Module One, A2 Biology, Unit 4, F214

Communication, Homeostasis & Energy

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.

All enzymes need a specific set of conditions in order to work efficiently. These include:

• A suitable environment.

• A suitable pH

• An aqueous environment that keeps the substrates and products in solution.

• Freedom from toxins and excess inhibitors.

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 can also change too – the build-up of CO2 as a result of respiration changes the pH of the tissue fluid, and therefore it inhibits enzyme activity.

Multicellular organisms need to coordinate different organs so they need a good communication system that will:

• Cover the whole body

• Enable cells to communicate with each other

• Enable specific communication

• Enable rapid communication

• Enable both short-term and long-term responses.

State that cells need to communicate with each other by the process of 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 changes in a parameter brings about an increase in that change.

Homeostasis: The maintenance of the internal environment in a constant state 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 the 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.

To maintain a constant core body temperature, ectotherms have physiological and behavioural responses;

Physiological:

• 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.

Behavioural

• 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 responses:

Physiological:

• Sweat Glands:

  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 evaporation of water from…