GCSE Biology OCR Gateway Higher Tier- B2 (Understanding Our Environment)

These are revision cards for "GCSE Biology OCR Gateway Higher Tier- B2 (Understanding Our Environment)". I have an exam next month so hopefully they will help!!!

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Classification- How Living Organisms Are Classifie

Classification systems can be artificial or natural:

Artificial classification systens are based on the appearence rather than genes. They're used to identify organisms.                                                                                    

Natural classification systems are based on the evolutionary relationships and genetic similarities between organisms.

Living things are divided into kingdoms (like the animal/ plant kingsdom e.t.c)

The kingdoms are then subdivided into smallergroups- phylum, class, order, family, genus, species.

A genus is a group of closely- related species and a species is a group of organisms who can interbreed to  produce a fertile offspring.       

It can be difficult to classify organisms into distinct groups because many organisms share characteristics of multiple groups.

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Classifcation Systems- How They Change Over Time

When a classification system is created it fits everything we know so far about different groups of organisms.

But as scientists discover new species they might have tho adapt classification systems to fit their new findings:

Newly discovered species might not fit into any of the categories. These could be living species or newly discovered fossils. E.g. the archaeopteryx fossil has features of two different classes (birds and reptile) so it's hard to know where to place it.

DNA sequencing allows us to see genetic differences between different groups. As this data is collected we might find out that two groups aren't actually as closely related as we thought- or two groups that we thought were very different may turn out to be relatives.

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Classification- Evolutionary Relationships

You can draw evolutionary trees to show how closely related different species are to each other.

Evolutionary trees show common ancestors and relationships between species. The more recent the common ancestor, the more closely related the two species- and the more characteristics they are likely to share.

To find out about evolutionary relationships between organisms, scientists analyse lots of genes responsible for certain characteristics.

Studying lots of characteristics involves analysing a huge amount of DNA data and is now only possible thanks to advances in ICT.

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Species- Problems With Classifying Organisms

A species is a group of living organisms which can interbreed to produce fertile offspring.

There are a few problems when it comes to classifying organisms:

Asexual Reproduction: an organism makes a copy of itself- there is no interbreeding so it doesn't fit the species defintion.

Hybrids: if you interbreed a male from one species with a female from another you'll get a hybrid, but hybrids are usually infertile so they aren't new species.

Evolution: organisms change and evolve over time, so the way that they have been classified might change. Sometimes a group of organisms will change so much it will form a new species- but it can be difficult to tell when this has happened.

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Species- Binomial System

In the binomial system every species is given a two part Latin name. The first part refers to the genus that the organism belongs to and the second part refers to the species.

E.g. Human are called Homo sapiens. 'Homo' is the genus and 'sapiens' is the species.

The binomial system is important as scientists use them all around the world.

It means that in different countries with different languages all the scientists call the species the same thing. It save a lot of potential confusion.

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Similar species often share a recent common ancestor, so they're closely related in evolutionary terms. They often look alike and tend to live in similar types of habitats. E.g. whales & dolphins.

This isn't always the case though- closely related species may look very different if they have evolved to live in different habitats. E.g. llamas and camels.


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Pyramids of Biomass

 Biomass is the dried mass of an organism.

Biomass pyramids are almost always pyramid shaped because biomass is lost at each stage in a food chain.

To construct a pyramid of biomass you use the dry biomass of the organisms. Measuring dry biomass can be difficult because ou hvae to kill the organisms to work it out. Atthough this is easy to do with a tree or grass it is unethetical to kill lots of animals everytime you want to make a pyramid.

It can sometimes be difficult to construct an accurate pyramid of biomass because some organisms feed at more than one trophic level. For example, partridges may eat more than one kind of bug.

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Pyramids of Numbers

Pyramids of numbers are similar to pyramids of biomass, but each bar on a pyramid of numbers shows the number of organisms at that stage of a food chain. Not its mass.

Pyramids of numbers are hardly ever pyramid shaped.


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Energy Transfer & Energy Flow

1) Energy from the Sun is the source for nearly all life on Earth.

2) Plants use a small percentage of light energy from the Sun to make food during photosynthesis. his energy then workd its way thorugh the food chain as animals eat plants and each other.

3) The energy lost at each stage is used for staying alive, i.e. in respiration which powers all life processes.

4) Most energy is eventualy lost into its surroundings as heat. This is especially true for mammals and birds, whose bodies need to maintain a constant temperature (normally higher than their surroundings).

5) Material and energy are also lost from the food chain as waste products. Egestion is when food that can't be digested passes out as faeces and excretion is when the waste products of bodily processes are released e.g. urine.

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Energy Transfer & Flow

6) Waste products and uneaten parts (e.g. bones) can become starting points for other food chains. For example houseflies eat faeces.

Material and energy are both lost at each stage of the food chain. This explains why you get biomass pyramids. Most of the biomass is lost and so does not become biomass in the next level up. It also explains why food chains hardly go above 5 trophic (feeding) levels. So much energy is lost that at each stage that there is not enough left to support more organisms after 4 or 5 stages.

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Energy Efficiency

efficiency= energy available to next level/ energy that was available to previous level x100

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Organisms Compete To Survive

1) In order to reproduce and survive organisms must compete against eachother for the resources they need to live (e.g. food, shelter).

2) Similar organisms in the same habitat will be in the closest competition because they will be competing for similar ecological niches.

A species' ecological niche is how it fits in to its ecotsystem. It depends on things like where the individuals live and what they eat...

3) There are 2 types of competition between organisms:

Interspecific competition is where organisms compete for resources agaianst individuals of another species.

Intraspecific competition is where organisms compete for resources against individuals of the same species.

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Organisms Compete To Survive- Part 2

Intraspecific compe***ion often has a bigger impact on organisms than interspecific compe***ion.

This is because individuals of the same species have exactly the same needs, so they'll compete for lots of resources.

E.g. the blue *** might compete with another blue *** for food, shelter and a mate, but a blue *** and a great *** might only compete for the same food source.

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Populaions of Prey & Predator Go In Cycles

1) The population of any species is usually limited by the amount of food available.

2) If the population of the prey increases, then so will the number of predators.

3) However as the population of predators increases, the number of prey will decrease.

4) Predator prey cycles are always out of phase with each other. This is because it takes a while for one population to respond to the changes in the other population.

E.g, when the number of rabbits goes up the foxes don't automatically go up as it takes a while to reproduce.

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Parasitic & Mutualistic Relationships

1) Parasites live off a host. They take what they need to survive, without giving anythign back. This often harms the host- which makes it a win-lose situation.

E.g. A tapeworm absorbs lots of nutrients from the host, causing them to suffer from malnutrition.

2) Mutualism is a relationship where both organisms benefit- so it's a win-win situation.

E.g. Plants are pollinated by insects, allowing them to reproduce. In return, the insects get a lot of sweet, sugary nectar.

E.g. Oxpeckers live on the backs of buffalos. Not only do they eat pests (ticks, flies, maggots e.t.c.) they also alert the animals to any predators that are near, by hissing.

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Adaptations are the features that organisms have that make them better suited to their environment.                                                                                                                                                          

Organisms that are adapted to their environments are better able to compete for resources. This means that they're more likely to survive, reproduce and pass on their adaptations to their offspring.

Specialists are organisms which are highly-adapted to survive in a specific habitat whereas generalists are organisms that are adpated to survive in a range of different habitats.

A habitat is a place where the conditions are stable (i.e. they're not changing), specialists will out-compete generalists as they're better adapted to specific conditions, however if the conditions in a habitat change, specialists will then be out-competed by generalists as they will have adapted to the new conditions.....

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1) Some organisms can tolerate extreme conditions.E.g. very high/ low temperatures or pHs.

2) Organisms that are adapted to live in seriously, extreme conditions are called extremophiles.

3) In order to survive these sorts of 'harsh conditions', organisms have some unique adaptations:

Extremophile bacteria: These live in very hot environments so they have enzymes that work best at a much higher optimum temperature than enzymes in other organisms. These enzymes are able to function normally at temperatures that would denature enzymes in other organisms. For example, the bacteria Thermus thermophilus grows best in environments around 65 degrees celcius.

Organisms that live in very cold environments sometimes have special antifreeze proteins. These proteins interfere with the formation and growth of ice crystals in the cells, stopping the cells from being damaged by ice.

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Anatomical Adaptations To Cold Environments

1) Having a thick coat or layer of blubber to insulate the body and trap heat in.

2) Having a large size and compact body shape to give a smaller surface area to volume ratio. This reduces heat loss as less body heat can be lost through the surface of the skin.

3) Having counter current heat exchange systems:

- Blood vessels going to and from the feet carry blood that flows in opposite directions.

- The vessels pass close to each other, allowing heat to transfer between them.

- Warm blood flowing in the arteries to the feet heats cold blood returning to the heart in the veins.

- This means that the feet stay cold, but it stops cold blood from cooling down the rest of the body.

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Behavioural Adaptations To Cold Environments

1) Many species migrate to warmer climates during the winter months to avoid having to cope with cold conditions.

2) Other species hibernate during the winter months. This saves energy as animals don't have to find food or keep itself warm.

3) Some species (like penguins) huddle together to keep warm....

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Anatomical Adaptations To Hot & Dry Environments

1) Animals that have adapted to hot environments are often small. This gives them a large surface are to volume ratio which allows them to lose heat to their surroundings.

2) Having large ears can also increase an animal's surface area to volume ratio and help them to lose heat. Large thin ears allow more blood to flow near the surface of the skin- so more heat from the blood can be radiated into the surroundings.

3) Some animals store fat in one part of their body (like camels)- this stops the rest of the body from being too well insulated and allows heat to be lost more easily.

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Behavioural Adaptations To Hot & Dry Environments

1) Animals that live in very hot climates often spend the day in the shade or underground to minimise the amount of heat they gain from their surroundings.

2) Animals can also reduce their heat gain by being active at night, when it is much cooler.

3) Animals can increase heat loss by bathing in water. As the water evaporates it transfers heat from the skin to the surroundings, cooling the animals down.

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How Organisms Have Adapted To Hot & Dry Environmen

Desert Plants

1) have a rounded shape, giving them small surface area to volume ratio to minimise water loss.

2) have a thick waxy layer and spines instead of leaves to prevent water loss.

3) store water in their stems to allow them to survive in times of extreme drought.

4) have shallow, but very extensive roots to absorb water quickly over a large area.

Desert Animals

1) have specialised kidneys that produce very concentrated urine, with a very low water content.

2) have no sweat glands, preventing them from losing water through sweating.

3) spend time in underground burrows, where the air contains more moisture than outside.

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Evolution & Speciation- Survival of The Fittest

Charles Darwin came up with the 'Theory of Natural Selection'.

1) Darwin knew that organisms in a species show wide variation. He also knew that organisms have to compete for limited resources in an ecosystem.

2) Darwin concluded that the organisms that are best adapted (the fittest) would be more successful competitors and woild be more likely to survive (the survival of the fittest).

3) The successful organisms that survive are more likely to reproduce and pass on their adaptations that made them succesful to their offspring.

4) The organisms that are less well adapted would be less likely to survive and reproduce, so they are less likely to pass on their characteristics to the next generation.

5) Over time, successful adaptations become more common in the population and the species changes- it evolves.

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Evolution & Speciation- New Discoveries Lead To De

1) Darwin's theory wasn't perfect- he couldn't give a good explanation for why new characteristics appeared or exactly how individual organisms passed on beneficial adaptations to their offspring.

2) That's because DNA wasn't discovered until 50 years after his theory was published.

3) We now know that adaptations are controlled by genes, New adaptations arise because of mutations (changes in DNA). Successful adaptations are passed on to future generations in the genes that parents contribute to their offspring.

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1) Over a long period of time, organisms may change so much (because of natural selection)  that a completely new species is formed. This is called speciation.

2) Speciation happens when populations of the same species change enough to become reproductively isolated- this means they can't interbreed to produde fertile offspring.

3) Reproductive isolation can be caused by geographic isolation. The next revision card describes how this happens.                                     

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- A physical barrier divides a population of a species e.g. the river changes it course. The two new populations are unable to mix and mingle.

 - Different mutations create new features in the two groups of organisms.

 - Natural selection works on the new features so that, if they are of benefit, they spread through the entire population.

-Eventually, individuals from the two populations will have such different features that they won't be able to breed together to produce fertile offspring. They'll have become reproductively isolated and the two groups will be seperate species.

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Theories of Evolution- Darwin

Not everyone could believe Darwin's theory for 3 main reasons:

1) The theory went against common religous beliefs about how life on Earth developed- it was the first plausible explanation that did not need or involve God. Religous authourities ridiculed this idea.

2) Darwin could not explain why new, useful characteristics appeared or how they were inherited...

3) There wasn't enough evidence to convince many scientists, because studies had not been done into how organisms changed over time.

Nowadays people accept Darwin's theory:

1) The theory has been debated and tested independently by lots of scientists and no-one has conclusively proved it wrong.

2) The theory offers a plausible explanation for so many observations of animals and plants.

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The Carbon Cycle


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1) Recycling of carbon and other nutrients takes longer in waterlogged soils than in well-drained soils.

2) This is because the bacteria and fungi that decompose organic material usually need oxygen to respire and produce energy. Waterlogged soil does not have much oxygen- so the decomposers have less energy and work slowly.

3) Nutrient recycling also takes longer in highly acidic soils than in neutral soils. This is because extremes of pH slow down the reproduction of decomposers or kill them outright.

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Theories of Evolution- Lamarck

1) Lamark argued that if a characteristic was used a lot by an animal then it would become more developed. Lamarck reckoned that these acquired characteristics could be passed on to the animal's offspring. For example, if a rabbit did a lot fof running and developed big leg muscles, Lamarck believed that the offsrping would also have big muscles.

2) However people eventually conclued that acquired characteristics do not have a genetic basis- so they're unable to be passed on to the next generation. This is why Lamarck's theory was rejected.

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Human Impact On The Environment

Human Population Is Increasing...

1) The world's human population is rising exponentially which means it's increasing rapidly.

2) Populations increase when the birth rate is higher than the death rate.

3) The rapidly increasing population is putting pressure on the environment- more resources are being used up and more pollution is being produced.

4) The higher standard of living amongst more developed countries demands even more resources, and although these developed countries have only a small proportion of the world's population, they cause a large proportion of pollution.

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Human Population Is Increasing...

1) The world's human population is rising exponentially which means it's increasing rapidly.

2) Populations increase when the birth rate is higher than the death rate.

3) The rapidly increasing population is putting pressure on the environment- more resources are being used up and more pollution is being produced.

4) The higher standard of living amongst more developed countries demands even more resources, and although these developed countries have only a small proportion of the world's population, they cause a large proportion of pollution.

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Global Warming

1) Fossil fuels are coal, oil and natural gas.

2) When they're burned, they release lots of carbon dioxide, which is a greenhouse gas. Greenhouse gasses trap heat in the atmosphere which causes global temperature to rise. This is called global warming.

3) Scientists have predicted that, if global temperature continues to go up, sea levels will rise, weather systems will become less predictable and agricultural output will fall.

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Acid Rain

1) When fossil fuels and waste materials are burned they release a gas called sulfur dioxide.

2) Sulfur dioxide reacts with water in the atmosphere to form sulfuric acid which falls as acid rain.

3) Acid rain damages soils and can kill trees.

4) Acid rain can cause lakes to become more acidic. This has a severe effect on the lake's ecosystems. Organisms that are are sensitive to changes in pH can't survive in more acidic conditions. This ends up killing many plants and animals.

5) Acid rain damages limestone, ruining buildings and stone statues.

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Ozone Depletion

1) CFCs (chlorofluorocarbons) used to be used in aerosols, fridges, air-conditioning units and polystyrene foam.

2) They break down ozone in the upper atmosphere.

3) This allows more harmful UV rays to reach the Earth's surfuce.

4) Being exposed to more UV rays increases the risk of skin cancer. Australia has high levels of skin cancer because it is under an ozone hole.

5) The increase in UV rays might also kill plankton in the sea- this could have a massive effect on the sea ecosystem (because plankton are at the bottom of the food chain). Scientists that fish levels will drop (this could mean we get less food)

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Indicator Species Can Be Used To Show Pollution

1) Some species can only survive in unpolluted conditions, so if you find lots of them, you know it's a clean area.

  Lichens are used to monitor air quality- they're damaged by pollution. The cleaner the air, the greater the diversity of lichens that survive.

Mayfly larvae ae usedto monitor water quality- they can't survive in polluted water.

2) Other species have adapted to live in polluted conditions- so if you see a lot of them you know there's a problem.

Water lice, rat- tailed maggots and sludgeworms all indicate polluted water. But out of these rat- tailed maggots and sludgeworms indicate a very high level of pollution.

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Ways of Measuring Pollution

Using indicator species you can:

1) See if a species is present or absent from an area. This is quick, but is not good for telling how polluted an area is.

2) Count the number of indicator species in an area allowing measurements from different areas to be compared so you can see how polluted an area is...

You can measure pollution directly by using:

1) Senstive instruments can measure the concentrations of chemical pollutants, e.g. carbon dioxide or sulfur dioxide in samples of air or water.

2) Satellite data to indicate pollutant level e.g. satellites can show where the ozone layer is thin or absent, which is linked to the CFC level....

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Advantages & Disadvantages With Measuring Methods

Living Methods

Advantages-Using living methods is relatively quick, cheap and easy way of saying whether an area is polluted or not. No expensive equipment or highly trained workers are required.

Disadvantages-Factors other than pollution (e.g. temperature) can influence the survival of indicator species so living methods are not always reliable.


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Non-living Methods

Advantages-Directly measuring the pollutants gives reliable, numerical data that’s easy to compare between different sites. The exact pollutants can be identified too.

Disadvantages-Non-living methods often require more expensive equipment and trained workers than methods using indicator species.

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Endangered Species

Factors that lead to endangered species include:

1) The number of habitats- it's hard for organisms to find food, shelter and other resources so there are not enough suitable habitats.

2) The number of individuals- if there are only a few individual species left it'll be hard to find mates. It means there will not be much genetic variation in the population.

3) Genetic variation- this is the number of different alleles in a population. If genetic variation is low, then a species is less likely to be able to adapt to changes in the environment or survive the appearance of a new disease.

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Exam Tip: Evaluting Conservation Programmes

Conservation Programmes are designed to help save endangered plants and animals. They involve things like protecting habitats, creating artificial environments and captive breeding.

In your exam you may need to EVALUATE how successful a conservation programme is likely to be. The evaluation criteria to use is:

1) GENETIC VARIATION- the species being conserved should have enough genetic varation to survive the apperance of new diseases and to cope with environmental change.

2) VIABLILTY OF POPULATIONS- populations should be able to reproduce- so they must contain both males and females of reproductive age. They should also be large enough to prevent related individuals having to breed together- this is called inbreeding and reduces gentic variation.....

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3) AVAILABLE HABITATS- there should be plenty of suitable habitats to live in. The right type of habitat is especially important if the organisms being conserved are specialists.

4) INTERACTION BETWEEN SPECIES- it's important that species interact with each other as they would in their natural environment. E.g. predator species should be able to hunt prey!

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Conservation Programmes Benefit Wildlife & Humans.

1) PROTECTING HUMAN FOOD SUPPLY- over fishing has greatly reduced fish stocks in the oceans. Conservation programmes ensure that future generations will have fish to eat.

2) ENSURING MINIMAL DAMAGE TO FOOD CHAINS- if one species becomes extinct it will affect all the organisms that feed on and are eaten by that species, so the whole food chain will be affected.

3) PROVIDING FUTURE MEDICINES- many of the medicines we use today come from plants. Undiscovered plant species may contain new medicine chemicals. If these plants are allowed to become extinct, perhaps through rainforest destruction we could miss out on the cure to  cancer or asperger's syndrome.

4) CULTURAL ASPECTS- individual species may be important in a nation's or an area's heritage. E.g. the bald eagle in America is being conserved in the USA as it is regarded as the national symbol....

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Sustainable Development

As the human population gets bigger....

1) We need to produce more food- so we'll need to continue farming,

2) We use up more energy. At the moment the vast majority of energy come form burning fossils fuels(but these re running out...)

3) We're producing more waste- it all needs to be disposed and at the moment it's polluting the Earth.


Sustainable development needs to be carefully planned and it needs to be carried out all over the Earth which means we need to cooperate locally, nationally and internationally...

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Examples of Sustainable Development

1) Fishing quotas have been introduced to prevent some types of fish, such as cod, from becoming extinct in certain areas.This means that they will still be around for the future generations to enjoy.

2) To make the production of wood and paper sustainable there are laws insisting logging companies plant new trees to replace those they've cut down.

Education is important. If people are aware of a problem they are more likely to help- e.g. not buying certain types of fish and only buying wood products from sustainably managed forests. Sustainable development also helps endangered species by considering the impacts on their habitats.

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thanks, very useful!

This is extremely helpful, i have my biology exam on the 14 of January... Good Luck in your exams... :) Just a little thing... page 38 gets cut off, could you possibly move the rest of the info onto a new card? Thanks :)

Kamya Gopal

I've sorted out page 38 for you... Sorry I didn't notice. Good luck with your exam!!

Vimbai Lynety

Thank you so much got an exam on monday 14th as well

Kamya Gopal

My exam is then as well. Just to point out my science teacher said I forgot to do the Nitrogen Cycle so remember to revise that as well... :)


can i ask what time the Biology exam on the 14th is? I'v lost my exam timetable.


umme ahmed

  1. s
umme ahmed

I need help on chemistry anyone want to help :)


This seems to be a popular set of notes with some useful diagrams and exam tips.They were written for the OCR GCSE syllabus but would be useful for many other specifications as well.There are a lot of slides here so students could take out just the slides they needed for their specification.


Some letters on Page 13 are cut off. Other than that these are really helpful


It does cover ALL the topics from B2 OCR Gateway to secure that A* grade right?


Seems like it's all copied from the CP book :/

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