June 2012 units 456

Question 1

1 The human eye is an organ of the nervous system.

(a) The eye is stimulated by light.

Which structure in the eye contains the light receptor cells? [1]

Answer 1

Retina

Question 2

(b) The pupil reflex causes the coloured part of the eye (the iris) to change size.The iris contracts if the light is suddenly switched off.

A scientist showed that this reflex could be conditioned.

A bell was rung at the same time as the light was switched off.

Eventually, the iris contracted whenever the bell was rung, even when the light remained on.

Which of the following statements about this experiment is true?

Put a tick (✓) in the box next to the correct statement.

The primary and secondary stimuli were the same.

The pupil reflex is a voluntary response.

The reflex response involved only motor neurons.

The bell stimulus was connected to a secondary stimulus.

The light stimulus was connected to a secondary stimulus.

[1]

Answer 2

The light stimulus was connected to a secondary stimulus.

Question 3

c) Damage to the fatty sheath around neurons leading to and from the eye can cause vision problems.

Complete the sentences to explain this.

The fatty sheath surrounds the …………………………………… of a neuron.

Neurons in the optic nerve that have lost their fatty sheath will transmit nerve impulses more …………………………………… .This could cause vision problems. [1]

Answer 3

The fatty sheath surrounds the AXON/ DENDRITE of a neuron.

Neurons in the optic nerve that have lost their fatty sheath will transmit nerve impulses more SLOWLY.This could cause vision problems.

Question 4

(d) Other reflexes involve the spinal cord. In these reflexes, the impulses travel along a spinal reflex arc.
(i) Write down two features of a spinal reflex arc that allow the response to be very fast. [1]

Answer 4

Any 2:

Few neurons (2 or 3) involved;
Few synapses;
Does not have to go up to the brain;
Shorter distance;
Involuntary;
No thought required... a bit like 21st century science GCSE

Question 5

(ii) Rachel has an injury to her spinal cord just above her waist. She cannot walk because she cannot make her legs move. [6]

A doctor tests Rachel’s knee jerk reflex and finds that it still works, even though she cannot walk.

Use information about the pathways followed by nerve impulses to suggest an explanation for these observations.

The quality of written communication will be assessed in your answer.

Answer 5

Reflex arc:

Stimulus detected by receptor;
Impulse created at receptor;
Impulse travels from receptor to sensory neuron, crossing the synapse;
Travels along relay neuron in spinal cord;
Crosses synapse;
Travels along motor neuron;
Ends at effector;
Leg straightens due to muscle contraction;
Brain not involved.

Impact of damage:

Damage must be above where reflex arc takes place;
Impulse transmission to and from brain is blocked.

Question 6

2 This question is about the brain.

(a) Oxygen and glucose levels affect brain activity.

Suggest why oxygen and glucose are needed by the neurons in the brain.

Put a tick (✓) in the box next to the best answer.

To bind to receptors in the synapses.

To release energy for the transmission of impulses.

To avoid the build up of carbon dioxide in the neurons.

To allow the diffusion of transmitter substances across the synapses.

[1]

Answer 6

To release energy for the transmission of impulses.

Question 7

(b) The brain contains billions of synapses.

Suggest why an impulse can only travel in one direction across a synapse. [2]

Answer 7

Chemicals only released from first neuron; receptors only found on the second neuron

Question 8

(c) Serotonin is a chemical that is released at synapses in the brain.

When a nerve impulse arrives at a synapse, serotonin is released from the neuron.

The serotonin allows the nerve impulse to be transmitted across the synapse.

The serotonin is then reabsorbed into the first neuron so that it can be released again when the next impulse arrives.

A new antidepressant drug stops the serotonin from being reabsorbed into the first neuron. The average (mean) dose of the drug over five days must be greater than 10 mg to cause this effect.

A patient takes part in two trials, A and B.

In trial A the patient takes the drug each day for five days. After a rest period of one week, the patient starts trial B and again takes the drug each day for five days.

The doses taken in trial A and trial B are shown in the tables.

trial A

day dose of drug in mg

1 6

2 6

3 8

4 9

5 9

trial B

day dose of drug in mg

1 14

2 14

3 16

4 18

5 20

(i) In which trial or trials would reabsorption of serotonin be blocked?

Explain your answer.

[2]

Answer 8

Trial B, because the average dose was 16.4 mg which is greater than 10 mg.

(Reverse argument that trial A is less is OK)

Question 9

(c) Serotonin is a chemical that is released at synapses in the brain.

When a nerve impulse arrives at a synapse, serotonin is released from the neuron.

The serotonin allows the nerve impulse to be transmitted across the synapse.

The serotonin is then reabsorbed into the first neuron so that it can be released again when the next impulse arrives.

A new antidepressant drug stops the serotonin from being reabsorbed into the first neuron. The average (mean) dose of the drug over five days must be greater than 10 mg to cause this effect.

A patient takes part in two trials, A and B.

In trial A the patient takes the drug each day for five days. After a rest period of one week, the patient starts trial B and again takes the drug each day for five days.

The doses taken in trial A and trial B are shown in the tables.

trial A

day dose of drug in mg

1 6

2 6

3 8

4 9

5 9

trial B

day dose of drug in mg

1 14

2 14

3 16

4 18

5 20

(ii) At the end of trial B the transmission of nerve impulses across the patient’s brain synapses increases.

Suggest why.

[1]

Answer 9

There is more serotonin in the synapse so the impulses will be transmitted more easily

Question 10

(c) Serotonin is a chemical that is released at synapses in the brain.

When a nerve impulse arrives at a synapse, serotonin is released from the neuron.

The serotonin allows the nerve impulse to be transmitted across the synapse.

The serotonin is then reabsorbed into the first neuron so that it can be released again when the next impulse arrives.

A new antidepressant drug stops the serotonin from being reabsorbed into the first neuron. The average (mean) dose of the drug over five days must be greater than 10 mg to cause this effect.

A patient takes part in two trials, A and B.

In trial A the patient takes the drug each day for five days. After a rest period of one week, the patient starts trial B and again takes the drug each day for five days.

The doses taken in trial A and trial B are shown in the tables.

trial A

day dose of drug in mg

1 6

2 6

3 8

4 9

5 9

trial B

day dose of drug in mg

1 14

2 14

3 16

4 18

5 20

(iii) It may be possible to change the trials to increase the confidence in the data obtained.

Put ticks (✓) in the boxes next to the suggestions that would improve the trials.

Carry out each trial for a shorter period of time.

Carry out the trials using female patients only.

Compare the drug against a placebo.

Decrease the dose of drug in the second trial.

Give the participants other drugs at the same time.

Use more than one patient.

[2]

Answer 10

Compare the drug against a placebo.

Use more than one patient.

Question 11

(d) Scientists can map the regions of the human brain using different techniques.

Name one of these techniques and discuss the ethical issues associated with it.

[2]

Answer 11

Techniques:

Transcranial magnetic stimulation;
Positron emission tomography;
Brain damaged patients;
Dissection of brain from dead person.

Ethics:

Many other patients could benefit

Patient may be unable to give informed consent; the patient could be harmed

Question 12

4 Tom investigates photosynthesis and respiration in plant leaves.

He sets up the experiment shown in the diagram.

                        light source

                 tube A	 tube B	     tube C

bung ____ ____ ____
! A ! ! B ! ! C !
¬¬¬¬ ¬¬¬¬ ¬¬¬¬¬
! ! ! ! ! !
! L ! ! L ! ! L !
! E ! ! E ! ! E !
! A ! ! A ! ! A !
! F ! ! F ! ! F !
! ! ! ! ! !
indicator \ —–/ \ —-/ -—–/
solution ! ! !
! ! !
! test tube !
! !
aluminium foil fabric mesh completely
completely covering test tube covering test tube

The indicator solution is red at the start of the experiment in all three tubes.

The indicator will change colour if the level of carbon dioxide in any of the tubes changes.The box summarises how the colour of the indicator can change.

decreased level of carbon dioxide –> increased level of carbon dioxide

indicator appears purple –>indicator appears red –>indicator appears yellow

After 24 hours Tom observes the colour of the indicator solution in each tube.

11 Here is his results table.

tube colour of indicator solution after 24 hours

A

B

C red

(a) Complete the table by writing the colour of the indicator solution you would expect to see in tube A and in tube B after the 24 hour period.

Tube C has been done for you. [1]

Answer 12

A Yellow;

B Purple

Question 13

4 Tom investigates photosynthesis and respiration in plant leaves.

He sets up the experiment shown in the diagram.

                        light source

                 tube A	 tube B	     tube C

bung ____ ____ ____
! A ! ! B ! ! C !
¬¬¬¬ ¬¬¬¬ ¬¬¬¬¬
! ! ! ! ! !
! L ! ! L ! ! L !
! E ! ! E ! ! E !
! A ! ! A ! ! A !
! F ! ! F ! ! F !
! ! ! ! ! !
indicator \ —–/ \ —-/ -—–/
solution ! ! !
! ! !
! test tube !
! !
aluminium foil fabric mesh completely
completely covering test tube covering test tube

The indicator solution is red at the start of the experiment in all three tubes.

The indicator will change colour if the level of carbon dioxide in any of the tubes changes.The box summarises how the colour of the indicator can change.

decreased level of carbon dioxide –> increased level of carbon dioxide

indicator appears purple –>indicator appears red –>indicator appears yellow

(b) Explain why the indicator solution in tube C was still red after 24 hours.

                                                                      [3]

Answer 13

Reduced photosynthesis due to fabric mesh;
respiration continues at same rate;
rate of photosynthesis matches respiration;
no change in carbon dioxide levels

Question 14

4 Tom investigates photosynthesis and respiration in plant leaves.

He sets up the experiment shown in the diagram.

                        light source

                 tube A	 tube B	     tube C

bung ____ ____ ____
! A ! ! B ! ! C !
¬¬¬¬ ¬¬¬¬ ¬¬¬¬¬
! ! ! ! ! !
! L ! ! L ! ! L !
! E ! ! E ! ! E !
! A ! ! A ! ! A !
! F ! ! F ! ! F !
! ! ! ! ! !
indicator \ —–/ \ —-/ -—–/
solution ! ! !
! ! !
! test tube !
! !
aluminium foil fabric mesh completely
completely covering test tube covering test tube

The indicator solution is red at the start of the experiment in all three tubes.

The indicator will change colour if the level of carbon dioxide in any of the tubes changes.The box summarises how the colour of the indicator can change.

decreased level of carbon dioxide –> increased level of carbon dioxide

indicator appears purple –>indicator appears red –>indicator appears yellow

c) Carbon dioxide and light can be limiting factors for photosynthesis.

Write down one other limiting factor that Tom should control in his experiment.

                                                                          [1]

Answer 14

temperature

Question 15

4 Tom investigates photosynthesis and respiration in plant leaves.

He sets up the experiment shown in the diagram.

                        light source

                 tube A	 tube B	     tube C

bung ____ ____ ____
! A ! ! B ! ! C !
¬¬¬¬ ¬¬¬¬ ¬¬¬¬¬
! ! ! ! ! !
! L ! ! L ! ! L !
! E ! ! E ! ! E !
! A ! ! A ! ! A !
! F ! ! F ! ! F !
! ! ! ! ! !
indicator \ —–/ \ —-/ -—–/
solution ! ! !
! ! !
! test tube !
! !
aluminium foil fabric mesh completely
completely covering test tube covering test tube

The indicator solution is red at the start of the experiment in all three tubes.

The indicator will change colour if the level of carbon dioxide in any of the tubes changes.The box summarises how the colour of the indicator can change.

decreased level of carbon dioxide –> increased level of carbon dioxide

indicator appears purple –>indicator appears red –>indicator appears yellow

d) Tom did the experiment with leaves from a plant that grows in bright sunlight.

He repeats the experiment using leaves from a plant that grows in shaded conditions. This time, the indicator solution in tube B changes colour more quickly.

Suggest why.
[2]

Answer 15

Plant is adapted to using light more efficiently;
Plant may have more chloroplasts;
More efficient at photosynthesis

Question 16

5 Yeast is a microorganism.

Yeast can respire by using aerobic and anaerobic respiration.

(a) (i) Write a word equation for anaerobic respiration in yeast.

………………………………. ………………………………. + ………………………………. (+ energy released) [1]

Answer 16

Glucose, ethanol, carbon dioxide

Question 17

(ii) Write a balanced symbol equation for aerobic respiration.

……………………………… + ……………………………… ……………………………… + ……………………………… (+ energy released)
[2]

Answer 17

C6H12O6 + 6O2 -> 6CO2 + 6H2O

Question 18

(ii) Scientists are investigating some properties of structures in a yeast cell.

They are examining the processes of aerobic respiration and anaerobic respiration.

Their results are shown in the table.

structure in yeast cell property

cell membrane freely permeable to gases

cytoplasm contains enzymes

mitochondria contain enzymes

nucleus holds the genetic code

Explain how the properties of these structures help the yeast cell to respire using aerobic respiration and anaerobic respiration. [6]

Answer 18

cell membrane:

allows oxygen to pass freely into cell;
oxygen needed for aerobic respiration;
allows carbon dioxide to pass out of cell;
carbon dioxide released from respiration;
ethanol passes out of cell;
ethanol produced by anaerobic respiration.

Cytoplasm contains enzymes which are used for aerobic/anaerobic respiration;
Cytoplasm used for enzyme synthesis

Mitochondria contain enzymes for aerobic respiration

Nucleus contains genetic code needed for the production of enzymes;
Enzymes needed for aerobic/anaerobic respiration;

All these structures needed for respiration;
Mitochondria only for aerobic respiration

Question 19

6 An embryo develops from a fertilised egg (zygote) in animals.

Scientists have shown that most embryo cells become specialised and form different types of tissue.

Some cells remain unspecialised and are called embryonic stem cells.

(a) All the embryonic stem cells in a zygote are identical to one another.

Put a tick (✓) in the box next to each correct statement.

Embryonic stem cells …
… are produced by mitosis.
… can switch off any gene during development of the embryo.
… contain different genes to those found in the specialised cells.
… contain half the number of chromosomes found in the zygote.

[2]

Answer 19

… are produced by mitosis.

… can switch off any gene during development of the embryo.

Question 20

(b) The medical use of embryonic stem cells is regulated by the Government.

An embryo is produced from a donor egg and sperm. Stem cells from this embryo are injected into a patient.

This procedure has ethical issues.

Put a tick (✓) in the box next to each ethical issue.

The patient will contain DNA from another person.

Embryonic stem cells may be larger than the patient’s cells.

Donated embryonic stem cells may be rejected by the patient’s body.

Embryos may be destroyed to collect the embryonic stem cells.

Scientists and doctors must decide who receives the embryonic stem cells.

The donated embryonic stem cells may not survive in the body of the patient.
[2]

Answer 20

The patient will contain DNA from another person.

Embryos may be destroyed to collect the embryonic stem cells.

Scientists and doctors must decide who receives the embryonic stem cells.

Question 21

(c) The growth and development of each cell in the embryo is controlled by its DNA.

What are the features of DNA?

Complete the table.

Put a ring around the correct box in each row.

number of strands 1 2 3 4

number of different types of bases 2 3 4 5

arrangement of bases between the strands
fours pairs single triplets

shape of molecule circular cube helix sheet

[1]

Answer 21

2 strands
4 bases
pairs form the “rungs” of the DNA molecule
helix shaped DNA

Question 22

d) Use your knowledge of the genetic code to explain where and how proteins are coded for and made.

The quality of written communication will be assessed in your answer.

                    [6]

Answer 22

DNA remains in nucleus
DNA holds code for protein synthesis
Genetic code is a series of bases
Four types of bases, AT CG 
Bases always pair in the same way
DNA is double helix
Two strands held together with bases
DNA "unzips" to form template for mRNA

mRNA copied from unzipped DNA
mRNA leaves the nucleus carrying the coded message to cytoplasm
protein synthesis can now take place in cytoplasm
triplet /order of bases codes for individual amino acid
order of amino acids determine the protein

Question 23

7 Ruth wants to develop a model of how plants grow in her garden.

She uses four trays of cress seedlings.There are 100 seedlings in each tray. All the seedlings are approximately 2 cm tall.

She places two of the trays in an open box, A, with a source of bright light above it. (Trays 1 and 2)

She places the other two trays in another open box, B, with a source of bright light on one side of it. (Trays 3 and 4)

Ruth records the appearance of the seedlings after 24 hours, and again after 48 hours.

She sees that some of the seedlings have grown with a straight stem but others have grown with a curved stem.

percentage (%) of seedlings with a curved stem

                            after 24 hours   after 48 hours

box A

tray 1 2 3
tray 2 1 3

box B

tray 3 48 89
tray 4 42 81

(a) (i) Explain the results for the cress seedlings grown in box A.

Use your understanding of auxin distribution in your answer.

[2]

Answer 23

Light from above means auxin is evenly distributed;
Auxin promotes plant growth;
Even growth means shoot is straight

Question 24

(ii) After 48 hours, Ruth changes the position of the trays in box B.
Ruth wants to develop a model of how plants grow in her garden.

She uses four trays of cress seedlings.There are 100 seedlings in each tray. All the seedlings are approximately 2 cm tall.

She places two of the trays in an open box, A, with a source of bright light above it. (Trays 1 and 2)

She places the other two trays in another open box, B, with a source of bright light on one side of it. (Trays 3 and 4)

Ruth records the appearance of the seedlings after 24 hours, and again after 48 hours.

She sees that some of the seedlings have grown with a straight stem but others have grown with a curved stem.

percentage (%) of seedlings with a curved stem

                            after 24 hours   after 48 hours

box A

tray 1 2 3
tray 2 1 3

box B

tray 3 48 89
tray 4 42 81

She places the trays so that the curved seedlings are facing away from the light source.

Suggest what will happen to the seedlings and explain why.

Use your understanding of auxin distribution in your answer.

[2]

Answer 24

Light from one side causes auxin to concentrate on shaded side;
Auxin causes growth;
shoot curves towards new light source;
shoot will firth straighten, then curve the other way

Question 25

Ruth wants to develop a model of how plants grow in her garden.

She uses four trays of cress seedlings.There are 100 seedlings in each tray. All the seedlings are approximately 2 cm tall.

She places two of the trays in an open box, A, with a source of bright light above it. (Trays 1 and 2)

She places the other two trays in another open box, B, with a source of bright light on one side of it. (Trays 3 and 4)

Ruth records the appearance of the seedlings after 24 hours, and again after 48 hours.

She sees that some of the seedlings have grown with a straight stem but others have grown with a curved stem.

percentage (%) of seedlings with a curved stem

                            after 24 hours   after 48 hours

box A

tray 1 2 3
tray 2 1 3

box B

tray 3 48 89
tray 4 42 81

(b) Does Ruth’s experiment accurately represent how plants would grow in her garden?

Give two reasons to support your answer. [2]

Answer 25

No, because

(any 2)

Plants grow differently to cress;
Sunlight changes throughout the day;
competition from other plants;
water/temperature vary;
predators in the garden, eg slugs;
plants grow for longer than 48 hours