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GCSE AQA biology chapter 2
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growth and differentiation in animals
growth and differentiation in animals
differentiation is the process that causes unspecialised cells to become specialised (have a specific function).
in animals, cells become specialised very early on in development.
unspecialised cells are called stem cells and are present in animal embryos - embryonic stem cells.
these can specialise into any cell (eg. muscle cell or white blood cell.
adult stem cells occur in babies, children and adults, wen the organism is fully developed.
adult stem cells can only specialise into a few cell types.
animal cells cannot re-differentiate.
Embryonic stem cells:
advantages...
can be made to differentiate into any cell
can be used to treat patients with nerve damage (eg. paralysis) and diabetes (pancreas cells)
disadvantages...
using stem cells damage or kill embryos
embryos cannot give consent
stem cell treatment many cause cancer
they can be contaminated with viruses (eg. HIV)
cloning plant and animal cells
cloning plant and animal cells
cloning - making genetically identical copies of an organism.
therapeutic cloning - animal:
making embryonic stem cells using patients DNA, so that the patient can be treated with their own cells (eg. making a replacement organ).
no rejection occurs
plant stem cells:
use meristem cells to produce multiple identical copes of the following, cheaply and easily...
endangered plants (eg. orchids)
crops that are, for example, disease resistant (eg. wheat and corn)
cell division
cell division
you actually have 46 chromosomes in 23 pairs.
mitotic cell division is important in growth, repair and development of multicellular organisms.
the cell cycle
stage 1: this is the longest stage. the cells replicate their DNA to form two copies of each chromosome ready for division. they also increase the number of sub-cellular structures such as mitochondria, ribosomes and chloroplasts ready for the cell to divide.
stage 2 (mitosis): in this process, one set of chromosomes is pulled to each end of the dividing cell and the nucleus divides.
stage 3: the cytoplasm and the cell membranes also divide to form two identical daughter cells.
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