Response to Stimuli (Chapter 14)

Question 1

Define Taxis

Answer 1

Moving towards or away from a favourable stimulus

Question 2

Define Tropism

Answer 2

Growth movement of a plant towards or away from a stimulus.

Question 3

Define Kinesis

Answer 3

Increase in random movements and change in direction in unfavourable circumstances

Question 4

Describe Hormones and their Role

Answer 4

Carried by the blood to affect different parts of the body to have a slow, widespread and long-lasting response.

Question 5

Describe the Role of Chemical Mediators

Answer 5

Released from mammalian cells to affect every cell in the vicinity and spread by diffusion.

Question 6

Describe the Role of Growth Factors

Answer 6

Plants do not have a nervous system so use growth factors. These affect growth, and are made in cells throughout the plant and can affect tissues that make them. They are spread by diffusion.

Question 7

Describe IAA (Indoleacetic Acid)

Answer 7

A plant growth factor which causes shoots to grow towards light and roots towards gravity.

Question 8

How does IAA cause shoots to bend towards light?

Answer 8

1) IAA made in cells in root tip
2) Transported down shoot on both sides
3) Light causes IAA to move to the shaded side of the shoot
4) Stimulates cells on dark side to elongate (shaded sides grow more)

Question 9

How does IAA cause roots to bend towards gravity?

Answer 9

1) IAA made in cells in root tip
2) Moves to lower side of root
3) Inhibits growth on lower side (upper side grows more and makes roots grow down)

Question 10

Describe the process for heart rate increasing

Answer 10

1) Increase in exercise creates more CO2 so pH is lowered.
2) Detected by chemoreceptors (in walls or aorta and carotid arteries)
3) Increase frequency of impulses to medulla which causes an increase in frequency of impulses to SAN via sympathetic nerve.
4) The SAN will increase the frequency of impulses speeding up the heart rate.

(The same will happen for decreased CO2 (higher pH) but the parasympathetic nervous system will be used)

Question 11

Describe the stages in increasing blood pressure

Answer 11

1) Detected by baroreceptors (in walls of carotid arteries and aorta)
2) Increases frequency of impulses to the medulla oblongata that will increase frequency of impulses via the parasympathetic nervous system to the Sino-atrial node (SAN) in the heart.
3) The SAN will decrease the frequency of impulses slowing the heart.

(The same will happen with reduced blood pressure by the sympathetic nervous system will be used)