Response to Stimuli

Question 1

Describe a Simple Neural pathway.

Answer 1

Stimulus — Receptor - (sensory neurone) - CNS - (Relay neurone) - CNS - (motor neurone) - Effector — Response

Question 2

Define Stimulus.
How does an organisms response to a stimuli affect their chances of survival?

Answer 2

A detectable change in the internal or external environment of an organism that leads to a response in the organism.
- Responding to a stimulus/changes in their environment can increase an organisms chances of survival.

Question 3

Name the two types of response to stimulus in animals.
Give two examples of the T… response.

Answer 3

• Taxes - a simple response that can maintain a motile organism in a favourable environment, which is determined by the direction of a stimulus. (e.g: Chemotaxis - response to chemicals, Phototaxis - response to light)
• Kinesis - a simple response that can maintain a motile organism in a favourable environment, which has no specific direction, but the harsher the stimulus the faster the reaction/movement.

Question 4

Name the response to stimulus that occurs in plants.
Give the three main examples.

Answer 4

• Tropisms - responses to directional stimuli that can maintain the roots and shoots of flowering plants in a favourable environment.
• Phototropism - Response to light.
• Gravitropism/Geotropism - Response to gravity.
• Hydrotropism - Response to water.

Question 5

What is the name of their hormone (plant growth factor) that affects cell elongation in plants?
How does its movement affect Phototropism and Gravitropism in roots and shoots.

Answer 5

• IAA (auxin) also called Indoleacetic acid.

Phototropism -
In shoots - IAA produced in the tip of the shoot moves toward the shaded side of the plant, causing a build up. High IAA conc stimulates cell elongation in the shaded side of the plant, causing the plant to bend towards the light (positive phototropic response)
In roots - IAA produced in the tip of the roots moves downward due to the pull of gravity/shaded side. High IAA conc inhibits cell elongation causing the root to bend away from the light (negative phototropism response).

FINISH….