OCR F214 Communication

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F214 Module 1: Communication and Homeostasis
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
All living things to maintain a certain limited set of conditions inside their cells as cellular activity relies on the
action of enzymes which only work efficiently at optimum conditions :
a suitable temperature ­ optimum for enzyme.
a suitable pH ­ optimum for enzyme.
an aqueous environment that keeps the substrates and products in solution ­ enzymesubstrate
complexes can easily form as the molecules are quite close together.
freedom from toxins and excess inhibitors ­ inhibit the enzyme.
Internal Environment External Environment
The internal environment in animals is the tissue The external environment will fluctuate ­ it may place
fluid. Unwanted or toxic products (CO2 , NH3
, etc)
stress on the living organism, e.g. a cooler
from metabolic reactions diffuse out of the cell into environment will cause a greater heat loss. The
the tissue fluid the activities of the cells alter their environmental change is the stimulus and the way in
own environment . The accumulation of excess waste which the organism changes its behaviour or
or toxins acts as a stimulus to cause removal of these physiology is its response . The external environment
wastes so that the cell can survive the response. The consists of: temperature , light intensity , humidity , air
composition of the tissue fluid is maintained by the pressure , pH , oxygen concentration , nutrients ,
blood . predators , etc.
(b) state that cells need to communicate with each other by a process called cell signalling
Cells communicate with each other by the process of cell signalling . This is where one cell releases a chemical
that is detected by another cell and will respond to the signal released by the first cell.
(c) state that neuronal and hormonal systems are examples of cell signalling
There are two major systems of communication that work by cell signalling:
Neuronal system an interconnected network of neurones that signal to each other across synapse
junctions. The neurones can conduct a signal very quickly and enable rapid responses to stimuli that may
be changing quickly.
Hormonal system uses the blood to transport its signals. Cells in an endocrine organ release the signal (a
hormone ) directly into the blood, where it is carried all over the body but only recognised by specific
target cells . The hormonal system enable longerterm responses to be coordinated.

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F214 Module 1: Communication and Homeostasis
(d) define the terms negative feedback, positive feedback and homeostasis
(e) explain the principles of homeostasis in terms of receptors, effectors and negative feedback
Negative feedback ­ a process that brings about the reversal of any change in conditions. It ensures that an
optimum steady state can be maintained, as the internal environment is returned to its original set of conditions
after any change. It is essential for
homeostasis .…read more

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F214 Module 1: Communication and Homeostasis
Homeostasis ­ the maintenance the internal environment in a constant state despite external changes, so
enzymes can work at an optimum .
(f) describe the physiological and behavioural responses that maintain a constant core body temperature in
endotherms and endotherms, with reference to peripheral temperature receptors, the hypothalamus and
effectors in skin muscles
Ectotherms organisms that relies on external sources of heat to regulate its body temperature.…read more

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F214 Module 1: Communication and Homeostasis
Ectotherms Endotherms
Physiologic A lizard with frills can absorb more heat. Sweating water in sweat evaporates ,
al The horned lizard can alter its surface using heat from blood to supply latent heat
area by expanding or contracting its rib of vaporisation .
cage . Panting increases evaporation of water
Locusts increase their abdominal from lungs, tongue and other moist
breathing movements to increase surfaces.
evaporation of water and aid cooling .…read more

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