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What is evolution?

Evolution is the change in the characteristics of a species over several generations and relies on the process of natural selection.


Examples of selection pressures

Things like predation, competition for resources (e.g. food, water, mates, etc.) and disease act as selection pressures.


How does selection pressures affect individuals?

-It will affect an organism’s chance of surviving and reproducing, as those individuals with heritable traits better suited to the environment will survive.
-This means the alleles that are responsible for the useful characteristics are more likely to be passed on to the next generation.


When will a new species form?

When reproductive isolation occurs new species will form.


What happens to beneficial characteristics over time?

The beneficial characteristics become more common in the population over time.


What are antibiotics?

Antibiotics – Antibiotics are drugs that are designed to kill bacteria or prevent them from reproducing


Evidence for evolution- antibiotic resistance

-Bacteria sometimes develop random mutations in their DNA. e.g. being less affected by a particular antibiotic.
-For the bacterium, the ability to resist this antibiotic is a big advantage, In a host who’s being treated to get rid of the infection, a resistant bacterium is better able to survive than a non-resistant bacterium.
-The emergence of antibiotic resistance provides evidence for evolution because it’s an example of natural selection taking place.
-Antibiotic resistance makes the bacteria better adapted to an environment in which a selection pressure (antibiotics) are present.
-As a result, antibiotic resistance becomes more common in the population over time.


What is a fossil?

Fossil – A fossil is any trace of an animal or plant that lived a long time ago (usually many millions of years ago).


Evidence for evolution — fossils

-They are most commonly found in rocks.
-Generally, the deeper the rock, the older the fossil.
-By arranging fossils in chronological (date) order, gradual changes in organisms can be observed.
-This provides evidence for evolution, because it shows how species have changed and developed over billions of years.


Charles Darwin

-Darwin was a naturalist and biologist known for his theory of evolution and process of natural selection
-He spent 5 years on a voyage around the world studying plants and animals on a ship
-Whilst on his travels, he noticed that there was variation in members of the same species and that those with characteristics most suited to the environment were more likely to survive.
-He also noticed that characteristics could be passed on to offspring.


Alfred Russel Wallace

-Alfred Russel Wallace and Darwin published their papers on evolution together and acknowledged each other’s work — although they didn’t always agree on the mechanisms involved in natural selection.
-Wallace’s observations provided lots of evidence to help support the theory of evolution by natural selection.
-But it was Darwin’s ‘On the Origin of Species’ that made other scientists pay attention to the theory.


How has the theory of evolution by natural selection has affected:

Classification —We now classify organisms (arrange them into groups) based on how closely related they are


How has the theory of evolution by natural selection has affected:

Antibiotic resistance— we now understand the importance of finishing the course of drugs to prevent resistant bacteria spreading and we know we need to constantly develop new antibiotics to fight newly evolved resistant bacteria.


How has the theory of evolution by natural selection has affected:

Conservation — we now understand the importance of genetic diversity (having a variety of different alleles in a population) and how it helps populations adapt to changing environments.


Who did humans evolve from?

Evidence from fossils suggests that humans and chimpanzees evolved from a common ancestor — a species of ape that existed around 6 million years ago.


What are hominids?

Human beings and their ancestors are known as hominids.


Hominid fossils


Hominid fossil of the species Ardipithecus ramidus. Found in Ethiopia and is 4.4 million years old.

-Ape-like big toe to grasp branches.
-Long arms and short legs (more like an ape than a human).
-Brain size same as a chimpanzee’s.
-But the structure of her legs suggests that she walked upright.


Hominid fossils

Hominid fossil of the species Ardipithecus ramidus. Found in Ethiopia and is 4.4 million years old.

-Ape-like big toe to grasp branches.
-Long arms and short legs (more like an ape than a human).
-Brain size same as a chimpanzee’s.
-But the structure of her legs suggests that she walked upright.


Hominid fossils

Hominid fossil of the species Australopithecus afarensis. She was found in Ethiopia and is 3.2 million years old.

-Lucy had arched feet, more adapted to walking than climbing, and no ape-like big toe.
-The size of her arms and legs was between apes and humans.
-Her brain was slightly larger than Ardi’s but still similar in size to a chimp’s brain.
-The structure of Lucy’s leg bones and feet suggest she walked upright, but more efficiently than Ardi.


Hominid fossils
Leakey’s fossils

“Turkana Boy” — a 1.6 million year old fossil skeleton of the species Homo erectus.

-Short arms and long legs. His brain size was brain size similar to human brain size.
-The structure of his legs and feet suggest he was even better adapted to walking upright than Lucy.


Homo habilis

-Lived between 2.5 and 1.5 million years ago.
-Tools- pebble tools by hitting rocks together to make sharp flakes.
-Used to scrape meat from bones or crack bones open.


Homo erectus

-Lived between 2 and 0.3 million years ago.
-They sculpted rocks into shapes to produce more complex tools like simple hand-axes.
-Used to hunt, dig, chop and scrape meat from bones.


Homo neanderthalensis

-Lived between 300 000 and 25 000 years ago.
-They made even more complex tools.
-There is evidence that they used flint tools, with sharp, pointed edges, and wooden spears.


Homo sapiens

-Homo sapiens are modem humans.
-First appeared about 200 000 years ago.
-Flint tools were widely used.
-Fish hooks, needles and arrowheads appeared around 50 000 years ago.


Dating stone tools and fossils

-Looking at the structural features of the tool or fossil. For example, simpler tools are likely to be older than more complex tools.
-Using stratigraphy — the study of rock layers.
-For a tool or fossil to be found in a rock layer, it must have been present at the time the layer was formed.
-Older rock layers are normally found below younger layers, so tools or fossils in deeper layers are usually older.


How is carbon used in dating stone tools?

-Stone tools are often found with carbon-containing material, e.g. a wooden handle.
-A process called carbon-H dating can be used to date this material.
-Carbon-14 dating works on the basis that all carbon-based material contains a small amount of a radioactive form of carbon called 14C and that the amount of 14C decreases over time as it decays.
-Other methods include potassium-argon and uranium-lead dating.


What is a pentadactyl limb?

-A pentadactyl limb is a limb with five digits.
-Pentadactyl limb can be seen in all organisms with four limbs, including mammals, birds, reptiles and amphibians.
-In each of these groups of animals, the pentadactyl limb has a similar bone structure, but usually a different function.


Evidence for evolution
pentadactyl limb

-The similarity in bone structure provides evidence that species with a pentadactyl limb have all evolved from a common ancestor (that had a pentadactyl limb).
-If they’d all evolved from different ancestors, it’d be highly unlikely that they’d share a similar bone structure.


Five kingdom classification

Animals — fish, mammals, reptiles, etc.
Plants — grasses, trees, etc.
Fungi — mushrooms, yeasts, mould.
Prokaryotes —all single-celled organisms without a nucleus (e.g. bacteria).
Protists — eukaryotic single-celled organisms, e.g, algae.


How are the kingdoms subdivided?

The kingdoms are then subdivided into smaller and smaller groups that have common features — phylum, class, order, family, genus, species.


How do gene sequences affected how closely related organisms are?

-Over time, technology has developed further and our understanding of things like biochemical processes and genetics has increased. The more similar the sequence of a gene, the more closely related the organisms.


What did Carl Woese suggest?

-Using RNA sequencing, Carl Woese found that some members of the prokaryote kingdom
were not as closely related as first thought.
-He proposed that this kingdom should be split into 2 groups archaea and bacteria
-In fact he said that all organisms should be divided into 3 domains: archaea, bacteria and eukarya


Archaea (primitive bacteria)

These cells usually live in extreme environments. They have no nucleus and have unused sections of genes.


Bacteria (true bacteria)

Bacteria cells have no nucleus and no unused sections of genes


Eukaryota (including protists, fungi, plants and animals)

These have a nucleus and have unused sections of genes.


What is selective breeding?

-Selective breeding is when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population.


Examples of selective breeding

-Animals that produce more meat or milk.
-Crops with disease resistance.
-Dogs with a good, gentle temperament.
-Plants that produce bigger fruit.


The process of selective breeding

1.From your existing stock, select the ones which have the characteristics you’re after.
2.Breed them with each other.
3.Select the best of the offspring, and breed them together.
4.Continue this process over several generations, and the desirable trait gets stronger and stronger. Eventually, all the offspring will have the characteristic


Uses of selective breeding

-In agriculture, selective breeding can be used to improve yields.

-Genetic variation means that some cattle will have better characteristics for producing meat than others (e.g. a larger size). To improve meat yields, a farmer could select the cows and bulls with these characteristics and breed them together. After doing this, and selecting the best of the offspring for several generations, the farmer would get cows with a very high meat yield.

-Selective breeding can also be used in medical research.


Disadvantages of selective breeding

-The main problem with selective breeding is that it reduces the gene pool. This is because the farmer keeps breeding from the “best” animals or plants — which are all closely related. This is known as Inbreeding.

-Inbreeding can cause health problems because there’s more chance of the organisms inheriting harmful genetic defects when the gene pool is limited.

-There can be serious problems if a new disease appears. There's not much variation in the population, so there's less chance of resistant alleles being present. All the stock are closely related to each other, so there is an increased chance that a disease will wipe out the entire population.


What are tissues?

Tissues are groups of similar cells that work together to perform a particular function.


What is tissue culture?

The process or technique of making body tissue grow in a culture medium outside the organism; a culture of tissue (such as epithelium)


Plant tissue culture

-Whole plants can be grown via tissue culture - the plants can be made very quickly, in very little space and can be grown all year
-Plants produced using tissue culture are clones - meaning you can create lines of clones with the same beneficial features


Process of plant tissue culture

1. Choose the plant you want to clone, usually based on its characteristics — e.g. a beautiful flower, a good fruit crop.
2.Remove several small pieces of tissue from the parent plant. You get the best results if you take tissue from fast-growing root or shoot tips.
3.Grow the tissue on a growth medium containing nutrients and growth hormones. This is done under aseptic (sterile) conditions to prevent growth of microbes that could harm the plants.
4.As the tissues produce shoots and roots they can be moved to potting compost to carry on growing.


Animal tissue culture

-Often used in medical research because it means that you can carry out all kinds of experiments on tissues in isolation
-You can look at the effects of a particular substance or environmental change on the cells of a single tissue, without complications from other processes in the whole organism


Process of animal tissue culture

1.A sample of the tissue you want to study is extracted from the animal.
2.The cells in the sample are separated from each other using enzymes.
3.Then they are placed in a culture vessel and bathed in a growth medium containing all the nutrients that they need. This allows them to grow and multiply.
4.After several rounds of cell division, the cells can be split up again and placed into separate vessels to encourage further growth.
5.Once the tissue culture has been grown, it can be stored for future use.


Genetic Engineering

Genetic engineering refers to the direct manipulation of DNA to alter an organism’s characteristics (phenotype) in a particular way.


Uses of genetic engineering

-Bacteria have been genetically modified to produce human insulin that can be used to treat diabetes.
-To improve the size and quality of fruit, or make them resistant to disease, insects and herbicides (chemicals used to kill weeds).
-Sheep and cows have been genetically engineered to produce useful human proteins in their milk, e.g. antibodies used in therapy to treat illnesses like arthritis, some types of cancer and multiple sclerosis.


Restriction enzymes

Restriction enzymes recognize specific sequences of DNA and cut the DNA at these points - the pieces of DNA are left with sticky ends


Ligase ezymes

Ligase enzymes are used to join two pieces of DNA together at their sticky ends


Recombinant DNA

Two different bits of DNA stuck together are known as recombinant dna


What is a vector?

A vector is something that's used to transfer DNA into a cell
There is two types:
-Plasmids - small circular molecules of DNA that can be transferred between bacteria
-Viruses - insert DNA into the organisms they infect


How genetic engineering works:

1. The DNA you want to insert (eg. gene for human insulin) is cut out with a restriction enzyme. The vector DNA is then cut open using the same restriction enzyme.
2. The vector DNA and the DNA you are inserting are left with sticky ends which are mixed together with ligase enzymes
3. The ligases join the pieces of DNA together to make recombinant DNA which is then inserted into the other cells
4. These cells can now use the gene you inserted to make the protein you want


Benefits of genetic engineering

-In agriculture, GM crops to be herbicide-resistant means farmers can spray their crops to kill weeds, without affecting the crop itself. This can increase crop yield.
-In medicine, GM bacteria has allowed human insulin for the treatment of diabetes to be produced relatively easily and cheaply in large quantities.


Risks of genetic engineering

-Transplanted genes may get out into the environment, e.g. a herbicide resistance gene may be picked up by weeds, creating a new ‘superweed’ variety.
-GM crops could adversely affect food chains — or even human health.


Benefits of genetically modifying crops

-GM crops can increase the amount of food that a crop provides (its yield). For example, crops can be produced that are resistant to pests or are able to grow better in drought conditions.
-GM crops could also be engineered to contain additional nutrients. This could help to combat certain deficiency diseases.
-Example: Vitamin A deficiency is common in parts of Africa and SE Asia. A lack of vitamin A can lead to blindness. ‘Golden rice’ is rice that’s been engineered to produce a chemical that’s converted in the body into vitamin A.


Concerns about genetically modifying crops

-There are fears that countries may become dependent on companies who sell GM seeds.
-Sometimes, poor soil is the main reason why crops fail in a certain area, and even CM crops won’t survive.
-Long term effects of exposure to GM crops on human health and the environment aren’t yet known.


Bt crops

-Bt stands for Bacillus thuringiensis.
-It is a type of bacterium which produces a toxin (poison) that kills many of the insect larvae that are harmful to crops.
-The gene for the Bt toxin can be inserted into crops, such as cotton and corn, which then produce the toxin in their stems and leaves — making them resistant to the insect pests.
-The toxin is specific to insect pests — it’s harmless to humans, animals and other insects.


Benefits and risks of Bt crops

-Modifying crops to produce the Bt toxin can improve crop yield.
-Insects that eat the crop are killed by the toxin, so less of the crop gets eaten by pests and more food is produced for humans.
-The insects that feed on the crops are constantly exposed to the toxin, so there’s a danger they’ll develop resistance and no longer be killed by it. Farmers try to avoid this happening by using other insecticides too.


Other methods of increasing food production

-Fertilisers is likely to be the best way to increase yields, contain minerals that are essential for plant growth, e.g. nitrates and phosphates.
-Excess fertilisers can cause problems in rivers and lakes through the process of eutrophication


Other methods of increasing food production

-Biological control is an alternative method for controlling pest numbers to chemical pesticides or pest-resistant GM crops.