stimuli, both internal and external, are detected and lead to a response: survival and response

Question 1

what is a stimulus?

Answer 1

a detectable change in the environment of an organism that produces a response

Question 2

explain why organisms must be able to respond to their environment

Answer 2

in order to-

1. obtain food
2. find or access shelter
3. maintain suitable temperatures
4. access enough light
5. exchange gases
6. enhance chances of survival

Question 3

explain what is meant by ‘innate behaviour’

Answer 3

• it is developed with little influence from the environment
• they are inherited
• often may be automatic

Question 4

Describe what is meant by taxis

Answer 4

• directional movement

- animal moving towards or away from a stimulus eg. away from predators, towards food ect.

Question 5

Describe what is meant by kinesis

Answer 5

• response is related to the speed and a random number of turns due to the intensity of a stimulus
• non-directional
• more unpleasant the stimulus, the more random number of turns there are.
• this is done to find the most favorable conditions, in order to increase chances of survival

Question 6

what are tropisms?

Answer 6

growth of a plant in response to a directional stimulus

Question 7

explain positive phototropism

Answer 7

1. IAA is synthesised in the shoot tip and transported down the shoot
2. asymmetrical illumination is detected by the shoot tip
3. this causes IAA to move into the shaded part of the shoot
4. IAA promotes the elongation of cells, causing the shoot to bend towards the light

Question 8

why can plant shoots still grow in the dark

Answer 8

plant cells still go through mitosis and the shoot grows non-directionally

Question 9

explain what happens in the plant roots under gravity

Answer 9

1. IAA is synthesised in the root tips and is transported along the root
2. gravity is detected by the root
3. Gravity causes IAA to accumulate along the lower side of the root
4. IAA inhibits the elongation of the lower cells
5. causing the root to grow downwards

Question 10

explain how a simple reflex arc works

Answer 10

1. receptor- detects a stimulus and generates nerve impulse in the sensory neuron
2. sensory neuron- passes impulse to the spinal cord
3. Intermediate/relay neuron- links sensory and motor in the spinal cord
4. Motor neuron- carries impulse from spinal cord to effector
5. effector- stimulates a response

Question 11

list the key features and importance of a reflex arc

Answer 11

1. automatic/involuntary
2. prevents tissue damage
3. involved in some homeostatic responses
4. helps maintain balance and posture
5. helps organisms escape from predators
6. helps in finding favourable conditions
7. very fast
8. usually involves 3 neurons

Question 12

what is the difference between reflex arcs and secondary responses?

note: secondary responses take place in addition to reflex arcs

Answer 12

secondary responses in the spinal cord will also have a synapse with another relay neuron
these transmit impulses to another muscle and the brain
the response is slower