6A - Stimuli and Responses

Question 1

What do sensory neurones do?

Answer 1

• transmit impulses from receptors to CNS (brain and spinal cord)

Question 2

What do motor neurons do?

Answer 2

• transmit impulses from CNS to effectors

Question 3

What do relay neurones do?

Answer 3

• transmit impulses between sensory and motor neurones

Question 4

What is the peripheral NS?

Answer 4

• made up of neurones that connect CNS to rest of the body

Question 5

What is the somatic NS?

Answer 5

• one division of peripheral NS

- controls conscious activities

Question 6

What is the autonomic NS?

Answer 6

• one division of peripheral NS

- controls unconscious activities e.g digestion

Question 7

What does the autonomic NS divide into and what is the difference between them?

Answer 7

• sympathetic and parasympathetic NS
• sympathetic gets body ready for action e.g fight or flight
• parasympathetic calms body down e.g rest and digest

Question 8

What is a reflex?

Answer 8

• a response to a stimulus without making a conscious decision to respond

Question 9

How is nervous system communication localised, short-lived and rapid?

Answer 9

• localised as neurotransmitter are directly secreted onto target cells
• short-lived as neurotransmitters are quickly removed
• rapid as impulses are really fast

Question 10

What is meant by a tropism?

Answer 10

• plant’s growth response to an external stimulus

Question 11

What is the difference between a positive and negative tropism?

Answer 11

• positive grows towards stimulus

- negative grows away from stimulus

Question 12

What type of tropisms do shoots have?

Answer 12

• positive phototropism

- negative gravitropism (grow upwards)

Question 13

What type of tropisms do roots have?

Answer 13

• negative phototropism

- positive gravitropism

Question 14

How is IAA transported around the plant?

Answer 14

• diffusion/active transport over short distances

- via the phloem over long distances

Question 15

How does IAA affect phototropism in shoots and roots?

Answer 15

shoots - concentration increases on shaded side, cells elongate and shoot bends toward light
roots - concentration increases on shaded side, growth is inhibited so root bends away from light

Question 16

How does IAA affect gravitropism in shoots and roots?

Answer 16

shoots - concentration increases on lower side, cells elongate so shoot grows upwards
roots - concentration increases on lower side, growth is inhibited so the root grows downwards

Question 17

What is meant by a tactic response?

Answer 17

• organism move towards or away from a directional stimulus e.g. light

Question 18

What is meant by a kinetic response?

Answer 18

• organisms’ movement is affected by a non-directional stimulus e.g. humidity

Question 19

What happens when a receptor is at resting state?

Answer 19

• difference in charge inside and outside of cells - generated by ion pumps and channels

Question 20

What happens when a stimulus is detected?

Answer 20

• cell membrane is excited and becomes more permeable, more ions move in and out of cell
• potential difference is altered, the change is called generator potential

Question 21

How is an action potential triggered?

Answer 21

• if generator potential reaches threshold level

- if stimulus is too weak, generator potential doesn’t reach threshold level, so no action potential

Question 22

What are Pacinian Corpuscles?

Answer 22

• mechanoreceptors (detect mechanical stimuli) in the skin e.g pressure and vibrations

Question 23

What happens when a Pacinian Corpuscle is stimulated?

Answer 23

• lamellae are deformed and press on sensory nerve ending
• causes sensory neurone’s cell membrane to stretch, deforming sodium ion channels
• channels open and sodium ions diffuse into the cell creating a generator potential
• if gen. potential reaches threshold, triggers action potential

Question 24

How do photoreceptors convert light into an electrical impulse?

Answer 24

• light is absorbed by light-sensitive optical pigments
• causes a chemical change and alters membrane permeability to sodium ions
• gen. potential is created and if it reaches threshold, a nerve impulse sent along bipolar membrane
• bipolar neurones connect photoreceptors to optic nerve, which takes impulses to the brain

Question 25

Where are rods found and what type of vision do they have?

Answer 25

• found in peripheral parts of the retina

- monochromatic vision (black and white)

Question 26

Where are cones found and what type of vision do they have?

Answer 26

• found clumped together in fovea

- trichromatic vision (colour)

Question 27

What is the degree of sensitivity and visual acuity in rods?

Answer 27

• very sensitive to light; many rods join one neurone, many weak generator potentials combine to create action potential
• low visual acuity; many rods join one neurone, light from 2 points close together can’t be told apart

Question 28

What is the degree of sensitivity and visual acuity in cones?

Answer 28

• less sensitive to light; one cone joins one neurone, more light is needed to trigger action potential
• high visual acuity; cones are close together, two action potentials go to brain

Question 29

What happens in a regular heartbeat?

Answer 29

• sinoatrial node sends out regular waves of electrical activity to atrial walls
• causes right and left atria to contract at same time
• collagen tissue prevents electrical activity from being passed directly from atria to ventricles
• waves are sent to atrioventricular node (AVN)
• AVN passes waves on to bundle of His
• bundle splits into finer muscle fibres in right and ventricle walls, called Purkyne tissue
• Purkyne tissue carries waves into muscular walls of left and right ventricles, causing them to contract at same time

Question 30

What are baroreceptors?

Answer 30

• pressure receptors in aorta and carotid arteries

- stimulated by high and low blood pressure

Question 31

What are chemoreceptors?

Answer 31

• chemical receptors in aorta, carotid arteries and medulla

- monitor oxygen, carbon dioxide and pH levels in blood

Question 32

Heart rate is unconsciously controlled in the brain by what?

Answer 32

• medulla oblongata