Cell Division

Question 1

What are the two stages of the
cell cycle in eukaryotes?

Answer 1

1. Interphase (growth and replication)
2. Mitosis (cell division)

Question 2

What are the 3 separate growth sstages of interphase?

Answer 2

1. Growth phase 1- the cell grows, increase in the number of organelles, proteins are made and ATP is synthesised
2. Synthesis of the DNA - semi conservative replication takes place
3. Growth phase 2 - cell keeps growing, proteins are made, ATP synthesised

Question 3

Interphase is the ……. phase of the cycle, normally ……than the whole phase of mitosis, unless the cell is ……. ………

Answer 3

Interphase is the longest phase of the cycle, normally longerthan the whole phase of mitosis, unless the cell is rapidly dividing

Question 4

What are homologous chromosomes?

Answer 4

Pairs of chromosomes that contain the same genes in the same loci(position of that gene) but not necessarily the same alleles (not genetically identical).

Question 5

What do homologous chromosomes consist of?

Answer 5

One pair of chromosomes is maternal
One pair of chromosomes is paternal

They are the same size and shape and the centromere is in the same place

Question 6

How many chromosomes do all somatic cells contain?

Answer 6

46 chromosomes in 23 homologous pairs

Therefore when a new daughter cell is produced it will also contain 46 chromosomes

Question 7

MATHS QUESTION:

A scientist observes a section of growing tissue under the microscope. He counts 100 cells undergoing mitosis. Of those, 10 cells are in mitosis
One cell cycle last 15 hours. How long do the cells spend in mitosis? Give your answer in minutes

Answer 7

Step 1: find the percentage of the number of cells undergoing mitosis

10/100 x 100 = 10%

Step 2: find 15 hours in mins

15x60 = 900 mins

Step 3: find the time the cells spent in mitosis

10% of 900 = 90 mins

Question 8

What 4 things occur during interphase?

Answer 8

1) DNA replicates
2) ATP synthesised to provide energy for cellular processes
3) organelles synthesised including centrioles to carry out cellular functions, centrioles take part in separation of chromosomes
4) proteins synthesises to carry out cellular functions

Question 9

How does DNA replicate in interphase?

Answer 9

• chromosomal DNA is replicated exactly and the two pieces of DNA are held together by the centromere
• if the copies are not done accurately, mutations may occur and daughter cells will not receive identical genetic material
• following mitosis the two new cells will contain one of each sister chromatids

Question 10

What are 5 things mitosis is important for?

Answer 10

1. All organisms need to produce genetically identical daughter cells
2. Asexual reproduction
3. Growth - grow by producing new cells genetically identical to each other and the parent cell
4. Repair - damaged cells need to be replaced by new ones that perform the same donation so must be identical
5. Replacement - red blood cells and skin cells need to be replaced

Question 11

What are the 4 stages of mitosis?

Answer 11

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

PMAT

Question 12

What is prophase?

Answer 12

• replicated chromosomes shorten and thicken (supercoil)
• each chromosome consists of a pair of sister chromatids.
• Nuclear envelope breaks down and disappears
• centriole divides into two and each daughter centriole moves to opposite ends of the cell to form a spindle (protein threads)

Question 13

What is metaphase?

Answer 13

• replicated chromatome line up down the equator (middle) of the cell
• each chromosome is attached to a different spindle fibre by its centromere

Remmeber Middle for Metaphase

Question 14

What is anaphase?

Answer 14

• Identical sister cheomatids are pulled to different poles by the shortening of the spindle fibres
• centrometres divide

Remember Apart for Anaphase

Question 15

What is telophase?

Answer 15

• Two new nuclei are formed
• sister chromatids reach poles and are now chromosomes
• spindle breaks down and disappears
• Chromosomes uncoil and can’t be seen in a light microscope anymore

Remember Two for Telophase

Question 16

What is cytokinesis?

Answer 16

Division of the cytoplasm - when the cell divides

It occurs between telophase and interphase. Each new daughter cell in identical to the parent cell and to each other

Question 17

What is cytokinesis in animal cells?

Answer 17

Microfibres from a “draw string” just inside the membrane which then fuses as it is pinched in

Question 18

What is cytokinesis in plant cells?

Answer 18

Microfibres direct vesicles to the middle of the cell to form a cell plate, which forms a new cell wall. New cell surface membrane is made on either side to enclose the two cells

Question 19

Look at the graph and answer the following:

1. When does synthesis take place
2. When does mitosis take place
3. How many cell divisions age shown

Answer 19

1. Between 12 -16 and 36-40 hours because mass of DNA doubles
2. 24 hours - mass returns to original mass
3. 2

Question 20

What are mitosis and cell cycle controlled by?

Answer 20

Genes

Question 21

What is uncontrolled cell division?

Answer 21

When there’s a mutation ( change in base sequence of DNA) in a gene that controls cell division, so the cells grow out of control.

This can lead to the formation of tumours

Question 22

Where are tumours commonly found?

Answer 22

Can develop in any organ in the body but most commonly found in lungs, prostate, breast and ovaries, large intestine, stomach, oesophagus and pancreas

A tumour can become cancerous if it changes from benign to malignant

Question 23

How is cancer treated?

Answer 23

• Involves killing dividing cells by blocking part of the cell cycle. If cell cycle is disrupted cancer growth stops.
• these treatments do NOT distinguish tumour cells from normal cells however tumour cells divide more frequently than normal cells so the treatment is more likely to kill tumour cells
• normal body cells that divide rapidly are also vulnerable (explaining frequent hair loss seen in patients undergoing cancer treatment)

Question 24

How do drugs that treat cancer disrupt the cell cycle?

Answer 24

• prevent DNA from replicating. Radiation and some drugs damage DNA. If severe DNA damage is detected the cell with kill itself
• inhibiting metaphase stage of mitosis by interfering with spindle formation
• preventing the synthesis of enzymes needed for DNA replication

Question 25

Who is Henrietta lacks and was are some ethical issues of HeLa cells?

Answer 25