs.
Topic 6.  Differences between Prokaryotic and Eukaryotic Cells
Size (diameter)1-10 µm10-100 µm
Number of organellesFewMany
OccurrenceBacteria & ArchaeaProtozoa, Algae, Fungi, Plants, Animals
Topic 6.  The Five Kingdoms

This is not the most modern way of classification of living beings, but still proves to be quite useful to understand and organise the huge diversity of the living beings:

Groups of organismsType of cellsOrganizationNutrition
MoneraBacteria and archaeaProkaryoticUnicellularBoth
 AlgaeEukaryoticUnicellular to multicellularAutotrophic
FungiYeasts, moulds, mushroomsEukaryoticUnicellular to multicellularHeterotrophic
PlantMosses, ferns, flowering plantsEukaryoticMulticellularAutotrophic
Mind Map: Common features to all cells
Topic 8.  Vocabulary: Types of Plants
BryophytesTerrestrial plants that lack a vascular system, are dependent on environmental moisture for reproductive and nutritive functions, and that disperse spores for reproduction. The group includes mosses, liverworts and hornworts.
TracheophytesPlants with a vascular system that helps them to stay upright and transports the sap, the plants' nutritive liquid mixture. The vascular system is made up of the vascular tissues xylem and phloem. The group includes pteridophytes and flowering plants.
PteridophytesTerrestrial plants with a vascular system that are dependent on environmental moisture for reproductive and nutritive functions and that disperse spores for reproduction. The group includes ferns and horsetails.
Flowering plantsOr seed plants. Plants with a vascular system that are not dependent on environmental moisture for reproductive and nutritive functions and that disperse seeds produced inside flowers for reproduction. The group includes gymnosperms and angiosperms.
GymnospermsVascular flowering plants in which the ovules are not protected by an ovary. As they don't have ovaries, they don't have fruits neither, but cones instead. Their flowers are not very conspicuous, as they lack petals and sepals. They are woody and most of them belong in the conifers (such as the pines, cedar-trees, fir-trees, spruces and cypresses).
AngiospermsA vascular flowering plant in which the ovules are enclosed inside protective ovaries and the seeds inside fruits. They use to have well-visible flowers that, when complete, are made up of sepals, petals, stamens and pistils. They can be herbaceous (like the poppy) or woody (like the oak).
Topic 8.  Vocabulary: Leaves
LeafIt is the photosynthesis and transpiration organ in plants. Its two main parts are usually the petiole (a slender stem that supports the blade) and the blade (the green and usually flat area, with a midrib and secondary veins). When they have one only blade, they are called "simple leaves", whereas if they have several leaflets (each one resembling a single leaf with its petiole and its blade) they are called "compound leaves". You can tell whether something is a leaf or just a leaflet by watching the stipules: two membranes that are always at the base of the leaf, and never in the base of a leaflet. Holm-oaks have simple leaves, while ash-trees have compound leaves.
PalmateCompound leaves can be palmate, resembling a hand, with the leaflets outspread.
PinnateCompound leaves can be pinnate, resembling a feather, with the leaflets arranged on both sides of a central axis.
WhorlTwo or more leaves or other structures surrounding a stem at the same point.
BractA leaf associated with the flowers or inflorescences of a plant. Bracts are usually different in appearance to the other leaves on the plant. The lime-tree has very conspicuous elongated, narrow and pale-green bracts.
InvolucreA whorl of bracts, often cup-like, at the base of a flower, an inflorescence or a fruit. Daisies have involucres at the base of their inflorescences, and oaks have involucres at the base of the acorns.
DeciduousTo fall off or shed seasonally; usually refers to the leaves of a plant. It's opposite to evergreen. A poplar has deciduous leaves, while a holm-oak is evergreen.
Mind Map: Dicotomous key of leaves
Mind Map: Mammals

ESO 2. Science

Topic 1.  Forces

A force is a push, a pull or a twist which is exerted in an specific direction. Forces are measured with balances. The small ones can be measured with a spring balance (= forcemeter). Their values are expressed in newtons (N).

Forces can have several effects upon the objects: they can (a) change their shape, (b) change their direction if they're moving; and (c) change their speed by slowing them down, speeding them up or putting them into movement.

The movement of an object in any medium (except the vacuum) produces automatically a force in exactly the opposite direction: this is the force of friction (of the air, the water, the ground). This force slows down the moving object and tends to ultimately stop it. It requires the moving object to use more energy to overcome the friction and reach the wanted speed.

But the force of friction doesn't only imply a higher use of energy: it can also be useful. For instance: it is the force of friction generated when you push your feet backwards against the ground, the one that, in return, pushes you forward when you are trying to run. And it is the force of friction done by a rubber pad against a wheel the one that makes a bike or a car slow down when you press the brake.

When two forces are acting on an object in opposite directions they can...

  • Be equal in size: these are balanced forces and cancel each other out, i.e., the resultant force is zero. One example is when the force of friction of the air and the ground (called drag) cancel out the driving force of a car (produced by the engine thrust). In this case the car moves at a steady speed, called terminal speed. Another example is when you are standing still on the floor: you know that the force of gravity is always pulling you downwards, so to keep you there, instead of being swallowed by the Earth, the floor must be doing a force upon you exactly the same size than the gravity force, but in the opposite direction.
  • Be different in size: these are unbalanced forces and do not cancel each other out. They change the motion of the object, which (a) will start to move in the direction of the bigger force, if the object was still; (b) will move faster, if the object was moving in the direction of the bigger force; (c) will slow down, if the object was moving opposite to the bigger force.
Topic 1.  Mass, Weight and Gravity

Gravity is a force. It is the force that pulls objects together. It is bigger the bigger and the closer these objects are. The gravity force between two small objects or between two very distant stars isn't perceptible, but it is clearly noticeable between the Earth and every object on its surface, because every object has a weight, and this is the force with which the Earth pulls any near object downwards.

Therefore, your weight will be bigger (a) the closer you are to the centre of gravity of the Earth (which is the centre of the Earth) and (b) the bigger you are, or more exactly, the more mass you have. Your mass is the amount of matter you have (atoms and molecules), and with the same mass you can have different weights: your weight will be smaller in the stratosphere, because you are further away of the Earth's centre of gravity, or in Mars, because it has about 8 times less mass than the Earth: in both cases the gravity acting on you is smaller than in the surface of the Earth. But your weight would be bigger in Saturn or Jupiter, for the opposite reason: there is a bigger gravity acting on you now.

As weight is a force, it is measured in newtons. In the Earth, at sea level, the numeric value of your weight, in newtons, is roughly ten times your mass. In the Moon, you have to multiply your mass by only 1.7 to find how many newtons you weight. And in the outer space, far away from the gravitational action of any celestial body, your weight would be almost zero. In the three cases you would have exactly the same mass.

Topic 1.  Changes of Position

Speed is the rate at which an object covers a distance. You calculate it dividing the space covered by an object, by the time taken on it. Its unit in the SI is m/s.

Distance-time graphs are useful to represent the variation of the distance covered by an object in every unit of time, i. e., they are useful to represent visually the speed of an object. When the line in the graph shows a steady slope (when it is a straight line), the object has a steady speed; otherwise, the graph will indicate some sort of positive or negative acceleration. Also, a steep slope will express a higher speed than a gentle slope. And a straight horizontal line will show that the object is stopped.

If you plot a speed-time graph you will represent visually the acceleration of an object. In this case, a straight horizontal line shows acceleration zero, i. e., the object is moving at a steady speed. A straight line with a positive slope will represent an object speeding up. And a straight line with a negative slope will represent a negative acceleration: the object is slowing down. If you want to represent a stopped object in this kind of graph, you have to draw a straight line along the X axis.

Topic 2.  Forms of Energy
KineticIt is the kind of energy that results from the movement of a body. The greater the speed and the mass of a body, the more the kinetic energy it has. It is a type of mechanical energy.
Gravitational potentialIt is the kind of energy that results from the position of a body with regards to the centre of gravity of the planet (or other type of celestial body) it is in. The greater the altitude, the mass of the body and the mass of the planet, the more the gravitational potential energy it has. It is a type of mechanical energy.
Elastic potentialIt is the kind of energy that results from the deformation of an elastic body. The greater the deformation, the more the tendency of the object to get back to its original shape, and so, the more the elastic potential energy it has. It is a type of mechanical energy.
ChemicalIt is the kind of energy that makes up the chemical bonds in the molecules, this is, the kind of energy that keeps the atoms together in a molecule.
ElectricIt is the kind of energy that shows up when the electrons of a group of atoms move in an specific direction, as in an electric current: the electrons of the copper threads move continuously from one end to the other.
NuclearDifferent to electrons, which are fairly easy to detach from their atoms, the protons and the neutrons of the nucleus of an atom are very difficult to separate. The nuclear energy is the kind of energy stored in those very powerful forces that keep together the particles of an atom's nucleus.
LightLight, and the other types of electromagnetic radiations (infrared, ultraviolet, etc.), is a type of energy transmitted by waves.
ThermalOr heat. It is a form of energy associated with the motion of atoms or molecules in a body: the quicker they move, the greater the amount of heat that that body contains. Heat shows up as a measurable property of the bodies: the temperature.
Topic 2.  Sources of Energy
FoodsIt is the kind of energy source that heterotroph living beings (or consumers) use. We use the chemical energy contained in the food molecules (the nutrients), and although all the nutrients have chemical energy (because they are molecules and have chemical bonds), the living beings get most of the energy they need from just carbohydrates and lipids, so you are more likely to obtain energy from pasta (rich in carbohydrates) than from chicken meat (rich in proteins).
Fossil fuelsCoal, oil (or petroleum) and natural gas. They are called fossil fuels because they come from the buried and highly transformed remains of organisms that lived in the past (plankton for natural gas and oil, woody ferns for coal). They are mixtures of molecules called hydrocarbons (such as the octane of the petrol or gasoline), and they are widely used as fuels because the chemical energy of the hydrocarbons is transformed into large amounts of heat when the hydrocarbons are ignited.
NuclearIt takes advantage of the large amounts of heat released when the nucleus of an atom is broken. This is achieved by making lonely neutrons strike the nuclei of atoms of uranium or plutonium, thus making two or three neutrons beeing expelled away from bombarded nuclei, along with a lot of heat, that can later be used in a nuclear power plant to produce electricity.
BiomassBurning certain structures of living beings that are rich in chemical energy (such as the wood or the peat) also releases great amounts of heat that can be harnessed by humans with several purposes, that range from heating a house to producing electricity in a biomass power plant.
AeolicThe kinetic energy of the moving air can be used by humans: in a windmill to grind flour, in an aerogenerator to produce electricity, etc…
HydraulicThe kinetic energy of a water current (such as a river) can also be used for similar purposes, for instance in a watermill or in a hydroelectric power station.
SolarThe energy contained in the light radiations can be used, for instance, to heat water for domestic supply, or to produce electricity in a solar field.
Topic 2.  Power Plants

The goal of power plants is to produce electricity that is later dumped into the general supply network. That electricity is produced by an electrical generator driven by a turbine, in all cases. The differences between the several types of power plants come with the way in which that turbine is moved:

  • In the hydroelectric power stations, it is the water flow of a river what moves the turbine.
  • In an aerogenerator it is the wind what moves the turbine (which consists of a set of three big blades).
  • In the rest of the cases it is water vapour at a very high pressure what moves the turbine. That water vapour is produced by heating water, and the heat can come from…
    • igniting coal or other fossil fuels or biomass (in thermal power plants);
    • breaking nuclei of uranium or plutonium (in nuclear power plants).

This way, the production of heat in a power plant goes through a series of stages in which a transfer and a transformation of energy take place. The following diagram summarizes what happens in a coal-fueled thermal power plant:

  • Chemical energy in the coal -> Thermal energy in the water vapour -> Kinetic energy in the turbine -> Electric energy in the generator and to the supply network wires
Mind Map: Energy
Topic 3.  Comparison of Temperature Scales
[Source: Wikipedia]
 Kelvin (K)Celsius (°C)Fahrenheit (°F)
Absolute zero0-273.15-459.67
Lowest recorded natural temperature on Earth
(Vostok, Antarctica - July 21, 1983)
Water freezes (at standard pressure)273.15032
Average surface temperature on Earth2881559
Average human body temperature309.9536.898.24
Highest recorded surface temperature on Earth
(Al 'Aziziyah, Libya - September 13, 1922)
Water boils (at standard pressure)373.133999.9839211.97102
Titanium melts194116683034
The surface of the Sun580055269980
Topic 6.  Physical Changes

Physical changes are those in which the substances that make up a physical body remain the same when the body undergoes a change.

A physical change can be produced…

  • When you apply a force to an object, as when you crumble a piece of paper with your hand;
  • When you give or take energy to/from an object, as when you heat up or cool down water.

Some examples of physical changes are…

  • A change of state, such as the condensation of water;
  • A change of temperature, as the cooling down of food inside the fridge;
  • A change in the shape, as when you shatter mom's favourite china vase;
  • A change in the amount or type of energy in an object: so happens when you drop a stone to the floor.
Topic 6.  Chemical Changes

Chemical changes (or chemical reactions) are those that transform some chemical/s into new other chemical/s.

They normally occur when different substances, prone to react between them, are put into contact. And so, when iron (Fe) and oxygen (O2) are put together, they will combine and disappear to form a new chemical: rust (Fe2O3). But the wine and the nitrogen (kept in the upper part of the bottles of wine) will never react, allowing the wine to preserve its properties over time. Not all chemicals will react when put into contact.

The initial molecules that react in a chemical reaction are called reactants, and the final resulting molecules are called products. In the previous reaction, the oxygen and the iron are the reactants, whereas the rust is the only product.

Some chemical changes imply a loss of energy, i.e., they are exothermic, because they release energy (usually heat) to the environment. Some other chemical changes are endothermic, they absorb energy from the environment, and the products will have a greater amount of energy than the reactants.

Nevertheless, most chemical reactions, either exothermic or endothermic, require an initial contribution of external energy to take place. If you want a piece of paper to combine with the atmospheric oxygen and go into combustion, you need to heat up the paper (what you usually do with a flame). But during the reaction, the paper releases a lot of energy (heat, light and even sound), so the reaction is exothermic: the paper and the oxygen had more energy than the ashes, the smoke, the CO2 and the water vapour produced.

Quite often, chemical changes can be noticed by some conspicuous events, such as…

  • A change in the temperature, as in any combustion;
  • A change in the colour, as in the rusting of iron;
  • The formation of bubbles, as when the calcite (CaCO3) reacts with hydrochloric acid (HCl);
  • A change in the volume, as in baking bread;
  • Etc.

Most chemical changes are irreversible: they can't be undone (e.g. a combustion), whereas most physical changes are reversible (e.g. the condensation of water).

Topic 6.  Chemical Equations

Chemical equations are the way by which chemical reactions are represented. To the left you write the formulas of the reactants (either elements, molecules or crystals) and to the right, the formulas of the products. In between, you draw an arrow that represents the direction of the change: from the reactants to the products. In case of a reversible reaction, you must draw a double arrow.

One example would be the following:

  • 3 H2 + N2 → 2 NH3

The number of molecules of each type is represented with a coefficient to the left of the molecule. The number of atoms for each kind of molecule is represented by a subindex to the right of its chemical symbol (nothing when it's just one). Thus, you can see that in the equation above we have six atoms of hydrogen and two of nitrogen in each side. This is because in a chemical reaction, neither the chemical elements, nor the number of atoms of each chemical element change. What changes is the arrangement of those atoms because a chemical change actually consists of the breaking down of some chemical bonds and the formation of some new chemical bonds.

The following chemical equation does not represent any real chemical reaction, because there aren't exactly the same atoms in each side of the equation:

  • H2 + N2 → NH3

Also, as the atoms of the reactants have to be the same as the atoms of the products, the overall mass does not change during a chemical reaction.

Balancing a chemical equation means writing the right coefficients to the right of each molecular species, to ensure that the number of each type of atoms (and so, the overall mass) remains the same along the equation.

Topic 6.  Chemical Reactions of Metals
Metals with oxygen and water

Metals react with oxygen and water depending on their reactivity. This means that some are highly reactive, some others are moderately reactive, and some others are very little reactive or even nothing at all. The following list shows the reactivity of some common metals: K > Na > Ca > Mg > Al > Zn > Fe > Sn > Pb > Cu > Ag > Au > Pt.

This way, while potassium reacts violently with O2, iron forms rust (Fe2O3), silver slowly tarnishes (forming Ag2O), and gold does not react at all and preserves its properties forever.

Likewise, as combustions are oxidations boosted by heat, the behaviour of metals when they are heated varies: some burn (Mg) while others just rust (Cu).

Metals with acids

Metals react with acids forming hydrogen gas (H2) and a salt. This reaction consists of the displacement of the hydrogen of the gas by the metal, as this one is more reactive than the hydrogen.

One example is sodium reacting with hydrochloric acid to form sodium chloride (table salt) and hydrogen:

  • Na + HCl → NaCl + H2

This type of reactions can be tested by testing the formation of H2, which is a gas that is able to put out the flame of a match.

Displacement of metals by metals

As some metals are more reactive than others, the more reactive metals can displace the less reactive metals from their compounds. For instance: magnesium is more reactive than iron, and so it can displace the iron from the ferric oxide:

  • 3 Mg + Fe2O3 → 3 MgO + 2 Fe

For the same reason, platinum would never displace any other metal from its compounds, as it is the least reactive metal of all.

These type of reactions are useful to purify metals that are rarely found in pure state in nature. This is the case of iron, that usually occurs forming the minerals hematite (Fe2O3) and magnetite (Fe3O4). Aluminium can be used to displace iron from its oxides, and thus, purify it:

  • 2 Al + Fe2O3 → Al2O3 + 2 Fe
Topic 6.  Acids, Alkalis and Salts
Acids and alkalis

Acids and alkalis are common everyday substances, such as acetic acid (in vinegar), citric acid (in lemon juice), caustic soda (lye, NaOH) or bicarbonate of soda (baking soda).

Acids and alkalis have a very different behaviour in solution: while acids release protons (H+), alkalis sequestrate the protons. The amount of free protons is measured with the pH scale: the greater the amount of free protons, the lower the pH, and the lower the amount of free protons, the higher the pH. Very acidic solutions have a pH of 1, whilst very alkaline solutions have a pH of 14. Neutral solutions and distilled water, neither acidic nor alkaline, have a pH of 7. Salts make neutral solutions; such is the case of a solution of table salt in water.

Indicators, such as litmus paper or a solution of phenolphthalein, can tell us whether a solution is acidic or alkaline: litmus paper or litmus solution will turn red in an acidic solution, and blue in an alkaline solution. Universal indicator is more precise, though: it is a mixture of dyes that can be present in paper strips or in solutions, and it yields a wide range of colours for the whole pH scale: from red (very acidic solutions) to green (neutral solutions) and to purple (very alkaline solutions).

Reactions between acids and bases

Alkalis are soluble substances that belong to a group of chemicals called bases. Bases react with acids producing a salt and water. These are called neutralisation reactions, as both the acid and the base "disappear" to form a salt, which gives a neutral solution

Some examples of everyday neutralisation reactions are the following:

  • Treating bee stings (acidic) with sodium bicarbonate (a base);
  • Treating wasp stings (alkaline) with vinegar (that contains acetic acid);
  • Upping the pH of an acidic soil with lime (CaOH, an alkali);
  • Neutralising the excess of HCl that your stomach produces during digestion with antacids such as baking soda (a base).

The reactions between acids and bases can produce a wide range of different salts. For example:

  • Salts of sulphuric acid are called sulphates:
  •     H2SO4 (sulphuric acid) + 2 NaOH (caustic soda) → Na2SO4 (sodium sulphate) + 2 H2O
  • Salts of nitric acid are called nitrates:
  •     HNO3 (nitric acid) + NaOH (caustic soda) → NaNO3 (sodium nitrate) + H2O
  • Salts of hydrochloric acid are called chlorides:
  •     2 HCl (hydrochloric acid) + CaCO3 (calcium carbonate) → CaCl2 (calcium chloride) + H2O + CO2
Topic 7.  The Vital Functions

Living matter is the one able to carry out the three so called vital functions:

  • Nutrition, which consists of taking in matter and energy in order to grow, survive and reproduce; waste matter and waste energy are produced as by-products. If a living being feeds directly off other living beings (such as animals, fungi and protozoa) it is called a consumer or heterotroph; but if it takes the matter and the energy that it needs from the inert matter (such as plants and algae) then it is a consumer or autotroph. Another way to express this difference is that consumers take in both organic and inorganic molecules, while the producers only feed on inorganic substances.
  • Interaction is (a) the ability to perceive what is going on in both the environment and the inside of the organism itself, and (b) the ability to produce responses coherent with the information that was perceived. It usually goes as follows: an stimulus is perceived by a receptor → a control centre analyses the stimulus and generates a response order → an effector performs the response.
  • Reproduction, the ability to produce living beings similar to the parental organisms. It may be sexual (when there is only one parental organism, as in bacteria) or sexual (when two different types of individuals, male and female, are required).

Every living being, and every cell in the multicellular living beings, is able to carry out these three vital functions.

Mind Map: What living beings have in common
Mind Map: The Cell
Topic 10.  Vocabulary: Flowers and Sexual Reproduction in Plants
Perfect flowersOr hermaphrodite flowers. They have both functional male parts (stamens capable of producing pollen) and functional female parts (pistil capable of producing seeds).
Staminate flowersStaminate (or "male") flowers are ones which have functional stamens, capable of producing pollen, but either have no ovary at all, or an ovary which is not fertile.
Pistillate flowersPistillate (or "female") flowers are ones which have a functional pistil, capable of producing seeds, but either have no stamens at all, or have stamens with anthers that are incapable of producing pollen.
DioeciousSaid of a plant species which has some individuals which bear only staminate flowers, and some which bear only pistillate flowers, and there are no perfect flowers. These are the species that are commonly referred to as having male and female plants. Willows and poplars are dioecius.
MonoeciousSaid of a plant species in which all individuals are hermaphrodites. This can be (a) because all the flowers in each individual are hermaphrodite (as in most cases) or (b) because all individuals bear both staminate and pistillate flowers (as in oaks, with male flowers in catkins, producing pollen, and female flowers on the stems, producing acorns).
PistilThe female reproductive organ of the flower, composed of a stigma, a style, and an ovary. Pistils are made of one carpel or more than one assembled carpels.
StigmaThe top part of the pistil, where pollen grains are received.
OvaryIn angiosperms, the protective structure that holds the ovules and surrounds the seed. After fertilization, it develops into a fruit.
OvuleCase-like structure that contains the female gamete in the flowering plants. After fertilization, it develops into a seed.
Pollen GrainsStructures that contain the male sex gametes in the flowering plants; they are meant to fertilize the ovules; they are produced in the anthers of the stamens.
Pollen TubeThe outgrowth of a pollen grain that creates a path through the pistil in order to penetrate to the ovules.
Cross-pollinationThe process, occurring in most angiosperms, by which the pollen grains of one plant fertilize ovules of another.
Self-pollinationThe process by which the pollen grains of one plant fertilize ovules of the same plant.
Topic 10.  Vocabulary: Asexual Reproduction in Plants
Vegetative PropagationA form of asexual reproduction in which plants produce clones of themselves, which then develop into independent plants. The main types are by fragmentation, by bulbs, by tubers, by runners and by grafting.
FragmentationWhen a severed plant part develops into a whole new plant.
BulbRoughly spherical underground bud containing additional buds that can develop asexually into new plants.
TuberFleshy underground storage structure, composed of an enlarged portion of the stem, that has on its surface buds (called "scale leaves") capable of producing new plants.
Runner / StolonSlender horizontal stem that can give rise, via specialized nodes, to new plants.
GraftingAn artificial form of vegetative propagation in which parts of two young plants are joined together, first by artificial means and then by tissue regeneration.
ScionTwig or bud that is grafted onto a plant with roots (called the stock) and develops into a new shoot system.
StockPlant with a root system onto which a twig or bud from another plant (called a scion) is grafted.
Topic 11.  Basic Concepts
The Ecosystems

One ecosystem is any area that happens to have an specific set of features (living species and physical-chemical conditions) that make it significantly different from its surroundings. Thus, a forest is an ecosystem, but a lagoon or a puddle of water in that forest, are themselves ecosystems too. A city is also an ecosystem: a man-made ecosystem.

The limits of many ecosystems are difficult to define. For instance, a lagoon in a forest can be fed with water from an aquifer that extends throughout an area much bigger than the forest itself, and that also feeds with water the farm-land that surrounds the forest. This way, the lagoon, the forest and the farm-land are connected. Ecosystems are not isolated in Nature: there are connections and transitional areas between them.

When an ecologist tries to describe an ecosystem, he/she has to describe the following sorts of facts:

  • The set of living species in it, that is, the biocenosis. For instance, in a forest there could be pines, oaks, mice, doves, butterflies, kites, ants…
  • The set of physical and chemical conditions, that is, the biotope. In a forest: the average temperature in the coldest month, the average temperature in the hottest month, the rainfall rate, the kind of salts that exist in the soil…
  • The relationships between the living species: the pines holding the nests that doves make, the kites eating the mice, the mushrooms feeding on the fallen leaves…
  • The relationships between the physical-chemical conditions: how temperatures alter the soil's humidity through evaporation, how wind wears away soil particles…
  • The relationships between the physical-chemical conditions and the living species: the way in which the animal activity is affected by the day-night cycle, the way in which temperature affects the loss of water vapour by plants through evapotranspiration, the way plants retain the soil particles with their roots and prevent them from being worn away by the wind, the way in which the decomposition of fallen leaves or dead animals adds new salts and minerals to the soil…
The Ecosphere

Every ecosystem can have other ecosystems inside of it. The Earth itself is one ecosystem and comprises all the other ecosystems. The Ecosphere is the name we give to our planet when we think of it as an ecosystem, and it has a biotope and a biocenosis. The biotope of the Ecosphere is made up by the Geosphere, the Hydrosphere and the Atmosphere. The biocenosis of the Ecosphere is called Biosphere, and comprises all the living beings of the Earth.

The Biomes

If we wanted to split the Ecosphere in the biggest possible ecosystems, we would split it into the biomes. A biome is a large ecosystem made up of all the ecosystems belonging to the same climatic zone. There are, for instance, the tropical rainforest biome, the mediterranean forest biome and the desert biome.

ESO 3. Biology and Geology

Topic 1.  Levels of Organisation in Living Beings

Living beings are formed by clusters of matter increasingly bigger and complex. These clusters of matter are classified in levels: every new level is more complex than the previous one. The simplest organisms (bacteria, protozoa, unicellular algae and yeasts) only reach the cellular level, but the more sofisticated ones also have tissues, organs and systems of organs.

BioelementsC, H, O, N, P, S
BiomoleculesCarbohydrates, proteins, lipids, vitamins, nucleic acids, water, mineral salts
CellsSperm cell, palisade cell, muscular cell, neurone…
TissuesMuscle tissue, nerve tissue, blood…
OrgansBrachial biceps, heart, brain, leaf, root…
Systems of organsDigestive system, nervous system, circulatory system, skeleton…
ApparatusMotor apparatus
Multicellular organismA person, a cat, a fungus, a black poplar…
Topic 1.  Bioelements and Biomolecules

The bioelements are most abundant chemical elements in a livig being, which are not much the same ones that you can find in a rock or in the air. The top six are C, H, O, N, P, S, and they're called primary bioelements.

The molecules that can be found in all living beings, from the simplest bacterium to the most complex animal, are called biomolecules, the molecules of Life. There are two types:

  • Organic: Carbohydrates, proteins, lipids, vitamins and nucleic acids. They all have an inner skeleton built mainly with carbon atoms, which allows for a really large size. The organic biomolecules can only be produced by living beings, if we discard artificial synthesis. This is, they can not be produced by geological or atmospheric processes, for instance.
  • Inorganic: Water and mineral salts. They don't have an inner skeleton of carbon atoms and can be produced in non-biological processes.
Topic 1.  Cells

All living beings are made up of complex structures called cells. Cells are made up of billions of biomolecules working together. Viruses are not regarded as living beings because they are not made up of cells.

Living beings can be (a) unicellular: made up of just one cell (bacteria, protozoa, many algae, yeasts); and (b) multicellular: made up of more than one cell: (some algae, most fungi, plants and animals).

All cells are able to perform the three vital functions: (a) they reproduce, quite usually by mitosis, a process that yields two daughter cells with almost identical genetic material; (b) they interact with their environment, giving responses to specific stimuli, as when a white blood cell is able to detect and destroy a bacterium; and (c) they feed, meaning that they are able to exchange matter and energy with their environment, as when a human cell takes oxygen from the blood and releases carbon dioxide.

All the cells have (a) a cell membrane, which is the cellular envelope, (b) a cytoplasm with organelles, which are specialized cell compartments where specific functions are fulfilled, and (c) genetic material, that carries the instructions that allow both the cellular work and its self-construction.

There are two main kinds of cells: (a) the cells of the bacteria and archaea have no real nucleus: they are said to be prokaryotic; (b) the cells of all the other living beings (algae, protozoa, fungi, plants and animals) have their genetic material separated from the cytoplasm by a nuclear membrane: they are said to be eukaryotic.

The cells of the plants can be easily distinguished from those of the animals because (a) they have a semi-rigid cell wall, made of cellulose, surrounding the cell membrane, that usually gives the cell a polyhedral shape; (b) they have one kind of organelles, called chloroplasts, where sunlight energy is used to start building their own organic substances through a chemical process called photosynthesis; (c) they use to have one or a few big vacuoles that contain sap (instead of lots of smaller ones without sap) which normally push the nucleus out to the periphery of the cell; and (d) although they have equivalent structures, they lack centrosomes, the organelles that control the arrangement of the chromosomes during mitosis in an animal cell.

Topic 1.  Common Structures in Eukaryotic Cells
Description Function Where
Cell wall Outermost layer of a plant cell composed of cellulose and other complex carbohydrates. Helps to support and protect the cell. P
Flagella (flagellum) Long and scarce threadlike structures that extend from the surface of the cell. Used for movement of the cell or to move fluids over the cell's surface for absorption. A
Cilia (cilium) Short and abundant threadlike structures that extend from the surface of the cell. Used for movement of the cell or to move fluids over the cell's surface for absorption. A
Cell membrane Outer layer composed of lipids and proteins. Controls the permeability of the cell to water and dissolved substances. A, P
Cytoplasm Viscous fluid mixture that occupies most of the cell's interior. Wraps the nucleus and contains biomolecules, organelles and a protein fiber network (the cytoskeleton). Medium in which organelles and other internal structures exist in. The fiber network makes the cytoskeleton, which supports the shape of the cell and anchor organelles to fixed positions. A, P
Elongated organelles enclosed in a double membrane, the inner one with folds called cristae. Sites of cellular respiration, which converts sugars and fats into energy through oxidation. A, P
Chloroplasts Elongated organelles enclosed in a double membrane and with vesicles containing chlorophyll. Sites of photosynthesis. P
Ribosomes Tiny organelles composed of proteins and RNA, not enclosed in a membrane. Some are free in the cytoplasm, some are attached to endoplasmic reticulum. They are the only organelles present in all cells, including prokaryotics. Sites of protein synthesis. A, P
Endoplasmic reticulum Extensive system of internal membranes. May be smooth or rough: the latter has ribosomes attached to its membrane. Site of synthesis, modification and transport of various organic biomolecules. A, P
Golgi apparatus Flattened stacks of membranes. Used in the collection, packaging, and distribution of synthesized molecules. A, P
Secretory vesicles Membrane enclosed sacks created at the Golgi apparatus. These structures contain cell secretions, like hormones and neurotransmitters. The secretory vesicles are transported to the cell surface where they release those substances outside the cell (exocytosis). A, P
Vacuoles Elongated organelles enclosed in a membrane. Few and large in plant cells. Used to store sap (water and sugars) or waste products. A, P
Lysosomes Spherical organelles enclosed in a membrane. Contain digestive enzymes for breaking down old cellular components or ingested food (smaller cells, big macromolecules). A
Centrosome A pair of hollow tubes (the centrioles) surrounded by protein fibers in a star-like arrangement. Plant cells have an equivalent structure. Move and organise chromosomes during mitosis and meiosis. A
Nucleus Double membrane structure that encases chromatine. Controls the cellular activity. A, P
Chromatine Long strands of DNA and protein. During cell division it is packaged into chromosomes. The DNA stores hereditary information in small units of information called genes, and expresses it. A, P
Nucleolus Highly condensed chromatine loops. Area were ribosomes are manufactured. A, P
Topic 1.  Tissues

In multicellular beings there may be different types of cells, each type being specialized in an specific function, and having the specific shape that allows them to fulfill that function the best. Each of those types is called a cellular tissue; examples are the vascular tissue (plants) or the blood tissue (animals). One tissue may have several subtypes of cells (e.g. white blood cells and red blood cells). The human body contains over 200 different types of cells.

The four main types of human tissues are the following:

Epithelial tissue Composed of layers of cells that line organ surfaces such as the surface of the skin or the inner lining of the digestive tract. Serves for protection of organs (as in the skin), secretion of substances (when it forms glands - in the skin, in the digestive tract, etc.), and absorption of substances (as in the intestine).
Muscle tissue Composed of very long cells (up to several cm) called muscle fibres. They have more than one nucleus, are able to expand and contract (thanks to a dense protein network that takes up most of the cellular space), and so, are specialized in movements. There are three kinds: cardiac muscle (found in the heart), skeletal muscle (attached to bones and under voluntary control) and smooth muscle (not in the heart or attached to bones and under involuntary control, as in the wall of the stomach).
Nerve tissue Composed of cells with many projections that are specialized in contacting other cells and transmitting messages via electrical signals.
Connective tissues Usually specialized in holding together different organs or tissues. It is composed of cells usually very separated by an abundant extracellular matrix. The main types are the bone tissue (in bones, with matrix rich in apatite, a mineral rich in P and Ca), the cartilage tissue (in cartilages), the adipose tissue (as in the fatty layer under the skin - the hypodermis), the fibrous connective tissue (in ligaments and tendons), the loose connective tissue (as in the skin's dermis) and the blood.
Topic 1.  Organs, Systems and Apparatuses

There are some tasks in a multicellular being that must be achieved by cells of different kinds working together (such as pumping blood throughout the human body). In this case, cells of different tissues gather and make up an organ (epithelial, connective, muscle and adipose cells make up the heart).

Several organs working together in a common general task make up an organ system, e.g., the heart and the blood vessels make up the circulatory system. And when two organ systems work cosely together in a common function are said to constitute an apparatus: the muscular system and the skeleton form the motor apparatus, because both contribute to the function of locomotion in an animal.

Put simple, the human organ systems contribute to the three vital functions as follows:

  • Nutrition is fulfilled through:
    • The Digestive System, which (a) takes in the food, (b) breaks it down into nutrients and other substances, (c) absorbs the nutrients into the blood, and (d) gets rid of the non assimilable substances in the form of faeces.
    • The Circulatory System (a) transports those absorbed nutrients to all the cells of the body and (b) transports waste substances to the kidneys, the sweat-glands and the lungs.
    • The Excretory System expells of the waste substances arriving to the kidneys, by producing and releasing urine.
    • The Respiratory System (a) takes in oxygen (a nutrient) which is absorbed into the blood and (b) gets rid of the carbon dioxide (a waste substance).
  • Reproduction is carried out through the male and female reproductive systems which (a) produce the specialized reproductive cells (sperm and egg cells), (b) allow those reproductive cells to join in pairs, and (c) grow the embryo coming out of a fertilised egg-cell.
  • Interaction is fulfilled through:
    • The Sensory Organs, which continuously detect bits of information coming from the inside of the body or from the environment.
    • The Nervous System, which collects that sensitive information, interprets it, and generates response orders.
    • The Endocrine System, which cooperates in conveying those response orders by means of substances, called hormones, that are released by glands and travel through the blood.
    • The Skeleton and the Muscle System, which carry out most of those response orders produced in the nervous system.
Topic 2.  Vocabulary: Nutrition
Nutrition Getting the matter and the energy that every living being needs to grow, survive and reproduce. As it also involves the removal of waste substances and residual energy, it can be described as an exchange of matter and energy with the environment.
Breathing The movements performed by the lungs (along with the rib cage) to inhale and exhale the atmospheric air.
Respiration The process carried by the mitochondria, whereby small energetic nutrients (monosaccharides, fatty acids) are burnt with the help of the oxygen to produce the energy that the cells need. This process also involves the removal of CO2, H2O(g), and heat.
Gas exchange You need to convey O2 from the atmospheric air to the mitochondria and to convey the CO2 produced in the mitochondria to the atmospheric air. To do this, two gas exchanges are needed: (a) between the alveoli and the blood and (b) between the blood and the cells of every organ in your body. The blood vessels that take part in both gas exchanges are always the capillaries, because of their very thin membranes.
Blood The fluid that, amongst other things, conveys (a) the oxygen from the lungs to the cells, (b) the other nutrients from the small intestine to the cells, (c) the CO2 from the cells to the lungs, and (d) the other waste substances from the cells to the kidneys and the sweat glands.
Heart The organ that pumps the blood throughout all the body. It has two chambers to receive the blood (right and left atria) and two others to expell the blood (the left and right ventricles). Two valves (tricuspid and mitral) control the passing of the blood from the atria to the ventricles, and two other valves (aortic and pulmonary) control the passing of the blood from the ventricles to the arteries.
Blood vessels The organs that transport the blood throughout all the body. The arteries transport the blood from the heart to the organs (small arteries are called arterioles), the veins from the organs to the heart (small veins are called venules), and the capillaries are the very thin ones that perform the exchange of gases between the blood and the cells or the blood and the alveoli.
Excretion Disposing of the waste substances produced by the cells. It is done through the exhalation movement of the lungs, the kidneys and the sweat glands.
Topic 2.  Vocabulary: Digestive System
Peristalsis The wavelike muscular contractions of the digestive tract by which its contents are forced to move onwards. It is performed by the ring-like muscles of the walls of the esophagus, the stomach and the intestines.
Bolus The food mass that crosses the esophagus after having undergone a first digestive stage in the mouth.
Chyme The fluid food mass that is produced in the stomach when the bolus undergoes a second digestive stage.
Chyle The very fluid food mass that is produced in the duodenum when the chyme undergoes the third digestive stage.
Enzymes They are special proteins that behave as catalysts, i.e., they accelerate each and every chemical reaction in your body; otherwise, those chemical reactions wouldn't take place, or would do at a very slow pace. Enzymes are very specific and each one can catalise only one chemical reaction: for instance, the only thing that salivary amylase can do is breaking the starch into maltose.
Digestive enzymes The enzymes that break down the long molecules in the foods into much smaller ones that can later on be absorbed into the bloodstream. The main ones are the amylases (break down carbohydrates into sugars), the proteases (break down proteins into aminoacids) and the lipases (break down the lipids into glycerol and fatty acids). They come in the following digestive juices: the saliva, the gastric juice, the pancreatic juice and the intestinal juice.
Bile One of the five digestive juices. It is produced by the liver, stored in the gall-bladder, and it is greenish. It is necessary mostly not to carry digestive enzymes to the duodenum, but to transport bile salts to the duodenum. The bile salts are necessary to help the lipids to "dissolve" in the chyle, forming small droplets, easy to be attacked by the lipases. This process is called emulsification.
Villi The finger-like folds in the small intestine. They increase greatly the absorption surface in the small intestine (otherwise, the absorption of the nutrients from every meal would last for weeks). To allow an easy passing of the nutrients, they are very thin. Inside them, the nutrients are collected by capillary vessels and lymphatic vessels, and end up in the bloodstream.
pH A measurement that expresses the level of acidity of a substance: the lower the pH, the greater the acidity; the higher the pH, the greater the alkalinity. Substances with a pH of 7 are neutral, i. e., neither acid nor alkaline.
Lymph A clear fluid that circulates through the vessels of the lymphatic system. It collects the lipids in the small intestine and transports them to the bloodstream near the neck; it also helps the maturing of the young white blood cells before they are sent to the blood.
Topic 2.  Functions of the Digestive System
What Where
Digestion Breaking down the foods into small molecules that the blood can absorb later on (the nutrients) and into somewhat bigger molecules that can't be absorbed (dietetic fibre and others). Mouth, stomach and duodenum
Absorption The small nutrients from the digested foods pass from the digestive tract to the blood and the lymph. Jejunum and ileum
Elimination The indigestible molecules of the foods and some other waste substances are expelled out of the body. Rectum and anus
Topic 2.  Digestive Juices
Produced by Released to
Saliva Salivary glands (parotids, sublinguals and submandibulars). Mouth
Gastric juice Small glands in the lining of the stomach. Stomach
Bile Liver (and stored in the gall-bladder). Duodenum
Pancreatic juice Pancreas. Duodenum
Intestinal juice Small glands in the lining of the duodenum. Duodenum
Mind Map: Food additives
Topic 3.  Vocabulary
CoordinationOne of the main three vital functions. It refers the ability of one living being to be aware of the events happening inside or outside itself and react to them accordingly. It requires (a) the detection of the stimuli by some receptor, such as the sensory organs, (b) the transmission of that sensory information to some control centre, (c) interpreting that sensory information and generating the response by the mentioned control centre, (d) transmitting the motor information that refers the response, and (e) performing the response by some effector, which, in the human body, is a muscle or a gland.
In the human body, the aforementioned stages are performed by the following structures:
 (a) by sensory organs or disperse sensory cells;
 (b) by the afferent nerves;
 (c) by the Central Nervous System;
 (d) by the efferent nerves, the endocrine glands and the hormones;
 (e) by the muscles and the glands.
NeuroneOr neuron (Am), or nerve cell. It is the main type of cells in the nervous system. They work in groups and communicate between each other by transmitting nerve impulses. There are three types: (a) sensory neurones, which transmit sensory information from the receptors to the CNS, (b) motor neurones, which transmit the motor information from the CNS to the effectors, and (c) relay neurones, that occur in the CNS, and are the ones that decide the responses once they have interpreted the sensory information generated by a stimulus.
Nervous circuitIt is a circuit formed by a sequence of neurones that connect a receptor with an effector, in order to trigger an appropriate response to the stimulus that has been detected. It consists of, at least, one sensory neurone, one relay neurone, and one motor neurone.
GanglionIt is a cluster of somas and dendrites of a group of neurones. They belong to the PNS, and often interconnect with other ganglia to form a more complex cluster known as a plexus.
NerveBundles of bundles of axons of many neurones packed together. They belong to the PNS and (a) convey sensory information from the receptors to the CNS (afferent nerves), or (b) motor information from the CNS to the neurones (efferent nerves), or (c) both (mixed nerves).
HormoneChemicals secreted by the endocrine glands into the bloodstream, that act as chemical messengers, this is, they trigger certain responses in the target cells that are meant to react to some variation of the external medium (as when a secretion of adrenaline helps you to face succesfully some sort of threat) or some variation of the internal medium (as when a secretion of insulin helps you to keep an adequate level of sugar in your blood).
Target cellThe target cells (which belong to the so called target organs) are called like that because they are the specific target of an specific hormone. This means that, although the hormones are released into the bloodstrem, and therefore reach every cell in the organism, only a group of cells are going to react to the arrival of any particular hormone: these are the target cells, and what makes them be such, is the possession in the surface of their membranes of molecules that act as specific receptors to one specific hormone. It is the coupling of a hormone to those receptors what triggers the final response accomplished by the target cells (opening up your pupils, lowering the levels of glucose, etc.).
Topic 3.  Structural Organisation of the Nervous System
Central Nervous System
  • Brain (= encephalon). Enclosed by the skull and the meninges. Main organs: cerebrum, cerebellum and brain stem.
  • Spinal cord. Enclosed by the backbone (= spinal column, = spine) and the meninges.
Peripheral Nervous System
  • Nerves: bundles of neurones' axons. Functional types: afferent, efferent or mixed. Structural types: cranial (12 pairs) or spinal (31 pairs).
  • Ganglia: clusters of neurones' somas.
Topic 3.  Facts About Neurones
  • They occur only in the Nervous System, but they are not the unique type of cells in it: there are, also, the glial cells, which assist the neurones in several tasks (nutrition, disposal of wastes, defense, regeneration…).
  • They have two parts: the cell body or soma, and the nerve fibers: these are prolongations of the soma that can be two kinds: the axon (single, long, branched only at the end) and the dendrites (usually many, short and highly branched). The dendrites may be lacking.
  • Their function is transmitting an electric current called nerve impulse along circuits that connect the sensory information collected by the receptors with the responses performed by the effectors.
  • The nerve impulse is transmitted always in the same direction: from the dendrites (if any) to the soma, and from the soma to the axon. The axon terminals will make connections with other neurones or, at the end of the circuit, with an effector.
  • Many axons (the ones of the PNS and the ones that make up the white matter of the CNS) are wrapped by Schwann cells, that make up the myelin sheath, which helps speeding up the transmission of the nerve impulse.
  • The demyelination of myelinated axons is characteristic of some serious diseases such as multiple sclerosis.
  • The regeneration of damaged neurones in the CNS is not possible, but the myeline layer helps regenerate the damaged axons of the PNS (only).
  • Two consecutive neurones in a nervous circuit do not touch each other, and so, the nerve impulse has two "jump" over that gap (the synapse); this is acomplished by means of certain molecules called neurotransmitters (e.g. dopamine, endorphin).
  • The low production of certain neurotransmitters (or the inhability to use them) is the hallmark of several diseases such as the Parkinson's disease.
Topic 3.  Endocrine Control

In many cases, when an endocrine gland releases a hormone, it is upon request of some controlling organ, which, at the end of the hierarchical chain, is always the brain. But who tells the brain to tell the hypothalamus (the so called master gland), to tell the hypophisis to tell the breasts (via the secretion of oxytocin) to secrete milk? The sensory cells (receptors) that detect the baby's suckling do. They send nerve impulses to the brain informing of this event, and then the brain starts the chain of orders.

There are also cases in which it is the same gland that produces the hormone the one that detects the stimulus that will finally lead to the secretion of the hormone. It is the pancreas itself the organ that learns about the rise of the level of sugar in blood, and responds to it by secreting insulin. And if the pancreas notices a low level of glucose in blood, it, without asking anyone, will release glucagon, which will help to take more glucose into the blood. Insulin and glucagon are antagonist hormones, because they do opposite things. The have in common who secretes them (the pancreas) and their target organs (chiefly the liver and the muscles).

As more glucose in blood leads to less glucose in blood (through the action of the insulin) and less glucose in blood leads to more glucose in blood (via glucagon), these two are examples of negative feedback in endocrine control. But secreting milk when the baby suckles leads to keep on secreting more milk: the stimulus empowers itself, and this is called positive feedback.

Topic 4.  Vocabulary: Male Reproductive System
[Adapted from]
ScrotumExternal sac enclosing the testes.
TestesMale gonads that produce sperm cells, a 2-5% of the seminal fluid, and secrete testosterone.
Seminiferous tubulesTightly coiled tubes within the testes that produce sperm.
EpididymisPortion of the testes in which sperm mature or fully develop.
Vas deferensAlso ductus deferens. Passageway that carries sperm from the epididymis to the ejaculatory duct.
Seminal vesiclesGlands located at the base of the bladder that produce around a 70% of the seminal fluid.
Ejaculatory ductDuct formed by the union of the ductus deferens and the duct of the seminal vesicle, that carries the semen up to the urethra.
ProstateMuscular gland in males that surrounds the first inch of the urethra. It produces almost a 30% of the seminal fluid.
Bulbourethral glandsAlso Cowper's glands. Glands located at the base of the penis, that at the beginning of sexual arousal secrete a fluid which helps to lubricate the urethra for spermatozoa to pass through, and to help flush out any residual urine. This fluid can carry sperms from previous ejaculations.
PenisMale organ of reproduction and urination.
PrepuceAlso foreskin. The fold of skin over the glans or tip of the penis.
CircumcisionSurgical removal of the prepuce of the penis.
ErectionStiffening, lengthening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. It is primarily due to the dilation of the arteries that supply blood to the penis (which allows more blood to fill the three spongy chambers in the penis) and the constriction of the veins that carry blood away from the penis. This way, more blood enters than leaves the penis until an equilibrium is reached and a constant size is achieved.
EjaculationSudden ejection of semen from the penis.
SemenThick, whitish, somewhat sticky fluid composed of sperms and seminal fluid that is propelled out of a male's reproductive tract during ejaculation. Normal human ejaculated semen, as defined by the WHO, has a volume of 2 ml or greater, pH of 7.2 to 8.0 (slightly alkaline), sperm concentration of 20 million spermatozoa per ml or more, and a motility of 50% of the spermatozoa, with at least a 25% being able to move forward.
Topic 4.  Vocabulary: Female Reproductive System
[Adapted from]
OvariesFemale gonads in which ova are produced and that secrete estrogens and progesterone.
Ovarian folliclesStructures within an ovary consisting of a developing egg surrounded by follicle cells.
Corpus luteumYellowish remains of a burst ovarian follicle that secretes progesterone.
OvulationRelease of a mature ovum from an ovary.
FimbriaeFingerlike projections at the end of a fallopian tube that partially surround an ovary.
Fallopian tubesAlso ovarian tubes. Tubes connecting an ovary to the uterus and through which an ovum is transported. They are the place of fertilization.
UterusAlso womb. The hollow organ in females that receives, retains, and nourishes a fertilized ovum or egg.
MyometriumMiddle layer of the uterus composed of interwoven muscle cells.
EndometriumInner layer of the uterus that provides nourishment for a developing embryo and fetus and that sloughs off during the regular menstrual cycle.
CervixLower necklike portion of the uterus leading into the vagina.
VaginaMuscular tube in women that extends from the cervix of the uterus to the vaginal opening.
VulvaFemale external genital organs, composed of the mons pubis, the labia majora, the labia minora, the clitoris, the urethral opening, the vaginal opening and the greater vestibular glands.
Mons pubisFatty, rounded, hairy area at the top of the vulva.
Labia majoraOuter, hairy skin folds of the vagina.
Labia minoraInner skin folds of the vagina.
ClitorisSmall protruding mass of erectile tissue at the top of the labia minora.
Greater vestibular glandsPair of mucus-secreting glands that lubricate the lower portion of the vagina.
HymenThin membrane partially covering the external opening of the vagina.
Topic 4.  Vocabulary: Menstrual Cycle
[Adapted from]
MenarcheBeginning of menstruation or the first menstrual period.
MenopausePeriod in a woman's life when menstrual activity ceases.
MenstruationAlso menses. Periodic (monthly) discharge of blood, secretions, tissue, and mucus from the endometrium in the absence of pregnancy.
Topic 4.  Vocabulary: Gametes
[Adapted from]
GonadsSex organs in which reproductive cells develop.
GametesReproductive or sex cells. They are different to any other cell in the body in which they only have half of the chromosomes than a normal somatic cell.
OvaFemale gametes or eggs (singular: ovum).
ZygoteFertilized ovum. By successive mitosis, it will convert into an embryo, then a fetus, and finally a newborn.
SpermAlso spermatozoon. Mature male sex or reproductive cell. They need to be produced at a slightly lower temperature than the usual in the inside of the human body.
AcrosomeTip of the head of a sperm cell that contains enzymes to digest the membrane of an ovum.
Topic 4.  Vocabulary: Pregnancy, Childbird and Nursing
[Adapted from]
ChorionThe outermost membrane that surrounds the embryo/fetus during pregnancy. It is in contact with the amnion and generates the placenta.
AmnionFluid-filled sac that surrounds a developing embryo/fetus. It provides room and cushioning to the embryo/fetus.
PlacentaTemporary organ developed after the implantation of an embryo, when the chorionic villi invade the endometrium. It provides nutrients to a developing fetus, carries away wastes, and produces hormones such as estrogens and progesterone.
Umbilical cordStructure that connects the embryo/fetus to the placenta.
Alveolar glandsGlands within the mammary glands that produce milk.
Lactiferous ductsDucts that carry milk from the alveolar glands to the surface of the nipple of a breast.
AreolaCircular, darkened area surrounding the nipple of each breast.
Topic 4.  Vocabulary: Hormonal Control of the Reproduction
[Adapted from]
Luteinizing hormoneHormone secreted by the anterior pituitary that stimulates, in women, ovulation and the release of estrogens and progesterone by the ovaries and, in men, the secretion of testosterone by the testes.
Follicle-stimulating hormoneHormone produced by the anterior pituitary gland that stimulates the development of follicles in the ovaries of females and sperm in the testes of males.
TestosteroneMale hormone secreted by the testes that stimulates the growth of the male reproductive organs and brings about the secondary sex characteristics.
EstrogensFemale hormones secreted by the ovaries that bring about the secondary sex characteristics and regulate the female reproductive cycle.
ProgesteroneFemale hormone secreted by the ovaries that makes the uterus more ready to receive a fertilized ovum and regulate the female reproductive cycle.
ProlactinHormone secreted by the anterior pituitary that stimulates the mammary glands to produce milk during nursing.
OxytocinHormone produced by the hypothalamus and stored in the posterior pituitary that stimulates contraction of the uterus during childbirth and secretion of milk during nursing.
Presentation: Smoke, the convenient truth
Topic 6.  Physical Properties of the Minerals
ColourThe colour of a mineral is one of its most obvious attributes and the easiest physical property to determine. Unfortunately, as it results from a mineral's chemical composition and structure, the impurities and structural flaws that may be present can alter completely the colour with regards to the pure mineral. Hence minerals like fluorite and quartz may display a really wide range of colours. This makes colour not the most useful property in helping to characterize a particular mineral.
StreakThe streak refers to the colour of a mineral's powder, which is almost always the same, regardless the impurities and structural flaws of the mineral. Thus, it is much more reliable to characterize a mineral than the colour of the mineral itself. The streak is usually obtained by rubbing the mineral across a plate of unglazed porcelain. The streak and the mineral's typical colour may or may not be the same. Some examples of streaks of common minerals are pyrite (black), magnetite (black), halite (white).
Transparency /
A transparent mineral (diamond) allows all light to cross through; a translucent mineral (quartz) allows part of the light to cross through; an opaque mineral (pyrite) does not allow the light to pass at all.
LustreIt refers to the way in wich a mineral's surface reflects light. To some extent it is related to the transparency of a mineral; for instance, metallic minerals are always opaque and vitreous minerals are always translucent.
CleavageIn some minerals, bonds between layers of atoms aligned in certain directions are weaker than bonds between different layers. In these cases, breakage occurs along flat surfaces parallel to those zones of weakness. In some minerals, a single direction of weakness exists, but as many as six may be present. Halite, which forms cubic crystals, presents 3 perfect cleavage directions.
HardnessIt depends on the strength of the chemical bonds and is measured by the ease or difficulty with which a mineral can be scratched. Diamond is the hardest mineral, because it can scratch all others. Talc is one of the softest; nearly every other mineral can scratch it. We measure a mineral's hardness by comparing it to the hardnesses of a standardized set of minerals first established by Friederich Mohs.
TenacityIt is a mineral's physical reaction to stress such as crushing, bending, breaking, or tearing. For example, according to its tenacity, a mineral can be brittle (easy to powder with a hammer), sectil (easy to cut with a knife), malleable (easy to flatten with a hammer, as metallic minerals) or ductile (easy to stretch into a wire, as metallic minerals).
Growth habitRefers to the shape a mineral develops when it is not constricted by lack of available space. For example, quartz forms six-sided prisms capped with pyramid-like faces; halite occur as cubes; and pyrite develop cubes or pentadodecahedrons (polyhedrons with 12 pentagonal faces).
Specific gravityIt's a comparison of the density of a mineral to that of water. For example, quartz has a specific gravity of 2.6 because it is 2.6 greater than that of water. You can also say that it has a density of 2.6 g/cm3
MagnetismWhen a mineral can be attracted by a magnet or act themselves as magnets. The best example is magnetite.
Electrical conductionWhether an electric current can easily pass through a mineral (such as in all metallic minerals and graphite) or not.
FeelWhat you perceive when you touch a mineral. It can be rough, smooth, greasy (talc), cold (diamond)…
TasteWhat you perceive when you lick a mineral. Halite, for instance, tastes salty.
Topic 6.  Main Types of Mineral Lustre
[Available in Google Docs]
VitreousTranslucentQuartz, Halite, Olivine
ResinousTranslucentYellow and red sphalerite varieties
GreasyTranslucentMilky quartz
SilkyTranslucentFibrous gypsum
PearlyPoorly translucentMica aggregates
Dull metallicOpaqueGraphite
MetallicOpaquePyrite, Galena, Magnetite
Topic 6.  Properties of Some Common Minerals
[Available in Google Docs]
CompositionColourStreakTransparencyLustreHardnessGrowth habit
GraphiteCDark greyBlackOpaqueDull metallic1.7Foliated, massive
PyriteFeS2Pale goldenBlackOpaqueMetallic6.5Cubes, pentadodecahedrons
CinnabarHgSVermilion redBright redOpaqueAdamantine / Dull metallic (aggr.)2.2Massive
GalenaPbSGreyGreyish blackOpaqueMetallic2.5Cubes, octahedrons
MagnetiteFe3O4BlackBlackOpaqueMetallic5.7Octahedrons, massive
HematiteFe2O3Reddish greyRedOpaqueMetallic6Tabular
HaliteNaClColourlessWhiteTranslucentVitreous2.5Cubes, etc.
FluoriteCaF2Colourless, yellow, green, blue…WhiteTranslucentWet vitreous4Cubes, etc.
CalciteCaCO3Colourless, white…WhiteTranslucentVitreous3Rhombohedrons
AragoniteCaCO3Reddish greyWhiteTranslucentVitreous4Hexagonal twinning, etc.
GypsumCaSO4·2H2OWhite, grey, redWhiteTranslucentSilky vitreous2Lamellar, fibrous
QuartzSiO2Colourless, white, grey, yellow, violet…WhiteTranslucentVitreous76-sided prisms
Biotite / Black micaSilicateColourless / Black (aggr.)GreyTranslucentVitreous / Pearly (aggr.)2.7Lamellar
Muscovite / White micaSilicateColourless / White (aggr.)WhiteTranslucentVitreous / Pearly (aggr.)2.2Lamellar
OlivineSilicateOlive greenWhiteTranslucentVitreous6.7Granular
TalcSilicatePale green, grey, whiteWhiteTranslucentWaxy vitreous1Massive
Topic 7.  Rock Grains

Sedimentary rocks can be made up of clasts or detritus (rock grains) weathered from other rocks by river waters, wind, coastal sea waters, glaciers, living beings, etc. This kind of sedimentary rocks are called detrital rocks.

They're classified upon the grains that they are made up of. First up, grains may be all the same size, uniform, as in a sandstone, or different sizes, as in a conglomerate. Secondly, grains may be bigger or smaller. The following table shows roughly how rock grains are classified upon their size:

Clay< 0.004 mm
Silt< 0.06 mm
Sand< 2 mm
Gravel< 6 cm
Cobble< 25 cm
Boulders> 25 cm

ESO 4. Biology and Geology

Topic 1.  Vocabulary: Cellular Reproduction
Genetic material In all cells the genetic material is DNA bound to proteins and organised in chromosomes. Bacteria have one chromosome, while humans have 46 in each cell. Its function is to store, express and transmit to the offspring the instructions that tell how every cell and living being will be self-constructed and how will they work.
Mitosis Cells with more than one chromosome, once they've synthesised a full copy of the whole set of chromosomes, have to carefully organise their division in order to produce two daughter-cells with exactly the same genetic information. Mitosis is the complex process whereby most eukaryotic cells tackle such a task.
Mind Map: Osmosis
Mind Map: Active transport
Mind Map: Enzymes in industry
Topic 2.  Vocabulary: Mendelian Genetics
Locus (pl. loci)A place in a chromosome where a gene resides. Each locus contains the encoded information for a trait, such as "colour of the eyes".
AlleleOr allelomorph gene. Any of a number of the alternative varieties of a gene that reside in the same locus. Each allele contains the encoded information for a quality or a value of a trait, such as "brown colour of the eyes". All the possible alleles for the same locus form a "family of allelomorph genes".
HaploidCell or individual or species with one single set of chromosomes, such as bacteria or the human gametes.
DiploidCell or individual or species with two sets of chromosomes, such as the body cells of humans (and most eukaryotes). Each chromosome of a set is similar to one chromosome of the other set in that they carry exactly the same loci, but they are not identical, as the specific alleles of each locus can be different.
HomologousIn diploid individuals, each pair of chromosomes that carry the same loci. Humans have 22 pairs of homologous chromosomes and one pair (the sex chromosomes) which are partially homologous.
HomozygousOr "pure breed". Diploid individuals are homozygous for a locus when the alleles present in that locus are the same in both homologous chromosomes.
HeterozygousOr "hybrid". Diploid individuals are heterozygous for a locus when the alleles present in that locus are different in each homologous chromosome.
DominanceA type of relationship between two different alleles of the same family whereby one allele (said to be the "dominant" one) cancels out the phenotypic effect of the other (said to be "recessive").
CodominanceA type of relationship between two different alleles of the same family whereby both alleles express their phenotypic effects without blending. This is the case of the alleles for the "A" and "B" human blood types, whose heterozygosis yields an "AB" type.
Incomplete dominanceA type of relationship between two different alleles of the same family whereby the phenotypic effects of each allele are blended in the phenotype. This is the case of the alleles for the red and white colour for the corolla of the flowers of the snapdragon plant, whose heterozygosis yields a pink colour.
Mind Map: First artificial cell
Topic 3.  The Birth of the Theory of Evolution

Before Darwin the general consensus was that species were created independently by some extranatural force, and that they died out without any major change. So, which were the steps needed for a theory of evolution of the biological species to be accepted in the XIX century?

  • Accepting the idea that species can change during their life span.
  • Accepting the idea that species can change so much that they can even generate new species, either by diversification (cladogenesis) or by a global transformation of one whole species (anagenesis).
  • Accepting the idea (that looks like an inevitable result of the previous one) of a common descent, i. e., that all species are related, have a kinship, and they all come from a common ancestor.
  • Accepting the idea that the Earth is old enough for these huge changes to have enough time to occur... so slowly that can't even be perceived during a human life span.
  • And most notably: knowing of any acceptable mechanism by which these types of changes can occur.

Considering that not so long ago, the Anglican bishop James Ussher had stated that the Earth had been created the night preceding 23 October 4004 BC, the idea of an old Earth was, quite possibly, the necessary precondition for all the others to be even borne in mind by anyone. And this revolutionary idea was just there in the right moment, when Darwin started his five years long journey in the Beagle, and was given the first volume of Charles Lyell's Principles of Geology, which set out the idea of masses of land slowly rising or falling over immense periods of time to finally yield the geological features that can be observed in present time. According to Lyell, the Earth was much older than what was thought by that time, probably even millions of years old (some 4,560 years old, to be more precise, and as we know today).

The concept of a gradual change of biological species, now that Darwin knew that there was enough time for it, arose from the observation of different races of tortoises, finches and others, adapted to the particular environments that the Galápagos islands had to offer. And more particularly, to the different nutritional niches available; while some finches had a beak specialised in cracking hard nuts, others were the perfect weapon for chasing insects, etc. And considering that those islands are some 1,200 km away from the continent, it was clear to Darwin that all those finches (or tortoises) had had to come from one (or a few) small group of ancestors that, departing from the mainland, happened to make their way to the islands. The Galápagos finches had evolved on-site, as it was highly unlikely that all those varieties could have possibly reached the islands from the continent, one by one.

That panorama was clearly speaking about gradual transmutation of those animals by adaptation to different environments (species can change), and with it, Darwin's mechanism of evolutionary change had started to develop.

But was that slow and gradual change powerful enough to produce new species, or were all those differently adapted finches simple varieties of the same species? Friends are to come to the rescue when needed, and so it was with Darwin's mate John Gould, an ornithologist, who announced that the specimens of finches that Darwin brought back to England after his trip belonged, in fact, to three different species. In Darwin's mind, that meant that gradual adaptation to the environment can actually produce new species.

Finally, how do species get to adapt to each one of the many specific environments that Nature provides? How can a population gradually reach its ecological niche, one that allows it to survive and thrive for generations? That was the last and greatest obstacle to overcome, and recent History showed that clearly. Jean-Baptiste de Lamarck had already come up with similar thoughts to Darwin's a couple of decades before the Beagle departed: species evolve, and do it by gradual adaptation to their environment. But Lamarck could never demonstrate that acquired-on-life traits can be passed on to the offspring, and we know nowadays that that just can't happen: the genes of your eggs or sperms will not change because of you dying your hair. And this is how Lamarck passed to History as an unsuccessful attempt to explain the how and the why of the evolutionary process.

But not Darwin. It turns out that among the many different types of individuals that are randomly produced every generation in every species, some happen to be better suited to their environment than others: the former feed better, grow faster, survive longer and as a result... reproduce more than the latter. And as the traits that make them the fittest were inherited, they will also pass those traits to their children. As a final result, those traits will be more present in the next generation than those that conferred a lesser success. This was what Darwin (and Alfred R. Wallace) elucidated, and that's why everyone is now celebrating his 200th anniversary. Or almost everyone.

Topic 3.  Main Evolutionary Ideas in Linné, Lamarck and Darwin
1Species can change gradually over their lifetime.NYY
2Species change by means of a progressive improvement in their adaptation to the environment.n/aYY
3Species can change so much that each one of them can transmute into a new different species (anagenesis).n/aYY
4Species can also change in a way that one species can give birth to several new descendent species by branching off (cladogenesis).n/aNY
5All species are thus related and come from a common ancestor.n/aNY
6Evolutionary change by progressive adaptation to the environment happens because every living being has an innate tendency to improve its adaptation to the environment, and so organs are developed or atrophied during life as needed.n/aYN
7Acquired-on-life changes (such as the atrophy or development of organs) are inherited.n/aYN
8Evolutionary change by progressive adaptation to the environment happens because the fittest leave a greater offspring.n/aNY
9The traits that confer a greater fitness were inherited from the parents, and so they can be passed on to the children.n/aNY
N.B.: 4 and 5 go together as 5 is the result of 4; 6 and 7 go together and make Lamarck's idea of the mechanism of evolutionary change; 8 and 9 go together and make Darwin's idea of the mechanism of evolutionary change.
N.B.: Carl von Linné (= Carl Linnaeus) is best known for having developed the binomial (= binominal) nomenclature of the species, by which all species have an official scientific name, called binary name or binomen because it is made of two latinised words. Thus the "wolf" is called "lobo" in Spanish or "loup" in French, but may be also called "Canis lupus" all throughout the world. The binomen is made of the genus name ("Canis") and an specific name ("lupus").
Topic 3.  How Does Natural Selection Work?

Natural Selection is all about a central event: some individuals reproduce more than others. And this has a cause and a result. Step by step:

  • There are many different types of individuals in any biological population. We all can see that. And it is due to mutation and recombination. Mutation increases the number of possible alleles for every loci throughout time, and even creates new loci, or gets rid of loci or alleles. But in the long run mutation tends to increase the number of genes (either alleles or loci) for every species. Mutation takes place mostly due to errors during the duplication of DNA prior to cell division. Also, the recombination of loci during meiosis multiplies the number of different possible gametes that any individual can produce.
  • Different types of individuals interact differently with their environment. Some of them are stronger, faster, bigger, smarter... and so some of them grow faster and reach fertility sooner, hide better from predators and manage to sort the threats out better, are more efficient absorbing nutrients or chasing the prey, are more convincing when looking for someone of the opposite sex to mate...
  • The individuals that have more successful interactions with their environment leave a greater offspring. No way it can be otherwise. If you reach fertility faster, survive longer, and your nutritional efficiency leaves you more free time, chances are that you are going to have a greater reproductive success.
  • Many of the traits that make these individuals more successful are inherited. Although in some species (us!) some "rules for success in Life" can be learned, capability for learning is itself an inherited trait. And, although your genes don't determine the weight that you'll have when you are 25, they do determine a certain range or weights you are likely to fall within.
  • The alleles of the individuals with a greater reproductive success will be present with a higher frequency in the next generation, and vice versa. As a result, the phenotypic traits coded by the successful alleles will be more present in the next generation, and this noticeable phenotypic change improves the overall fitness of the population gradually, generation after generation.

In short, Natural Selection takes place through the following sequence of events:

  1. Variation due to mutation and recombination.
  2. Differential fitness.
  3. Differential reproduction.
  4. Heritability of phenotypic traits.
  5. Change in the frequencies of the alleles of a population.
  6. Overall phenotypic change in a population.
Topic 3.  The Formation of New Species

The formation of new species or speciation is one of the main outcomes of the evolution of Life, the opposite to extinction, and the most visible result of adaptation.

Sexually reproducing species (virtually all that exist, except prokaryotes) are defined as those groups of individuals that can leave fertile offspring by sexual reproduction, and thus share a common gene pool: the genome of species. This is so because sexual reproduction can be considered as a way to produce new combinations of genes (new genotypes) by means of sharing half of the genes of each one of the two partners. Sexual reproduction is a bit like dealing sets of, say, five cards after having shuffled the deck. In the analogy, each card would be a gene, each set of five cards the genotype of a new individual, and the deck of cards is the genome of the species.

The members of the same species also share the same ecological niche, this is, they dwell on the same habitat, they feed the same way, they prefer a similar amount of humidity or sunlight, the are prey to the same predators, etc.

If two individuals of opposite sex that can leave fertile offspring by sexual reproduction belong to the same species, then, speciation must be the process by which two populations, that originally belonged to the same species, split apart and, after a time of adaptation to different environments (or ecological niches), evolve differently to the end that eventually they become unable to leave fertile offspring by sexual reproduction. This end point of speciation is called reproductive isolation.

This process can take place by different ways. Sometimes the appearance a new geographical barrier is the decisive event. That is the case of the Galápagos tortoises, presumably descendants of a common ancestor, that after colonising the different islands of the archipelago, the sea between the islands posed an almost invincible obstacle for them to meet and mate. This way, the different populations settled down in the different islands, couldn't share a common gene pool anymore, and natural selection made them to evolve differently by improving their adaptation to each particular island. Eventually, they changed so much that if individuals of these different populations happened to meet due to the sea currents or the action of men, they were so different that they would not able to leave fertile offspring by sexual reproduction. Those different populations were now different species.

But speciation does not always need huge geographic barriers. In the case of Galápagos finches, different species appeared in the same islands because when this virgin territory was colonised by their ancestors, a variety of ecological niches were at their disposal, and while some of the finches specialised in feeding off insects, other preferred grains, and so forth. They shared a common habitat, but occupied different places in it and performed different ecological roles. The enhancement of that specialisation (the improvement of their adaptation) to each specific ecological niche by means of natural selection did the rest, and, like the tortoises, with time enough took them to be so different that one day they were reproductively isolated.

But how different two individuals of the opposite sex have to be, to be reproductively isolated? The answer is: either...

  • So different that the male wouldn't be able to fertilise the female, because...
    • They don't attract each other sexually anymore: courting does not work for them;
    • Their genitals have become incompatible;
    • The sperms are unable to make their way towards the egg, in the case of mammals;
    • etc.
  • Or so different that even if the male can fertilise the female, they can't leave fertile offspring, because...
    • The zygote can't divide by mitosis (consider a sperm with 23 chromosomes and an egg with 24: this makes a total diploid number of 47, which is odd, and mitosis cannot take place with an odd number of chromosomes);
    • The embryo degenerates soon;
    • The children are weak and die before sexual maturity;
    • The offspring is sterile, as in the case of the mules;
    • etc.
Topic 4.  Fossils
What are fossils?

Fossils are the petrified remains of the living beings from the past or of their vital traces. They are studied by the science of the Paleontology.

Fossils are commonly found in sediments or sedimentary rocks (limestone, sandstone, mudstone, shale), typically as a result of the burial of the remains of a living being within a layer of sediments. Heavy metamorphism and the extreme temperatures of the magmas (> 700ºC) are likely to destroy any remain or trace of a living being, and so fossils are not found in heavily metamorphosed rocks (schist, gneiss) or igneous rocks (granite, diorite). Only sedimentary rocks that have undergone a gentle metamorphism, such as slates, are likely to contain fossils.

The totality of fossils and their placement in the rocks containing them constitute the fossil record. This placement may be as important as the fossil itself, because it can give a lot of information about the way and the type of ecosystem in which the fossilised organism lived. For instance, if a fossil is found within a conglomerate, which is a rock formed from the sediments deposited by a river, we'll know that it is one of a land organism. Or if an unknown fossil is found in the same rock where we also find fossils of seashells, it will probably be the fossil of a marine living being.

The fossil record is gappy and uneven. It is gappy because fossilisation is a rare event that happens sporadically and irregularly, depending heavily on the environmental conditions in the moment when a living being dies. If a land animal dies in a place that undergoes a landslide a short time after its death, most likely it will be well preserved inside the sediments. But if it dies in a place where strong winds, or heavy river flow or marine currents drag its corpse for a long time before it is left in a quiet place to be buried as sediments are deposited, chances are that the corpse will be destroyed by those currents, and the scavengers, detritivores and decomposers during the long time that it took before it was buried. And it is uneven because not all species have the same chances to leave any kind of fossil remain. As a start, hard structures (bones, teeth, shells) are commonly necessary, because soft tissues decay rapidly when the scavengers and decomposers (chiefly invertebrates, bacteria and fungi) start to predate on them. Organisms such as jellyfish or worms have really low possibilities to leave body fossils; traces such as imprints or burrows in the sediments are amongst their very few chances to leave a sign of their existence.

Types of fossils
  • Body fossils are the petrified remains of living beings from the past, and are produced by the substitution of the biomolecules that pertained to the deceased organism by mineral substances that precipitate from the groundwater that circulates through the sediments in which the corpse is buried. This requires a rapid burial of the organism following its death; otherwise, it will be soon destroyed, as explained above. Other times the remains can be destroyed once covered by sediments, but leaving an organism-shaped hole in the rock: this is called an external mould. If this hole is later filled with other minerals, it is called a cast. An internal mould is formed when sediments or minerals fill the internal cavity of an organism, such as the shell of a bivalve or the skull of a vertebrate.
  • Trace fossils are the physical remains of the vital activity of living beings from the past, and are produced by their movement (trackways left by trilobites, footprints from hominans), their reproduction (eggs of dinosaurs), their nutrition (coprolites, gastrolites, holes drilled in the shells of the prey), and other living habits (burrows, root cavities, stromatolites...). The oldest physical fossils on Earth fall into this category. They are stromatolites, and the oldest might be the 3.5 by old found in Warrawoona, Australia. Stromatolites are layered rocks generated by communities of microorganisms, usually dominated by cyanobacteria, which produced the precipitation of mineral substances dissolved in the seawater, generating layers of sediments that stacked one on top of another creating a stratified biogenic rock.
  • Biochemical fossils are the biochemical remains of the vital activity of living beings from the past. The best examples are carbon-rich rocks (such as the stromatolites) or minerals (such as graphite granules) that have more 12C than usual and less 13C than normal. As the CO2 molecules with 12C weigh 44 u instead of the 45 u of a molecule of CO2 with 13C, the former move faster (they are called "light CO2") than the latter, and have more chances to randomly reach the places of a living being capable of capturing them. This way a plant captures light CO2 in a greater proportion than it is found in the atmosphere, and so the fossilised remains of a plant will contain 12C in a greater proportion than it is found in the atmosphere. The oldest fossils on Earth might be 3.8 by old graphite granules found in Isua, Greenland, that contain a greater than normal proportion of 12C.
Topic 4.  Main Geochronologic Units
EonEraPeriodStart date (m.y.)
Hadean  4,570
Archaean  4,000
Proterozoic  2,500
Topic 4.  Earth's Timeline
Geological eventsTime (m.y.)Biological events
· The Big Bang: the origin of time, space, matter and energy, all formed from one single point. The Universe is expanding ever since.13,700 
· The Sun, formed from a giant cloud of gas and dust (a nebula), ignites and becomes a young star.
· The nebula starts taking a flat shape and forms the protoplanetary disk or accretion disc that revolves around the young Sun.
· The Earth and all rocky matter in the current Solar System start forming by accretion: the accumulation of matter in increasingly bigger nuclei due to the pull of gravity.
· The Earth's atmosphere initially lacks oxygen.
· Theia, a planet of the size of Mars, collides with the Earth, which causes a massive ejection of matter into orbit around the Earth, which will finally coalesce to form the Moon.4,530 
· Zircons found in Australia are the oldest known minerals.4,400 
· The surface of the Earth cools enough for the crust to solidify and the first continents ("shells") form. The atmosphere and the oceans form.4,100 
· The Acasta gneisses, in Canada, are the oldest known rocks.4,030 
· The inner planets receive the continuous impact of meteors, which probably boiled the oceans away and killed off any form of Life that could have developed.≤ 3,850 
 3,800· First possible fossils: chemical imprints of Life in graphite granules found in the oldest known rocks with a sedimentary origin, in Greenland.
· The first living beings were similar to prokaryotes, and obtained the carbon from CO2 and the energy from inorganic substances such as H2S, that could have been obtained from the thermal vents that are found in the undersea tectonic boundaries.
 3,430· First possible physical fossils: possible biogenic stromatolites found in Australia. These are layered rocks created by a multispecific community of microorganisms dominated by cyanobacteria.
· The concentration of oxygen starts to rise in the Hydrosphere and the Atmosphere, which is the most critical ecological change in the History of Earth, killing off most prokaryotes (which were anaerobic) and paving the road for the evolution of all the aerobic forms of life, including plants and animals.2,400 
 2,100· Eukaryotic cells appear, probably derived from prokaryotes engulfing others via phagocytosis.
· Supercontinent Columbia.1,700 
 1,200· Sexual reproduction appears, increasing the rate of evolutionary change.
· First multicellular organisms appear as colonies of cells with some kind of division of labour.
· Supercontinent Rodinia.1,000 
· Ice age: Snowball Earth.750 
· Supercontinent Pannotia.580· Ediacara biota: first complex multicellular organisms.
 540· Cambrian explosion: most modern types of animals appear, including trilobites, ancestors of modern arthropods.
 500· First vertebrates (fish).
· First land plants.
· First land fungi.
· First land arthropods.
 380· Amphibians, first four-limbed tetrapods, evolved from fish, start colonising the continents.
· Fern forests start to dominate the land.
· Supercontinent Pangaea starts forming.300 
 250· A massive extinction at the end of the Permian eliminates 95% of living species.
 230· Dinosaurs appear.
· Seed plant (gymnosperms) forests start to dominate the land.
· Supercontinent Pangaea starts breaking up.180 
 130· Rise of angiosperms (flowering plants).
 66· A massive extinction at the end of the Cretaceous, possibly caused by a 10 km across meteorite that left the crater of Chicxulub, in Mexico, eliminates about half of all animal species, including all dinosaurs (except the ancestors of modern birds) and ammonites.
· Mammals will take advantage of this event and will diversify rapidly, occupy most ecological niches left by dinosaurs, and become the dominant vertebrates on land.
 6-7· Hominans (biped primates) appear in Africa, maybe with Sahelanthropus tchadensis (-7my) or Orrorin tugenensis (-6my).
 2.5· Humans (Homo habilis) appear in Africa.
 0.2· Modern humans (Homo sapiens) appear in Africa.
 0· With a human population approaching 7 billion, the impact of humanity is felt in all corners of the globe. Overfishing, anthropogenic climate change, industrialisation, intensive agriculture, clearance of rain forests and other activities contribute to a dramatically rising extinction rate.
Mind Map: Events after fertilisation
Mind Map: The Nitrogen cycle
Presentation: We are eating up our world
Topic 8.  Vocabulary
Geological agentAny agent able to alter the surface of our planet.
External geological agentGeological agents powered by the Sun or the Earth's gravity: the water flows (streams, torrents, rivers, glaciers), the sea, the wind, the atmospheric phenomena (rainfall, thunderstorms, cyclones), the temperature variations or the living beings.
Weathering / ErosionWeathering is the decomposition of rocks, soils and their minerals through the action of some of the external geological agents. It is called erosion when the decomposing agent also transports the resulting fragments away.
ClastsThey are the resulting rock grains of the weathering process. They are classified upon their size as follows: clay (< 0.004 mm), silt (< 0.06 mm), sand (< 2 mm), gravel (< 6 cm), cobbles (< 25 cm) and boulders (> 25 cm).
Frost shatteringOr freeze-thaw weathering. It's a kind of physical weathering usually produced by the expansion of the water filling the cracks in the rocks of the mountain areas where the daily temperature variation is around 0°C. The nightly pieces (wedges) of ice thus formed exert a pressure in the cracks called ice-wedging.
GullyLandform that resembles a series of sharp and very short channels carved by intermittent running water, usually by streams, and typically formed on deforestated hillsides.
RavineDeep, narrow and short channel with steep sides, carved by intermittent running water, usually by torrents. Bigger than gullies and smaller than valleys.
Canyon / GorgeAn extreme type of V-shaped valley: narrow, deep and with very steep sides (cliffs), carved by running water, usually by rivers. If the sides are stepped, reflecting alternating rock resistances, it is called a canyon; otherwise it is a gorge.