5.1 Communication and Homeostasis

Question 1

Cell signalling

Answer 1

This is when one cell will release a chemical that is detected by another cell. The second cell will respond to the signal released by the first cell.
(The way in which cells communicate with each other)

Question 2

Effector

Answer 2

A cell, tissue or organ that brings about a response

Question 3

Homeostasis

Answer 3

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

Question 4

Negative feedback

Answer 4

The mechanism that reverses the change, bringing the system back to its optimum.

e.g. rise/fall in core temperature

Question 5

Positive feedback

Answer 5

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

e.g. dilation of cervix.. stimulates posterior pituitary gland to secrete hormone oxytocin, which dilates cervix etc. Birth ends production of oxytocin - BENEFICIAL

N.B. usually PF destabilises system and is harmful.

Question 6

Flow diagram for mechanism of negative feedback

Answer 6

Conditions change away from optimum -
-->
 detected by receptors                 
--> 
sends input to coordination centre
-->
coordination centre sends output to the effectors
-->
effectors respond to output (reverses change - closer to optimum)
-->
eventually back to optimum condition

Question 7

What 3 processes must occur for negative feedback to work?

Answer 7

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

Question 8

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

Answer 8

Neuronal system: an interconnected network of neurones that signal to each other across synapse junctions. The neurones can conduct a signal very quickly and enable rapid responses to stimuli that may be changing quickly.

Hormonal system: a system that uses blood to transport in signals. Cells in an endocrine organ release the signal (a hormone) directly into the blood. The hormone is transported throughout the body, but is only recognised by specific target cells. The hormonal system enables longer-term responses to be coordinated.

Question 9

Standard response pathway

Answer 9

Stimulus –> receptor –> communication pathway (cell signalling) –> effector –> response

Question 10

Sensory receptors

Answer 10

cells/ sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials.

Question 11

Role of sensory receptor

Answer 11

to detect changes in the environment

Question 12

Role of effector

Answer 12

To carry out a response

Question 13

Input

Answer 13

Information sent from the sensory receptors to the coordination centre.

Question 14

Output

Answer 14

Information sent by coordination centre to the effectors

Question 15

Explain the difference between negative feedback and positive feedback

Answer 15

Negative feedback occurs where the change in conditions detected by the sensory receptors is reversed by the action of the effectors. Positive feedback occurs where the initial change in conditions is increased by the action of the effectors.

Question 16

Ectotherm

Answer 16

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

Question 17

Endotherm

Answer 17

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

Question 18

What would ectotherms do if they were cold?

Answer 18

• move into a sunny area (bask in sun)
• lie on a warm surface
• expose a larger SA to the sun

Question 19

What would ectotherms do if they were hot?

Answer 19

• move out of sun (into shade)
• move underground
• reduce the body surface exposed to the usn

Question 20

Advantages of ectothermy

Answer 20

• Less of their food is used in R
• More of the E and nutrients gained from food can be converted to growth.
• They need to find less food
• They can survive for long periods without food.

Question 21

Disadvantages of ectothermy

Answer 21

• less active in cooler temperatures
• at risk from predators when they are cold as unable to escape
• cannot take advantage of food that is available when cold

Question 22

Advantages of endothermy

Answer 22

• Can maintain a fairly constant body temperature whatever the temperature externally.
• remain active even when the external temperatures are low, which means they can take advantage of prey that may be available or escape from potential predators.
• inhabit colder parts of the planet.

Question 23

Disadvantages of endothermy

Answer 23

• Use significant part of their E intake to maintain body temperature in the cold
• need more food
• use for growth a lower proportion of the E and nutrients gained from food
• may overheat in hot weather

Question 24

Role of peripheral temperature receptors

Answer 24

Monitor the T in the extremities. This information is fed to the thermoregulatory centre in the hypothalamus.
–> will signal brain that external environment is either very hot or very cold ad brain can initiate behavioural mechanisms for maintaining the body temperature (e.g. moving to shade)