SP4 Natural Selection

SP4 Natural Selection

1. Evidence for Human Evolution

   • Evolution is a gradual change in the characteristics of a species overtime.
   • Fossils like "Lucy" and "Ardi" show is that humans could have evolved as their bone structure is very similar to modern humans. However, these fossils do not show smooth changes as there is missing evidence in between the fossils discovered.
     • Stone tools are also evidence. Scientists can work out the ages of the layers of rock. The oldest stone tools are very simple but the recent tools are more sophisticated.

2. Darwin's Theory

   • Natural selection is the variations of some individuals make them better at coping with the change than others, and are more likely to survive. (Battle of the fittest)
     • E.g Mammoths and elephants could be linked, but one was hairier, so they adapted to the colder climate. They were more likely to survive.
   • Warfain was used to kill rats in the 1940s. Some rats were resistant to it due to some rats being genetically variated to not be affected by it. Most rats died.
     • However, within ten years most rats were resistant to it. The poison killed the non resistant rats, leaving the ones left that were resistant to breed.

3. Development of Darwin's Theory

   • Darwin went to the Galapagos Islands where there were different mockingbird types. All with different characteristics on the different islands. These mockingbirds were adapted to the island each whether that was competition or food.
     • The pentadactyl limb, a limb with five fingers. Darwin questioned why does the same limb have different purposes?
   • Darwin published his book "On the Origin of Species" which also talked about finches and their beak shapes to battle for the fittest.

4. Classifiction

   • Three main domains:
     • Archea (cells with no nucleus, genes contain unused sections of DNA)
     • Bacteria (cells with no nucleus, no unused sections in genes)
     • Eukarya (cells with a nucleus, unused sections in genes)

5. Breeds and Varities

   • Artificial selection is when humans choose certain organisms because they have useful characteristics, e.g sheep and thick wool
     • Plants and animals are often selectively bred for:
       • Disease resistance
       • Yield
       • Fast growth
       • Flavour
   • Genetic enginerring
     • This involves changing the DNA of one organism, its genome, often by inserting genes from another
       • This creates genetically modified organisms (GMOs)
         • For example, Golden Rice is a GMO with two genes inserted into its genome, one from a daffodil and a bacterium. This lets it produce more beta-carotene, used for making of vitamin A

6. Tissue Culture

   • Tissue culture is the growing of cells or tissues in a liquid containing nutrients
     • It can be used to produce new plants of very rare species which are at risk of extinction
       • But can also make clones of GM plants
     • Has also been made in medicine to study how cells communicate with each other
       • Cultures of cancer cells can be used to see how they develop and spread

7. Genes in Agriculture and Medicine

   • Selective breeding risks
     • Genes also exist in allele form, which causes variation in characteristics
       • For example, the different alleles in wild wheat plants cause different seed sizes. In selective breeding, only certain alleles are selected, others disappear
         • Also, if farming on a huge scale the same breed, one disease or a change in condition can affect all organisms
   • Genetic engineering of bacteria [H]
     • A bacterium has one large loop of DNA called plasmids.
       • Scientists use restriction enzymes to cut a useful gene out of an organism's DNA
         • This cutting leaves strands of DNA with jagged ends, called sticky ends.
           • If two match, they can be joined together using an enzyme called ligase

8. GM and Agriculture

   • A soil bacterium that makes a natural insecticide protein called Bt toxin. This can be sprayed onto crops as insecticide
     • The genes of the bacterium were introduced into the plants
       • One advantage is that only the insects that eat the tissues will die as broken cells release the toxin
         • However, insects that suck sap from the plant, such as aphids, do not chew plant tissue so do not eat the toxin
           • Additionally, insects can develop resistance to the toxin
         • GM seeds are more expensive than non but farmers make more profit as long as people want to buy food from GM crops
           • Some people are concerned that it can harm their health but there is no evidence

9. Fertilisers and Biological Control

   • Using organisms to control pests is known as a biological control
     • For example, Chinese farmers placed ant nests to kill any insect pests
       • BUT these can turn out disasters as the control can eat everything and ruin the food chain
     • For example, beetles can prevent a weed from growing
   • Fertilisers can also be used to increase growth and yield in plants
     • Fertilisers contain mineral ions such as N, K and phosphorus
       • BUT if are not all absorbed they can get into water streams and cause pollution and lead to the death of organisms in the water

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