b2 - cell division Flashcards
why is cell division necessary?
- for growth
- development of an organism
- repair of damaged tissues
define the cell cycle
series of stages the cell divides iny
- short in embryos as cells divide rapidly
- slower process in adults but some cells still do divide rapidly
give the three stages in the cell cycle
1) cells grow, increase in mass, carry out normal cell activities, at end cells replicate DNA to make two copies of every chromosome, make more sub-cellular structures
2) mitosis: one set of chromosomes is pulled to each end of the dividing cell and nucleus divides
3) cytoplasm and cell membran divide to form two new identical cells
what do chromosomes contain?
genes (made of DNA) which must be passed on to each new cell
how man chromosomes do human body cells have?
- 23 pairs of chromosomes
- one of each pair from mother, other from father
how many chromosomes do gametes (eggs and sperm) have?
- 23 chromosomes each
- they combine tof orm the 46 chromosomes in body cells
what is the growth of an organism a result of?
cell enlargement and cell division
what happens as cells grow, divide and develop?
the differentiate
define what is meant by ‘differentiation’?
the process by which cells become specialized to perform specific functions in an organism
define stem cells
unspecialised cells in early development of animals and plants
what is cell division mainly for in animals?
repair and replacement since most animal cells differentiate early in development
why are some differentiated cells replaced by adult stem cells?
some differentiated cells cannot divide so they are replaced
e.g: stem cells found in bone marrow
what can plant cells do throughout their life?
plant cells can differentiate throughout the life of the plant as it continues to grow
define meristems
regions of unspecialised cells in plants that are capable of cell division
what happens to the cells produced by mitosis in the meristem?
they elongate then differentiate
define cloning
producing genetically identical offspring
why are plants easy to clone?
because cells can become unspecialised, divide by mitosis, and then differentiate into various types of plant cell
why is it difficult to clone animals?
once the cells are differentiated they cannot become unspecialised again
define stem cells and where they can be found
unspecialised cells found in the human embryo and in adult bone marrow
what do an egg and a sperm fuse to form?
a zygote which divides many times to form a ball of cells - embryo
- the inner layers of the wall are embryonic stem cells
what could stem cells be used to treat?
- paralysis, by differentiating into new nerve cells
- macular degeneration in the eye, to restore lost vision
- diabetes, by producing cells that are sensitive to blood sugar and can produce insulin
what can the stem cells from plant meristems be used for?
to make clones of the mature parent quickly and economically
what are the benefits of cloning plants?
- rare plants can be saved from extinction
- large populations of genetically identical plants can be produced with special features, such as resistance to disease
- in horticulture, large numbers of ecotic plants can be produced for sale
- in agriculture, plants can be produced with special features such as resistance to disease
where do embryonic stem cells come from?
come from aborted embryos or spare embryos from fertility treatment
