b2 - cell division

Question 1

why is cell division necessary?

Answer 1

• for growth
• development of an organism
• repair of damaged tissues

Question 2

define the cell cycle

Answer 2

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

Question 3

give the three stages in the cell cycle

Answer 3

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

Question 4

what do chromosomes contain?

Answer 4

genes (made of DNA) which must be passed on to each new cell

Question 5

how man chromosomes do human body cells have?

Answer 5

• 23 pairs of chromosomes
• one of each pair from mother, other from father

Question 6

how many chromosomes do gametes (eggs and sperm) have?

Answer 6

• 23 chromosomes each
• they combine tof orm the 46 chromosomes in body cells

Question 7

what is the growth of an organism a result of?

Answer 7

cell enlargement and cell division

Question 8

what happens as cells grow, divide and develop?

Answer 8

the differentiate

Question 9

define what is meant by ‘differentiation’?

Answer 9

the process by which cells become specialized to perform specific functions in an organism

Question 10

define stem cells

Answer 10

unspecialised cells in early development of animals and plants

Question 11

what is cell division mainly for in animals?

Answer 11

repair and replacement since most animal cells differentiate early in development

Question 12

why are some differentiated cells replaced by adult stem cells?

Answer 12

some differentiated cells cannot divide so they are replaced
e.g: stem cells found in bone marrow

Question 13

what can plant cells do throughout their life?

Answer 13

plant cells can differentiate throughout the life of the plant as it continues to grow

Question 14

define meristems

Answer 14

regions of unspecialised cells in plants that are capable of cell division

Question 15

what happens to the cells produced by mitosis in the meristem?

Answer 15

they elongate then differentiate

Question 16

define cloning

Answer 16

producing genetically identical offspring

Question 17

why are plants easy to clone?

Answer 17

because cells can become unspecialised, divide by mitosis, and then differentiate into various types of plant cell

Question 18

why is it difficult to clone animals?

Answer 18

once the cells are differentiated they cannot become unspecialised again

Question 19

define stem cells and where they can be found

Answer 19

unspecialised cells found in the human embryo and in adult bone marrow

Question 20

what do an egg and a sperm fuse to form?

Answer 20

a zygote which divides many times to form a ball of cells - embryo
- the inner layers of the wall are embryonic stem cells

Question 21

what could stem cells be used to treat?

Answer 21

• 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

Question 22

what can the stem cells from plant meristems be used for?

Answer 22

to make clones of the mature parent quickly and economically

Question 23

what are the benefits of cloning plants?

Answer 23

• 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

Question 24

where do embryonic stem cells come from?

Answer 24

come from aborted embryos or spare embryos from fertility treatment

Question 25

what are the ethical issues of embryonic stem cells?

Answer 25

• people believe its a violation of the embryos rights as it cannot give permission - ethical objection
• people believe we should not interfere with natural processes of reproduction - religious objection
• people think a lot of money, which could be used to treat other medical conditions is wasted on stem cell research - ethical and social problem

Question 26

give three more ethical issues of using embryonic stem cells?

Answer 26

• scientists finding it difficult to ‘persuade’ stem cells to differentiate - development of process is slow and expensive
• concern for cancer since they divide rapidly
• they’re preferred to adult stem cells since it is possible adult stem cells transmit virus’ to another person r trigger an immune response

Question 27

define therapeutic cloning

Answer 27

• embryo produced with same genes as patient
• stem cells from embryo can be transplanted into the patient without being rejected by the patients immune system
• once inside the patient, stem cells can differentiate to replace the cells which have stopped working correctly