Stimuli & Response

Question 1

Why do plants respond to simuli

Answer 1

Increase chance of survival e.g towards light for more photosynthesis

Question 2

Define tropism

Answer 2

Response of a plant to a directional stimulus

Question 3

How do plants perform a tropism

Answer 3

• Use growth factors such as auxins (Indoleacetic acid, gibberelins)

Question 4

What does IAA do?

Answer 4

Cause cell elongation in the shoots and inhibit cell growth in the roots

Question 5

What do gibberellins do?

Answer 5

Control flowering and germination

Question 6

Where are growth factors made?

Answer 6

In growing regions of the plants

Question 7

How do growth factors move?

Answer 7

Short distances by diffusion and active transport and long distance by phloem

Question 8

Summarise phototropism

Answer 8

• IAA moves to shadow side
• Cell elongation in shoots
• Inhibits cell growth in roots

Question 9

Summarise gravitropism

Answer 9

• IAA moves to underside
• Cell elongation in shoots
• Inhibits cell growth in roots

Question 10

What is the purpose of taxes and kineses

Answer 10

Keep mobile organisms in a favourable environment

Question 11

Define taxes

Answer 11

A Mobile organisms moves away from or towards a directional stimulus

Question 12

Define kinesis

Answer 12

When mobile organisms change their movement and speed in response to a non-directional stimulus

Speed faster/turn more in unfavourable and slower in favourable

Question 13

Define reflex

Answer 13

A rapid response to a stimulus without conscious control

Question 14

Summarise a reflex

Answer 14

Stimulus detected by receptor, travels along sensory neurone, then relay neurone, then motor neurone, then effector then response where the relay neurone is in the CNS

Question 15

Advantages of a reflex

Answer 15

Avoid damage or danger
No thinking so faster
No learning so protects infants

Question 16

What is the pacinian corpuscle

Answer 16

A receptor in skin detecting pressure touch and vibration

Question 17

Summarise how a pacinian corpuscle causes a generator potential

Answer 17

• Pressure causes lamellae to stretch and deform
• Sodium ion channels are stretch mediated and hence open
• Na+ diffuse into neurone
• Greater stimulus, more deformation so more channels open
• Depolarisation occurs (generator potential)
• If threshold reached, AP occurs

Question 18

What does the fovea consist of

Answer 18

Lots of photoreceptors, mostly cones

Question 19

Summarise what happens when light hits a photoreceptor

Answer 19

• Light focuses on retina by lens
• Light absorbed by pigments in photoreceptor
• Causes sodium ion channels to open (generator potential)
  If threshold is reached, AP occurs, travels across bipolar neurone and optic nerve to CNA

Question 20

Summarise ROD cells

Answer 20

• Monochromatic
• More sensitive to low light
• Low visual acuity
• Edges of the retina

Question 21

Why do ROD cells have low visual acuity?

Answer 21

Spacial summation to the bipolar neurone, so many rod cells to one bipolar neurone, so one AP generated, regardless of the number of ROD cells

Question 22

Summarise CONE cells

Answer 22

• Trichromatic
• Less sensitive to low light
• High visual acuity
• Focused on the fovea

Question 23

When do atrioventricular valves open?

Answer 23

When atria pressure is higher than ventricle pressure

Question 24

What is the purpose of valves?

Answer 24

Blood flows in one way and no back flow

Question 25

Summarise how a heart beats

Answer 25

• SAN sends out electrical impulse as heart tissue is myogenic
• Impulse sent to AVN which delays impulse, allowing atria to contract first
• Does not pass through atria due to nonconducting tissue
• AVN sends impulse down bundle of His down centre of heart
• Then along purkyne fibres
  causing ventricles to contract from the base upwards

Question 26

Summarise the role of chemoreceptors/baroreceptors in decreasing heart rate

Answer 26

• Detected high O2 levels due to less CO2 or detect high pressure
• Impulse sent to medulla oblongata
• Sends NERVE impulse via parasympathetic neurones
• Causes less SAN electrical impulses

Question 27

Summarise the role of chemoreceptors/baroreceptors in increasing heart rate

Answer 27

• Detect low blood O2 due to more CO2 so less pH or low pressure
• Receptors send more impulses to the sympathetic centre of medulla oblongata
• More impulses sent to SAN via symapthetic
• SAN increase heart rate