Download Why do cells need a stable environment?

Week 1
•
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.
•
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.
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What environment do cells need?
Right temperature
Right amount of
salts and glucose
Right pH
Right amount
of water
Right levels of
gases
enzymes
No toxins or
inhibitors
Responses to changes in the environment
• External environment – is the air, water or soil
around an organism.
• Any changes in the environment must be monitored
and the organism must respond in order to reduce
stress.
• This response may be behavioural or physiological.
Behavioural:
Physiological:
• The internal environment – refers to conditions
inside the body. The environment influencing cells
is the tissue fluid which surrounds them.
• The internal environment may change due to the
products of metabolism diffusing into the tissue
fluid. E.g. CO2 is a waste product of respiration. If
allowed to build up it changes the pH of the
environment and therefore enzyme action.
• Blood helps to maintain the internal environment
by removing wastes or toxins, preventing them
accumulating in the tissue fluid and allowing them
to be excreted.
Communication Systems
• Multicellular organisms need to pass information
between their different parts so they can
coordinate the response to changes in the internal
and external environment.
• For example, if food is seen or smelt, saliva is
produced.
Covers the
entire body
Allows inter cellular
communication
A good communication system
Can be short
or long term
Specific
Rapid
Cell signalling
• This is the process by which information is
passed from one cell to another.
• One cell releases a chemical that is detected
by another cell. The 2nd cell responds.
• There are 2 main cell signalling systems:
• Neuronal system, - a network of neurones
which signal across synapses, bringing about
rapid, short-term changes.
• Hormonal system, where blood transports
signals (hormones) which are recognized by
specific target cells. Hormones usually act
more slowly but have longer term effects.
What is the standard pathway which
enables cells to communicate with one
another?
Stimulus and response pathway
Stimulus
Receptor
Communication
system
Effector
Response
Receptors and effectors
• Receptors - monitor conditions inside the body. If
a change is detected, the receptor is stimulated
to communicate with the effector.
• Communication systems – may be nervous or
hormonal. They use cell signalling to transmit
messages to the effector.
• Effectors – are cells which respond to reverse the
change.