Communcation And Homeostasis

Question 1

What two communication systems do animals have

Answer 1

Nervous system: produces rapid responses

Endocrine system: tends to carry-out longer-lasting communication.

Question 2

What is cell signalling

Answer 2

Both nerves and hormones are examples of cell signalling. This is how individual cells communicate with others in a different location in the body, but the method by which hormones transmit those signals is different to nerves.

Question 3

How endocrine gland send signals

Answer 3

They secrete hormones to target cells. These cells have receptors on their membrane which have a complimentary shape to the hormone.

Question 4

The two types of cell signalling

Answer 4

Paracrine signalling: occurs between cells that are close together
Endocrine signalling: involves sending signals over longer distances, with the signalling molecule transported in the circulatory system.

Question 5

What can cell signalling molecules be

Answer 5

These signalling molecules can be proteins, amino acids, lipids, glycoproteins and phospholipids.
In endocrine glands, these signalling molecules are hormones which can also be proteins.

Question 6

What are the receptor molecules normally made of

Answer 6

These are generally proteins or glycoproteins. Some, steroid hormones such as oestrogen can diffuse through the membrane. Because of this, some receptors may be found in the cytoplasm.

Question 7

Example of cell signalling (neurotransmitters)

Answer 7

Chemicals that transfer an impulse from one nerve cell across a small gap(the synapse) to another nerve cell.

Question 8

Another example of cell signalling

Answer 8

The production of histamine in response to a chemical signal, an antibody called immunoglobulin E.

Question 9

Example of cell signalling in plants

Answer 9

Plant hormones act as signalling molecules; for example, ethylene, which promotes fruit ripening, is detected y protein receptors, resulting in the activation of genes that cause ripening.

Question 10

What is negative feedback

Answer 10

In these mechanisms, a change initiates a series of events which then reverses the change.

Question 11

Example of negative feedback (metabolic rate)

Answer 11

If the metabolic rate drops, then the hormone, thyrotopin-releasing hormone, is released by the hypothalamus in the brain. This triggers the secretion of thyroid-stimulating hormone by the pituitary gland. This hormone is turn causes thyroid hormones to be secreted by the thyroid gland.
When the metabolic rate has returned to normal, the TSH ‘switches off’ the release f TRH from the hypothalamus.

Question 12

What is positive feedback

Answer 12

This causes proliferation rather than control, and so is not involved in maintaining a steady state in the body.

Question 13

An example of positive feedback (pregnancy)

Answer 13

The hormone, oxytocin, in secreted during contractions in childbirth. This hormone is responsible for intensifying uterine contractions. Contractions actually stimulate the release of oxytocin, so the increase it causes results in more oxytocin being released. Birth stops the release of this hormone.

Question 14

Thermoregulation

Answer 14

Control of temperature

Question 15

What is the optimum body temperature

Answer 15

37 degrees centigrade

Question 16

Definition of endotherms

Answer 16

They have physiological mechanisms to control their body temperature.
These are animals that maintain its body temperature using heat generated within its body tissues.
Examples are mammals and birds

Question 17

What are ecototherms

Answer 17

These animals rely on their behavioural adaptations to maintain their internal body temperature
So, they absorb heat from its environment to help regulate its body temperature.p

Question 18

How can heat be lost from the body through radiation

Answer 18

This is the loss of heat in the form of electromagnetic radiation from hot objects into cooler surroundings. This is also how we can gain heat from the Sun, or a fire.

Question 19

Heat loss through convection

Answer 19

This is the movement of currents or warm air upwards because the density of air decreases when it is warm.

Question 20

Heat loss through conduction

Answer 20

This is the transfer of heat energy from a warmer material to a cooler one. The body can lose heat o the air by conduction, but air is a good insulator. If a layer of air can be trapped around the body it will reduce further heat loss by radiation.

Question 21

Heat loss through evaporation

Answer 21

Water evaporates off the surface of the skin. This is because heat necessary to change the water into water vapour is extracted from the skin.

Question 22

Why does water temperature not fluctuate

Answer 22

It has a high heat capacity.

Question 23

What does ectothermic animals do to avoid overheating themselves

Answer 23

They do not expose themselves to extremes of temperature, and must warm their bodies rapidly if they get cold (which is unavoidable at night).

Question 24

Low body temperature effects on ectothermic animals

Answer 24

Sluggish and slow movements; difficult to catch prey or to escape from predator.

Question 25

What do ectotherms do if they re in danger of overheating

Answer 25

Seek shade or water so they can cool down.

Question 26

Adaptations of different ectotherms

Answer 26

Fish have blood vessels brings cold blood from the body surface that pass very close to those bringing warm blood from the internal organs and muscles. This ultimately evens out the temperature.
Ectotherms living in the cold are often dark in colour. This is because dark colour allows their body to retain heat better. Ectotherms tend to tolerate a much greater range of temperatures than endotherms.

Question 27

Why does endotherms need a higher metabolic rate

Answer 27

Ectotherms are more restricted by environmental temperature than endotherms. They cannot easily colonise in hold or cold habitats.However, endotherms need a lot of energy to maintain their body temperature, which means that they have a higher metabolic rate and need more food. Ectotherms can survive better in situations where food is limited.

Question 28

Cooling mechanisms in endotherms

Answer 28

Vasodilation. Arterioles have muscles in their walls which contracts or relaxes when needed. The muscles of the arterioles that travel near the surface of the skin contract to release heat from the blood.

Question 29

How does sweating help

Answer 29

The skin has sweat glands which produce sweat in hot conditions. As temperature rises, secretion would increase too.
Evaporation of sweating off the skin cools it.

Question 30

How does flattening of the hair work

Answer 30

Air trapped between the hairs on the skin forms an insulating layer. The hair erector muscles (effectors) in the skin can raise the hairs by contracting, and lower them again when they relax. In warmer conditions, these muscles relax to thin the insulating layer. This allows heat to be lost.

Question 31

What are warming mechanisms- boosting metabolic rate

Answer 31

The great majority of the chemical reactions in the body are exothermic (release heat). In cold conditions, one of the hormones, thyroxine, is released from the basal metabolic rate and so increases heat production. Another hormone, adrenaline also boosts metabolism but its action is short-term. The liver is massively responsible for producing heat because many chemical reactions occur here.

Question 32

How does shivering produce heat

Answer 32

This is a reflex action in response to a slight drop in core temperature, and so is a nervous rather than hormonal mechanism. The effectors are the muscles and the rapid and regular muscle contractions which comprise shivering generate heat which warms the blood. The heat is caused by friction- rather by the heat released by metabolic reactions.

Question 33

How does vasoconstriction aid warming

Answer 33

The muscles in the walls of the arteries constrict so that not so much blood reaches the capillaries near the surface. The blood is diverted through shunt vessels, which are deeper into the skin and so do not lose heat to the surroundings.

Question 34

How does erection of hair aid the warming mechanism

Answer 34

Each hair has an erector muscle attached to it. These hair strands stand, trapping a layer of air. Air is a good insulator. Therefore it reduces heat loss.

Question 35

What is behavioural homeostatic responses

Answer 35

Endotherms also will seek shade when its too warm.
In order for these behaviours to take place, the animals must have a means of detecting external temperatures. This is done by peripheral receptors.

Question 36

Monitoring temperature in endotherms

Answer 36

The centre of temperature control is located in the hypothalamus in the brain, which monitors the core blood temperature as it passes through. As well as temperature receptors, it contains two control centres: the heat loss centre and the heat gain centre.

Question 37

What are caused by nervous impulse

Answer 37

Sweating, shivering, vasoconstriction and vasodilation are controlled by nervous impulse via the autonomic nervous system.