Communication And Homeostasis

Question 1

Why do multicellular organisms need communication systems ?

Answer 1

• To respond when their internal & 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 endocrine signalling
- Paracrine signalling between adjacent cells occurs directly or aided by extra cellular fluid
- In autocrine signalling, cell releases signals to stimulate its own receptors & triggers a response within itself

Question 3

What is homeostasis ?

Answer 3

Maintaining internal environment within set limits around an optimum

Question 4

Define positive and negative 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 on 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

Organisms that cannot increase its respiration rate to increase production of heat
Relies on external sources to regulate its body temperature. Responds to temperatures 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 endotherms use to regulate their body temperature

Answer 8

• Basking in the sun
• Pressing against warm surfaces
• Digging Burrows
• Hibernation/ aestivation
• Panting (heat lost as water evaporates from mouth)

Question 9

How does the autonomic nervous system enable endotherms to thermoregulate ?

Answer 9

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

Question 10

Explain the role of the skin in thermoregualtion

Answer 10

Vasodilation/Constriction of arterioles supplying skin capillaries controls heat loss to skin surface
Hair erector muscles contract & follicles protrude to trap air for insulation
Evaporation do swear cools skin surface