5.1 - Communication and Homeostasis

Question 1

State the conditions within a cell that need to be maintained.

Answer 1

Suitable temperature - this may not be 37°C.
Suitable pH.
An aqueous environment - to allow successful collisions between enzyme active sites and substrates, the maintenance of products in solution for transport etc; hydrolysis and condensation reactions.
Freedom from toxins and inhibitors - carbon dioxide, urea, etc.

Question 2

Which external changes does an organism need to monitor?

Answer 2

Temperature, sunlight darkness, predator/prey.

These are all stimuli, they bring about a response.

Question 3

Describe the features of an effective communication system.

Answer 3

Covers the whole body; allows cell to cell communication; specific; rapid; short and long term responses.

Question 4

Describe how an organism coordinates a response to a stimulus.

Answer 4

Cell signalling. Hormonal signalling - uses endocrine system, hormone released into blood, targets cells with specific receptor, often slow acting, long lasting response. Electrical impulses - uses neurones, synapses and chemical messengers, rapid, short term response.

Question 5

What is homeostasis?

Answer 5

The maintenance of an internal environment despite internal and external factors.

Question 6

Explain the importance of maintaining body temperature and blood pH?

Answer 6

Temperature - too low enzymes work slowly and cellular metabolism drops, too high and enzymes denature.
Blood pH - too low or high and enzyme tertiary structure and active site disrupted, cellular metabolism drops.

Question 7

Explain the importance of maintaining a constant blood glucose concentration.

Answer 7

Too high and the water potential of blood is reduced and water diffuses out of cells by osmosis, cells become crenated.
Too low and cellular metabolism drops as cells do not have enough glucose for respiration.

Question 8

Describe the mechanism of homeostasis.

Answer 8

Stimulus> receptor> communication pathway/ cell signalling> effector> response.

Question 9

Define a sensory receptor.

Answer 9

Cells/sensory nerve endings that detect/respond to a stimulus. Stimulus may be internal or external. An action potential or hormonal response is initiated.

Question 10

Describe a communication pathway.

Answer 10

Neuronal or hormonal system.

Responds to receptor and transits message from receptor cells, input, to effector cells, output via coordination centre.

Question 11

What is an effector?

Answer 11

Muscle - neuronal response.

Gland - hormonal response.

Question 12

What is negative feedback?

Answer 12

An action that reverses the initial change in conditions. Effective response. Restores systems to their original level/an optimum. System stabilised. Usually beneficial e.g. blood glucose, body temperature.

Question 13

What is positive feedback?

Answer 13

An increase to the initial change. Further increase away from original levels/an optimum. System destabilised. Usually harmful e.g. hypothermia, reduction in body temperature. Release of oxytocin is an example of beneficial positive feedback. Increase uterine contraction causing cervix to stretch. In turn stretching causes release of more oxytocin.

Question 14

What is overshoot?

Answer 14

Overcorrection to the system that takes conditions past the optimum, away from the stimulus.

Question 15

What is an ectotherm?

Answer 15

An organism that relies on external sources of heat to maintain body temperature e.g. lizard.

Question 16

Why must body temperature be maintained?

Answer 16

Changes in temperature affect kinetic energy. Increase in temperature = increase in KE = increase in successful collisions between molecules. Too high and proteins and enzymes denature, shape of active site altered. Decrease in temperature = decrease in KE = decrease in successful collisions. Too low and collisions cease, metabolism slows/stops.

Question 17

Describe the behaviours of ectotherms in response to temperature change.

Answer 17

Too cold - move into sun/warmth; lie on warm surface; expose large surface area to sun, or reduce surface area exposed to cold.
Too hot - move from sun/warmth; burrow; reduce surface area exposed to sun.

Question 18

Describe the advantages of ectothermy.

Answer 18

Less food needed for respiration.
More energy from food available for growth and repair.
Survive long periods without food.
Longer lived when compared to endotherms of similar size.

Question 19

Describe the disadvantages of ectothermy.

Answer 19

Less active in cooler temperatures, at risk from predation.

Must live within a habitat with suitable temperature range.

Question 20

What is an endotherm?

Answer 20

An organism that relies upon heat from metabolic reactions within the body to maintain body temperature.

Question 21

What is an exergonic reaction?

Answer 21

A chemical reaction that releases energy in the form of heat, e.g. respiration.

Question 22

Describe the advantages of endothermy.

Answer 22

Body temperature fairly constant despite external temperature.
Remain active even at lower external temperatures, evade predation. Capture prey.
Inhabit colder places.

Question 23

Describe the disadvantages of endothermy.

Answer 23

Significant part of food intake required to generate eat energy/ maintain internal temperature.
Need more food, more often.
Fewer nutrients available for growth and repair.
May overheat in higher temperatures.

Question 24

Where are the temperature receptors that detect and initiate change?

Answer 24

The brain, hypothalamus.

Question 25

Describe the roles of peripheral thermoreceptors.

Answer 25

Receptors in skin detect change. Information passed to hypothalamus via neurones. Changes initiated, often behavioural before physiological.

Question 26

Compare behavioural responses to changes in body temperature.

Answer 26

Too hot: Hide away from sun in shade or burrow; orientate body to reduce surface area exposed to sun; remain inactive; spread limbs to increase surface area and increase heat loss; wet skin to use latent heat of evaporation to remove heat energy. Too cold: Lie in sun; orientate body towards sun to increase surface area exposed; move to generate heat in muscles; in extreme cases curl into a ball to reduce surface area and reduce heat loss; remain dry.

Question 27

Compare physiological responses to changes in body temperature.

Answer 27

Organ: Skin. Response if too hot: Sweat glands open, heat from blood uses latent heat vaporisation to remove heat. Hairs and feathers lie flat to reduce insulation and encourage heat loss. Vasodilation of arterioles and precapillary sphincters directs blood flow to surface of skin so more heat radiates from body. Response if too cold: Sweat glands close, less evaporation, less heat loss. Hairs and feathers stand up, air trapped forming insulating layer. Vasoconstriction of arterioles and precapillary sphincters restricts blood flow to surface of skin, less heat loss. Organ: Gas exchange system. Response if too hot: Panting, increase of evaporation of water from moist membranes of mouth and airways, latent heat of vaporisation. Response if too cold: No panting, less heat loss from moist membranes of mouth and airways. Organ: Liver. Response if too hot: Reduction in respiration, less heat produced. Response if too cold: Increase in respiration, more energy from food converted to heat. Organ: Skeletal mucle. Response if too hot: Fewer contractions, less heat released. Response if too cold: Spontaneous contractions/ shivering, heat released. Organ: Blood vessels. Response if too hot: Dilation to direct blood to extremities to more heat lost. Response if too cold: Constriction to limit blood flow to extremities, less cooling of blood, less heat lost; can lead to frostbite.