1.6 Cell division

Question 1

What is the point of cell Division ?

Answer 1

GATE mnemonic

1. Growth
2. Asexual reproduction
3. Tissue Repair
4. Embryonic Development

Question 2

Definition of Mitosis

Answer 2

mitosis is type of cell division where a single cell divides into two identical daughter cells (cell division).

Question 3

What is the definition of cell cycle and what are the different phases of the cell cycle ?

Answer 3

series of events cells go through to divide and create two identical cells

different phases G1, S, G2, mitosis and cytokinesis

Question 4

Explain each phase of the cell cycle

Answer 4

G1 and G2 have the same processes

• increase in vol. of cytoplasm
• organelles duplicated
• proteins synthesised
• normal metabolic processes (respiration, growth, excretion)

S phase
- DNA replicated

Question 5

What are the different phases of Mitosis and explain each phase ?

Answer 5

P rophase - DNA supercoiling, chromatin condensing, spindle fibres form, centrosomes move to opposite poles, nuclear membrane disintegrates (break down into smaller parts)

M etaphase - spindle fibres bind to centromere of sister chromatids, sister chromatids line up in the equator

A naphase - sister chromatids separated (now they are chromosomes) , pulled to opposite poles by spindle fibres.

T elophase - chromosomes at opposite poles, nuclear membrane starts reforming. spindle fiber breaks down. cell elongates for cytokinesis, nucleolus appears in each new nucleus

Question 6

Describe the process of cytokinesis in an animal cell

Answer 6

Cytokinesis - division of the cytoplasm after mitosis, often starts at the end of telophase

Animal cell - microfilaments beneath the plasma membrane at the equator pulls the membrane inward forming the cleavage furrow. when cleavage furrow reaches the middle, it is pinched apart to form two identical daughter cells

Question 7

Cytokinesis in plant cell

Answer 7

golgi apparatus forms vesicle which consists of material to build a new cell wall. vesicles form together to form the cell plate

cell plate grows and divides into two daughter cells

Question 8

Define cyclins and explain how they work

Answer 8

cyclins is a family of proteins which controls the progression of cell through the cell cycle, ensure that tasks are performed correctly and make sure cells moves onto the next stage when appropriate

• bind to enzymes called cyclin-dependent kinases ,
• these kinases become active and releases phosphate groups to other proteins in the cell
• phosphate triggers protein - they become active and then carry out specific functions

Question 9

there are four type of cyclins and unless these cyclins reach a _________ _________ the cell ____ _____ _____ _______ _____ ______ ______

Answer 9

threshold concentration, does not progress to the next level

Question 10

State the two types of tumours and explain them

Answer 10

benign tumours - tumours that are unlikely to cause harm localised, does not spread to other parts of the body

malignant tumours - life threatening, the one that cause cancer, spread to other parts to the body

Question 11

define mutation and mutagens (examples of mutagens)

Answer 11

mutation is a rare and random change in the base sequence of genes

mutagens are agents that can cause gene mutation (all mutagens are carcinogenic)

• chemicals (carcinomas are malignant tumours)
• high energy radiation such as x rays
• short wave UV light
• some viruses such as hepatitis B

Question 12

Explain the theory of cell mutation that might lead to cancer

Answer 12

most genes do not cause cancer if they mutate

oncogenes - cancer causing gene after mutation
(because oncogenes control cell cycle and division)

mutated oncogenes —> uncontrolled cell division —> tumour formation

Question 13

Other factors apart from mutagens that might increase probability of tumour development

Answer 13

• The vast number of cells in a human body – the greater the number of cells the greater the chance of a mutation
• The longer a life span the greater the chance of a mutation.

Question 14

Explain the development of secondary tumours

Answer 14

the process where secondary tumour forms is metastasis or we say that the tumour is metastasized

PROCESS
- cancerous cells detach from primary tumour

• some of these cancer cells have the ability to penetrate the wall of lymphs of blood vessels
• they circulate around the body and invade tissues at different locations and develop by uncontrolled cell division

Question 15

Define mitotic index and state the equation

Answer 15

mitotic index = (P+ M + A + T) / total cells

ratio between the number of cells undergoing mitosis and the number of cells not undergoing mitosis

Question 16

Why is the mitotic index important ?

Answer 16

It can tell us how many cells in a tissue are dividing at a given time

in tumour, mitotic index is higher than normal due to uncontrolled cell division

which helps doctor predict how quickly a cancer can spread