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.

Question 21

what are the 3 types of pathogens?

Answer 21

Bacteria
viruses
Fungi

Question 22

what do viruses lack compared to a cell?(5)

Answer 22

Nucleus
organelles
cell surface membrane
cytoplasm

Question 23

How do viruses replicate

Answer 23

Must be in a host cell

They attach to host cells via there attachment proteins which are complimentary to receptor proteins

they inject genetic material
cell replicates the viral nucleic acids and proteins which form more of the virus.

Question 24

What are the 4 defence mechanisms in the body

Answer 24

Physical barrier
Phagocytosis

Cell mediated response (T Lymphocytes)
humoral response (B lymphocytes

Question 25

How does phagocytosis happen?

Answer 25

The microbes are detected by chemicals They are engulfed by the membrane. phagosome forms lysozyme containing hydrolytic enzyme fuses to phagosome microbe is hydrolysed indigestible matter is discharged

Question 26

where can antigens be found and what are they?

Answer 26

Antigens are proteins or glycoproteins that appear foreign They can be found on the surface of a pathogen on the cell surface membrane of other organisms of the same species abnormal body cells as a toxin

Question 27

explain the humoral response

Answer 27

Every type of B cell produces a specific antibody They secret antibodies onto their membranes specific antigens may attach to the complimentary antibody on the B Cells Helper T cells stimulate the division of B cells Mitosis leads to a large population of plasma cells. These plasma cells will go to the blood stream and secrete identical antibodies some B cells differentiate into memory b cells

Question 28

What are the regions of an antibody and how many polypeptide chains are they made of

Answer 28

variable region constant region 4 polypeptide chains ( 2 heavy and 2 light) joined by Disulphide bonds

Question 29

where do antigens attach to antibodies

Answer 29

antigen binding site