Extensive notes tailored to the specification points for OCR 2015 (new) Spec, needed for both the AS and A2 components.
My revision from then got me an A* equivalent raw mark last year, and I received an A* at A2.
They contain as much if not more information than your textbook, in a much more c...
(a) The need for communication systems in multicellular organisms
● To include the need for animals and plants to respond to changes in the internal and
external environment and to coordinate the activities of different organs.
All living organisms need to maintain a certain set limited set of conditions inside their cells—
including suitable temperature, pH, aqueous environment that keeps substrates and products in
solution, and freedom from toxins and excess inhibitors.
Communication systems are needed to maintain the constant internal environment in a changing
external environment. As the external environment changes, it places stress on living organisms.
For example, a cooler environment will increase heat loss. In order to survive these changes
must be monitored and the organism must change its behaviour and physiological process to
reduce the stress. This occurs through the hormonal system. More immediate changes in the
external environment require quicker response, and thus a quicker communication of the
stimulus through the neuronal system.
Communication systems allow organisms to respond to a changing internal environment. The
metabolic processes of cells alter the internal environment, reducing the concentration of
substrates, and increasing the concentration of products, which may be toxic. In order for the
metabolic processes to be maintained, these changes must be offset, requiring detection of the
changing conditions and communication between cells to offset the changing internal
environment. For example, if carbon dioxide levels increase in the blood, it lowers the pH of the
tissue fluid, which can disrupt the action of enzymes. Communication between chemoreceptors
in the blood, the brain, and the gaseous exchange system are required to offset this change.
As multicellular organisms cells are differentiated to perform their various functions such as
gaseous exchange more efficiently, with groups of specialised cells performing a specific
function forming tissues and organs, a good communication system is needed to ensure that
different organs working together to perform the same function, such as excretion of waste work
together effectively even if they are not adjacent to each other. For example, the receptor may be
far away from the effector.
A good communication system, then, will cover the whole body, enable cells to communicate
with each other, enable specific communication, rapid communication, and short and long term
responses.
(b) The communication between cells by cell signalling
● To include signalling between adjacent cells and signalling between distant cells.
The two major systems of communication that work by cell signalling between distant cells are
the neuronal system and the hormonal system.
The neuronal system is a network of interconnected neurons 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.
The hormonal system uses the blood to transport chemical signals. Cells in endocrine glands
release a hormone directly into the blood and it is transported throughout the body, but it only
recognised by target cells with the a complementary cell-surface receptor to the shape of the
signalling molecule. The hormonal system enables longer-term responses to be coordinated.
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