5.2 Regulating Mechanisms in Animals and Plants

Question 1

What is a stimulus?

Answer 1

An environmental factor that an organism can detect and respond to (excites or stimulates the receptor).

Question 2

What is a receptor?

Answer 2

Specialised structures capable of responding to specific stimuli, which produce either an electrical or chemical signal.

Question 3

List the 4 types of receptors and give an examples of each:

Answer 3

• Mechanoreceptors: Pressure, tension
• Chemoreceptors: Chemicals (taste, smell)
• Thermoreceptors: Temperature
• Other: Pain, touch

Question 4

What is the control center?

Answer 4

The brain and spinal cord, which receives messages and determines which action to take.

Question 5

What are positive feedback mechanisms?

Answer 5

• Produce stability (brings it back to its original state)

- Are stimulus-response models in which the response reduces the original stimulus

Question 6

What are negative feedback mechanisms? Give an example:

Answer 6

• Decreases stability
• Mechanisms in which the disturbances cause a change that increases the initial disturbance
• Eg. Oxytocin-hormone released by the uterus during childbirth. Uterus contracts caused by oxytocin which leads to more oxytocin being released.

Question 7

What are hormones? Give 3 examples:

Answer 7

Chemical messengers that cause cellular responses, which are secreted directly into the bloodstreams so that that can trigger specific reactions from far away.
Eg. Stress, reproduction, growth

Question 8

List the 3 types of hormones:

Answer 8

• Peptide hormone
• Protein or amino acid derived hormone
• Steroid hormone

Question 9

What is the difference between steroid and protein hormones?

Answer 9

Steroid proteins are lipid soluble and pass through the cell membrane and bind to specific receptors, while protein hormones are water soluble and cannot pass through the cell membrane and bind on the outside of the cell membrane and trigger physiological responses within the cell.

Question 10

What are tropisms in plant hormones?

Answer 10

Growth in response to an external stimulus.

Question 11

What are the 2 types of tropisms in plant hormones:

Answer 11

• Positive tropism: Growth towards a stimulus

- Negative tropism: Growth away from a stimulus

Question 12

What are the 3 things hormones in plants are responsible for?

Answer 12

• Apical dominance
• Ripening of fruit
• Abscission

Question 13

What is apical dominance?

Answer 13

Inhibition of lateral branches

Question 14

What does the ripening of fruit refer to?

Answer 14

Conversion of starches to sugars

Question 15

What is abscission?

Answer 15

Shedding of leaves and flowers

Question 16

What is phototropism and what is it caused by?

Answer 16

The bending and growing of plants towards a source of light to maximise photosynthesis. Is caused by the hormone Auxin which is produced in the growing tip.

Question 17

What is geotropism and what is it caused by?

Answer 17

The production of root growth in response to gravity caused by the hormone Auxin produced in root tips.