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GCSE Biology Revision

Simran Bains Sira

on 16 May 2011

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Transcript of Biology

Environment Charles Darwin described life as a struggle for survival. All species interact and complete with each other for resources so only the fittest ones survive. Over time a species will gradually evolve and adapt to improve its chances of survival, this is a lenghty process known as natural selection. Any species that fails to adapt will soon become extinct. Competition for Resources All living things will compete with eachother for the things that they need, for example, predators will compete with eachother for prey. Competition between different species is known as inter-species competition, but competition between the same species is known as intra-species competition. The general rule is that the most adapted animals get the most food. These animals are the ones who survive, allowings them to reproduce and therefor incerease in population. This increase is at the expense of the weaker and less adapted animals. Some species adapt just so that they can live comfortably with other species. Species also compete for water, shelter, suitable mates and places to breed, as well as food. Biology Predators are the hunters, and prey are the hunted. Scavengers are animals that will eat the left over prey that have been killed by the predators. The change in number of one organism can affect the number of another. Population decrease in prey could be due to extreme weather conditions, disease, or an increased population in predators. The predator and prey population are very colsely linked with one-another. Sampling and Estimating Population It is important for us to know how many of each species are living in an area, but this may be hard for us as these species are always moving and when there are a lot its hard to count them. Plants can be tricky to count aswell. This is because there are a lot of them, and they are so small. A population is the total number of a species in an area. A good way to smaple in a small area is by using a quatdrat. This is a small square frame that is usually used to sample plants and animals that dont tend to move around a lot. The quatdarat/s are placed randomly in a field and every species found is identified and counted. Population changes over time and it is hard to keep track of it all. Temperature, availability of food and water, and disease can all effect population Computer models can be used to simulate a change in weather condidtions and then its possible effect on the population. The computers can aslo be useful as they can predict what may happen to a population, and then humans can interfere if needed. Chains, Webs and Pyramids Producers --> Primary comsumer (herbivore) --> Secondary comsumer (carnivore) --> Tertiary comsumer Pyramids of biomass: is the dry mass of the living matter. Less energy is passed on through the food chain. Only about 10% of the energy is passed on to the next organism as at every stage energy is lost and used up for things like respiration. Going Organic Organic farmers often use biological control, tis mean they use predators to kill unwanted pests. This proccess doesn't harm any benificial insects, and it doesnt leave any poisonous residue. This proccess also works best in closed environments, suck as green houses. Changing Organsims Selective Breeding is when chosen organisms, with with desired features, are deliberately mated together. By chosing the best, and breeding them, humans have developed animals to suit their needs. Genetic Engineering is the transfer of a single gene from one organism to another. Genetically Modified (GM) organisms contain genes that have been altered. This method is very quick and enables single characteristics to be changed within just one generation. Natural Selection Charles Darwin developed the theory of evolution through natural selection. All organisms over-produce; but populations remain fairly constant, some offspring must die; all organisms show variatiopn, the ones who are best adapted to their environment are most likely to survive and breed; some characteristics are inherited, well-adapted parents must pass on these useful charateristics to future generations which can evolve into new species. Evolution is a consiquence of natural selection. Natural selection is when a population gradually changes over time and through the generations, this process is known as evolutiaon. This evolution means that some species will adapt to help them to survive in their environment. Evidence of Evolution Fossils: are usually found im sedimentry rock. The deeper, and orlder rocks contain different fossil to the younger rocks. The fossils found in the younger rocks are more similar to the the animals and plants today. Genes & DNA Genetics is only 150 years old. DNA is the molecule that makes genes. The knowledge of genes has allowed scientists to develop tests for genetic disorders, like cystic fibrosis. Genetics allows scientists to to find out why genes are mutated, and how they can be fixed. For example, scientists can now screen embryos to check if they are free from serious genetic disorders. Genes are made up of small chemicals called DNA, they are found in the nucleus of a cell and they carry intructions. These inrtuctions are for making any living thing. Some plants and animlas sue asexual reproduction, this is when the offspring only has one parent. This means that they have the same genes are the parent, making the clones. However, they can differ slightly, depending on the environment that they live. Plants that use asexual reproduction use 'runners' with small plantlets on the end. This will produce plants that contain the same genes are the parent, and they will spread across the land. Because the offspring plant is the same are the parent, it means that they too are inume to any diesease, so they too can produce lots of identical plants. However, if one plant gets a disease, all the other plants may get it too. Asexual Reproduction Your charactersitics depend on the genes that you inherit form your parents. Each gene is an instruction for one of your characteristics. The cell's nucleus are X-shaped chromosomes, made up of strings of genes. Everyone has two versions of each chromosome, one from the mother and one from the father. Equal numbers of the genes are inherited from each parent. The mixture of genews is what makes you look different to your parents and other siblings, however, this is not the case for identical twins. Every time a cell divides it makes an identical copy of itself. Sometimes this copying goes wrong and it cretes a mutant gene, this is a small change to the gene, but it could be a large change to the characteristic. To identify a genetic disorder, you must examine the DNA, one step to do this is by cutting the DNA into smaller peices useing chemicals called enzymes. These enzymes act as chemical 'scissors' and they cut the DNA when they find a particular code. These different lenghts of DNA are seperated and studies, this is called a DNA Fingerprint, this is because your fingerprints help to identify you, so your DNA Fingerprints help to identify people using their uniques characteristics. Forensics can be used to find out whether people are related to each other. Variation
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