Response To Stimuli

Question 1

What is taxes?

Answer 1

A simple response determined by the direction of a stimulus, causing the organism to grow either towards or away from the stimulus.

Question 2

What is kineses?

Answer 2

Response to a stimulus in rapid, random movements changing direction often.

Question 3

What is a tropism?

Answer 3

A growth movement of a plant in response to a directional stimulus.

• phototropism
• geotropism
• hydrotropism

Question 4

What is the reflex arc?

Answer 4

Stimulus 
Receptor
Sensory neurone
Intermediate neurone 
Motor neurone 
Effector 
Response

Question 5

• Two major divisions in the nervous system are…
• One is divided into…
• One is further subdivided into…

Answer 5

• central nervous system (brain and spinal cord)
• peripheral nervous system (pairs of nerves originating from either the brain or spinal cord)
• sensory neurone (carries impulse from receptors to the CNS)
• motor neurone (carries impulse from CNS to effectors)
• voluntary nervous system (conscious)
• autonomic nervous system (subconscious)

Question 6

The autonomic nervous system

Answer 6

• sympathetic nervous system
  Stimulates effectors, speeding up activity. Fight or flight response.
• parasympathetic nervous system
  Inhibits effectors, slowing down activity. Controls activity at normal resting conditions.

Question 7

How is heart rate controlled by chemoreceptors?

Answer 7

• Found in the walls of the carotid arteries and aorta.
• Detect changes in blood CO2 concentration. (pH lowers if more CO2 present)
• Lower pH causes chemoreceptors to increase frequency of impulses to the medulla oblongata.
• impulses sent down sympathetic nervous system to the SAN increases heart rate.
• More CO2 is removed by the lungs and pH rises to normal levels.

Question 8

How is heart rate controlled by pressure receptors?

Answer 8

Blood pressure is higher

• transmit impulse to medulla oblongata to decrease heart rate (parasympathetic nervous system)
• decreases heart rate

Blood pressure is lower

• transmit impulse to medulla oblongata to increase heart rate (sympathetic nervous system)
• increases heart rate

Question 9

Features of a sensory receptor

Answer 9

• specific to a particular type of stimulus (pacinian corpuscle responds to mechanical pressure)
• produces a generator potential by converting the information from the stimulus into a nerve impulse

Question 10

How does a stretch-mediated sodium channel work?

Answer 10

Resting state
- channels are too narrow to allow sodium ions through. (Resting potential)

Pressure is applied

• changing the shape of the channels so they stretch, widening them.
• influx of sodium ions (depolarisation) producing a generator potential.
• generator potential creates an action potential

Question 11

Rod cells

Answer 11

• only produce images in black and white
• many cells share a sensory neurone (greater chance of exceeding the threshold value)
• respond to a low light intensity
• breaks down the pigment rhodopsin
• low visual acuity as it cannot distinguish between separate sources of light
• found at periphery

Question 12

Cone cells

Answer 12

• see in full colour
• three different types, responding to different wavelengths of light
• own bipolar cells to each sensory neurone
• respond to high light intensity
• breaks down iodopsin
• good visual acuity
• found at the fovea