6.1.1 Survival and response

Question 1

Whats a stimulus?

Answer 1

Something that can be detected by an organism. It can either be internal in multicellular organisms or external in any organism

Question 2

What is a receptor?

Answer 2

A receptor is a organ or specialised cell that can detect the change that is causing the stimulus

Question 3

What is a response?

Answer 3

As a result of the stimulus that is detected by the receptor a response is caused. This may be movement of the organism or a change in behaviour

Question 4

What are plant growth factors?

Answer 4

Chemical that regulate plant growth response to direction stimuli

Question 5

Where are plant growth factors produced?

Answer 5

Produced in plant growing regions. Diffuse from cell to cell / phloem mass transport

Question 6

Explain why shoots show positive phototropism

Answer 6

1. Indoleacetic acid (IAA) diffuses to shaded side of shoot tip
2. As IAA diffuses down shaded side, it causes active transport of H+ ions into the cell wall
3. Disruption to H-bonds between cellulose molecules and action of expansins make cell more permeable to water
4. Cells on shaded side elongate faster due to higher turgor pressure
5. Shoot bends towards light

Question 7

Explain why roots show positive gravitropism

Answer 7

1. Gravity causes IAA to accumulate on lower side of the root
2. IAA inhibits elongation of root cells
3. Cells on the upper side of the root elongate faster, so the root tip bends downwards

Question 8

Define taxis

Answer 8

Directional movement in response to external stimulus

Question 9

Define kinesis

Answer 9

Non-directional response to presence and intensity of external stimulus

Question 10

State the advantage of taxis and kinesis

Answer 10

Maintain mobile organism in optimum environment

Question 11

Many organisms response to temperature and humidity via kinesis rather than taxis. Why?

Answer 11

Less directional stimuli ; often no clear gradient from one extreme to the other

Question 12

How could a student recognise kinesis in an organism’s movement?

Answer 12

1. Organisms crosses sharp division between favourable and unfavourable environment: turning increases
2. If organism moves considerable distance into unfavourable environment: turning slowly decreases ; begins to move in long, straight lines ; sharper turns

Question 13

Outline what happens in a simple reflex arc

Answer 13

• Receptor detects stimulus
• Sensory neuron
• Relay neuron in central nervous system (CNS) coordinates response
• Motor neuron
• Response by effector

Question 14

Give the advantage of a simple reflex

Answer 14

1. Rapid response to potentially dangerous stimuli since only 3 neurons involved
2. Instinctive

Question 15

Suggest a suitable statistical test to determine whether a factor has a significant effect on the movement of an animal in a choice chamber

Answer 15

Chi-squared

Question 16

What features are common to all sensory receptors?

Answer 16

• Act as energy transducers which establish a generator potential
• Respond to specific stimuli