Communication & Homeostasis (4.1.1)

What is cell signalling?
Information passed from one cell to another.
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What are the two main forms of cell signalling?
Hormones and nerves.
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What is a stimulus?
Any change in the environment which causes a response.
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What is a response?
A change in behaviour and/or physiology as a result of a stimulus.
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Describe how the external environment may change slowly.
As the seasons pass- summer to autumn.
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Describe how the external environment may change quickly.
The changes from day to night.
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What is the waste product released from cells?
Carbon dioxide.
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Why must carbon dioxide not be allowed in the tissue fluid?
When carbon dioxide dissolves, it creates an acidic solution (carbonic acid) and a reduction in pH. This would affect enzymes and cellular reactions.
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What should the pH of tissue fluid be?
pH 7.4
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What acts as a stimulus to remove the waste from cells?
The accumulation of waste products in the internal environment.
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How is the internal environment maintained?
The composition of tissue fluid is maintained by blood flow. Tissue fluid is constantly being made at the arteriole end of a capillary and carried away at the venule end. Any waste products are carried away from cells this way and are then excreted.
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Why is important that the concentrations of all substances in the blood are closely monitored?
To ensure that the body doesn't excrete too many useful substances, but removes enough waste to remain in good health.
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Why is a multi-cellular organism more efficient than a single-celled organism?
The cells are differentiated- they become specialised to perform a particular function.
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What are the features of a good communication system?
Covers the whole body. Enables cells to communicate with each other. Enable specific communication. Enable rapid communication. Enable both short-term and long-term responses.
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How is the short-term control brought about?
Using the nervous system- a system of interconnected neurones. These signal to each other across synapses and they conduct nerve impulse signals very quickly. This enables very rapid responses to stimuli in a changing environment.
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What does the nervous system consist of?
The CNS (central nervous system- brain and spinal chord) and the PNS (peripheral nervous system- in the limbs).
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How is the long-term control brought about?
Using the hormonal system which involves being transported in the bloodstream to target tissues. Hormones are made in special endocrine glands and released directly into the blood. The system allows longer term response to stimuli to be coordinated.
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What is the difference between endocrine and exocrine?
Endocrine is released without ducts, directly into blood. Exocrine is released without a duct.
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What is homeostasis?
Keeping the internal environment constant despite any changes in the external environment.
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What conditions in the body have to be kept constant?
Temperature- affects enzymes. Blood glucose conc.- needed for cell respiration. Blood water potential & salt conc.- to control osmosis. Blood carbon dioxide conc.- acidic when dissolves, affects enzymes. Blood pressure-ensure optimum circulation rate
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What is negative feedback?
The reversal of a change in the internal environment to return it back to its optimum position.
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What processes must occur for negative feedback to occur?
Any change in the internal environment must be detected. The change must be signalled to other cells. There must be a response that reverses the change.
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Describe the general process of negative feedback?
Optimum conditions. Change away from optimum conditions. Sensory receptors detect change. Communication system informs effector (cell signalling). Effector acts to reverse the change. Conditions return back to normal.
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What are sensory receptors?
Specialised group of cells that monitor conditions inside the body and at the body's surface. If they detect a change, they will be stimulated to send a message.
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What is a communication system?
The nervous and hormonal systems signal between cells in different parts of the body.
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What are effector cells?
The cells making up muscles and glands. They bring about responses to reverse the changes detected by the receptors.
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Why will a negative feedback system not maintain a perfectly constant set of conditions?
There's a short delay between a factor changing and being detected by a receptor. Then another slight delay while the receptor communicates with the effector. Then another delay while the effector responds.
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What is positive feedback?
When there is a response to increase the original change. It's usually not a good thing.
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What is an example of positive feedback?
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How does hypothermia demonstrate positive feedback?
Below a certain temperature, the enzymes in the body become less active so reactions will slow down & less heat will be generated. This will cool the body down further, slowing down enzyme reactions even more.
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What happens in hyperthermia?
Too hot, so faster enzyme rate of reaction. More heat energy and so a faster rate of reaction to a point where the body shuts down.
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Give an example of when positive feedback can be useful.
Bringing about the dilation of the cervix for childbirth. As the cervix begins to stretch, a signal is sent to the pituitary gland in the brain, which then secretes oxytocin. This increases uterus contractions, which stretches the cervix more..etc.
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Why do women release oxytocin when under stress?
It results in a tendency to pacify or protect. It prompts a mother to protect her children.
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Other cards in this set

Card 2


What are the two main forms of cell signalling?


Hormones and nerves.

Card 3


What is a stimulus?


Preview of the front of card 3

Card 4


What is a response?


Preview of the front of card 4

Card 5


Describe how the external environment may change slowly.


Preview of the front of card 5
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