AQA Bio A Level Unit 2

Question 1

How does the cell prepare for nuclear division after DNA replication? (3)

Answer 1

1 Replicating organelles;
2 Increasing/synthesising protein;
3 ATP synthesis;

Question 2

In the cell cycle, in which phase does DNA replication occur?

Answer 2

Interphase

Question 3

What term is used to describe the mass of uncondensed DNA in a nucleus during interphase?

Answer 3

Chromatin

Question 4

What determines how long a cell spends in interphase as a proportion of its cell cycle? (2)

Answer 4

1. How rapidly that type of cell divides;
2. Rapidly dividing cells spend much less time in interphase;

Question 5

Does DNA replication change the chromosome number? Explain your answer. (2)

Answer 5

1. No
2. Chromosomes are replicated to give two chromatids – but each pair of chromatids is still just one chromosome. (count the centromeres…)

Question 6

What happens to the mass of DNA in DNA replication?

Answer 6

It doubles

Question 7

In which phase of mitosis do chromosomes condense?

Answer 7

Prophase

Question 8

In which phase of mitosis do chromosomes line up on the equator?

Answer 8

Metaphase

Question 9

Which organelle produces the spindle fibres?

Answer 9

Centrioles

Question 10

How many chromatids would there be in a human cell at metaphase of mitosis? Explain your answer (2)

Answer 10

1. 92;
2. Each of the 46 chromosomes consists of two sister chromatids

Question 11

In which phase does the nuclear membrane break down?

Answer 11

Prophase

Question 12

What do spindle fibres attach to in mitosis?

Answer 12

Centromeres

Question 13

In which phase of mitosis do chromatids separate?

Answer 13

Anaphase

Question 14

What is the consequence of uncontrolled cell division?

Answer 14

Formation of tumours – which may be cancerous.

Question 15

Suggest likely targets of anti-cancer drugs.

Answer 15

1. Prevention of DNA replication – e.g. modified nucleotides that cannot be joined together, or inhibition of DNA polymerase
2. Prevention of cell division, often by inhibiting spindle-fibre formation.

Question 16

Why do anti-cancer drugs cause side-effects?

Answer 16

1. All tissues need cells that divide.
2. Anti-cancer drugs often cannot discriminate and have their effects on both cancer cells and healthy cells.

Question 17

Do bacteria divide by mitosis?

Answer 17

No. They do not have chromosomes.

Question 18

How do bacteria divide?

Answer 18

By binary fission. They replicate their genetic material and then spilt in half.

Question 19

As they do not have linear DNA and chromosomes, what forms does bacterial genetic material take? (2)

Answer 19

1. Circular DNA
2. Plasmids

Question 20

How are plasmids distributed during bacterial fission?

Answer 20

Randomly. Plasmids are replicated, but the daughter cells each receive a variable number of them.