Chap.6 Cell cycle/division

Question 1

When do chromosomes become visible

Answer 1

Chromatin condenses before cell division, coiling up, after each DNA molecule is replicated and has an exact copy of itself

Question 2

What is the structure of the chromosome after chromatin condensation

Answer 2

2 sister chromatids, joined by a centromere

Question 3

What is a centromere and it’s function

Answer 3

Specialised region of a chromosome where 2 chromatids join, and where the spindle fibres attach at cell division

Question 4

Difference between a haploid and a diploid

Answer 4

A haploid consists of 1 complete set of chromosomes while a diploid has 2

Question 5

Is a normal human cell a haploid or a diploid

Answer 5

Diploid as it receives one complete set of chromosomes from each parent. Chromosome come in pairs so are homologous pairs. 23 pairs of chromosomes, 2 complete sets

Question 6

What is ploidy level

Answer 6

Refers to the number of complete sets of chromosomes in an organism. Human’s ploidy level is 2 in a body cell

Question 7

What is mitosis

Answer 7

A type of cell division in which 2 daughter cells carry the identical genetic material as that in their parent cells

Question 8

What is a cell cycle

Answer 8

A sequence or pattern of process a cell goes through continuously
Regular alternation of DNA synthesis and cell division

Question 9

What are the 3 big categories of a cell cycle

Answer 9

Interphase, mitosis and cytokinesis

Question 10

Main features of interphase

Answer 10

Longest phase in the cell cycle when organelles in a cell replicate.
DNA doubles
Histones, enzymes (proteins) synthesised
Chromosomes not visible yet
*Remember that DNA started duplicating in interphase, not prophase

Question 11

What are the 4 stages in mitosis

Answer 11

Prophase, metaphase, anaphase, telophase

Question 12

What happens in prophase

Answer 12

Chromosomes condense, coil up, get shorter but thicker, so are visible as pairs of chromatids
Centrioles start to separate and move to opposite poles
Protein microtubules start to form, spindle fibres extend

Question 13

How is the nucleus changed in later prophase

Answer 13

Nuclear envelope disintegrates and nucleolus disappears

Question 14

What happens in metaphase

Answer 14

Centrioles approach opposite poles, organise spindle fibres to attach centromeres
Chromosomes line up on equator

Question 15

What happens in anaphase

Answer 15

Centromeres separate and spindle fibres shorten

Separated chromatids are pulled to the opposite poles

Question 16

Features of telophase

Answer 16

Final stage of mitosis
No longer called chromatids but chromosomes
Chromosomes uncoil and lengthen
Spindle fibres break down
Nuclear envelope reforms
Nucleolus reappears

Question 17

Describe the stage of cytokinesis

Answer 17

Division of cell cytoplasm
Differences between animal and plant cells
Animal: constriction of parent cell around equator, cleavage furrow
Plant: cell plate forms

Question 18

Differences between mitosis in plant and animal cell

Answer 18

Plants experience no shape changes
Plant cells do not have centrioles
Animal cells form cleavage furrow while plant cells form cell plates
Cleavage furrow from outward to inward
Cell plate from inward to outward
Spindle fibres in animal degenerate at telophase
Remain in plants throughout the whole new cell wall formation

Question 19

Why is mitosis significant (3 reasons)

Answer 19

Gives genetic stability as cells produced from mitosis are genetically identical to parent cells
Replace worn out tissues, repair
Asexual reproduction in yeasts and bacteria

Question 20

In what form damage and disease can happen to a cell

Answer 20

Potential cause such as mutations, so genes that control the cell cycle gets damaged.
Disrupting the timing of the cell cycle

Question 21

Possible factors that damage the genes controlling the cell cycle

Answer 21

Mutations, exposure to radiation, chemicals, viral infections

Question 22

How can damage to genes lead to cancers

Answer 22

Genes can control timings of a cell cycle, like a brake
Are tumour suppressing genes
Without them cells could divide too rapidly
Prevent rapid replication thus avoid tumour formation

Question 23

What is an oncogene

Answer 23

A gene with potential cause to cancer. Before altered, are called proto-oncogenes

Question 24

What is meant by meiosis

Answer 24

Two stage cell division in sexually producing organisms
Produces 4 genetically not identical daughter cells with half the number of chromosomes of parent cell
A haploid

Question 25

Why does the number of chromosomes change in meiosis

Answer 25

Chromosome number halves
So when 2 haploid gametes fuse in fertilisation, zygote formed, consisted of 2 complete sets of chromosomes, one from each gamete, to restore the diploid condition
To avoid doubling of chromosome number for each generation

Question 26

What are the sequences of meiosis

Answer 26

Same cell division sequence from prophase to telophase
But repeats twice
Chromosome behaviours are different
Have to specify I and II

Question 27

What takes place in meiosis I prophase I

Answer 27

Paternal and maternal chromosomes come in homologous pair, called synapsis, chromosome pair is bivalent
Chromosomes coil up, centrioles move to opposite poles forming spindle fibres
Chromatids wrap around each other at chiasmata where DNA is exchanged
Crossing over, gives genetic variation
Mixing genes of 2 parents so have different alleles
Nucleolus disappears, envelope disintegrates

Question 28

Events at metaphase I meiosis

Answer 28

Arrange on equator
Lie randomly so combination of chromosomes in daughter cells is random as in which parent they come from
Independent assortment
Random mixture of maternal and paternal chromosomes

Question 29

What happens in anaphase, metaphase, telophase II

Answer 29

Chromosomes in bivalent separate, spindle fibres shorten, pulled to each end of the pole randomly
Nuclear envelope reforms, chromosomes decondense in telophase
Cytoplasm divides in cytokensis
Independent assortment still happens in metaphase II

Question 30

Comparing mitosis and meiosis stage 2

Answer 30

Very similar. Pretty much like reassembling process of mitosis

Question 31

What is the importance of meiosis

Answer 31

Keeps chromosome number constant from one generation to another
Generates genetic variations
More able to adapt with the changing environment

Question 32

Differences between meiosis I and II

Answer 32

No DNA replication or crossing over in II
Not homologous pair but chromosomes in stage II
2 daughter cells in I, 4 in II
Separation and independent assortment of chromatids in II instead of chromosomes in I