Survival and Response

Question 1

What is a stimulus?

Answer 1

A change in the environment.

Question 2

What are receptors?

Answer 2

These are cells of proteins on the cell membrane that detect a stimulus.

Question 3

What are effectors?

Answer 3

Muscles or glands that bring about an effect in response to a stimulus.

Question 4

What are sensory neurones?

Answer 4

They carry a nerve impulse from the receptors to the CNS.

Question 5

What are relay neurones?

Answer 5

These take a nerve impulse from the sensory neurone to the motor neurone.

Question 6

What are motor neurones?

Answer 6

They carry a nerve impulse from the CNS to the effector.

Question 7

Why is it important that organisms respond to changes in their environment?

Answer 7

Responding to changes in their external environment makes them more likely to survive. Responding to changes in their internal environment allows them to maintain optimal conditions for their metabolism.

Question 8

What is a tactic response?

Answer 8

Directional movement in response to a stimulus.

Question 9

What is a kinetic response?

Answer 9

random movement in response to a stimulus.

Question 10

What is a simple reflex?

Answer 10

a rapid, involuntary movement in response to a stimulus.

Question 11

Why are simple reflexes automatic?

Answer 11

The nerve impulse travels through the spinal cord but does not travel to the conscious parts of the brain.

Question 12

How do simple reflexes protect organisms from harm?

Answer 12

Since you don’t need to waste time processing the information a response happens quickly and that allows organisms to respond to danger before it does them harm.

Question 13

What are tropisms?

Answer 13

The growth of a plant in response to a directional stimulus.

Question 14

What controls tropisms?

Answer 14

auxins

Question 15

What are auxins?

Answer 15

hormone-like chemicals that control the growth of a plant.

Question 16

How do auxins control phototropisms?

Answer 16

They diffuse backwards to stimulate the cells behind the tips to elongate.

Question 17

What is a phototropism?

Answer 17

The growth of a plant in response to light.

Question 18

Describe how Indoleactic acid controls phototropisms in the shoots and roots.

Answer 18

In the shoots, the indoleacetic acid builds up on the shaded side of the shoots and causes that side to grow faster compared to the other side. This causes the shoots to bend towards the light. In the roots, the acid builds up on the underside of the roots and inhibits growth. This causes the upper side to grow faster and the shoots to bend downwards away from the light.

Question 19

What are gravitropisms?

Answer 19

growth of a plant in response to gravity

Question 20

Describe how Indoleactic acid controls gravitropism in the shoots and roots.

Answer 20

In the shoots, the indoleacetic acid builds up on the underside of the shoots and causes that side to grow faster compared to the other side. This causes the shoots to bend towards the light. In the roots, the acid builds up on the underside of the roots and inhibits growth. This causes the upper side to grow faster and the shoots to bend downwards towards gravity.

Question 21

How does indoleacetic acid travel around the plant?

Answer 21

1. It travels via diffusion and active transport over small distances.
2. it travels via the phloem over large distances.