Continuity of cells

Question 1

Explain what happens at G1

Answer 1

-proteins are made
-organelles are made
-volume of cytoplasm increases
-cell carries out functions as usual

Question 2

Explain what happens in the S phase

Answer 2

-Is the replication of DNA
-Histones form
-Chromatids form within the nucleus

-The cell will only enter this phase of cell division is to follow

Question 3

Explain what happens in G2

Answer 3

-Proteins are used to make microtubles which compose the spindle
-Mitochondria and chloroplasts (if present) divide and produce the energy needed for mitosis
-Chromosomes are checked for errors

Question 4

Where are the 3 checkpoints in the cell cycle ?

Answer 4

-End of G1
-End of G2
-End of metaphase

Question 5

What happens if the G1 criteria isn’t met?

Answer 5

The cells enter a resting phase known as G0

Cells can remain in G0 for a short time, long time or permanently

Question 6

What does the checkpoint at the end of G1 check for ?

Answer 6

-That the cell has reached a critical size
-That there are enough nutrients available for the next stage to take place
-There is no DNA damage

Question 7

What does the checkpoint at the end of G2 check for ?

Answer 7

-Checks that DNA replication has taken place
-Checks that there is no DNA damage

Question 8

What does the checkpoint at the end of metaphase check for ?

Answer 8

-That all chromosomes have attached properly to spindle fibres

Question 9

What happens in G0?

Answer 9

-Activities linked to cell division are suspended
- Cells can still carry out all other functions

• Highly differentiated cells do not return to the cell cycle
• Some cells don’t enter the G0 at all

Question 10

Explain how Vincristine works

Answer 10

It inhibits Microtubule formation, it binds to the tublin in microtubles and prevents them from functioning
This stops the spindle fibres contracting and pulling the chromatids apart (prevents anaphase)

Question 11

Explain how Antimetabolites work

Answer 11

Act as S phase inhibitors
Prevent DNA synthesis from occurring

E.g fluorouracil inhibits an enzyme involved in making the nucleotides, contains the base thymine and prevents DNA synthesis

Question 12

Name (in order) The stages of mitosis

Answer 12

Prophase
Metaphase
Anaphase
Telophase

Question 13

Explain prophase in mitosis

Answer 13

The chromatin in the nucleus condenses and becomes more visible
The nucleolus disappears
The centrioles migrate to opposite poles of the cell and are involved in the formation of spindle fibres
Nuclear membrane will be broken down

Question 14

Explain metaphase in mitosis

Answer 14

Once the chromosomes are aligned in position along the equator of the cell the spindle fibres affect to the centromeres

Question 15

Explain anaphase in mitosis

Answer 15

The centromeres attaching the two chromatids split and the contraction of the spindle fibres pill the chromatids apart

Question 16

Explain telophase in mitosis

Answer 16

The chromatids now end up at opposite poles of the cell
The chromosomes decondense and become less visible
Nucleolus re appears
Nuclear membrane reforms around the two groups of chromosomes
The spindle disappears as it is broken down

Question 17

When does cytokinesis take place in the cell cycle ?

Answer 17

After mitosis

Question 18

What happens in cytokinesis

Answer 18

The cell divides to form two daughter cells each have identical chromosomes

Question 19

Explain Cytokinesis in animal cells

Answer 19

A cleavage furrow forms as the cell surface membrane invaginate’s and eventually splits the cell into 2

Question 20

Explain cytokinesis in plant cells

Answer 20

A cell plate is laid down along the centre of the cell
The Golgi apparatus plays an important role in synthesising the materials needed in the formation of the new wall.

Question 21

Explain 3 differences between mitosis and meiosis

Question 22

where does independent assortment take place in the cell cycle?

Answer 22

During metaphase 1

Question 23

What is independent assortment

Answer 23

It is the random alignment of homologous chromosomes at the equator, this results in millions of possible combinations for any one gamete

Question 24

Where does crossing over take place in the cell cycle ?

Answer 24

During prophase 1

Question 25

What is crossing over ?

Answer 25

It is when two sister chromatids break and exchange sections of genes with each other. This results in chromatids with unique sequences of alleles that did not exist in parental chromosomes

Question 26

Explain prophase 1 in meiosis

Question 27

Explain metaphase 1 in meiosis

Question 28

Explain anaphase 1 in meiosis

Question 29

Explain telophase 1 in meiosis

Question 30

Explain prophase 11 in meiosis

Question 31

Explain metaphase 11 in meiosis

Question 32

Explain anaphase 11 in meiosis

Question 33

Explain telophase 11 in meiosis