Communication And Homeostasis

Question 1

Why do multicellur organisms need communication systems?

Answer 1

To respond when their internal and external environment changes
To coordinate organ function

Question 2

What is cell signalling

Answer 2

• Long distance endocrine signalling
• Paracrine signalling between adjacent cells occur directly or aided by extracellular fluid
• 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 results 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

Organism that cannot increase its respiration rate to increase the internal production of heat
Relies on external sources to regulate its body temperature. Responds to temperature changes behaviourally e.g. may orient body to minimise / maximise sun exposure

Question 7

What is an endotherm

Answer 7

Organism that can regulate its body temperature independently of external sources. Thermoreceptors send signals to the hypothalamus, which triggers a physiological or behavioural response

Question 8

Outline behavioural methods ectotherms 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 thermoregulate

Answer 9

Negative feedback. Peripheral thermoreceptors detect changes in skin temperature. Thermoreceptors in hypothalamus detect changes in blood changes
Hypothalamus sends impulses to effectors in skin (vasodilation / constriction, piloerection, sweating) & muscles (shivering)

Question 10

Explain the role of the skin in thermoregulation

Answer 10

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