5.1 - C - Communication And Homestasis

Question 1

Define cell signalling

Answer 1

The way in which cells communicate with each other

Question 2

What does cell metabolism rely on?

Answer 2

Enzymes

Question 3

List the set of conditions in cells that all living things need to maintain

Answer 3

A suitable temperature
A suitable pH
An aqueous environment that keeps the substrates and products in solution
Freedom from toxins and excess inhibitors

Question 4

What does an external environment consist of?

Answer 4

Air
Water
Soil

Question 5

What is the composition of the tissue fluid maintained by?

Answer 5

The blood

Question 6

What will a good communication system do?

Answer 6

Cover the whole body
Enable cells to communicate with each other
Enable specific communication
Enable rapid communication
Enable both short-term and long-term responses

Question 7

What are the 2 major systems of communication that work by cell signalling?

Answer 7

Neuronal system

Hormonal system

Question 8

What is a receptor?

Answer 8

A cell that detects a stimulus and creates action potentials (nervous impulse)

Question 9

What is an effector?

Answer 9

A cell, tissue or organ that brings about a response

Question 10

What is a stimulus?

Answer 10

A change in an environment that causes a response

Question 11

What is a response?

Answer 11

A change in behaviour/physiology as a results of a stimulus

Question 12

What is an internal environment?

Answer 12

The conditions inside an organism

Question 13

What is an external environment?

Answer 13

The conditions outside an organism

Question 14

Why do plants and animals need communication systems?

Answer 14

In order to respond to both internal and external environments and coordinate the activities of organs

Question 15

What is the importance of organisms being able to respond to their internal environment?

Answer 15

Some products of metabolic activities are harmful ‐ their build up
could be toxic ‐ they act as a stimulus for their own removal.
Maintains constant internal conditions (homeostasis)

Question 16

What is the importance of organisms being able to respond to the
external environment?

Answer 16

To be able to adjust internal environment in response to external
e.g. temperature
To adapt to changes in environment e.g. weather or scenery (camouflage)
Find resources e.g. tropisms

Question 17

Compare the neuronal system and the hormone system

Answer 17

H: slower response to stimuli
N: faster response to stimuli
H: hormones carried in blood
N: electrical impulses carried by neurones, neurotransmitters carry message across synapse
H: longer term responses
N: short term responses
H: hormones are specific to target 
N: cells but can have quite a general effect

Question 18

Define homeostasis

Answer 18

The maintenance of the internal environment in a constant state despite changes to internal and external environments

Question 19

Define negative feedback

Answer 19

A process that brings about a reversal of any change in conditions in order to return to an optimum set point. This is essential for homeostasis.

Question 20

Define positive feedback

Answer 20

A process that increases any change detected by the receptors, taking the conditions further from the optimum set point. (Tends to be harmful and does not lead to homeostasis)

Question 21

List 6 aspects maintained by homeostasis

Answer 21

Body temperature
Blood glucose concentration
Blood salt concentration
Water potential of the blood
Blood pressure
Carbon dioxide concentration

Question 22

What has to happen to bring about any form of homeostasis?

Answer 22

Receptor detects stimulus ‐‐> cell signalling ‐‐> effector brings about response

Question 23

Explain the cycle (steps) in negative feedback

Answer 23

Optimum conditions,
Change from optimum,
Receptor detects change,
Communication system informs effector (cell signalling),
Effector reacts to reverse change,
Return to optimum condition,
Repeat

Question 24

Explain the cycle (steps) in positive feedback

Answer 24

Optimum condition,
Change away from the optimum,
Receptor detects change,
Communication system informs effector,
Effector reacts to increase change,
Repeat back to step 2

Question 25

What 3 processes must occur for negative feedback to work

Answer 25

A change to the internal environment must be detected
The change must be signalled to other cells
There must be an effective response that reverses the change in conditions

Question 26

Define metabolic waste

Answer 26

Waste substances that may be toxic or are produced in excess by the reactions inside cells

Question 27

What is an ectotherm?

Answer 27

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

Question 28

What is an endotherm?

Answer 28

An organism that can control the generation or loss of heat to maintain its body temperature using physiological or behavioural responses

Question 29

Why do organisms need to control their body temperatures?

Answer 29

Temperature will affect rate of metabolic reactions
Cooler temperatures ‐ reactions would slow down
Too hot ‐ enzymes would denature ‐ stop metabolic reactions

Question 30

Evaluate ectothermy

Answer 30

\+ less food used in respiration
\+ need less food
\+ more energy used for growth
\+ they can survive for long periods without food
- less active in cold
- winter months

Question 31

Evaluate endothermy

Answer 31

+ can maintain constant body temp despite external conditions
+ can be active in colder conditions
+ remain active even when external temperatures are low, which means they can take advantage of prey that may be available or escape from potential predators
- a large portion of energy intake is needed to maintain body temperature
in cold
- more food required
- less energy from food used for growth
- may overheat in hot weather

Question 32

What does the hypothalamus do?

Answer 32

Coordinates homeostatic responses

Question 33

What is the hypothalamus an example of and why?

Answer 33

Negative feedback
It monitors the blood temperature and if it moves away from the optimum core temperature, it will send signals to bring about the reverse of the changes.

Question 34

What do peripheral thermoreceptors do?

Where are they found?

Answer 34

In the skin
They sense changes of temperature in the external environment. It too much change is detected this information is sent to the hypothalamus which brings about the relevant responses.

Question 35

List 4 behavioural adaptations used by endothermic to maintain body temperature

Answer 35

Hide away from/ lie in the sun
Wet/lick skin/ spray water over themselves, remain dry
Remain inactive/move to generate heat
Reduce/increased body surface area exposed to the sun

Question 36

How does skin respond if the organism is too hot/cold?

Answer 36

More/less swear
Hairs feathers lie flat when hot, stand when cold (insulation)
Vasodilation of arteriolar and precapillary sphincters directs blood to skin surface so more heat can be radiated away from the body / vasoconstriction - opposite of above - less heat lost

Question 37

How do gaseous exchange systems respond if the organism is too hot/cold?

Answer 37

Some animals pant, increasing evaporation from lung and airways surfaces.
Less panting, less heat lost

Question 38

How does the liver respond if the organism is too hot/cold?

Answer 38

Less respiration takes place so less heat is released.
Or
Increased respiration in the liver cells means that more energy from food is converted to heat.

Question 39

How do skeletal muscles respond if the organism is too hot/cold?

Answer 39

Fewer contractions mean that less heat is released.
Or
Spontaneous muscle contractions (shivering) release heat.

Question 40

How do blood vessels respond if the organism is too hot/cold?

Answer 40

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