Module 5.1 - Communication And Homeostasis

Question 1

Define cell signalling

Answer 1

The way in which cells communicate with each other

Question 2

Why is it important to respond to internal changes?

Answer 2

Some products of metabolic activities (e.g. CO2) are harmful, build up can be toxic
This acts as a stimulus for their own removal

Question 3

Why is it important to respond to external changes?

Answer 3

To be able to adjust the internal environment in response to external environment (e.g. temperature)
To adapt to the changes in environment (e.g. wether/scenery, camouflage)
To find resources (e.g. tropisms)

Question 4

What are the two systems of cell signalling?

Answer 4

Neuronal system

Endocrine system

Question 5

Points about the neuronal system

Answer 5

Neurones signal to each other across synapses
Quicker (short-term)
Very specific effect
Electrical impulses carried by neurones, neurotransmitters carry message across synapse

Question 6

Point about the endocrine system

Answer 6

Hormones transported in blood to specific target cells
Slower (long-term)
Specific to target cells, more general overall effect
Hormones carried in blood

Question 7

Define homeostasis

Answer 7

The maintenance of the internal environment in a constant state despite external and internal changes

Question 8

Define effector

Answer 8

A cell, tissue or organ that brings about a response

Question 9

Define negative feedback

Answer 9

A process that brings about a reversal of any change in conditions in order to return to an optimum set point
Essential for homeostasis

Question 10

Define positive feedback

Answer 10

A process that increases any change detected by the receptors, taking the conditions further from the optimum set point
Tends to be harmful and does not lead to homeostasis

Question 11

Process of negative feedback

Answer 11

Optimum conditions
Change from optimum
Sensory receptor detects change
Cell signalling communicates change (CNS coordinates response)
Effector cells bring about change to reverse the response
Return to optimum

Question 12

Process of positive feedback

Answer 12

Optimum conditions
Change from optimum
Sensory receptor detects change
Cell signalling communicates change (CNS coordinates response)
Effector cells increase change further

Question 13

Define ectotherm

Answer 13

An organism that relies on external sources of heat to regulate body temperature

Question 14

Define endotherm

Answer 14

An organism that can control the generation or loss of heat to maintain its body temperature using physiological or behavioural responses

Question 15

Ectotherm advantages and disadvantages

Answer 15

Advantages: less food used in respiration as less energy needed; less food needed; more energy used for growth
Disadvantages: less active in cold; can’t adapt to change in external temperature

Question 16

Endotherm advantages and disadvantages

Answer 16

Advantages: can maintain a constant body temperature despite external conditions; can be active in colder conditions
Disadvantages: large portion of energy intake needed to maintain body temperature; more food required; less energy from food used for growth

Question 17

Examples of behavioural mechanisms in thermoregulation

Answer 17

Too cold - move into sun, decrease surface area, move to warm surface
Too hot - move out of sun, increase surface area, move to cooler surface

Question 18

Examples of physiological mechanisms in thermoregulation

Answer 18

Too cold - no sweat, no panting, vasoconstriction in arterioles, more respiration in liver cells, repaid contraction and relaxation of skeletal muscles (shivering), hairs/feathers stand up
Too hot - sweat evaporates, panting evaporates, vasodilation of arterioles, less respiration in liver cells, no shivering, hairs/feathers lie flat

Question 19

Explain thermoregulation

Answer 19

Example of negative feedback
Peripheral thermoreceptors in the skin sense temperature changes in the external environment
If too much change is detected this information is sent to the hypothalamus which brings about the relevant responses