5.1.1 Communication And Homeostasis

Question 1

Why do multicellular organisms require communications systems ?

Answer 1

•To respond when their internal or external environment changes
•To coordinate organ function.

Question 2

What is cell signalling ?

Answer 2

Communication between cells : electrical signals carried by neurones or chemical signals as hormones

Long-distance is endocrine signalling
Paracrine signalling between adjacent cells occurs directly or aided by extracellular fluid to carry hormones
In autocrine signalling, the cell releases signals to stimulate its own receptors and triggers a response within itself.

Question 3

What is homeostasis ?

Answer 3

Internal environment is maintained within set limits around an optimum.

Question 4

Define negative and positive feedback

Answer 4

Negative feedback - self regulatory mechanisms return internal environment to optimum when there is a fluctuation
Positive feedback - a fluctuation triggers changes that result in an even greater deviation from the normal level.

Question 5

What are receptors and effectors ?

Answer 5

Receptors - specialised cells located in sense organs that detect a specific stimulus
Effectors - usually muscles or glands which enable a physical response to a stimulus.

Question 6

What is an ectotherm ?

Answer 6

An organism that cannot increase it’s respiration rate to increase the internal production of heat.
It must rely on external sources to regulate its body temperature, and it must respond to fluctuations in temperature behaviourally e.g. may orient body to maximise sun exposure.

Question 7

What is an endotherm ?

Answer 7

An organism that can regulate its body temperature independently of external sources
Thermoreceptors send signals to the hypothalamus which triggers a psychological or behavioural response.

Question 8

Outline the behavioural methods endotherms use to regulate their body temperature.

Answer 8

-Basking in the sun
-Pressing against warm surfaces
-digging burrows
-hibernation / aestivation
-panting

Question 9

How does the autonomic nervous system enable endotherms to autoregulate ?

Answer 9

Negative feedback
Peripheral thermoreceptors detect changes in the skin temperature
Thermoregulators in the hypothalamus detect changes in the blood temperature
The hypothalamus sends impulses to effectors in skin to induce vasodilation/constriction, piloerection, sweating
Impulses are also sent to the muscles to induce shivering.

Question 10

Explain the role of the skin in thermoregulation.

Answer 10

Vasodilation/constriction of the arterioles supplying skin capillaries controls heat loss to the skin surface
Hair erector muscles contract and follicles protrude to trap air for insulation
Evaporation of sweat cools skin surface.