Biology OCR A2 F214 Specification & Answers

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  • Created on: 30-05-13 12:41

4.1.1. Communication

(a) 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 coordinate the activities of different organs


Multicellular organisms need a communication system because they are large and there are many differentiated/specialised cells, tissues and organs that require instruction as a way of responding to internal/external stimuli. This is important as certain conditions are required internally for enzymes and optimum activity. 

Example internal changes: metabolic activity, blood pH, concentration of O2 .

Example external changes: temperature, light intensity, time of day, weather.

(b) state that cells need to communicate with each other by a process called cell signalling


Cells need to communicate with each other via Cell Signalling.

(c) state that neuronal and hormonal systems are examples of cell signalling


Neural and Hormonal systems are examples of cell signalling.

(d) define the terms negative feedback, positive feedback and homeostasis


Homeostasis: The maintenance of the internal environment in a constant state, despite external changes.

Negative Feedback: A process that brings about a reversal of any change in conditions. It ensures an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change.

Positive Feedback: A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis.

(e) explain the principles of homeostasis in terms of receptors, effectors and negative feedback


(taken from

(f) 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 muscles


-Ectotherms - rely on external environment for heat.


Adaptation                                           How it helps                                 Example organism

Expose body to the sun         Enables more heat to be absorbed                        Snakes

Orientate body to sun       Exposes large surface area for more heat absorption   Locusts

Orientate body away from sun Exposes lower surface area so less heat is absorbed  Locusts

Hide in Burrow            Reduces heat absorption by keeping out of the sun            Lizards

Alter body shape               Exposes more/less surface area to the sun           Horned Lizards

Increase breathing                         Evaporates more water                                 Locusts

-Endotherms - generate heat internally.

Physiological Mechanisms to maintain body Temperature

Body Part      …


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