3.6.1.1 Survival and response

Question 1

What is a stimulus?

Answer 1

A change in the internal or external environment.

Question 2

Name the three main types of neurone.

Answer 2

• Sensory neurones
• Motor neurones
• Relay neurones

Question 3

What is a reflex?

Answer 3

A rapid and an automatic response to stimuli.

Question 4

How can reflexes help protect the body?

Answer 4

The body responds rapidly to dangerous stimuli.

Question 5

An animal responds to a stimulus in its environment.
State the role of receptors and effectors in this response.
[2 marks]

Answer 5

• Receptors detect stimuli.

- Effectors bring about a response to a stimulus to produce an effect.

Question 6

A human blink reflex is an involuntary response, which results in the automatic closing of the eyelids (a blink) when an object touches the surface of the eye.
Describe the reflex arc involved in this response.
[4 marks]

Answer 6

• Touch receptors on the surface of the eye are stimulated.
• An electrical impulse is sent along the sensory neurone to a relay neurone.
• The impulse is then passed to a motor neurone,…
• …which stimulates effector muscles causing them to contract and the person’s eyelids to close.

Question 7

The knee-jerk is a reflex response.
Suggest why the absence of this response could indicate some damage to a person’s CNS.
[1 mark]

Answer 7

Damage to the CNS could interrupt the transmission of the reflex, preventing the reflex response from occurring.

Question 8

Polio is a virus that can cause damage to the CNS. In severe case, the virus can damage motor neurones.
Suggest and explain how this might lead to paralysis.
[3 marks]

Answer 8

• Motor neurones carry electrical impulses from the CNS to effectors which then respond.
• Damage to the motor neurones means the CNS can’t communicate with effectors such as muscles,…
• …so muscles don’t respond and move.

Question 9

Why is it important that organisms respond to changes in their internal environment?

Answer 9

To make sure that the conditions are always optimal for their metabolism.

Question 10

What is the role of the sensory neurones?

Answer 10

They transmit electrical impulses from receptors to the CNS.

Question 11

What is the role of the motor neurones?

Answer 11

They transmit electrical impulses from the CNS to effectors.

Question 12

What is the role of the relay neurones?

Answer 12

They transmit electrical impulses between sensory neurones and motor neurones.

Question 13

What is positive gravitropism?

Answer 13

The growth of a plant towards gravity.

Question 14

Explain the role of auxins in the control of phototropism in the shoots.
[3 marks]

Answer 14

• Auxin is redistributed to the shaded side of the shoot.
• Auxin stimulates cell elongation on the shaded side…
• … so the shoot bends to grow towards the light.

Question 15

What is tropism?

Answer 15

A tropism is a plant’s growth response to an external stimulus.

Question 16

E. coli, a type of bacteria, have been observed to move towards the highest concentration of oxygen in their surroundings.
What type of simple response is this?

Answer 16

Tactic/taxis

Question 17

E. coli, a type of bacteria, have been observed to move towards the highest concentration of oxygen in their surroundings.
Suggest why E. coli move in this way?

Answer 17

An environment higher in oxygen is a more favourable environment for them to be in.

Question 18

Why is it important that organisms respond to stimuli?

[1 mark]

Answer 18

To increase their chances of survival.

Question 19

What is a tactic response?

[1 mark]

Answer 19

Directional movement in response to a stimulus.

Question 20

What is a kinetic response?

[1 mark]

Answer 20

Non-directional (random) movement in response to a stimulus.

Question 21

The knee-jerk reflex involves lightly tapping a person on the patellar tendon with a tendon hammer. When this happens, the quadriceps muscle immediately contracts, causing the person’s lower leg to jerk forward.
This response is a reflex. Suggest one way in which the response would differ if it was not a reflex.
[1 mark]

Answer 21

The response would be slower/voluntary.

Question 22

The knee-jerk reflex involves lightly tapping a person on the patellar tendon with a tendon hammer. When this happens, the quadriceps muscle immediately contracts, causing the person’s lower leg to jerk forward.
Name the stimulus and the effector in the knee-jerk reflex.
[2 marks]

Answer 22

Stimulus - light tap/touch.

Effector - quadriceps muscle.

Question 23

The knee-jerk reflex is unusual because the sensory neurone synapses directly onto the motor neurone in the spinal cord.
Describe how this differs from a simple reflex, such as the hand-withdrawal response to heat.
[2 marks]

Answer 23

• The knee-jerk reflex doesn’t involve a relay neurone in the spinal cord.
• There are usually three neurones involved in a simple reflex.

Question 24

The knee-jerk reflex is unusual because the sensory neurone synapses directly onto the motor neurone in the spinal cord.
Suggest what effect tapping the patellar tendon might have in someone with a spinal cord injury. Explain your answer.
[3 marks]

Answer 24

• The quadriceps muscle may not contract/there may be no response.
• If the spinal cord is damaged then the sensory neurone may not be able to transmit nervous impulses to the motor neurone.
• The motor neurone may not be able to transmit nervous impulses to the leg muscle.

Question 25

Many nociceptors (pain receptors) are located in the skin. Describe the pathway of nervous communication that would take place in a healthy person if they pricked their finger with a pin. [3 marks]

Answer 25

- The nociceptors detect the stimulus and impulses are passed to a sensory neurone. - This passes the electrical impulses to a relay neurone in the spinal cord/CNS which carries the impulse to a motor neurone. - The motor neurone carries impulses to an effector (e.g. a biceps muscle).

Question 26

Congenital insensitivity to pain is a condition where the body does not feel physical pain. The condition is a result of non-functional nociceptors. The ability of sufferers to feel a light touch is usually normal. Suggest why people with this condition are able to feel a light touch even though they're unable to feel pain. [2 marks]

Answer 26

- Particular receptors are specific to a particular stimulus. - While their pain receptors aren't functional (so pain isn't felt), their touch receptors are, allowing light touches to be felt.

Question 27

Suggest why it's beneficial to an organism to be able to detect and respond to pain. [1 mark]

Answer 27

It helps to protect the body by reacting to situations/environments that could cause the body harm.

Question 28

What is the role of a receptor? | [1 mark]

Answer 28

To detect stimuli.

Question 29

Give two types of cell that act as effectors. | [2 marks]

Answer 29

- Muscle cells | - Cells found in glands

Question 30

Describe the pathway of nervous communication from stimulus to response, in a voluntary response. [3 marks]

Answer 30

- Receptor cells detect a stimulus. - Sensory neurones transmit electrical impulses from the receptors to the CNS. - The CNS processes the information and sends impulses along motor neurone to effectors, which respond.

Question 31

Which part of the pathway acts as the coordinator in a voluntary response? [1 mark]

Answer 31

CNS

Question 32

Explain why nervous communication leads to a localised and short-lived response. [2 marks]

Answer 32

- The response is localised because neurotransmitters are secreted directly onto cells. - The response is short-lived because neurotransmitters are quickly removed once they have done their job.

Question 33

Reflexes are involuntary responses to stimuli. Explain why they are involuntary. [2 marks]

Answer 33

- The pathway of communication goes through the spinal cord but not through conscious parts of the brain,... - ...so the response is automatic.

Question 34

Why do simple reflexes help an organism to avoid damage to their body? [1 mark]

Answer 34

They're rapid.

Question 35

What name is given to the growth of a plant in response to light?

Answer 35

Phototropism

Question 36

Plant shoots are negatively gravitropic. | What does this mean?

Answer 36

They grow in the opposite direction to the force of gravity.

Question 37

What parts of a plant produce growth factors?

Answer 37

The growing regions of the plant / shoot and root tips.

Question 38

How do auxins affect plant growth?

Answer 38

They stimulate growth by cell elongation.

Question 39

What is indoleacetic acid (IAA) and where is it produced?

Answer 39

IAA is an auxin that's produced in the tips of shoots and roots in flowering plants.

Question 40

How does IAA move around a plant?

Answer 40

By diffusion and active transport over short distances, and via the phloem over long distances.

Question 41

Explain how the distribution of IAA affects the growth of shoots in response to light.

Answer 41

- IAA concentration increases on the shaded side of the shoot. - This means the cells on the shaded part of the shoot grow faster than the cells most exposed to light. - This pattern of growth causes the shoot to bend towards the light.

Question 42

Explain how the distribution of IAA affects the growth of roots in response to gravity.

Answer 42

- IAA concentration increases on the underside of roots. - This means the cells on the underside of the root don't grow as quickly as the cells on the upper-side. - This pattern of growth causes the root to grow downwards in the same direction as gravity.