Biology b1 notes for aqa
Darwins theory of natural selection Organisms produce large numbers of offspring Individual organisms within a particular species may show a wide range of variation because of differences in their genes Page 37 AQA GCSE Biology Unit 1 summary notes There is a struggle for all organisms to exist eg.
Genes are passed on in the gametes, from which the offspring develop. Very low doses of the drug are given at the start of the clinical trial.
Changes in the body do not change the genes. GM crops generally show increased yields. Because of the cold and short growing seasons, arctic plants grow very slowly. They produce male and female sex cells gametes. Drugs are tested in a series of stages to find out if they are safe and effective.
Gcse biology revision notes pdf
Conflicting theories on evolution Scientists may produce different hypotheses to explain similar observations. Oral contraceptives may contain oestrogen and progesterone to inhibit egg maturation. The auxin diffuses away from the stimulus. LH causes release of an egg from the ovary The use of artificial fertility controlling hormones Hormones can be synthesised artificially. Before Darwin, Lamarck used a different theory. Genetic factors Sexual reproduction - leads to genetic variety in the offspring. Models allow us to suggest relationships between organisms. Gradually, this can result in changes in the characteristics of a species. Some scientists work to develop drugs that cannot be detected by these tests. Tobacco smoke contains carcinogens, which are chemicals that cause cancer: o The link between smoking tobacco and lung cancer has been known about for about years. Asexual reproduction Involves only one individual as a parent. People take drugs to get enjoyment, relieve stress and relax. Occasionally, some mutations are useful.
He argued that an individuals characteristics will change over its lifetime due to amount of use. Some drugs make them work slower eg.
Gcse biology revision notes
Genetic factors Sexual reproduction - leads to genetic variety in the offspring. Lichens absorb sulphur dioxide dissolved in water. Modern cloning techniques include: Tissue culture This uses small groups of cells from part of a plant to grow new plants. They are white which camouflages them against the snow. It indicates that humans share a common ancestor with chimpanzees more recently than with any other ape species. Tobacco smoke also contains carbon monoxide which reduces the oxygen-carrying capacity of the blood. These new individuals are genetically identical to the parents. Some species grow in polluted air. Some possess a light, fuzzy covering to insulate the buds so they can grow. Giraffes necks get longer due to stretching for leaves. The mixture of the genetic information from two parents leads to variety in the offspring. Some people are concerned about the use of hormones that control fertility. Examples: Bacteria or yeast cells use binary fission Plants can use runners, bulbs or vegetative propagation. Slime capsule around some bacterial cell wall sticks them to surfaces and prevents them drying out.
When new medical drugs are devised, they have to be extensively tested and trialled before being used.
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