5.1 Communication and homeostasis

Question 1

What is an effector?

Answer 1

A cell, tissue or argan that brings about a responce.

Question 2

What is homeostasis?

Answer 2

Maintaining a constant internal enviroment despite changes in external and internal factors.

Question 3

What is negative feedback?

Answer 3

The mechanism that reverses a change, bringing the system bacl to the optimum.

Question 4

What is positive feedback?

Answer 4

The mechanism that increases a change, taking the system further away from the optimum.

Question 5

What are sensory receptors?

Answer 5

Cells, sensory never endings that respond to a stimulus in the internal or external enviroment of an organism and can create action potentials.

Question 6

What aspects may be maintained by homeostasis?

Answer 6

• Body temperature
• Blood glucose concentration
• Blood salt concentration
• Water potential in the blood
• Blood pressure
• Carbon dioxide concetration

Question 7

For negative feedback to occur, what processes must occur?

Answer 7

• A change in the internal enviroment must be detected.
• The change must be signalled to other cells.
• There must be an effective responce that reverses the change in conditions.

Question 8

Is positive or negative feedback more common?

Answer 8

Negative feedback is more common than positive feeback.

Question 9

What is an example of harmful positive feedback?

Answer 9

When the core body temperature enzymes become less active and the exergonic reactions that release heat are slower and release less heat, allowing the body to cool further.

Question 10

What is an example of benificial postive feedback?

Answer 10

At the end of preganancy, the cervix begins to stretch, causing the poterior putuitary gland to secrete the hormone oxycotin. Tjis increases the uterine contractions which stretch the cervix more so the baby can be born.

Question 11

What conditions do exymes require to work effeciently?

Answer 11

• A suitable temperature
• A suitable pH
• An aqueous enviroment that keeps the substrates and products in solution
• Freedom from toxins and excess inhabitors

Question 12

What are the two major systems of communication that work by cell siganlling?

Answer 12

• Neuronal system
• Hormonal system

Question 13

What is an ectrothrem?

Answer 13

An oranism that relies on external sources of heat to maintain body temperature.

Question 14

What is an endotherm?

Answer 14

An organism that uses heat from metabolic reactions to maintain body temperature.

Question 15

What happens to enzymes if temperature is increased too high?

Answer 15

They denature, changoing their shape, loosing their function.

Question 16

What happens to enzyme activity if body temperature drops 10°C, what does this affect?

Answer 16

The rate of enzyme-controlled reactions drop by a half. Many reactions, which help to maintain body temperature, but if the temperature drops and reactions slow down, less heat is released, allowing the body to cool further. This is a form of positive feedback.

Question 17

How do ecrotherms control their body temperature?

Answer 17

They reply on external sources of heat, however, once they’re active, their muscle contractions will generate some heat from increased respiration.
If an ecrotherm is not warm enough, they may:
* Move to a sunny area
* Lie on a warm surface
* Expose a larger area to the sun.

If an ecrotherm is too hot, they can:
* Move out of the sun
* Move underground
* Reduce body surface exposed to the sun.

Question 18

What are the advantages of ecrothermy?

Answer 18

• less food used in respiration.
• More of the energy and nutrients gained from food can be converted to growth.
• They need to find less food.
• They can survive for longer pierods without food.

Question 19

What re the disadvantages of ectothermacy?

Answer 19

They are less active in cooller conditions. This means they are at risk from predators while they’re cold and unable to esacpe and they cannot take advantages of food that is available when they are cold.

Question 20

What is the hypothalamus?

Answer 20

The partof the brain that coordinates homeostatic responces.

Question 21

In endotherms, how does the skin react to changes in temperaure?

Answer 21

If too hot:
* Sweat gland secrete fluid onto the surface of the skin.
* Hairs lie flatter to the skin, reducing insulation.
* Vasodilation of arterioles and precapillary sphincters direct blood flow to the skin so more heat can be radiated away.
If too cold:
* Less sweat.
* Hairs stand up to stap air.
* Vasoconstriction of arterioes and precapillary sphincters so blood is diverted away from the skin.

Question 22

In endotherms, how does the gaseous exchange system react to changes in temperaure?

Answer 22

If too hot:
* Increasing evaporation of watwr from the surface of the lungs and airways. Evaporation uses heat from the blood as the latent heat of vaporisation.
If too cold:
* Less panting so less is lost.

Question 23

In endotherms, how does the liver react to changes in temperaure?

Answer 23

If too hot:
* Less respiration takes place so less heat is released.
If too cold:
* Increased respiration in the liver cells means more energy from food is converted into heat.

Question 24

In endotherms, how does the skeletal muscles react to changes in temperaure?

Answer 24

If too hot:
* Fewer contactions means that less heat is released.
If too cold:
* Spantanous muscle contractions (shivering) release heat.

Question 25

In endotherms, how does the blood vessles react to changes in temperaure?

Answer 25

If too hot:
* Dilation to direct blood to the extremities so that more heat can be lost.
If too cold:
* Constriction to limit blood flow to the extremities, so that blood is not cooled too much- this can lead to frostbite in extreme conditions.

Question 26

What are the advantages of endothermy?

Answer 26

• Maintain a fairly constant body temperature whatever the temperature externally.
• Remain acitive even when external temperatures are low, which means they can take advantage pf prey that may be available of escape from potential predators.
• Inhibit colder parts of the planet.

Question 27

What are the disadvantages of endotherms?

Answer 27

• Use a significant part of their energy intake to maintain body temperature in the cold.
• Need more food.
• Use for growth a lower proportion of the energy and nutrients gained from food.
• May overheat in hot weather.

Question 28

Wher in the brain are the temperature receptors in endotherms?

Answer 28

In the hypothalamus.

Question 29

What does the hypothalamus detect?

Answer 29

monitors blood temperature and detects changes in the core body temperatures.