biology4alevel600

1 All living organisms may be classified into one of the five kingdoms: prokaryotes, protoctists, fungi, plants and animals. 2 Biodiversity includes the range of habitats (environments) and species in an area, and the genetic diversity within a species. 3 There are moral and ethical reasons for maintaining biodiversity, and also more practical ones. For example, we may be able to use plants to provide medicines, and animals to provide alleles to use in animal breeding. 4 Species may become in danger of extinction through habitat loss, change to their environment (perhaps as a result of pollution) and overexploitation by humans. 5 Conservation of an endangered animal species may involve captive breeding programmes, in which viable populations are built up in zoos and wildlife parks. These programmes try to ensure that the gene pool is maintained and inbreeding is avoided. At the same time, attempts are made to provide a suitable habitat in the wild, so that captive-bred animals can even...

1 Genetic variation within a population is the raw material on which natural selection can act.  2 Meiosis, random mating and the random fusion of gametes produce genetic variation within populations of sexually reproducing organisms. Variation is also caused by the interaction of the environment with genetic factors, but such environmentally induced variation is not passed on to an organism’s off spring. The only source of new alleles is mutation.   3 All species of organisms have the reproductive potential to increase the sizes of their populations, but, in the long term, this rarely happens. This is because environmental factors come into play to limit population growth. Such factors decrease the rate of reproduction or increase the rate of mortality so that many individuals die before reaching reproductive age.   4 Within a population, certain alleles may increase the chance that an individual will survive long enough to be able to reproduce successfully. Th...

1 Meiosis consists of two divisions. The first division, meiosis I , separates the homologous chromosomes, so that each cell now has only one of each pair. The second division, meiosis II, separates the chromatids of each chromosome. Meiotic division therefore produces four cells, each with one complete set of chromosomes. 2 Diploid organisms contain two copies of each gene in each of their cells. In sexual reproduction, gametes are formed containing one copy of each gene. Each off spring receives two copies of each gene, one from each of its parents. 3 The cells produced by meiosis are genetically different from each other and from their parent cell. This results from independent assortment of the chromosomes as the bivalents line up on the equator during metaphase I, and also from crossing over between the chromatids of homologous chromosomes during prophase I.  4 Genetic variation also results from random fertilisation, as gametes containing diff erent varieties of genes fuse to...

 1 Gene technology involves altering the genes in an organism, which is then said to be genetically modifi ed.  2 The usual way of genetically modifying bacteria is to insert a plasmid containing the desired gene into them.  3 The steps involved in the production of bacteria capable of synthesising human insulin are:    identifying the human insulin gene;    isolating mRNA and making cDNA using reverse transcriptase;    cloning the DNA using DNA polymerase;    inserting the DNA into a plasmid vector using restriction enzymes and DNA ligase;    inserting the plasmid vector into the host bacterium;    identifying the genetically modifi ed bacteria;    cloning the bacteria; and harvesting the human insulin.  4 The main advantage of treating diabetics with human insulin produced by gene technology is that it is chemically identical to the insulin that they would have produced had they not been diabetic...