Bology revision - competition to evolution. from the new GCSE science and additional science revision book.

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  • Created by: katie
  • Created on: 06-06-12 12:43


  • if resources are in short supply then organisms need to compete for them.
  • plants compete for light so the tallest win the competition.
  • The best ones for competing will survive. The ones that aren't good at competing will die and won't be able to pass on their genes to the next generation.
  • If there's not enough females around then the males will compete with each other for a mate.
  • Animals also compete for territory.
  • They don't always compete for resources, they can also compete to see who's better.
  • Many organisms have adapted in ways ehich alows them to live in places others can't, therefore there's no competition for them.- this increases chances of survival and they're able to produce large numbers of offspring.
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Adaptations for survival.

  • plants that usually live in dry places have: 
    • long, wide spread roots that grow deep into the soil to allow them to get water.
    • Small, or no leaves - the smaller they are the less the amount of water that is evaporating away.
    • tissues that can store water.
  • Animals that live in dry places have to find ways of regulating their water usage.
  • camel's stomach can hold over 20 litres of water, they drink quickly, store water as fat in their humps, and they produce very little urine.
  • Desert animals usually have large ears. A large surface area allows them to stay cool.
  • Animals in the arctic and cold conditions have thick fur and thick layers of fat. the insulation stops heat loss. they're coloured white so they can camoflauge.
  • plants sometimes have spikes or poisons to deter predators.
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Adaptations for survival. - cont'

  • extremophiles - microorganisms that can live in extreme conditions. - they have very stable protein molecules that aren't affected by extreme conditions.
  • Extremophiles can withstand extremely cold or hot temperatures.
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Environmental change.

  • Environmental changes are caused by living and non- living factors. for example: 
    • non-living factors include global warming, which has caused rainfall in central Australia to decrease 
    • Living factors include the grey squirrel into britain causing the native red squrrel's numbers to decrease.
  • Honeybees help polonate flowers.
  • In recent years, the number of honeybees has declined,
  • We are not sure why; many suggestions have been put forward though.
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Pollution indicators.

  • In the UK, the air, waters, rivers and streams are all being measured so we can track any changes in the composition.
  • Oxygen meters measure the concentration levels of dissolved oxygen. unpolluted water contails a high level of dissolved oxygen.
  • Rain gauges measure rainfall.
  • We can use the didtribution of organisms to find out about pollution.
    • if there's alot of sulfur dioxide in the air then Lichens won't grow.
    • If the levels of oxygen in a river are low then the oxygen-loving mayfly larvae won't be there, instead you will find rat-tailed maggots and bloodworms.
  • Polluted water contains low levels of dissolved oxygen, some spieces of inverterbrate are able to live in this but others are not.
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Food chains and energy flow.

  • Green plants capture only a small amount of the energy from the light that falls on them, this is because:
    • Some light misses the leaves altogether
    • Hits the leaf and reflects back from the leaf surface
    • hits the leaf but goes all the way through missing the chlorophyll
    • hits the chlorophyll but is not absorbed because it's the wrong wavelength (colour)
  • As a result, very little of the light that falls on a plant is used for photosynthesis and gets transferred into chemical energy in carbohydrates and other substances.
  • A food chain shows energy passed from producer to consumers.
  • whenever energy is transferred, some of it is wasted.
  • to calculate efficiency of energy transfer you use the formula:

Efficiency= useful energy transferred x 100%

   Original amount of energy.

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( This is a pyramid of biomass.

  • the food chain loses energy because:
    • Urination and Faeces.
    • Breathing.
    • Regulating body temprature.
    • Not all of the organism's tissues are eaten.
  • Mammals and birds use glucose to keep their body temprature high.
  • This means that energy loss from birds and mammals are high.
  • other animals - cold blooded animals stay the same temprature as their environment.
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  • Most of the fungi that carry out decay need:
    • Oxygen for aerobic respiration
    • A warm temperature for their enzymes to work at an optimum rate.
    • moisture for reproduction.
  • Increasing the temperature of microorganisms slows or stops decay.
  • Compost heaps are kept warm, moist and aerated to speed up the decay of plant waste into compost. compost is high in nutrients and is used to promote plant growth.
  • If food is not to decay, it can be treated to slow down, or stop the activity of microorganisms.
  • this includes: 
    • Canning
    • pickling
    • Drying food
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  • Decay microorganisms feed on every organism in the chain.
  • They will break down the waste and then they will break down the bodies when they die.
  • Dead whale carcasses feed entire communities of organisms.
  • Crabs, worms and fish eat the whale's body.
  • Microorganisms eat the rest. this process usually take decades.
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Processes in the carbon cycle.

  • Animals, plants and decomposers all interact with each other in the carbon cycle.
  • Photosynthesis converts carbon dioxide into carbohydrates and other food molecules such as proteins.
    • Carbon dioxide + water -> glucose + oxygen
  • When animals eat plants (or other animals) the food goes into their cells and is broken down by respiration.
    • Glucose + oxygen -> carbon dioxide + water.
  • Carbon dioxide is returned to the air when the animal breathes out.
  • Some dead organisms do not decay. they become buried and compressed, deep underground and turn into fossil fuels.
  • carbon dioxide is returned to the air when we burn fossil fuels (combustion).
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Energy in the carbon cycle.

  • Energy is transferred in the carbon cycle.
  • During photosynthesis, energy from sunlight is transferred to energy stores as chemicals in carbohydrates.
  • Some of this energy is transferred to other living things when they eat the plant.
  • Both energy and carbon atoms can't be destroyed or created. they are constantly being recycled around the planet.
  • Some of the energy is wasted, heating the soil and the air.
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Genes and chromosomes.

  • Chromosomes are long sections of DNA.
  • Most human cells have 46 chromosomes, 23 from the sperm and 23 from the egg, each carry about 25,000 genes.
  • Each gene contains coded information that controls one characteristic.
  • Most of the genes come in more than one form. For example,a gene that controls hair colour may have one form that produces brown hair and another one that produces red hair.
  • Variations in organisms may be due to either:-
    • The genes they have inherited.
    • Conditions which they've grew up (environmental causes).
    • Or a mixture of both.
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  • In sexual reproduction, gametes and fertilisation are always involved.
  • The new cell that is produced by fertilisation is called a zygote. it divides repeatedly to produce a little ball of cells. This develops into an embryo and finally into an adult animal.
  • Sexual reproduction produces a variety in the offspring because each zygote has a different mix of genes from its parents and siblings.
  • Asexual reproduction, an individual splits in two (bacteria) or a part divides off. this is offspring.
  • There is no variation with asexual reproduction. they are clones.
  • Sexual reproduction does not need two parents. some plants and flowers can do it themselves.
  • In birds and mammals the Male's sperm fertilises the Woman's egg inside her body. this is known as internal fertilisation.
  • In other animals, such as fish, the male and female shed sperm and eggs into water, this is known as external fertilisation.
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Cloning plants and animals

  • Taking cuttings from a plant then dipping it into rooting powder then placing it in soil produces an exact clone of the parent plant.
  • Tissue culture can be used to clone plants 
    • A small piece of tissue is cut away from the plant then grown in jelly containing all the nutrients it needs.
    • Everything has to be kept sterile so it's usually done in a labrotory.
    • Eventually, each tiny group of cells would have grown into a complete adult plant.
  • Embryo transpants are another way of cloning things - usually farm animals.
    • Egg cell is taken from a cow and fertilised with the sperm from the bull.
    • one embryo is chosen and split into two, or more then placed back into the host mother.
    • the calfs are born exact clones of eachother. - they have the same genes.
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Genetic Engineering

  • Bacteria have been genetically engineered to make human insulin.
  • Farmers spray fields with herbicides to kill weeds that compete with soya plants. the spray contains glyphosate.
  • When a farmer sprays the field with glyphosate, the weeds die but the plants do not.
  • Some genetic modification crop plants are resistant to attack by pests. this can greatly increase the yields that keep prices down. it also reduces the amount of pesticide that has to be sprayed. 
  • Some people have concerns about GM plants
    • Genes for a toxin to kill insects could be transferred to a wild plant, which could then disrupt natural food chains.
    • May be effects on humans.
  • GM plants have to be thoroughly tested before they are allowed to be grown on a large scale.
  • There's no evidence that GM plants do us harm.
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  • Jean-Baptiste Lamarck suggested that the changes in organisms caused by their environment were passed on to their offspring. this is incorrect.
  • Charles Darwin suggested that species gradually changed because of natural selection. Darwin thought that the best adapted individuals survived and then passed their genes onto future generations.
  • Darwin's ideas challenged the established thinking of the day, so his ideas were not accepted at first. they undermined the idea that god created all plants and animals.
  • In the late 19th century, there was not much scientific evidence to support the theories of evolution and natural selection. At the time no one even knew that genes existed yet alone how they are inherited. this was not discovered until 50 years later.
  • The earliest forms of life on earth were single celled organisms. Today, many organisms are very complex.
  • Some bacteria remain unchanged, they're almost the same as the ones that lived billions of years ago. they are supremely well adapted to their environment.
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Natural Selection

  • This is how natural selection happens.
    • Living organisms produce many offspring.
    • offspring vary from one another, because their genes are different.
    • The genes that give them the better chance of survival are most likely to reproduce.
    • their genes will bee passed on to their offspring.
  • Occasionally, unpredictable changes to chromosomes in genes happen - genetic mutation.
  • Occasionally, the genetic mutation helps the organism's chance of survival. over time this 'genetic mutation' becomes more common in the species as they're better adapted.
  • The pepper moth changing from pale to dark is a good example of this.
  • Some forms of bacteria have become resistant to antibiotics.
  • This has happened as a result in the mutation in the bacteria producing a form of gene that helped them survive when the antibiotic was present in their environment.
  • This process is random, you can't decide to genetically mutate.
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Evidence for evolution

  • You can get clues about evolution from organisms that are alive today.
  • For example, human's arms, bat's wings and bird's wings all have the same bones in the same places. things like this have suggested that humans, birds and bats are quite closely related and that, we all have a common ancestor.
  • There are 5 main classification groups; bacteria, protoctists, fungi, plants and animals.
  • Scientist are still discovering new species which change their ideas about how organisms should be classified.
  • Recently, they have found out that there are two distinct groups of these microorganisms. they are as different from one another as animals are to bacteria.
  • these are now split into two groups - Bacteria and Archaea.
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