Genes are found in our chromosomes,which parents pass on to offspring in their sex cells in reproduction. Different versions of the same gene are called alleles, and these can determine features like eye colour, and the inheritance of disorders such as cystic fibrosis.

Chromosomes

Chromosomes are structures found in the nucleus of most cells. They consist of long strands of a substance called DNA . A section of DNA that has the genetic code for making a particular protein is called a gene. The proteins can either be:

• structural proteins such as the ones found in muscles and hair
• enzymes, such as protease's and other digestive enzymes.

Variation

Individuals differ in all sorts of ways, even when they are offspring of the same parents. These differences are called variation.Most characteristics, such as height, are determined by several genes working together. They are also influenced by environmental factors. These include:

• climate
• diet
• physical accidents
• culture
• lifestyle

For example, an individual might inherit a tendency to tallness, but a poor diet during childhood will result in poor growth and a shorter individual.

Identical twins

Identical twins are genetically the same. They are a good example of the interaction between inheritance and the environment. For example, an identical twin who takes regular exercise will have better muscle tone than one who does not exercise. All of the differences that you see between identical twins, for example, in personality, tastes and aptitude, are due to differences in their experiences or environment.

chromosomes

Human body cells each contain 23 pairs of chromosomes. Parents pass on their genes to their offspring in their sex cells. Sex chromosomes are responsible for certain genetic traits

• female sex cells are called egg cells
• male sex cells are called sperm.

Process of fertilisation

A pair of chromosomes carry the same genes in the same place, on each chromosome within the pair. However, there are different versions of a gene called alleles. These alleles may be the same (homozygous) on each pair of chromosomes, or different (heterozygous), for example, to give blue eyes or brown eyes.

Sex cells only contain one chromosome from each pair. When an egg cell and sperm cell join together, the fertilised egg cell contains 23 pairs of chromosomes. One chromosome in each pair comes from the mother, the other from the father.

Which chromosome we get from each pair is completely random. This means different children in the same family will each get a different combination. This is why children in the same family look a little like each other and a little like each parent, but are not identical to them.

Different versions of the same gene are called alleles. They can be either recessive or dominant. Genetic testing can determine whether a person is carrying the alleles that cause genetic disorders.

Genotype describes the genetic make-up of an organism (the combination of alleles).Phenotype describes the observable, physical characteristics that an organism has. This is often related to a particular gene.

cystic fibrosis caused by recessive allele symptoms:  thick sticky mucus ,breathing difficulty, chest infections ,digestion problems

huntingtons caused by dominant allele symptoms:

• tremors
• clumsiness
• memory loss
• mood changes
• poor concentration

• when embryos are produced in IVF,doctors can test the embryos to check if they've got certain genetic disorders.this is know as PGD and is especially important if there's concern that one of the parents might carry alleles for a genetic disorder.when the embryos are tested,only healthy ones are chosen to be implanted into the mothers womb-embryos with a genetic disorder are discarded

• children and adults can be checked to see if they carry alleles for genetic disorders.for example,couples might do this to find out if their children are likely to inherit a particular genetic disorder

• the results of genetic tests may not be 100% accurate.there are often errors due to things like samples getting contaminated or misinterpretation of results.false possitive and false negative because of this people might make discissions based on incorrect information
• tests carried out during pregnancy arnt 100% safe e.g doing a gentic test on the fluid around a fetus cause a miscarraige in 0.5 to 1% of cases
• if a test result is positive,should other members of a family be tested?some people may prefer not to know,but is this fair on any partners or future children they might have?
• terminate the pregnancy?some people think abortion is always wrong  whatever the circumstances .parents might not be able to cope with sick or disabled child
• results become avaliable to others might cause discrimination.employers might not want to give a job to someone who is likely to get ill
• insurance companies might refuse to give life insurance to people with the "wrong alleles"

clones are genetically identical organisms

asexual reproduction means that there is only one parent,and the offspring are genetically identical to each other and the parent.

bacteria reproduce by simply dividing into two

Some plants produce side branches with plantlets on them. The Busy Lizzie plant does this. Others, such as strawberry plants, produce runners with plantlets on them.

few animals-female greenfly dont need to mate-they can just lay eggs

identical twins are also clones

a single egg is fertillised by a sperm,and an embryo begins to develop as normal.occasionally,the embryo splits into two,and two seperate embryos begin to develop.the two embryos are genetically identical.so,two genetically identical babies are born

There are two types of stem cells:

• adult stem cells - these are unspecialised cells that can develop into many (but not all) types of cells
• embryonic stem cells - these are unspecialised cells that can develop into any type of cell.

some people object to stem cell research and treatments.they say that using stem cells is playing god

stem cells may be used to treat many illnesses

• people with some blood diseases(e.g sickle cell anaemia)can be treated by bone marrow transplants.bone marrow contains adult stem cells that can turn into new blood cells to replace the faulty old ones
• embryonic stem cells could also be used to replace faulty cells in sick people-you could make beating heart muscle cells for people with heart disease,insulin-producing cells for people with diabetes and so on

the volcanoes gave out lots of gas including,carbon dioxide,water Vapour and nitrogen.we think this was how  the atmosphere was formed.according to this theory,the early atmosphere was mostly c02 and water vapour with virtually no oxygen.the oceans formed when the water vapour condensed when the earth cooled

green plants evolved over most of the earth they were quite happy with the co2 in the atmosphere.a lot of the early co2 dissolved into the oceans.the green plants also removed co2 from the air and produced 02 by photosynthesis.when plants died they were buried under layers of sediment,the carbon they had removed from the air(as co2)become locked up in sedimentary rocks as insoluble carbonates and fossil fuels.

the build up of oxygen in the atmosphere killed off some early organisms that couldn't tolerate it allowed other more complex organisms to evolve.there is virtually no c02 left now

nitrogen 78% oxygen 21% argon 1%

all substances are made from atoms when atoms are joined together they make molecules

In a chemical reaction, the substances that react together are called the reactants, while the substances that are formed are called the products.

The products have different properties from the reactants.

As a chemical reaction takes place, atoms in the reactants are rearranged to make the products. No atoms are added or taken away. This is called the conservation of atoms.

fossil fuels are hydrocarbons

coal is mainly made from carbon

burning also known as combustion,is a type of chemical reaction.when a hydrocarbon burns,the hydrocarbon atoms in the fuel combine with oxygen atoms from the air to make water(h2o) and the carbon atoms in the fuel combine with oxygen atoms from the air to make carbon dioxide

any reaction where oxygen is added is called an oxidation reaction.reactions where oxygen is lost are called reduction reactions.combustion is an example of an oxidation reaction

carbon dioxide

• carbon dioxide,like any other atmospheric pollutant,will stay in the atmosphere causing problems until its removed
• co2 can be removed from the atmospher naturally.plants use up co2 from the air when they photosynthesise.co2 also dissoles in rainwater and in seas,lakes and rivers
• an increased co2 level increases the greenhouse effect,which is warming up the earth 

carbon monoxide

• carbon monoxide is poisonous.carbon monoxide is produced if theres not enough oxygen avaliable when fuel burns

particulate carbon

• carbon particulate caused by incomplete combustion.when they escape into the atmosphere,they just float around.eventually they fall back to the ground and deposit themseles as soot a lot falls onto buildings making them look dirty.
  

sulfur pollution comes from impurities in fuels

• when the fuel burns,the sulfur burns too.when the sulfur atoms burn,they combine with the oxygen in the air to produce the pollutant sulfur dioxide.

• so when power stations and vehicle einegines burn fossil fuels like coal and petrol,small amounts of the pollutant sulfur dioxide are produced.this sulfur dioxide usually ends up in our atmosphere

sulfur pollution causes acid rain

• the way sulfur dioxide usually leaves our atmosphere is in the form of acid rain
• when the sulfur dioxide emitted from vehicle einegines and power stations reacts with the moisture in clouds,dilute sulfuric acid is formed
• eventually,much of this acid will fall as acid rain,which is bad news for the enviroment
• acid rain causes lakes to become acidic,killing plants and animals.it also kills trees and damage buildings and statues made from some kinds of stone e.g limestome

nitrogen pollution involves nitrogen from the air

• fossil fuels burn at such high temperature's that nearby atoms in the air react with each other
• nitrogen in the air reacts with the oxygen in the air to produce small amounts of compounds known as nitrogen oxides-nitrogen monoxide and nitrogen dioxide
• this happens in car engines

here's how nitrogen oxides are formed:

nitrogen monoxide-nitrogen monoxide forms when nitrogen and oxygen in the air are exposed to a very high temperatures.this happens when fuels are burnt in places like car einegines

nitrogen dioxide-once the nitrogen monoxide is in the air,it will go on to react with more oxygen in the air to produce nitrogen dioxide

as pollutants nitrogen oxides are very similar to sulfur dioxide.when they're formed they usuallyend up in the atmosphere-where they stay till they react with mositure.this produce a dilute nitric acid which eventually falls to the earth as acid rain

we can reduce pollution from power stations..

• the less electricity we use,the less fossil fuels need to be burnt in power stations so less pollution is created
• much of the sulfur can be taken out of the natural gas and fuel oil that power stations use.this means that little sulfur dioxide is produced when it burns
• when coal is burnt in power stations,most of the sulfur dioxide and particulates such as carbon particles and ash can be removed from the flue(chimney)gases before theyre releasesd into the atmosphere
• the only way to reduce co2 emissions is to reduce the amount of fossil fuels burnt,either by using less electricity,or by finding alternatie energy sources
  

...and from our cars

• moter vehicles now have more efficient einegines,which burn less fel and so create less pollution.low-sulfur fuel for cars is now avaliable,which means less sulfur dioxide is emitted from the exhaust
• many cars are now fitted with catalytic converters.theese convert harmful nitrogen monoxide into harmless notrogen and ocygen.this is an example of a reduction reaction-the nitrogen looses oxygen
• catalytic converters also convert the toxic gas carbon monoxide into carbon dioxide by adding oxygen-an oxidation reaction
• theres a legal limit on the amount of polluting emissions that cars can give out.a cars emissions are checked once a year in the MOT test
• we could reduce pollution by using cars less.if everyone used public transport instead of individual cars then less fuel would be burnt overall

fossil fuels aren't the only option for powering cars

• car engines can be run by burning bio fuels.bio fuels fuels are renewable energy sources made from plants and waste-they are great for the environment as they only produce carbon dioxide and water when burned.bio fuels are said to be carbon neutral as the plants that are used to make the fuel take in as much co2 from the atmosphere as is given out by burning the fuel.however,in some places large amounts of Forest has been cleared to grow plants to make bio fuels resulting in species losing their natural habitats.
• you can also power cars using electric batteries.electric cars produce no exhaust gases and you just plug them into the mains to recharge them.but the electricity is still made by burning fossil fuels in a power station-so you don't get rid of pollution,you just move it somewhere Else

planets reflect sunlight and orbit the sun in ellipses

the solar system consists of a star(the sun) and lots of other stuff orbiting it:

• there are eight planets orbiting the sun in almost circular paths(ellipses)
• there are also various other things-dwarf planets,comets,dust and so on..all in orbit around the sun.these also count as part of the solar system

planets and stars are very different from each other

• stars are huge(the suns diameter is over 100 times bigger than the earths) very hot and very far away.they give out lots of light-which is why you can see them even though they're far away.
• planets are much smaller and they just reflect sunlight falling off them.the planets in the solar system are also much much closer to us than any star(except the sun).

the solar system is about 5 thousand million years old

• the solar system was formed over a very long period from big clouds of dust and gas
• for some reason(maybe a nearby star exploading),one cloud started to get squeezed slightly
• once the particles had moved a bit closer to each other,gravity took over.it pulled things closer and closer together until the whole cloud started to collapse in on itself
• at the centre of the collapse,particles came together to form a protostar.when the tempreture got high enough,a process called fusion started-hydrogen nuclei joined together to make helium.
• fusion gives out massive amounts of heat and light,so... a  star,our sun was born.(the sun and other stars' energy comes from the fusion of hydrogen nuclei
• all of the chemical elelments in the clouds with heavier atoms than helium and hydrogen were also formed in the stars by the fusion of differnt nuclei
• around the sun,material from the cloud containg hydrogen,helium and heavier elements started to clump together and theese clumps became planets(so the sun and planets have similar ages)
• the oldest rocks on earth are actually meterorits these are about 4500 million years old-so we know the solar system is at least that old

we're in the milky way

• our sun is one of thousands of millions of stars which form the milky way galaxy
• the sun is about halfway along one of the spiral arms of the milky way
• the distance between neighbouring stars in a galaxy is usually millions of times greater than the distance between planets in the solar system

every galaxy is made up of thousands of millions of stars,and the universe is made up of thousands of millions of galaxies

300 000km/s speed of light.a light year is the distance that light travels through a vacuum(like space)in one year.

• the diameter of the Earth is 12,800km (7,953 miles)
• the diameter of the Sun is 109 times that of the Earth’s
• the Earth is 150 million km (93 million miles) from the Sun
• the distance to the nearest star is four light years.

earth 5000 million years old      sun 5000 million years old   universe 14 000 million years old

radiation can tells us alot about stars and galaxies

parralax - the apparent movement ofd a star betweeen the two photos lets you work out how far away it is.stars furthur away appear to move less(the really distant stars dont appear to move at all-the movement is too small to detect

light pollution

In the last 200 years, it has become very difficult to make astronomical observations in industrialised countries such as the UK.It is due to the bright lights found in cities and towns, and on roads. This light pollution means that it is hard for many people to see more than a few of the very brightest stars at night.

Telescopes are now placed in the few remote, dark places left on our planet, or out in orbit around the Earth.

we see stars and galaxies as they were in the past

since the sun is about 150 million km away from the earth,the radiation from the sun that reachesus must left about 8 mins before we actually see it

distant galaxies are moving away from us

• by seeing how much light has been red shift,you van work out how quickly its moving away.the greater the red shift,the faster its moving away and from observations of different red shifts of different galaxies we know that:
• the more distant the galxy,the faster it moves away from us

the big bang theory-the universe is expanding

• right now,all the galaxies seem to be moving apart at great speed from a single point.what got them going was probably a big explosion
• according to this theory,all the matter and energy in the universe must have been compressed into a very small space.then it exploded and started expanding,and the expansion is still going on now

we dont know how(or if)the universe will end..

The eventual fate of the Universe is hard to predict due to the uncertainty in measuring such large distances and studying motion of distant objects. A better idea of the mass of the Universe would lead to better predictions.

rocks provide a record of changes in the earth

Rocks provide evidence for changes in the Earth. In 1785 James Hutton presented his idea of a rock cycle to the Royal Society. He detailed ideas of erosion and sedimentation taking place over long periods of time, making massive changes to the Earth’s surface.

Geologists can use other evidence from the rocks themselves such as:

• looking at cross-cutting features (rock that cuts across another is younger)
• using fossils (species existed/ became extinct during certain time periods)
• deepness of the rock (younger rocks are usually on top of older ones).

This kind of evidence only shows that some rocks are older than others. To get a more accurate idea of the age of rocks radioactive dating is used.

His idea was that the Earth's continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other. But it took a long time for the idea to become accepted by other scientists.

Wegener’s evidence for continental drift was that:

• the same types of fossilised animals and plants are found in South America and Africa
• the shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle
• matching rock formations and mountain chains are found in South America and Africa.
• the theory wasn't accepted at first-for a variety of reasons

• wegener's theory explained things which couldn't be explained by 'land bridge theory'
• wegener's explanation of how the drifting happened wasn't convincing(and the movement wasn't detectable)
• wegener wasn't a geologist

Then, in the 1950s, evidence from magnetism in the ocean floor showed that the seafloors were spreading by a few centimetres each year. This showed movement of large parts of the Earth’s crust, now called tectonic plates. This new evidence allowed Wagener's theory to be accepted.

seaflor spreeding

In the centres of many oceans, there are mid-ocean ridges. At these places, the tectonic plates are moving apart. Molten material, known as magma from inside the Earth oozes out and solidifies. This movement of the mantle is referred to as convection due to heating by the core of the Earth. This process is called seafloor spreading. It results in seafloors spreading by a few centimetres each year.

1. The crust, which is relatively thin and rocky
2. The mantle, shown here as dark red, which has the properties of a solid, but can flow very slowly
3. The outer core, shown as orange, which is made from liquid nickel and iron
4. The inner core, shown as yellow, which is made from solid nickel and iron

The Earth’s crust, together with the upper region of the mantle, consists of huge slabs of rock called tectonic plates. These fit together rather like the segments on the shell of a tortoise. 

Volcanoes, mountains and earthquakes occur at the edges of tectonic plates - their creation depends on the direction the plates are moving.

if the plates are moving apart, as at mid-ocean ridges, volcanoes are produced as molten magma is allowed to escape. This happens in Iceland.

If the plates are moving towards each other, the edges of the plates crumple, and one plate ‘dives’ under the other. This is called subduction. It produces mountains, like the Himalayas. The friction of the movement can also melt rocks and produce volcanoes.

If the plates are moving sideways, stresses build up at the plate boundary. When the stress reaches some critical value, the plates slip suddenly, causing an earthquake. It is hard to predict when such an event may happen.

P-waves (P stands for primary) arrive at the detector first. They are longitudinal waves which mean the vibrations are along the same direction as the direction of travel. Other examples of longitudinal waves include sound waves and waves in a stretched spring.

S-waves (S stands for secondary) arrive at the detector of a seismometer second. They are transverse waves which mean the vibrations are at right angles to the direction of travel. Other examples of transverse waves include light waves and water waves.

Both types of seismic wave can be detected near the earthquake centre but only P-waves can be detected on the other side of the Earth. This is because P-waves can travel through solids and liquids whereas S-waves can only travel through solids. This means the liquid part of the core blocks the passage of S-waves.

wave speed = frequency x wavelength