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Slide 1

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5.1.1 Communication and
Homeostasis
A Level Biology…read more

Slide 2

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Why we need communication systems
· To allow us to detect and respond to changes in both our internal and
external environments use the information to maintain a dynamic
equilibrium ­ all about enzymes**, changes that may affect enzyme
activity/ damage them include:
-pH
-temperature
-toxins/enzyme inhibition
-desiccation (drying out- substrates need to be in solution)
· To allow us to co-ordinate the activities of different organs
· **enzyme-controlled reactions of life can only take place if the conditions
are right, concentrations of chemicals e.g. glucose and sodium ions must
be kept within a narrow range, as must the pH and water balance of the
bodily fluids and the core temperature of the body…read more

Slide 3

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Nervous Endocrine
Electrical impulses and synapses Chemical messages
Sensory Glands
to · Can involve brain to
Relay/brain Bloodstream
· Communication to
to systems
Motor Target organs
Fast response -involuntary, not a
to · Cell signalling
Effector conscious thought
-voluntary, · Control responses
conscious thought to changes in the
-reflex environment Slow response
Short-living Longer acting…read more

Slide 4

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Cell Signalling
· Cells communicating with one another and the environment
· Cell signalling molecule fits into and binds to the receptor of a
specific/target cell (usually a glycoprotein or a glycolipid on their
plasma membrane)
· If it doesn't fit, it is not a target cell
· Paracrine signalling occurs between cells which are close
together, sometimes directly, sometimes via extracellular fluid
· Endocrine signalling involves signalling over large distances, often
where the signalling molecule is transported in the circulatory system…read more

Slide 5

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Cell Signalling
· Both communication systems essentially work in the same way:
Stimulus
Receptor cells
Communication (cell signalling)
Co-ordination (not always co-ordinated e.g. a reflex arc)
Effector
Response…read more

Slide 6

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Types of effector (what
Internal conditions controlled by enzymes: brings about a response):
· Temperature · Muscle
· Glucose concentration · Gland
· Water balance
· Heart rate
· Salt balance
· pH
· CO2 concentration
· Blood pressure
· Breathing rate Types of receptor:
· Heat
· Sound
· Light
Cell Signalling: · Pressure
· Paracrine (local) · Balance
· Synaptic (neurones) · Chemical (mouth and nose)
· Endocrine · Cell signalling
· Contact…read more

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