Communication & Homeostasis:
Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to co-ordinate the activities of different organs.
Organisms need to respond to external stimuli, e.g. temperature, oxygen concentration and levels of sunlight. These may be over time, e.g. winter fur to summer fur, or quickly, e.g. changing size of pupils.
Internal environments change too- the build up of carbon dioxide as a result of respiration changes the pH of the tissue fluid, and therefore inhibits enzyme activity. Multicellular organisms need to coordinate different organs, so this requires a good communication system which will:
• Cover the whole body
• Enable cells to communicate with each other
• Enable specific communication
• Enable rapid communication
• Enable both short and long-term responses.
State that cells need to communicate with each other by a process called cell signalling.
State that neuronal and hormonal systems are examples of cell signalling.
Define the terms negative feedback, positive feedback and homeostasis.
Negative feedback- A process in which any change in a parameter brings about the reversal of that change
so that the parameter is kept fairly constant.
Positive feedback- A process in which any change in a parameter brings about an increase in that change
Homeostasis- The maintenance of a constant internal environment despite external changes
Explain the principles of homeostasis in terms of receptors, effectors and negative feedback.
Any change is detected by receptors, the communication system transmits a message from the receptor to
the effector and, through negative feedback, the effectors reverse the change.
Describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms
and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and
To maintain a constant core body temperature, ectotherms have physiological and behavioural responses;
The horned lizard expands its ribcage and the frilled lizard uses its frill to expand its surface
area to absorb more heat from the sun
Locusts increase their abdominal breathing movements to increase water loss when hot
Snakes expose their body to the sun so more heat is absorbed
Locusts orientate their body towards the sun to expose a larger surface area & so more
heat is absorbed. By orientating their body away from the sun, more heat is lost.
Lizards hide in burrows to prevent heat absorption by staying out of the sun.
To maintain a constant core body temperature, endotherms have physiological and behavioural
When hot they secrete sweat onto the skin. Water evaporates using heat from the
blood to supply latent heat of vaporisation.
When cold, less sweat is secreted, less water evaporates and so less loss of latent heat
Lungs, nose and mouth
When hot, panting increases water evaporation from lungs, tongue and moist
surfaces. Loss of latent heat as above.
When cold, no panting, less water evaporates, no loss of latent heat.
Hairs on skin
When hot, the hairs…