AQA Biology 1b

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Desert Animal Adaptations

Large surface area compared to volume:
This lets desert animals lose more body heat - which helps to stop them over heating.

Efficient with water:
They lose less water by producing small amounts of concentrated urine. They also make very little sweat. Camels can tolerate big changes in body temperature, kangaroo rats live in burrows underground where it's cool.

Good in hot conditions:
They have very thin layers of body fat and a thin coat to help them lose body heat. E.g. camels keep nearly all their fat in their humps.

Camouflage:
A sandy colour gives good camouflage - to help them avoid predators, or sneak up on prey.

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Arctic Animal Adaptations

Small surface area compared to volume:
They have a compact (rounded) shape to keep their surface to a minimum - this reduces heat loss.

Well insulated:
They have a thick layer of blubber; this also acts as an energy source when food is scarce. Thick hairy coats keep body heat in. Greasy fur sheds water which prevents cooling due to evaporation.

Camouflage:
White fur to help them avoid predators or sneak up on prey.

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Desert Plant Adaptations

Small surface area:
Plants lose water vapour from the surface of their leaves. Cactus have spines instead of leaves to reduce water loss. They also have a surface area 1000 times smaller than normal plants which also reduces water loss.

Water storage tissues:
A cactus stores water in its thick stem.

Maximising water absorption:
Cactus have shallow but extensive roots to absorb water quickly over a large area. Others have deep roots to access underground water.

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Other Adaptations

Some plants and animals are adapted to deter predators:

  • some plants and animals have armour - roses (thorns), cacti (sharp spines), tortoise (shells).
  • others produce poisons - bees and poison ivy.
  • some have amazing warning colours to scare off predators - wasps.

Microorganisms have a huge variety of adaptations so that they can live in a wide range of environments, for example:

  • some microorganisms (e.g. bacteria) are known as extremophiles - they're adapted to live in seriously extreme conditions like super hot volcano vents, in very salty lakes or at high pressures on the sea bed,
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Competition for Resources

Organisms need things from their environment and from other organisms in order to survive and reproduce:

  • plants need light, space, water and minerals (nutrients) from the soil
  • animals need space (territory), food, water and mates

Organisms compete with other species ap(and member of the own species) for the same resources. E.g. red and grey squirrels live in the same habitat and eat the same food. Competition with the grey squirrels for these resources mean there's not enough food for the reds - so the population of red squirrels is decreasing.

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Environmental Changes

The environment in which plants and animals live change all the time.
These changes are caused by living and non-living factors.

Living factors:

  • a change in the occurrence of infectious diseases
  • a change in the number of predators
  • a change in the number of prey or the availability of food sources
  • a change in the number of types of competitors

Non-living factors:

  • a change in average temperature
  • a change in average rainfall
  • a change in the level of air or water pollution
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Environmental Changes Affect Populations

Environmental changes can affect animals and plants in three ways.

Population size INCREASES
e.g. if the number of prey increases, then there's more food available for predators, so more predators survive and reproduce, and their numbers increase too.

Population size DECREASES
e.g. the number of bees in the US is falling rapidly, experts are t sure why but they think it could be because:

  • some pesticides may be having a a negative effect on bees
  • there's less food available - there aren't as many nectar-rich plants
  • there's more disease - bees are being ill end by new pathogens or parasites

Population distribution CHANGES
(A change in distribution means a change in where an organism lives.)
For example, the distribution of bird species in Germany is changing because of a rise in average temperature, e.g. the European Bee-Eater bird is a Mediterranean species but it's now present in parts of Germany.

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Environmental Changes can be Measured Using Living

1) Some organisms are very sensitive to changes in their environment and so can be studied to see the effect of human activities - these organisms are known as indicator species.

2) Air pollution can be monitored by looking st particular types of lichen that are sensitive to the concentration of sulfur dioxide in the atmosphere (and so can give a good idea about the level of pollution from car exhausts, power stations etc.). The number and type of lichen at a particular location will indicate how clean the air is (e.g. the air is clean if there are lots of lichen).

3) If raw sewage is released into a river, the bacterial population in the water increases and uses up the oxygen. Some invertebrate animals, like mayfly larvae, are good indicators for water pollution because they're very sensitive to the concentration of dissolved oxygen in the water. If you find mayfly larvae in a river, it indicates the water is clean.

4) Other invertebrate species have adapted to live in polluted conditions - so if you see a lot of them you know there's a problem. E.g. rat-tailed maggots and sludgeworms indicate a very high level of water pollution.

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...and Non-Living Indicators

To find out about environmental change, scientists are busy collecting data about the environment.

1) They use satellites to measure the temperature of the sea surface and the amount of snow and ice cover. These are modern, accurate instruments and give us a global coverage.

2) Automatic weather stations tell us the atmospheric temperature at various locations. They contain thermometers that are sensitive and accurate - they can measure to very small fractions of a degree.

3) They measure rainfall using rain gauges, to find out how much the average rainfall changes year on year.

4) They use dissolved oxygen meters, which measure the concentration of dissolved oxygen in water, to discover how the level of water pollution is changing.

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Constructing Pyramids of Biomass

There is less energy and less biomass every time you move yo a stage (trophic level) in a food chain. There are usually few organisms every time you move up a level too.

  • 100 dandelions feed 10 rabbits which feed one fox

This isn't always true though - for example, if 500 fleas are feeding on the fox, the number of organisms has increased as you move up that stage in the food chain. A better way to look at the food chain is to think about biomass instead of number of organisms. You can use information about biomass to construct a pyramid of biomass to represent the food chain.
1) each bar on a pyramid of biomass shows the mass of living material at that stage in the food chain - basically how much all of the organisms would "weigh" if you put them all together.
2) the one fox would have a big biomass and the hundreds of fleas would have a very small biomass.

The big bar at the bottom of the pyramid always represents the producer (i.e. a plant). The next bar will be the primary consumer (the animal that eats the plant), then the secondary consumer (the animal that eats the primary consumer) and so on up the food chain.

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Interpreting Pyramids of Biomass

You need to be able to look at pyramids of biomass and explain what they show about the food chain.

For example:
Lots (probably thousands) of aphids are feeding on a few great big trees. Quite a lot of ladybirds are then eating the aphids, and a few partridges are eating the ladybirds. Biomass and energy are still decreasing as you go up the levels - it's just that one tree can have a very big biomass, and can fix a lot of the sun's energy using all those leaves.

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Energy Transfer

Material and energy are both lost at each stage of the food chain.
1) Energy from the sun is the source of energy for nearly all life on Earth.
2) Green plants and algae use a small percentage of the light energy from the sun to make food during photosynthesis. This energy's stored in the substances which make up the cells of plants and algae, and then works its way through the food chain as animals eat them and each other.
3) Respiration supplies the energy for all life processes, including movement. Most of the energy is eventually lost to the surroundings as heat. This is especially true for mammals and birds, whose bodies must be jets at a constant temperature which is normally higher than their surroundings.
4) Some of the material which makes up plants and animals is inedible (e.g. bone), so it doesn't pass to the next stage of the food chain. Material and energy are also lost from the food chain in the organisms' waste material.
5) This explains why you get biomass pyramids. Most of the biomass is lost and so does not become biomass in the next level up.
6) It also explains why you hardly ever get food chains with more than about 5 trophic levels. So much energy is lost at each stage that there's not enough left to support more organisms after four or five stages.

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Decay

1) Living things are made of materials they take from the world around them.
2) Plants take elements like carbon, oxygen, hydrogen and nitrogen from the soil or the air. They turn these elements into the complex compounds (carbohydrates, proteins and fats) that make up living organisms, and these then pass through the food chain.
3) These elements are returned to the environment in waste products produced by the organisms, or when the organisms die. These materials decay because they're broken down (digested) by microorganisms - that's how the elements get put back into the soil.
4) Microorganisms work best in warm, moist conditions. Many microorganisms also break down material faster when there's plenty of oxygen available. Compost bins recreate these ideal conditions.
5) All the important elements are thus recycled - they return to the soil, ready to be used again by new plants and put back into the food chain again.
6) In a stable community the materials are taken out of the soil and used are balanced by those that are out back in. There's a constant cycle happening.

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Compost Bin

Kitchen waste (e.g. food peelings) can be made into compost. Compost is decayed remains of animal and plant matter that can be used as a fertiliser. It recycles nutrients back into the soil - giving you a lovely garden.

  • Extra decomposers added (compost maker)
  • Finely shredded waste is best
  • Warmth generated by decomposition helps it all along
  • Mesh sides to let air in
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The Cabon Cycle

Diagram:

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The Carbon Cycle Explained

Learn these points:

1) There's only one arrow going down from the atmosphere. The whole thing is "powered" by photosynthesis. Carbon dioxide is removed from the atmosphere by green plants and algae, and the carbon is used to make carbohydrates, fats and proteins in the plants and algae.

2) Some of the carbon is returned to the atmosphere as carbon dioxide when the plants and algae respire. Some of the carbon becomes part of the fats and proteins in animals when the plants and algae are eaten. The carbon then moves through the food chain.

3) Some of the carbon is returned to the atmosphere as carbon dioxide when the animals respire.

4) When plants, algae and animals die, other animals (called detritus feeders) and microorganisms feed on their remains. When these organisms respire, carbon dioxide is returned to the atmosphere.

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The Carbon Cycle Explained (Cont.)

5) Animals also produce waste, and this too is broken down by detritus feeders and microorganisms. Compounds in the waste are taken up from the soil by plants as nutrients - they're put back into the food chain.

6) Some useful plant and animal products, e.g. wood and fossil fuels, are burnt (combustion). Thus also releases carbon dioxide back into the air.

7) So the carbon is constantly being cycled - from the air, through food chains and eventually back out into the air again.

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Organisms of the Same Species Have Differences

Different species look different.

But even organisms of the same species will usually look at least slightly different - e.g. in a room full of people you'll see different colour hair, individually shaped noses, a variety of heights etc.

These differences are called the variation within a species - and there are two types of variation: genetic variation and environmental variation.

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Different Genes Cause Genetic Variation

All plants and animals have characteristics that are in some ways similar to their parents' (e.g. I've got my dads nose).

This is because an organism's characteristics are determined by the genes inherited from their parents. (Genes are codes inside your cells that control how you're made).

These genes are passed on in sex cells (gametes), which the offspring develop from.

Most animals (and quite a lot of plants) get some genes from the mother and some from the father.

This combining of genes from two parents causes genetic variation - no two of the species are genetically identical (other than identical twins).

Some characteristics are determined only by genes (e.g. violet flower colour). In animals these include: eye colour, blood group and inherited disorders (e.g. haemophilia or cystic fibrosis).

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Characteristics are also Influenced by the Environ

The environment that organisms live and grow in also causes differences between members of the same species - this is called environmental variation.

Environmental variation covers a wide range of differences - from losing your toes in a piranha attack, to getting a suntan, to having yellow leaves and so on.

Basically any difference that has been caused by the conditions something lives in, is an environmental variation.

A plant grown on a nice sunny windowsill would grow luscious and green.
The same plant grown in darkness would grow tall and spindly and its leaves would turn yellow - these are environmental variations.

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Most Characteristics are Due to Genes AND the Envi

Most characteristics (e.g. body weight, height, skin colour, condition of teeth, academic or athletic prowess, etc.) are determined by a mixture of genetic and environmental factors.

For example, the maximum height that an animal or plant could grow to is determined by its genes. But whether it actually grows that tall depends on its environment (e.g. how much food it gets).

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Genes, Chromosomes and DNA

1) Most cells in your body have a nucleus. The nucleus contains your genetic material in the form of chromosomes.

2) The human cell nucleus contains 23 pairs of chromosomes. (One from each parent.)

3) Chromosomes carry genes. Different genes control the development of different characteristics, e.g. hair colour.

4) A gene is a short length of the chromosome which is quite a long length of DNA.

5) The DNA is coiled up to form the arms of the chromosome.

There can be different versions of the same gene, which give different version of characteristic, like blue or brown eyes. The different versions of the same gene are called alleles instead of genes.

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Sexual Reproduction Produces Genetically Different

1) Sexual reproduction is where genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent.
2) In sexual reproduction the mother and father produce gametes - e.g. Egg and sperm cells in animals.
3) In humans, each gamete contains 23 chromosomes - half the number of chromosomes in a normal cell. (Instead of having two of each chromosome, a gamete has just one of each.)
4) The egg (from the mother) and the sperm cell (from the father) then fuse together (fertilisation) to form a cell with the full number of chromosomes (half from the father, half from the mother).
5) This is why the offspring inherits features from both parents - it's received a mixture of chromosomes from its mum and its dad (and the chromosomes decide how you turn out).
6) This mixture of genetic material produces variation in the offspring.

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Asexual Reproduction Produces Genetically Identica

1) An ordinary cell can make a new cell by simply dividing in two. The new cell has exactly the same genetic information (i.e. genes) as the parent cell - this is known as asexual reproduction.
2) Here's how it works:

  • X-shaped chromosomes have two identical halves.
  • So each chromosome splits down the middle to form two identical sets of 'half-chromosomes' (i.e. two sets of DNA strands).
  • A membrane forms around each set and the DNA replicates itself to form two identical cells with complete sets of X-shaped chromosomes.
    3) This is how all plants and animals grow and produce replacement cells.
    4) Some organisms also produce offspring using asexual reproduction, e.g. bacteria and certain plants.
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Definitions

SEXUAL REPRODUCTION involves the fusion of male and female gametes. Because there are TWO parents, the offspring contain a mixture of their parents genes.

In ASEXUAL REPRODUCTION there's only ONE parent. There's no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring. The offspring are genetically identical to the parent - they're clones.

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Plants Can Be Cloned from Cuttings and by Tissue C

Cuttings:

1) Gardeners can take cuttings from good parent plants, and then plant them to produce genetically identical copies (clones) of the parent plant.
2) These plants can be produced quickly and cheaply.

  • Cuttings are taken, each with a new bud on.
  • The cuttings are kept in moist conditions until they are ready to plant.

Tissue Culture:

This is where a few plant cells are put in a growth medium with hormones, and they grow into new plants - clones of the parent plant. These plants can be made very quickly, in very little space, and be grown all year.

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Animal Clones Using Embryo Transplants

Farmers can produce cloned offspring from their best bull and cow - using embryo transplants.

1) Sperm cells are taken from a prize bull and egg cells are taken from a prize cow. The sperm are then used to artificially fertilise an egg cell. The embryo that develops is then split many times (to form clones) before any cells become specialised.

2) These cloned embryos can then be implanted into lots of other cows where they grow into baby calves (which will all be genetically identical to each other).

3) Hundreds of "ideal" offspring can be produced every year from the best bull and cow.

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Adult Cell Cloning

1) Adult cell cloning involves taking an unfertilised egg cell and removing its genetic material (the nucleus). A complete set of chromosomes from an adult body cell (e.g. skin cell) is inserted into the 'empty' egg cell.

2) The egg cell is then stimulated by an electric shock - this makes it divide, just like a normal embryo.

3) When the embryo is a ball of cells, it's implanted into an adult female (the surrogate mother) to grow into a genetically identical copy (clone) of the original adult body cell.

4) Thus technique was used to create Dolly - the famous cloned sheep.

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Many Issues Surrounding Cloning

1) Cloning quickly gets you lots of "ideal" offspring. But you also get a "reduced gene pool" - this means there are fewer different alleles in the population. If a population are all closely related and a new disease appears, they could all be wiped out - there may be no allele in the population giving resistance to the disease.

2) But the study of animal clones could lead to greater understanding of the development of the embryo, and of ageing and age-related disorders.

3) Cloning could also be used to help preserve endangered species.

4) However, it's possible that cloned animals might not be as healthy as normal ones, e.g. Dolly the sheep had arthritis, which tends to occur in older sheep (but the jury's still out on if this was due to cloning).

5) Some people worry that humans might be cloned in the future. If it was allowed, any success may follow many unsuccessful attempts, e.g. children born severely disabled.

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Genetic Engineering

The basic idea is to copy a useful gene from one organism's chromosome into the cells of another.
1) A useful gene is "cut" from one organism's chromosomes using enzymes.
2) Enzymes are then used to cut another organism's chromosome and then to insert the useful gene.
3) Scientists use this method to do all sorts of things - for example, the human insulin gene can be inserted into bacteria to produce human insulin.

Diagram:

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Genes can be Transferred into Animals and Plants

The same method can be used to transfer useful genes into animal and plants at the very early stages of their development (i.e. shortly after fertilisation). This means they'll develop useful characteristics, e.g:

1) Genetically modified (GM) crops have had their genes modified, e.g. to make them resistant to viruses, insects and herbicides (chemicals used to kill weeds).

2) Sheep have been genetically engineered to produce substances, like drugs, in their milk that can be used to treat human diseases.

3) Genetic disorders like cystic fibrosis are caused by faulty genes. Scientists are trying to treat these disorders by inserting working genes into sufferers. This is called gene therapy.

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Genetic Engineering is a Contraversial Topic

Genetic engineering is an exciting new area in science which has the potential for solving many of our problems (e.g. treating diseases, more efficient food production etc.) but not everyone thinks it's a great idea.

There are worries about the long-term effects of genetic engineering - that changing a person's genes might accidentally create unplanned problems, which could then get passed on to future generations.

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Pros and Cons of GM Crops

1) Some people say that growing GM crops will affect the number of weeds and flowers (and so the population of insects) that live in and around the crops - reducing farmland biodiversity.
2) Not everyone is convinced that GM crops are safe. People are worried they may develop allergies to the food - although there's probably no more risk for this than for eating usual foods.
3) A big concern is that transplanted genes may get out into the natural environment. For example, the herbicide resistance gene may be picked up by weeds, creating a new 'superweed' variety.
4) On the plus side, GM crops can increase the yield of a crop, making more food.
5) People living in developing nations often lack nutrients in their diets. GM crops could be engineered to contain the nutrients that's missing. For example, they're testing 'golden rice' that contains beta-carotene - lack of this substance causes blindness.
6) GM crops are already being grown elsewhere in the world (not the UK) often without any problems.

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Evolution

THEORY OF EVOLUTION : More than 3 billion years ago, life on Earth began as simple organisms from which all the more complex organisms evolved (rather than just popping into existence).

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All Organisms are Related... even if Only Distantl

Looking at similarities and differences between organisms allows us to clarify them into groups. E.g:

1) Plangs make their own food (by photosynthesis) and are fixed in the ground.
2) Animals move about the place and can't make their own food.
3) Microorganisms are different to plants and animals, e.g. bacteria are single celled.

Studying the similarities and differences between organisms also help us to understand how all living things are related (evolutionary relationships) and how they interact wit each other (ecological relationships).

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Evolutionary Relationships

1) Speices with similar characteristics often have similar genes because they share a recent common ancestor, so they're closely related. They often look very alike and tend to live in similar types of habitat, e.g. whales and dolphins.

2) Occassionally, genetically different species might look alike too. E.g. dolphins and sharks look pretty similar because they've both adapted to living in the same habitat. But they're not closely related - they've evolved from different ancestors.

3) Evolutuonary trees show common ancestors and relationships between organisms. The more recent the ancestor, the more closely related the two species.

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Evolutuonary Tree Example

Whales and dolphins have a recent common ancestor so are closely related. They're both more distantly related to sharks.

Diagram:

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Ecological Relationships

1) If we see organisms in the same environment with similar characteristics (e.g. dolphins and sharks) it suggests they might be in competition (e.g. for the same food source).

2) Differences between organisms in the same environment (e.g. dolphins swim in small groups, but herring swim in massive shoals) can show predator-prey relationships (e.g. dolphins hunting herring).

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Natural Selection Explains How Evolution Occurs

Charles Darwin came up with the idea of natural selection.
(Genetic differences are caused by sexual reproduction and mutations.)

1) Individuals within a species show variation because of the differences in their genes, e.g. some rabbits have big ears and some have small ones.

2) Individuals with characteristics that make them better adapted to the environment have a better chance of survival and so are more likely to breed successfully. E.g. big-eared rabbits are more likely to hear a fox sneak up on them, and so are more likely to live and have millions of babies. Small eared rabbits are more likely to end up as fox food.

3) So, the genes that are responsible for the useful characteristics are more likely to be passed on to the next generation. E.g. all the baby rabbits are born with big ears.

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Evolution can Occur Due To Mutations

1) A mutation is a change in an organism's DNA.

2) Most of the time mutations have no effect, but Occassionally they can be beneficial by producing a useful characteristic. The characteristic may give the organism a better chance of surviving and reproducing.

3) If so, the beneficial mutation is more likely to be passed on to future generations by natural selection.

4) Over time, the beneficial mutation will accumulate in a population, e.g. some species of bacteria have become resistant to antibiotics due to mutation.

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Not Everyone Agreed with Darwin

There's lots of evidence for the theory of evolution by natural selection, but back in the day, poor Charles Darwin didn't have half as much evidence to convince people.

Darwin's ideas were very contraversial at the time - for various reasons...

1) It went against common religious beliefs about how life on Earth developed - it was the first plausible explanation for our own existence without the need for a "Creator" (God).

2) Darwin couldn't give a good explanation for why these new, useful characteristics appeared or exactly how individual organisms passed on their beneficial characteristics to their offspring. But then he didn't know anything about genes or mutations - they weren't discovered until 50 years after his theory was published.

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

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Lamarck

There were different scientific hypothesis about evolution around at the same time, such as Lamarck's:

1) Lamark (1744-1829) argued that if a characteristic was used a lot by an organism then it would become more developed during its lifetime. E.g. if a rabbit used its legs to run a lot (to escape predators), then it's legs would get longer.

2) Lamark believed that these acquired characteristics would be passed on to the next generation, e.g. the rabbis offspring would have longer legs.

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Developing Hypotheses from Similar Observations

1) Often scientists come up with different hypotheses to explain different observations.

2) Scientists might develop different hypotheses because they have different beliefs (e.g. religious) or they have been influenced by different people (e.g. other scientists and their way of thinking)... or they just darn well think differently.

3) The only way to find out whose hypothesis is right is to find evidence to support or disprove each one.

4) For example, Lamarck and Darwin both had different hypotheses to explain how evolution happens.

5) There's so much evidence for Dawin's idea that it's now an accepted hypothesis (a theory)

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Lamarck and Darwin

  • Lamarck's hypothesis was eventually rejected because experiments didn't support his hypothesis. You can see it for yourself e.g. if you dye a hamster's fur bright pink, it's offspring will still be norm without the normal fur colour because the new characteristic won't have been passed on.
  • The discovery of genetics supported Darwin's idea because it provided an explanation of how organisms born with beneficial characteristics can pass them on (i.e. via their genes).
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Comments

hanipatel

this is really useful 

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