Homeostasis

Question 1

What is homeostasis?

Answer 1

The maintenance of the internal environment within an optimum range

Question 2

State an example of a stimulus in the external environment and a corresponding response in animals

Answer 2

• Cooler environment -> arctic fox grows a much thicker coat in winter (gradual response)
• warmer environment -> moving into the sunlight
• appearance of a predator -> fleeing

Question 3

State an example of a stimulus in the internal environment and a corresponding response in animals

Answer 3

Stimulus: Build up of waste products eg. Carbon dioxide in respiration -> response: removal of these products by cells

Question 4

How is the internal environment maintained?

Answer 4

Composition of the tissue fluid is maintained by the blood as toxins enter and are carried away. They must be removed by excretion to prevent accumulation in the blood.

Question 5

What is the neuronal system?

Answer 5

A network of neutrons that signal across synapse junctions through neurotransmitters. They can conduct quickly and therefore elicit rapid responses to stimuli

Question 6

What is the hormonal system?

Answer 6

A system that uses blood to transport its signals. Cells in an endocrine organ release a hormone directly into the blood which are recognised by target cells. These create longer term responses to stimuli

Question 7

What factors to homeostasis maintain?

Answer 7

• Body temperature
• blood glucose conc
• blood salt conc
• water potential of the blood
• blood pressure

Question 8

What are sensory receptors?

Answer 8

They monitor changes in the external or internal environment and stimulate cell signalling
Eg. Temperature receptors on the skin

Question 9

What is negative feedback?

Answer 9

When a change away from the optimum occurs negative feedback counteracts this
Change from optimum -> receptor detects change -> communication system informs effector -> effector acts to reverse change -> return to optimum

Question 10

What is positive feedback?

Answer 10

When a change occurs and the response is to increase that original change. It is often harmful eg. In enzyme controlled reactions. However it can be useful

Question 11

What is an overshoot?

Answer 11

When a stimulus occurs but it takes a while for the body to produce a response

Question 12

What is an ectotherm?

Answer 12

They aren’t able to control their body temp as effectively, rely on external sources of heat and body temp fluctuates with environment

Question 13

How is temperature regulated in ectothermic?

Answer 13

Behavioural responses:

• move into sunny area/shade
• lie on warm surface/move underground
• expose a large/smaller area of the body to the sun

Question 14

What are some advantages of ectothermy?

Answer 14

• less of their food is used up during respiration
• more nutrients gained from food can be converted to growth
• need to find less food/can survive without it for longer

Question 15

What are some disadvantages of ectothermy?

Answer 15

• less active in cooler temperatures

- at risk from predators when cold

Question 16

What are endotherms?

Answer 16

They do not rely on external sources of heat - use physiological adaptations to control temp

Question 17

What are some mechanisms used to regulate temperature in endotherms?

Answer 17

-Skin: sweat glands secrete fluid
hairs and feathers lie flat to reduce insulation / stand erect to trap air
vasodilation / vasoconstriction
-less respiration takes place in the liver so less heat released / more respiration
-fewer contractions / shivering

Same behavioural responses as ectotherms

Question 18

What is

A) vasodilation?

Answer 18

A) sphincters are open to allow blood to flow to the extremities to increase heat loss

B) sphincters are closed to restrict blood from flowing to the extremities so it isn’t cooled too much- can lead to frostbite

Question 19

What are some advantages of endothermy?

Answer 19

• Maintain constant body temp despite external temperature

- can remain active and take advantage of prey/escape predators while cold

Question 20

What are some disadvantages of endothermy?

Answer 20

• require more food

- lower proportion of the energy from food is used for growth

Question 21

What is thermoregulation?

Answer 21

Temp receptors on the hypothalamus detect change and send out impulses to cause different responses eg. Changes in skin to reduce heat loss, shivering, increased metabolism. Controls rapid responses

Question 22

What is the role of peripheral temp receptors?

Answer 22

They monitor the temperature in the extremities which is fed to the thermoregulatory centre in the hypothalamus. Detect external temperature so the brain can initiate behavioural mechanisms for maintaining body temp prior to temp change in the body.