cells and control sample questions and answers

Question 1

How many pairs of chromosomes are present in a diploid nerve cell?

Answer 1

23

Question 2

What happens immediately before mitosis in the cell cycle?

Answer 2

Checking for errors in copied DNA

Question 3

What phase in mitosis involves the pulling of chromosomes and their copies to different ends of the cell?

Answer 3

Anaphase

Question 4

Explain the difference between sensory, relay and motor neurones in terms of the direction that their electrical signals travel. [3 marks]

Answer 4

• sensory neurones carry electrical signals from receptors to the central nervous system
• relay neurones carry electrical signals within the central nervous system (brain and spinal cord)
• motor neurones carry electrical signals away from the central nervous system to effectors (muscles and glands)

Question 5

Explain why reflex arc signals do not immediately go to the brain. [2 marks]

Answer 5

• because it would take longer to react if they did

- this might increase any damage to the body

Question 6

Describe how are embryonic and adult stem cells different? [2 marks]

Answer 6

• adult stem cells are only found in specific locations like the nose and bone marrow
• embryonic stem cells make up all of an embryo
• adult stem cells can only differentiate into a small number of cell types
• embryonic stem cells can differentiate into all cell types

Question 7

State what types of human cells are not produced by mitosis? [1 marks]

Answer 7

Gametes (sperm and ova)

Question 8

Describe how someone with short sight can see more clearly? [3 marks]

Answer 8

• they can wear concave lenses in glasses

- they could also wear contact lenses or undergo laser surgery

Question 9

Explain the process of accommodation. [4 marks]

Answer 9

Answer (four from):

• to focus on a near object, the lens becomes thicker
• thicker lens allows the light rays to refract (bend) more strongly
• thicker lens allows light to focus on the retina
• to focus on a distant object, the lens is pulled thin
• thinner lens this allows the light rays to refract slightly
• thinner lens allows light to focus on the retina

Question 10

A baby boy is born in the 9th percentile for height. Explain what this means for him in terms of the rest of the population. [1 mark]

Answer 10

For every 100 boys, 91 will be taller than him and only 8 will be shorter.

Question 11

Describe the method used to investigate the speed of reaction times. [4 marks]

Answer 11

Answer (four from):

• person A holds out their hand with a gap between their thumb and first finger
• person B holds the ruler with the zero at the top of person A’s thumb
• person B drops the ruler without telling Person A and they must catch it
• the number level with the top of person A’s thumb is recorded in a suitable table - repeat this ten times
• swap places, and record another ten attempts
• you can use the conversion table to help convert your ruler measurements into reaction time or just record the catch distance in cm

Question 12

Describe how you could adjust this method to show the effect of stimulants in reaction times. [2 marks]

Answer 12

Answer (two from):

• both person A and B both drink a caffeinated drink after they have measured their reaction times
• wait fifteen minutes for the caffeine to have an effect on the nervous system
• repeat the experiment and compare the results

Question 13

Describe the structure and function of the nerves in the nervous system. [6 marks]

Answer 13

• the central nervous system is made up of the brain and spinal cord
• the peripheral nervous system is a network of nerves that cover the rest of the body
• receptor cells in sense organs start electrical signals which travel along sensory neurones to the central nervous system (two marks)
• relay neurones carry electrical signals around the central nervous system
• motor neurones carry electrical signals away from the central nervous system to effectors which are muscles or glands (two marks)
• gaps between neurones are called synapses
• all neurones have extended projects called axons along which electrical signals travel
• axons are insulated by myelin sheaths to speed up the electrical signals

Question 14

Describe the structure of DNA in a eukaryotic cell. [6 marks]

Answer 14

• DNA is made of four base pairs
• A-T, T-A, C-G, G-C
• bases are joined together by weak hydrogen bonds
• DNA is coiled into a double helix shape
• a section of DNA that codes for a protein is called a gene
• genes come in pairs called alleles
• chromosomes are long lengths of DNA which contain many genes
• an organism’s entire DNA is called a genome

Question 15

Describe the steps in mitosis. Give their names in your answer. [6 marks]

Answer 15

• interphase - the DNA in chromosomes copies itself ready for mitosis
• prophase - the membrane around the nucleus disappears
• metaphase - chromosomes and their copies line up in the middle of the cell
• anaphase - chromosomes and their copies are pulled to different ends of the cell
• telophase - new membranes form around the chromosomes at each end of the cell
• cytokinesis - the cell membrane pinches in and eventually divides into two daughter cells

Question 16

Describe the differences in the cells produced in mitosis and meiosis. [4 marks]

Answer 16

• mitosis produces two [1 mark] identical [1 mark] diploid [1 mark] daughter cells
• meiosis produces four [1 mark] non-identical [1 mark] haploid [1 mark] daughter cells

Question 17

Explain how and where cell differentiation in plants occurs. [4 marks]

Answer 17

Answer (four from):

• mitosis in plant cells occurs in the meristems
• these are areas in the tips of roots and shoots
• mitosis produces stem cells in meristems
• these can differentiate into any type of cell
• as the root or shoot grows further stem cells are produced
• older stem cells differentiate to become part of the shoot or root
• this means they become larger [1 mark] and form permanent vacuoles [1 mark]

Question 18

Describe how mutations in DNA are caused and explain their possible effects. [5 marks]

Answer 18

Answer (five from):

• mutations are changes in the DNA sequence of an organism
• they can be insertion, deletion, substitution or inversion of base pairs
• this can be advantageous / disadvantageous / have no effect
• mutations are caused at random, or by ionising radiation and mutagenic chemicals (carcinogens)

-rapid cell growth of mutated cells can form cancerous tumours
benign tumours grow slowly / are easily removed / do not invade other parts of the body

-malignant tumours grow rapidly / more difficult to remove / do invade other parts of the body