5.1 Homeostasis

Question 1

How do cells in the nervous system communicate?

Answer 1

By secreting neurotransmitters to adjacent cells

Question 2

Why must organisms respond to changes in their external environment?

Answer 2

To ensure their survival

Question 3

Why must organisms respond to changes in their internal environment?

Answer 3

To ensure the conditions are always optimal for their metabolism

Question 4

What is a stimulus?

Answer 4

Any change in the internal or external environment

Question 5

How do distant cells communicate?

Answer 5

The hormonal system, where chemicals travel in the blood and signal distant cells.

Question 6

What do cell surface receptors do?

Answer 6

They allow cells to recognise chemicals involved in cell signalling

Question 7

What is homeostasis?

Answer 7

Maintenance of an internal environment, kept within a narrow range- roughly constant

Question 8

What is positive feedback?

Answer 8

When a change acts to further increase the change, away from the normal level

Question 9

When is positive feedback useful?

Answer 9

When something needs to be rapidly activated, e.g. a blood clot

Question 10

What is negative feedback?

Answer 10

When a response acts to counteract a change or stimulus. It keeps things at a normal level

Question 11

Why is negative feedback useful?

Answer 11

Maintains a relatively normal level e.g. body temperature at 37C

Question 12

Why is cell signalling important?

Answer 12

It insures organ activity is coordinated, and that messages can be sent between receptors and effectors

Question 13

The activity of neurones relies on _________ feedback.

Answer 13

Positive

Question 14

What hormone promotes uterine contractions during birth?

Answer 14

Oxytocin

Question 15

How is cervical dilation an example of positive feedback?

Answer 15

• As cervix begins to stretch, oxytocin is released

- Oxytocin increases contractions which cause the cervix to dilate more which increases the amount of oxytocin secreted

Question 16

What is an ectotherm?

Answer 16

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

Question 17

Why is temperature control important?

Answer 17

Enzyme controlled reactions are temperature sensitive, too hot and they denature, too cold and they are too slow

Question 18

What is Q10 rule?

Answer 18

As the temperature increases by 10 degrees, the rate of enzyme controlled reactions doubles

Question 19

Why do ectotherms lie on their side in the sun when they feel cold?

Answer 19

To warm up they expose a larger surface area of their skin to the sun

Question 20

How do ectotherms cool down?

Answer 20

By increasing heat loss to the environment: like moving to shade, into burrows etc

Question 21

In terms of energy, what is an advantage of ectothermy?

Answer 21

Because they rely on external heat sources, they do not use their energy on keeping warm- so they can live longer without food

Question 22

What are disadvantages of ectothermy?

Answer 22

• Less active in cold

- Risk from predators when cold

Question 23

Why do locusts ‘breathe’ deeper in the heat?

Answer 23

An increased depth of breathing movements allows more water to evaporate from the tracheal system, cooling the body

Question 24

Why do locusts climb to the top of plants at midday?

Answer 24

To escape the hot soil surface and cool down

Question 25

How can horned lizards warm up?

Answer 25

By expanding their rib cage they increase the SA of their skin so more heat can be absorbed

Question 26

Why do ectotherms like to have burrows?

Answer 26

Burrows tend to have a more stable temperature than the air outside- it will be colder inside when it’s hot outside and warmer inside when it’s cold outside

Question 27

What do lizards do to maintain their body temperature?

Answer 27

Hide in burrows or crevices in between rocks

Question 28

How do snakes warm up?

Answer 28

Basking in the sun to absorb its heat

Question 29

What is an endotherm?

Answer 29

An organism that maintains its body temperature by homeostasis and generates its own heat

Question 30

What is a disadvantage of endothermy, in terms of energy?

Answer 30

A significant part of our energy intake is used on body temperature maintenance, meaning more food is needed to survive

Question 31

What monitors changes in external skin temperature?

Answer 31

Peripheral skin receptors

Question 32

What monitors the blood temperature/core temperature?

Answer 32

Thermoregulatory centre in the hypothalamus

Question 33

Why would an organisms hairs/feathers lie flat on the skin?

Answer 33

To reduce insulation and allow greater heat loss

Question 34

What is vasodilation?

Answer 34

Arterioles directing blood to the skin and extremities

Question 35

Why is vasodilation useful?

Answer 35

It allows blood to the skins surface allowing greater heat loss

Question 36

Why does panting cool an animal down?

Answer 36

It increases evaporation from the lungs and airway surface

Question 37

Why do we shiver when cold?

Answer 37

Spontaneous muscle contraction and respiration release heat

Question 38

Why do people get frostbite in extreme cold conditions?

Answer 38

Vasoconstriction limits blood flow to the extremities

Question 39

Why do hairs/feathers stand erect when cold?

Answer 39

To trap air in the gaps which insulates the skin, reducing heat loss

Question 40

Why are peripheral temperature sensors useful in maintenance of body temperature?

Answer 40

They can act as an early warning sign that the body temperature may drop, allowing the hypothalamus to respond more quickly

Question 41

What are the advantages of endothermy?

Answer 41

• Can remain active when cold
• Can escape predators when cold
• Can inhabit colder habitats

Question 42

What muscle makes hair stand up?

Answer 42

Erector pili muscle

Question 43

What hormones increase metabolism and allow more heat to be produced?

Answer 43

Adrenaline and thyroxine