6.1.1 - Survival and response

Question 1

Suggest two advantages of simple reflexes. (2)

Answer 1

• Rapid
• Protect against damage to body tissues
• Do not have to be learnt
• Help escape from predators
• Enable homeostatic control

Question 2

Define the term tropism. (1)

Answer 2

• Growth/movement (usually of a plant) in response to a directional stimulus / named stimulus

Question 3

Organisms can only survive if they are able to respond to changes in their environment. Describe how the plant growth factor, indoleacetic acid (IAA), allows plants to respond to light stimuli from their surroundings. (2)

Answer 3

• (IAA) is produced in the meristem of the plant shoot/tip
• IAA moves to the shaded region of the shoot in response to a stimulus/light
• This then promotes cell elongation (in that region)
• The elongation is facilitated by allowing cellulose microfibrils to stretch / by triggering osmosis/movement of water into the cell
• This is a positive phototropic response / positive phototropism

Question 4

State the key difference between kinesis and taxis. (1)

Answer 4

• Kinesis is a non-directional response whereas taxis is a directional response to a stimulus
• A kinesis response depends on the intensity of the stimulus whereas a taxis response is simply a movement away or towards the stimulus

Question 5

Explain how growth on the shaded side of a young shoot helps to keep the leaves in a favourable environment for survival. (2)

Answer 5

• Causes the plant to bend/grow towards the light source/ positive phototropism
• Light is required for photosynthesis

Question 6

Describe and explain two ways in which an axon may be adapted to conduct impulses at a faster rate in the nervous system. (4)

Answer 6

• Larger diameter
• So there is less resistance to the flow of ions
• Myelination
• Allowing for saltatory conduction / allows impulses to jump between nodes of Ranvier

Question 7

Synapses ensure that nerve impulses travel unidirectionally towards a muscle fibre. Explain how. (2)

Answer 7

• Neurotransmitter is only made/stored in/released from the pre synaptic neurone
• Neuroreceptors are only found on the post-synaptic membrane