Cell Cycles

Question 1

what is meiosis

Answer 1

it produces cells which have half the normal number of chromosomes

Question 2

what happens to a cell post fertilisation in terms of the cell cycle?

Answer 2

after the two gametes have fused, the new cell divides by mitosis to make a copy of itself.

Question 3

where does meiosis take place?

Answer 3

in the ovaries (egg cells) and the testes (sperm cells)

> meiosis produces gametes (cells with half the normal number of chromosomes)

Question 4

what do chromosomes do?

Answer 4

they carry the genes that contain instructions for making new cells and all tissues + organs.

Question 5

what is a gene?

Answer 5

a small pocket of informations that controls a characteristic of your body.
a section of DNA

Question 6

explain the first stage of the cell cycle by mitosis.

Answer 6

STAGE 1:

• cells grow bigger, increase in mass
• replicate DNA to form two copies of each chromosome
• increase number of sub cellular structures (mitochondria, ribosomes etc.)

Question 7

why do multicellular organisms use mitosis?

Answer 7

to grow or replace cells that have been damaged

Question 8

how does mitosis differ throughout life?

Answer 8

child: mitosis produces new cells faster than the old ones die
adult: balanced
elderly: mitosis slows down and there are signs of ageing

Question 9

explain the first stage of meiosis.

Answer 9

STAGE 1:
duplicates genetic material, forming two armed chromosomes
> post replication chromosomes arrange themselves into pairs

Question 10

explain the second stage of the cell cycle by mitosis

Answer 10

STAGE 2:

• cell fibres pull the chromosomes apart to opposite ends of the cell
• the nucleus divides

Question 11

explain the third stage of the cell cycle by mitosis

Answer 11

STAGE 3:

- cytoplasm and cell membrane divide to make two identical daughter cells.

Question 12

explain the second stage of meiosis

Answer 12

STAGE 2:
1st division:
- chromosome pairs in the centre
- cps get pulled apart so each new cell has one copy of each chromosome
- mixture of mother and father’s chromosomes go into each new cell

Question 13

explain the third stage of meiosis

Answer 13

STAGE 3:
2nd division:
- chromosomes line up in the centre and the arms of the chromosomes are pulled apart

Question 14

explain the product of meiosis

Answer 14

end up with 4 gametes
- each genetically different
> chromosomes get shuffled around during the process and each gamete only gets half of them at random