Evolution and Environment.

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Science Exam: B1b revision.
Reproduction and genes
. Individuals need to reproduce to prevent a species from dying out.
. There are two types of reproduction: sexual and asexual.
. Asexual reproduction requires only one parent and produces genetically identical offspring (clones).
. Asexual reproduction allows organisms to reproduce very quickly, for example bacteria.
. Sexual reproduction requires two parents.
. Gametes (sex cells) from each parent join together (fuse) at fertilisation.
. Offspring contain genes from each parent and so show more variation.
You and your genes
. Genetic information is found in the nucleus of a cell.
. Chromosomes are made up of the chemical DNA ( deoxyribonucleic)
. A gene is a section on DNA that `codes' for a characteristics, such as eye colour.
. Human body cells contain 23 pairs of chromosomes (46 in total).
. Sperm and egg cells each contain a set of 23 individual chromosomes.
. At fertilisation, the two sets of chromosomes combine to give an embryo which half of it's genes
coming from the mother and half from the father.
Genetic engineering
. Genetic engineering involves removing genes from one species and transferring them into another.
. For example, bacteria have been genetically engineered to produce human insulin.
. The insulin gene is first identified and removed from human cells.
. Restriction enzymes act like chemical `scissors' to snip the wanted gene from the rest of the
. This gene is then attached to chromosomes taken from bacteria.

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The modified chromosomes are put back into the bacteria, which now produce human insulin.
. Genes for resistance to pests and weed killers can be transferred into plant cells by genetic
. Clones are genetically identical individuals.
. Producing new plants by taking cuttings from older plants is an example of cloning.
. Tissue culture can be used to take a small group of plant cells and use these to grow a whole new plant.
.…read more

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Similarities between fossils and living species provide evidence for evolution.
. Jean-Baptiste Lamarck thought that an organism's environment caused it to change, and that these
changes were passed on to offspring.
. Darwin later put forward his theory of evolution by natural selection.
Natural selection
. Charles Darwin observed how different species are adapted to their environments.
. Individuals differ within populations and some are better adapted than others.
.Those that are best adapted are more likely to survive long enough to reproduce.
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More land is used for agriculture and building.
. Fertilisers and pesticides used in agriculture pollute the environment.
. More waste is produced and raw materials such as fossil fuels are being used up.
. Land which was once a habitat for plants or animals is no longer available.
Pollution and acid rain
. Pollution is caused by improper handling of waste from human activity.
. Water may be polluted with sewage or fertilisers from agriculture.
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Sustainable development requires management at local, regional and global levels.
. Measures that can be taken include:
. Recycling of resources such as paper, glass and aluminium.
. Use of renewable energy resources, such as wind power and solar power.
. energy-efficient homes, using insulation and double glazing.
. Reducing the use of Moto vehicles by walking, cycling or using public transport.
. Planting a new tree from each tree cut down.
. quotas on pollution imposed on governments.…read more


lisa linsdell

Good revision notes with sub-headings. Covers information on genetics, cloning ect.

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