Module 6- Module 6 - Stimuli, both internal and external, are detected and lead to a response

Question 1

What is a tropism?

Answer 1

A response to a plant of a directional stimulus

Question 2

What are 2 examples of tropism?

Answer 2

• phototropism is the growth of a plant in response to light and gravitropism is the growth of a plant in response to gravity

Question 3

What are growth factors and where are they produced?

Answer 3

They stimulate growth of a plant by cell elongation and are produced in growth regions of the plant and then move to were they are needed in a plant.
E.G of a growth factor is an auxin

Question 4

What is the distribution of IAA in a plant?

Answer 4

Phototropism = IAA may be concentrated in the shaded regions of the plant to stimulate cell elongation so that the shaded areas reach sunlight
Gravitropism = Increased concentration on the lower side which increases cell elongation moving it upwards

Question 5

Explain phototropism shoot

Answer 5

1. IAA produced in the tip of the shoot
2. IAA diffuses evenly
3. IAA moves to the shaded side
4. IAA stimulates elongation of cells in a shoot
5. The shoot bends towards light
6. Positive phototropism

Question 6

Explain gravitropism shoot

Answer 6

1. IAA produced in the tip of the shoot
2. IAA diffuses evenly
3. IAA moves to the lower side
4. IAA stimulates elongation of cells in a shoot
5. The shoot will bend against gravity
6. Negative gravitropism

Question 7

Explain phototropism root

Answer 7

1. IAA produced in the tip of the root
2. IAA diffuses evenly
3. IAA moves to the shaded side
4. IAA inhibits elongation of the cells in the shoot
5. The shoot will bend away from the light
6. Negative phototropism

Question 8

Explain gravitropism root

Answer 8

1. IAA produced in the tip of the root
2. IAA diffuses evenly
3. IAA moved to the lower side
4. IAA inhibits elongation of cells in a hoot
5. The shoot will bend in the direction of gravity
6. Postive gravitropism

Question 9

Explain why the student removed the shoot tip from each seedling?

Answer 9

The shoot tip of the seedlings is where IAA is produced and so it affects the shoot length elongation

Question 10

How can choice chambers be used to investigate animal responses - light?

Answer 10

1. A petri dish is divided in half and has a lid placed on top
2. Place damp filter paper on both sides and then cover one half of the lid with black paper including the sides
3. Place a thin piece of mesh over the petri dish and then place woodlice over this mesh
4. After 10 minutes, record the number of lice on each side of the chamber

Question 11

Investigating humidity using choice chambers?

Answer 11

Add damp filter paper to one side of the dish and then a desiccating drying agent to the other side.

Question 12

What are tactic responses (taxes)?

Answer 12

This is when an organism moves towards or away from a directional stimulus

Question 13

What are kinetic responses (kinesis)

Answer 13

Movement is affected by a non-directional stimulus

Question 14

Suggest why the student added glucose solution to each petri dish

Answer 14

• This allows the plant to respire so that it can produced ATP which provides energy for growth

Question 15

2 marks

When a young shoot is illuminated from one side, IAA stimulates growth on the shaded
side. Explain why growth on the shaded side helps to maintain the leaves in a favourable
environment.

Answer 15

1. The shoot will bend towards the light
2. Light required for photosynthesis;

Question 16

Give one similarity and one difference between a taxis and tropism

Answer 16

Similarity: Movement toward/ away from a directional stimulus
Difference: Taxis –> whole organism moves
Tropism–> A growth response

Question 17

The woodlice were left for 15 minutes before their movement was recorded. Give 2 reasons for this

Answer 17

Time for required humidity to be established/ Time for substance to absorb water
So that behaviour typical to humidity
Woodlice is no longer affected by handling

Question 18

3 marks

The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.

Answer 18

1. High visual acuity
2. Each cone is connected to a single bipolar nerve
3. Cones send separate sets of impulses to brain

Question 19

3 marks

The retina of an owl has a high density of rod cells.
Explain how this enables an owl to hunt its prey at night.

Answer 19

1. High visual sensitivity (retinal convergence)
2. Several rods connected to a bipolar nerve
3. Spatial summation to overcome threshold

Question 20

3 marks

A student had stared at a purple square, he saw a green afterimage.
Suggest why.

Answer 20

1. When staring at purple red sensitive and blue sensitive cones are stimulated / green sensitive cones are not stimulated
2. Red and blue cone cells become exhausted
3. Afterimage due to green sensitive cone cells working

Question 21

What causes vision using the fovea to have a high visual acuity

Answer 21

Impulses along separate optic nerve from each receptor cell / each receptor cell connects to separate bipolar nerve

Question 22

3 marks

What causes vision using the fovea to be in colour

Answer 22

Colour detected by cone cells
Fovea contains mainly cone cells
Three types of cone cells: red/green/ blue light sensitive

Question 23

3 marks

Explain why vision using other parts of the retina has high sensitivity to light.

Answer 23

Many rods in other parts of retina
Rhodopsin / rod cells works in low light
Rods connected in groups to bipolar nerve
Summation
If enough light above threshold hits any cells in the group, then get nerve impulses to brain/along optic nerve

Question 24

4 marks

Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in this process

Answer 24

1. Chemoreceptors detect rise in CO2
2. Send impulses to medulla
3. More impulses to SAN
4. By sympathetic

Question 25

# 4 marks What would happen if CO2 increased (chemoreceptor action)

Answer 25

1. Increase CO2 2. More impulses to medulla from carotid and aorta receptors 3. More impulses along sympathetic 4. Fewer impulses along parasympathetic 5. To SAN 6. Heart rate increases

Question 26

# 4 marks What would happen if pressure increased (baroreceptor action)

Answer 26

1. Increase in blood pressure 2. Two types of barorecptor- one detects too low, one detects too high 3. More impulses sent to medulla from the 'too high' detecting recptor in carotid and aorta 4. More impulses sent on parasympathetic pathway to SAN 5. Heart rate decreases

Question 27

# 6 marks Explain what causes the heart rate to increase when we exercise

Answer 27

1. Rate of respiration increases in muscle cells 2. Carbon dioxide concentration increases 3. In blood plasma 4. Chemoreceptors 5. In aorta and carotid 6. Send impulses to medulla oblongata 7. Increased frequency of impulses 8. Along sympathetic pathway 9. To SAN

Question 28

Where is SAN located in the heart

Answer 28

Right atrium

Question 29

# 6 marks Explain how a rise in blood pressure results in a decrease in the rate of heartbeat.

Answer 29

1. Increase in blood pressure detected by baroreceptors 2. Two types of barorecptor- one detects too low, one detects too high 3. More impulses sent to medulla from the 'too high' detecting receptor in carotid and aorta 4. More impulses sent on parasympathetic pathway to SAN 5. Decreases impulses from SAN 6. Decreases impulses from AVN

Question 30

# 6 marks Explain how a rise in blood pressure results in a decrease in the rate of heartbeat.

Answer 30

1. Increase in blood pressure detected by baroreceptors 2. More impulses send to medulla oblongata from carotid and aorta receptors 3. More impulses along parasympathetic, fewer impulses along sympathetic 4. to SAN 5. Decreases impulses from SAN 6. Decreases impulses to AVN

Question 31

# 5 marks The cardiac cycle is controlled by the SAN and AVN. Describe how

Answer 31

1. SAN initiates heart beat 2. Impulse arrives at SAN, sends a wave of excitation at atria only casuing atria to contract 3. AVN delays 4. Delay in contraction in ventricles. Allowing ventricles to refill with bloods 5. AVN sends wave of excitation down bundle of his to purkyne fibres 6. Causing ventricles to contract from base up

Question 32

Describe how a heart beat it initiated and coordinated

Answer 32

1. Impulses arrives from medulla oblongata 2. Sympathetic to increase HR/ parasympathetic to decrease HR 3. Impulses arrive at SAN 4. Sends wave of excitation at atria only, atria contracts 5. Non-conductive tissues prevent impulse travelling to ventricles 6. Delay in contraction of ventrcile- allowing ventricle to refill with blood 7. Wave of exciiation sent to AVN 8. Impulse travels doen bundle of his to purkyne fibres 9. Contraction stats in apex 10. Ventricles contracts from base up

Question 33

Loss of nutrients into Lake Malawi has resulted in a decrease in some fish populations. Explain why.

Answer 33

1. Algal bloom blocks light 2. Reduced photosynthesis so plants die 3. Saprobiotic aerobically respire 4. Less oxygen for fish to respire

Question 34

Which of the following statements is associated with high sensitivity to light in the retina? 1. A single photoreceptor connecting to one neurone and spatial summation 2. A single photoreceptor connecting to one neurone and temporal summation 3. Several photoreceptors connecting to one neurone and spatial summation 4. Several photoreceptors connecting to one neurone and temporal summation

Answer 34

**3**. Several photoreceptors connecting to one neurone and spatial summation

Question 35

# 2 marks Explain how the resting potential of –70 mV is maintained in the sensory neurone when no pressure is applied.

Answer 35

1. Membrane more permeable to potassium ions and less permeable to sodium ions 2. Sodium ions actively transported/pumped out and potassium ions in

Question 36

# 3 marks Explain how applying pressure to the Pacinian corpuscle produces the changes in membrane potential recorded by microelectrode P.

Answer 36

1.(Pressure causes lamellae to become deformed 2. Sodium ion channels in membrane open and sodium ions move in 3. Greater pressure more channels open= sodium ions enter

Question 37

The membrane potential at Q was the same whether medium or heavy pressure 2 markswas applied to the finger tip. Explain why

Answer 37

1. Threshold has been reached 2. All or nothing principle

Question 38

# 2 marks Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones are destroyed. Explain how this results in slower responses to stimuli.

Answer 38

1. No saltatory conduction 2. More depolarisation over length of membranes

Question 39

# 2 marks Suggest two advantages of simple reflexes.

Answer 39

1. Rapid 2. Protect against damage to body tissues 3. Do not have to be learnt 4. Help escape from predators 5. Enable homeostatic control