Cell Division

Question 1

How long does the cell cycle take place and what does the duration depend on

Answer 1

It takes a long time and the duration depends on the type of cell.

Question 2

What does the cell cycle consist of

Answer 2

Two different phases or parts

Question 3

What are the two different phases

Answer 3

M phase or mitosis phase as well as interphase.

Question 4

What is M phase or mitotic phase and how long does it take

Answer 4

It is when mitosis takes place and the cell divides in two. And this phase takes up only a relatively short period of time.

Question 5

What can the cell appear to be during interphase and what occurs during it

Answer 5

The cell may appear to be inactive but lots of different processes are occurring. During interphase the cell is carrying out the functions of that particular cell type.

Question 6

What are the specific processes that occur during interphase

Answer 6

DNA is replicated and checked for errors in the nucleus.
Protein synthesis occurs in the cytoplasm
Mitochondria grow and divide increasing their number in the cytoplasm.
Chloroplasts grow and divide in plant and algae cells increasing their number in the cytoplasm.
The normal metabolic processes of the cell occur.

Question 7

What are the 3 different stages of interphase

Answer 7

G1, S, G2

Question 8

What occurs during G1

Answer 8

The cell replicates organelles such as mitochondria.

Replicating organelles requires lots of proteins, so a high level of transcription and translation take place.

The size of the cell also increases, so that when the cell divides the two daughter cells are the correct size.

Question 9

What occurs during S phase

Answer 9

All of the chromosomes are replicated
So a large amount of DNA is synthesised.

Question 10

What occurs during G2 phase

Answer 10

The cell replaces the energy stores that are used up during S phase
The cell also continues to carry out transcription and translation
If any of the chromosomes have been damaged they are repaired too
The cell also continues to grow

Question 11

What happens once a cell exits G2 phase

Answer 11

It enters the M or mitotic phase.

Question 12

What can the mitotic phase be divided into and what does each stage do

Answer 12

Mitosis - the chromosomes separate into 2 nuclei
Cytokinesis - the cell divides into two

Question 13

What is G0 phase

Answer 13

When some cells exit the cell cycle and this is called G0 phase.

Question 14

What are the three different reasons that cells enter G0 phase

Answer 14

Fully differentiated cells enter G0 and stay there for the rest of their lives.
Overtime the DNA in cells can be damaged and at a certain point will no longer be able to divide, these are called senescent cells and they enter G0 permanently.
Some cells enter G0 temporarily from example B memory cells.

Question 15

What are checkpoints in the cell cycle

Answer 15

At certain points in the cell cycle the cell checks that the cycle should continue.

Question 16

What happens if a cell fails at a checkpoint

Answer 16

It will leave the cell cycle and enter G0

Question 17

What is the first checkpoint

Answer 17

Before the S phase the cell must pass through the G1 checkpoint.

Question 18

What does the cell check for at the first checkpoint and if it is successful what occurs.

Answer 18

The cell checks that it has grown to the correct size
The cells checks for DNA damage

If successful then it enters into S phase and carries out DNA replication.

Question 19

What is the second checkpoint and what does the cell do and what occurs if it is successful

Answer 19

The second checkpoint is at the end of G2 before the cell passes into mitotic phase.

The cell checks for DNA damage and whether it has grown to the correct size

If the checkpoint is passed it moves into the mitotic phase.

Question 20

What is the last checkpoint what does the cell do and what occurs if it is successful

Answer 20

It is the metaphase checkpoint
This checks that the chromosomes are arranged correctly in the mitotic spindle.
If this occurs the cell completes mitosis and proceeds through cytokinesis.

Question 21

what are diploid cells

Answer 21

when cells contain chromosomes in pairs they are referred to as diploid cells.

Question 22

What occurs in terms of diploid cells in mitosis

Answer 22

We start with one diploid cell and end up with two identical diploid daughter cells

Question 23

When does cell division by mitosis occur and why

Answer 23

It is used in asexual reproduction and in growth and repair as we want identical copies of a cell.

Question 24

During interphase what can’t you see in the nucleus, and what do you see instead

Answer 24

You can’t see chromosomes as they are not visible as distinct structures instead you see a dark material called chromatin.

Question 25

In chromatin what is a feature of the structure of DNA

Answer 25

the chromosomes have a loose open structure so that the DNA is accessible for transcription and replication.

Question 26

What is a chromosome

Answer 26

It is a single long molecule of DNA

Question 27

In interphase what occurs

Answer 27

The chromosomes are replicated so now there are two identical molecules of DNA. And this process occurs for every chromosome.

Question 28

What are the stages of mitosis

Answer 28

Prophase, metaphase, anaphase and telophase.

Question 29

What occurs during prophase (1)

Answer 29

The chromosomes condense and become visible in the nucleus.
Each chromosome consists of 2 sister chromatids, joined at the centromere.
The nucleolus becomes disorganised and is no longer visible and the nuclear membrane starts to break down

Question 30

What occurs during prophase (2)

Answer 30

A pair of centrioles move to either side/pole of the cell
Proteins begin to form spindle fibres attaching to the centromere of each chromosome.
They start to move the chromosomes towards the centre of the cell.

Question 31

What is metaphase and what occurs during it

Answer 31

The second stage of mitosis
The spindle apparatus has completely formed and the chromosomes are lined up at the centre of the cell.

Question 32

What is anaphase and what occurs during it

Answer 32

The chromosomes divide into two and the spindle fibres begin to shorten.
This pulls the sister chromatids towards opposite poles of the cell.

Question 33

What occurs during telophase

Answer 33

The chromatids reach the poles of the cell and are now referred to as chromosomes again.
The spindle apparatus breaks down and the nuclear membrane reforms.
The chromosomes uncoil back to their chromatin state.
The nucleolus also forms in each nucleus.
The cell finishes nuclear division by mitosis.

Question 34

What occurs during cytokinesis

Answer 34

The central cell membrane is pulled in by the cytoskeleton
This creates a groove/furrow which gradually deepens
The membranes eventually fuse to form 2 independent cells.
At this stage cell division by mitosis has finished.

Question 35

How is mitosis different in plant cells (1)

Answer 35

1. centrioles don’t play a role in forming the spindle apparatus in plant cells. As plant cells don’t contain centrioles.
2. When plant cells undergo cytokinesis the cell membrane can’t form a groove/furrow like in animal cells. Instead vesicles from the Golgi apparatus form membrane structures down the centre of the cell which fuse together to form a central membrane dividing the cytoplasm into 2.

Question 36

How is mitosis different in plant cells (2)

Answer 36

A new cellulose cell wall also forms down the centre