Reproduction and Growth : Cell Division

Question 1

what do sexual and asexual reproduction require?

Answer 1

cell division

Question 2

what are the two types of cell division?

Answer 2

• mitosis
• meiosis

Question 3

what happens before cells divide?

Answer 3

• the chromosomes replicate, making an exact copy of themselves, which doubles the amount of DNA in the cell

Question 4

what are cells produced by mitosis?

Answer 4

• genetically identical daughter cells
• cells are diploid (have one pair of each chromosome in each nucleus)
• human diploid cells have 23 pairs of chromosomes, 46 in total

Question 5

what is mitosis used for?

Answer 5

• growth, repair and asexual reproduction

Question 6

what are cells produced by meiosis?

Answer 6

• produce haploid gametes which aren’t genetically identical
• human haploid cells have 23 chromosomes in total (unpaired)

Question 7

what are examples of haploid gametes?

Answer 7

• sperm
• eggs
• pollen

Question 8

what is meiosis used for?

Answer 8

• only used to produce gametes for sexual reproduction

Question 9

what is a consequence of meiosis?

Answer 9

• every gamete produced is genetically different (it carries different alleles to every other gamete)
• it is random which sperm / pollen grain fertilises an egg

Question 10

what is variation in offspring produced by?

Answer 10

• genetic variation in gamete cells produced by meiosis
• random fertilisation of ova (egg cells) by male gametes

Question 11

what are differences in the processes of mitosis vs meiosis?

Answer 11

MITOSIS
- produces genetically identical daughter cells
- produces two cells
- involves one division
- produces diploid cells in humans
- keeps the same chromosome number
MEIOSIS
- produces genetically non-identical daughter cells
- produces four cells
- involves two cell divisions
- produces haploid cells in humans
- halves the number of chromosomes

Question 12

what are differences in the roles of mitosis vs meiosis?

Answer 12

MITOSIS
- generates all adult cells except gametes (growth and repair)
- occurs throughout the human body
- occurs throughout a plant
- used for asexual reproduction (cloning)
MEIOSIS
- only used to produce gametes
- only occurs in ovary and testis
- only occurs in ovary and anther
- used for sexual reproduction

Question 13

what is mitosis?

Answer 13

• mitosis is a type of cell division in which a diploid body cell copies itself and finally divides into two identical diploid daughter cells
• the daughter cells are clones of each other
• every base pair of their DNA is identical

Question 14

state the steps for mitosis.

Answer 14

1. the cell grows
2. the DNA replicates (is copied) to form two copies of each chromosome. these copies (chromatids) are joined together at a single point (the centromere)
3. the nuclear membrane breaks down. the chromosomes line up across the centre of the cell, attached to special spindle fibres
4. the chromatids (copies of chromosomes) are pulled apart and move to opposite ends of the cell
5. the cytoplasm and cell membrane divides to form two identical cells

Question 15

what is meiosis?

Answer 15

• type of cell division which gives rise to cells which are genetically different
• meiosis takes place in the sex organs (e.g. the testes and ovaries of mammals)
• the cells formed are gametes (sperm and egg cells in mammals)
• gametes are different from other cells because they have half the normal number of chromosomes (they are haploid)
• produces four genetically different haploid cells
• meiosis is a reduction division - chromosome number is halved from diploid
• as a result of meiosis and fertilisation, the maternal and paternal chromosomes meet in different combinations in the zygotes. consequently, the offspring will differ from their parents and from each other in a variety of ways

Question 16

state the steps for meiosis.

Answer 16

1. the parent cell grows
2. the DNA replicates (is copied) to form two copies of each chromosome. these copies (chromatids) are joined together at a single point (the centromere)
3. the nuclear membrane breaks down. the homologous pairs of chromosomes join together
4. the homologous pairs of chromosomes exchange sections of DNA. they then attach to the spindle fibres in pairs, at the centre of the cell
5. the homologous pairs of chromosomes are pulled apart and move to opposite ends of the cell. the cell divides.
6. the chromosomes line up along the centre of the cell, attached to the spindle fibres. the chromatids separate and move to opposite ends of the cell. each cell divides again.