Response to Stimuli

Question 1

Name 3 different types of neurones.

Answer 1

• Sensory Neurones
• Motor Neurones
• Intermediate Neurones

Question 2

Describe the structure and activity of sensory neurones.

Answer 2

Made up of one axon and one dendron

Carry signals from receptor to intermediate /motor neurones.

Question 3

Describe the structure and activity of motor neurones.

Answer 3

Made up of a long axon and many short dendrites

Carry signals from intermediate/sensory neurones to an effector.

Question 4

Describe the structure of intermediate neurones.

Answer 4

Made up of short dendrites.

Question 5

What is an axon?

Answer 5

A single long fibre that carries nerve impulses away from the cell body.

Question 6

What are dendrons?

Answer 6

Small extensions of the cell body which subdivide into smaller branched fibres, called dendrites, that carry nerve impulse towards the cell body.

Question 7

What are Nodes of Ranvier?

Answer 7

Gaps between adjacent Schwann cells where there is no myelin sheath.

Question 8

What are Schwann cells?

Answer 8

They surround the axon, protecting it and providing electrical insulation. They also carry out phagocytosis and play a part in nerve regeneration.

Question 9

What is a myeline sheath?

Answer 9

Forms a covering to the axon and is made up of the membranes of Schwann cells.

Question 10

What is a cell body?

Answer 10

Contains a nucleus and large amounts of RER. This is associated with the production of proteins and neurotransmitters.

Question 11

What are reflex arcs so important?

Answer 11

• Automatic
• Reduces/avoids damage to tissues e.g. burning
• Role in homeostasis
• Role in posture/balance
• Finding food/mate/suitable conditions
• Escape from predators

Question 12

Describe Control by Chemoreceptors

Answer 12

• Increased muscle contraction
• Increased respiration
• Increased production of carbon dioxide gas
• Causing blood pH to become more acidic
• Detected by chemoreceptors in the walls of the aorta and carotid sinus.
• Nerve impulses to medulla of the brain
• Coordination by the medulla
• More impulses to the SAN
• Increased HR

Question 13

Describe how a rise in blood pressure results in a decrease in HR (6marks)

Answer 13

• Pressure receptors
• In aorta
• Send impulses
• To medulla
• Send Impulses
• Parasympathetic nerves
• To SAN
• Inhibits SAN
• Decreases impulses to AVN

Question 14

Describe the role of receptors

Answer 14

Receptors only respond to a specific stimuli

• Produce a generator potential by acting as a transducer
• Receptors transduce one form of energy to another
• Stimulus is one form of energy e.g. heat/light
• Nerve impulses is another form of energy known as a generator potential.

Question 15

Describe rod cells

Answer 15

• Rod shaped
• Greater numbers than cone cells
• Distribution- more at the periphery of the retina, absent at the fovea
• Give poor visual acuity
• Sensitive to low-intensity light

Question 16

Describe cone cells

Answer 16

• Cone-shaped
• Fewer than rod cells
• Fewer at the periphery of the retina, concentrated at the fovea.
• Give good visual acuity
• not sensitive to low-intensity light

Question 17

Why do rod cells have poor visual acuity?

Answer 17

Several rod cells share the same neurone and so the brain is unable to tell exactly which rod cell the light fell on.

Question 18

Why are rod cells sensitive to low-intensity light?

Answer 18

Summation- Sub-Threshold levels of stimulation added together might be enough to generate an impulse down one neurone that they are connected to.

Question 19

What effect does indoleacetic acid have on plants?

Answer 19

• Cells in the tip of the shoot produce IAA, which is then transported down the shoot
• The IAA is initially transported to all sides of the shoot
• Light causes the movement of IAA from the light side to the shaded side of the shoot
• A great conc. of IAA builds up on the shaded side of the shoot
• As IAA causes elongation of cells, the cells in the shaded side elongate more
• The shaded side grows faster, causing the shoot to bend towards the light.