Exam practice answers 9

OCR A2 Biology
9 Cloning in plants and
1 (a) (i) Production of genetically identical cells or tissues. There is no intention to produce a whole
new organism.
(ii) Growth of new tissue such as skin to repair damage to a patient. Growth of cells for research
into the effectiveness of medical drugs.
(b) (i) Reproducing a new individual that is genetically identical to the original.
(ii) A rare plant can be reproduced in large numbers quickly. A new variety that has been produced
by careful selective breeding or genetic engineering can be reproduced without the risk of
changing its genotype. Plants grown from a meristem will be free from disease.
(iii) Remove the nucleus from a donor egg. Extract a cell from the animal to be cloned. Fuse the cell
with the empty egg cell using electric shock. Allow mitosis to occur and produce many cells,
which can be separated. Each will grow into a new embryo. Place each embryo into the uterus
of a surrogate mother to develop.
2 (a) (i) Quick; uniform growth of crop; all potatoes have same good flavour and texture.
(ii) All the potatoes planted were from the same clone. All the potato plants were genetically
identical. None had any resistance to the fungus. Plants were grown close together in large
monocultures, making it easy for the fungus to spread.
(b) (i) Fungus-resistant strains could be found to cross with the good-tasting variety. Allow the
hybrids to grow and select any potatoes or potato plants that are exposed to the disease but not
damaged by it. Resistance may also arise by mutation. Cross two slightly resistant plants
together. Collect and grow the seeds. Test the offspring by exposing them to the disease and
again select the most resistant as parents of the next generation. This is selective breeding by
artificial selection.
(ii) Tissue culture using the apical buds or apical meristems. Cut the meristem into smaller pieces
and sterilise these explants. Then grow them on nutrient medium with correct proportion of
plant growth regulators. The callus produced can be subdivided to make more plants. Transfer
to other media with the correct growth regulation substances to encourage growth of roots and
shoots. Transfer to grow on in soil.
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