Module 2: Cell Division

Question 1

What are the 2 main phases in the cell cycle?

Answer 1

Interpahse

Mitosis

Question 2

Why is it wrong to say interphase in the resting phase of the cell cycle?

Answer 2

Very active phase 
DNA replication occurs 
Production of enzymes and hormones 
Protein synthesis occurs
Growth and replication of organelles e.g. mitochondria and chloroplasts

Question 3

How many stages are in interphase? Name them

Answer 3

3 stages

G1, S and G2

Question 4

Describe G1

Answer 4

1st growth phase
Cell gains size
Proteins synthesised
Organelles synthesised

Question 5

Describe the S phase

Answer 5

DNA replication
Leads to production of genetically identical sister chromatids
In the nucleus

Question 6

Describe the G2 phase

Answer 6

2nd growth phase
Proteins form spindle fibres
Checking of genetic material before mitosis for errors
Energy stores increased

Question 7

What are the 2 stages of the mitotic phase?

Answer 7

Mitosis

Cytokinesis

Question 8

What is the G0 phase?

Answer 8

The cell leaves the cell cycle either temporarily or permanently

Question 9

What can cause a cell to enter the G0 phase?

Answer 9

1) Differentiation = cell no longer able to divide due to being specialised to carry out a particular function
2) DNA may be damaged = no longer viable - apoptosis - no longer able to divide and enters permanent cell arrest - majority of cells only divide a certain number of times before becoming senescent
3) Age = number of senscent cells increase

Question 10

Which types of cell can enter the G0 phase and be stimulated to return to the cell cycle?

Answer 10

Lymphocytes in an immune response

Question 11

What are checkpoints in the cell cycle?

Answer 11

Control mechanisms of the cell cycle to monitor and verify whether processes at each phase of the cell cycle have been accurately completed before progression into the next phase

Question 12

Where are chckpoints found in the cell cycle?

Answer 12

G1 checkpoint at the end of G1 before entry into the S phase - if requirments not met entry into the G0 phase occurs
G2 checkpoint - before mitosis - ensure DNA has been replicated without error
Spindle fibre/ metaphase - all chromosomes should be attached to spindle fibres and be aligned - mitosis cannot occur without this

Question 13

What happens to chromosomes during DNA replication in interphase?

Answer 13

Converted into 2 DNA molecules called chromatids, joined by a centromere.

Question 14

What is the significance of mitosis?

Answer 14

Growth = produce genetically identical cells to allow multicellular organisms to grow
Tissue repair
Asexual reproduction = amoeba and plants like strawberries form runner and yeast cells (fungi) reproduce by budding

Question 15

What is cell division in prokaryotes called?

Answer 15

Binary fission

Question 16

What are the 4 stages of mitosis?

Answer 16

Prophase, metaphase, anaphase, telophase

Question 17

Describe interphase

Answer 17

Replication of DNA and organelles, protein synthesis, increase in metabolic rate
Chromosomes not visible

Question 18

Describe prophase

Answer 18

Chromosomes shorten and thicken - visible
Centrioles in the cytoplasm migrate to the poles and form spindle fibres
Nucleolus disappears
Nuclear membrane has disintergrated

Question 19

Describe metaphase

Answer 19

Pairs of chromatids (chromosomes) line up along the equator/metaplate of the cell
Attached to spindle fibres by their centromeres

Question 20

Describe anaphase

Answer 20

Spindle fibres shorten
Centromere splits
Sister chromatids pulled towards opposite poles of the cell by the centromere first
Gives a distinct V shape

Question 21

Describe telophase

Answer 21

Chromatids (now chromosomes) reach the poles
New nuclear envelope forms
Cell now contains 2 genetically identical daugheter diploid nuclei

Question 22

Describe cytokinesis for an animal

Answer 22

Cleavage furrow around the middle of the cell
Plasma membrane pulled inwards by the cytoskeleton util close enough to fuse aroudn the middle, forming 2 new genetically identical daughter diploid cells

Question 23

Describe cytokinesis in plants

Answer 23

Not possible for a cleavage furrow due to a cell wall
Vesicles from the golgi assemble along the equator
Vesicles fuse with each other forming an end plate dividing the cell in two
New sections of the cell wall form along the new membrane

Question 24

What is the significance of meiosis?

Answer 24

Production of haploid cells

Provide genetic varieation through independent assortment and crossing over

Question 25

What is different about meisosis compared to mitosis?

Answer 25

Meiosis has 2 lots of cell division to produce 4 genetically identical haploid daughter cell Mitosis has 1 cell division to procuce 2 genetically identical diploid daughter cells

Question 26

Describe prophase 1 of meiosis

Answer 26

Chromosomes shorten and thicken - visible Nuclear envelope disintergrates Nucleolus disappears and spindle fibres form Homologous pairs of chromosomes come together to form a bivalent Non-sister chromatids from homologous chromosomes cross over at points called chiasmata -

Question 27

What is the purpose of crossing over of non-sister chromatids?

Answer 27

Provides genetic variation by giving new allele combinations

Question 28

Describe metaphase 1

Answer 28

Homologous pair of chromosomes arrange themselves along the equator of the cell Independent assortment occurs

Question 29

What is the purpose of independent assortment?

Answer 29

Means the combinations of chromosomes in daughter cells is random Gives genetic variation

Question 30

Describe anaphase 1

Answer 30

Homologous pairs of chromosomes separate One chromosome from each pair are pulled to opposite poles by spindle fibres Recombinant chromatids occur here whereby sections of DNA on sister chromatids from crossing over break off and exchange DNA Provides genetic variation from new allele combinations

Question 31

Describe telophase 1

Answer 31

Chromosomes assemble at the poles and the nucler membrane reforms Does not occur in plants - straighth to metaphase 2 Chromosomes uncoil to form chromatin

Question 32

Describe prophase 2

Answer 32

Chromosomes shorten and thicken by condensing - visible Nuclear envelope disintergrates Spindel fibre formation

Question 33

Describe metaphase 2

Answer 33

Individual chromosomes arrange at the equator Independent assortment and segregation of the chromatids occurs Provides genetic variation

Question 34

Describe anaphase 2

Answer 34

Spindle fibres contract Centromeres separate Chromatids move towards opposite poles

Question 35

Describe telophase 2

Answer 35

Chromosomes uncoil and form chromatin Nuclear envelope reforms and the nucleolus becomes visible Cytokinesis occurs after this

Question 36

What are the levels of multicellular organisation?

Answer 36

``` Specialised cells Tissues Organs Organ system Whole organism ```

Question 37

Define differentiation

Answer 37

Process by which stem cells become specialised into different types of cell to carry out specific functions

Question 38

Describe erythrocytes

Answer 38

Flattened bi-concave shape = increases surface area to volume ratio Beneficial to role in the transport of oxygen around the body No nuclei to increase space for haemoglobin Flexible to move through narrow capillaries

Question 39

Describe neutrophils

Answer 39

White blood cell in immune response Muti-lobed nucleus = easy to move through gaps to reach sights of infection Granular cytoplasm contains many lysosomes whith hydrolytic enzymes to kill pathogens

Question 40

Describe sperm cells

Answer 40

Male gametes Deliver genetic material to the female gamete Flagellum to move and swim towards the egg cell/ovum Many mitochondria in the middle to provide energy to swim Acrosome on the head contains hydrolytic enzymes to digest the protective layers around the ovum for fertilisation