Module 5: Homeostasis

Question 1

Define homeostasis. Why is it important in organisms?

Answer 1

Process of maintaining constant internal conditions despite external changes. Maintains optimal conditions for enzyme action and cell function.
Factors controlled by homeostasis include conc of glucose in blood, body temp, blood pH.

Question 2

What is negative feedback? (homeostasis)

Answer 2

Action taken by the body to return something to a normal level after deviation e.g. controlling body temp.

Question 3

What is positive feedback?

Answer 3

Amplifies a response to a stimulus, causing it to deviate further from the normal range e.g. blood clotting.

Question 4

Explain what happens to the body when you are hot.

Answer 4

1. Sweat - water evaporates from skin to cool it down.
2. Hairs lie flat - less insulating air is trapped. Heat can be lost more easily. ERECTOR PILI MUSCLES relax.
3. Vasodilation - ARTERIOLES near surface of the skin dilate. More heat is lost from skin.

Question 5

Explain what happens to the body when you are cold.

Answer 5

1. Shiver - increase respiration in muscles so more thermal energy is released.
2. More adrenaline and thyroxine are produced so more metabolism.
3. Hairs lie flat - traps an insulating layer of air to prevent heat loss. ERECTOR PILI MUSCLES contract.
4. Vasoconstriction - ARTERIOLES near surface of skin contract.

Question 6

Thermoreceptors in skin …
Thermoreceptors in hypothalamus …

Answer 6

Detects external temp.
Detects temp of blood.

Question 7

What is the function of thermoreceptors?

Answer 7

Send impulses along sensory neurones to the hypothalamus, which sends impulses along motor neurones to effectors. The effectors respond by returning the body back to normal.

Question 8

Why are you more hungry when you’re cold?

Answer 8

Higher metabolic rate, so more glucose for respiration of contracting muscles as you shiver.

Question 9

What is the first and second messenger for adrenaline?

Answer 9

1st - adrenaline that transmits a signal around the body.
2nd - cAMP transmits signal inside the cell.

Question 10

What is an ectotherm?

Answer 10

Depends on external heat sources. Their body temperature changes if temp in environment changes.

Question 11

What is an endotherm?

Answer 11

Uses internally generated heat to maintain body temperature, regardless of environment.

Question 12

Mammals are …
Reptiles/fish/amphibians are …

Answer 12

Endotherms.
Ectotherms.

Question 13

Thermoreceptors are found in the …

Answer 13

Thermoregulatory centre in hypothalamus.

Question 14

What happens during vasodilation/constriction?

Answer 14

ONLY the sphincters contract, the vessels don’t. The vessel lumen dilates/constricts.

Question 15

What is the integrating centre?

Answer 15

Region in the brain, usually the hypothalamus, that signals part of the body to respond to stimuli.

Question 16

What is an effector?

Answer 16

Organ or cell that acts in response to a stimulus.

Question 17

State the order of transmission of a message around the body.

Answer 17

1. Stimulus
2. Receptor
3. Integrating centre
4. Effector
5. Response

Question 18

Chemoreceptors detect (chemicals) low pH in blood so …

Answer 18

Medulla stimulates increased rate and depth of breathing. More removal of CO2 in body, so level of CO2 decreases and blood pH returns to normal.

Question 19

How do red blood cells communicate with the body?

Answer 19

They don’t have nuclei or typical signaling mechanisms like other cells; their communication is mainly through chemical transport and gas exchange with oxygen and carbon dioxide.
They bind oxygen in the lungs and release it in tissues, facilitated by haemoglobin. Additionally, RBCs help regulate pH levels and carry signaling molecules, such as nitric oxide, which plays a role in vasodilation and blood flow regulation.

Question 20

How do plants coordinate their growth and responses?

Answer 20

Plant hormones (like auxins, gibberellins, cytokinins) regulate growth, development, and responses to environmental stimuli. Auxins promote cell elongation and can direct growth toward light.
Environmental Cues: Plants respond to light (phototropism), gravity (gravitropism), and water availability (hydrotropism), adjusting their growth patterns accordingly.
Also, plant cells communicate through plasmodesmata, allowing the exchange of signaling molecules and nutrients.

Question 21

Hormone receptors:
Antigens:
Signal receptor:
Binding site:

Answer 21

Communication between cells.
Cell recognition.
Coordination of actions to trigger a response inside the cell.
Neurotransmitters/antibodies.

Question 22

Describe some examples of signalling.

Answer 22

1. Paracrine signalling - between cells that are close together.
2. Endocrine signalling - between cells that are far apart, which involves the signalling molecule being transported in the circulatory system. The signalling molecules are always hormones.
3. Synaptic signalling.
4. Hormonal signalling.