F214 module 1 Communication and homeostasis

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F214-Communication, Homeostasis and Energy
Module 1-Communication and Homeostasis
4.1.1 Communication
a. Outline the need for communication systems within multicellular organisms
External environmental changes
o Changes in the external environment can cause stress.
o It may change slowly so there will be a gradual response.
o It may be a quick change so a rapid response is needed.
Internal environmental changes
o The environment of internal cells is that they are protected by epithelial
cells and they are bathed in tissue fluid.
o The activities of cells alter their environment e.g. releasing toxic
products that need to be removed.
Coordination of activities of organs
o Groups of specialised cells form tissues and organs.
o Cells monitor the blood and can release a substance into the blood to
remove certain substances.
b. State that cells need to communicate with each other by a process known as
cell signalling
Cells need to communicate to ensure that the different parts of the body work
together effectively.
Cell signalling -The process where one cell releases a chemical that is detected
by another cell which will react and respond to the signal.
c. State that neuronal and hormone systems are examples of cell signalling
Neuronal systems
o Interconnected network of neurones that signal to each other across
synapse junctions.
Hormonal systems
o The blood is used to transport signals.
o Cells in an endocrine organ release a hormone which is the signal into the
blood which is then carried around the body and recognised by specific
target cells.
d. Define the terms negative feedback, positive feedback and homeostasis
Negative feedback
o Process that brings about a reversal of any change in conditions.
o Maintains and optimum steady state due to the return of the internal
environment to its original set of conditions.

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Positive feedback
o Process that increases the change detected by the receptors.
o It destabilises the system meaning that it tends to be harmful.
o This is when the internal environment is kept constant even though there
are external changes.
o It can include conditions such as body temperature, blood glucose
concentration, blood pressure and carbon dioxide concentration.
e. Explain the principles of homeostasis in terms of receptors, effectors and
negative feedback
1. Sensory receptor
Internal receptor to monitor conditions inside the body.…read more

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Orientate body away from
the sun to expose a smaller
surface area to the sun.
Move higher up a plant to
get away from the hot
ground e.g. locusts.
Endotherms Secrete more sweat onto Move into shade.
skin so the water in the Hide in burrow.
sweat evaporates using Orientate body away from
latent heat from the the sun to expose a smaller
blood. surface area.
Increase panting so water Remain inactive.…read more

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The movement of the sodium ions causes a change in the potential
difference so the inside of the cell is less negative. This is called
o A generator potential is caused when one or two sodium ion channels
open and if more open and enough sodium ions enter the cell and action
potential will be initiated.
b. Describe the structure and function of sensory and motor neurones
Sensory neurones
o Carry the action potential from a sensory receptor to
the Central Nervous System.…read more

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ATP is used to pump three sodium ions out of the cell for every two potassium
ions pumped in.
The cell membrane is polarised because there is a potential difference across it.
d. Describe and explain how an action potential is generated
When some of the sodium ion channels open causing some of the sodium ions to
diffuse down their concentration gradient into the cell causing a depolarisation
of the membrane.…read more

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The membrane is at its resting potential and is polarised.
2. Sodium ion channels open and some sodium ions diffuse into the cell. The
membrane depolarises as it becomes less negative the outside and reaches the
threshold of -50mV. Voltage-gated sodium ion channels open and sodium ions
flood in making the inside of the cell positively charged compared to the
outside. The potential difference reaches +40mV.
3. Sodium ion channels close and potassium channels open.…read more

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Compare and contrast the structure and function of myelinated and
non-myelinated neurones
Myelinated neurones Non-myelinated neurones
Fast speed of conduction- Slow speed of conduction-
100-200ms-1. 0.5-10ms-1.
Has nodes of Ranvier. Does not have nodes of Ranvier.
Has a myelin sheath with each Does not have a myelin sheath but
neurone wrapped in several several neurones may be
Schwann cells. surrounded by one Schwann cell.…read more

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Sodium ion channels open.
9. Sodium ions diffuse into the postsynaptic neurone.
10. A generator potential is created.
11. If there are enough generator potentials then it will reach the threshold
potential creating a new action potential in the postsynaptic neurone.
k. Outline the roles of synapses in the nervous system
Connect two neurones together so a signal can be passed from one to another.…read more

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Adrenaline is the first messenger.
When the adrenaline binds it makes the Adenyl Cyclase active.
The Adenyl Cyclase converts ATP to Cyclic AMP.
Cyclic AMP is the second messenger and it activates enzyme action in the cell.
c. Describe the function of the adrenal glands
Adrenal glands
o They lie just above the kidneys, one on each side of the body.
o Each gland has a medulla and a cortex region.
o Adrenal medulla
In the centre of the gland.…read more

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Glucocorticoids control the metabolism of carbohydrates and
proteins in the liver.
d. Describe the histology of the pancreas and outline its role as an endocrine
and exocrine gland
Exocrine function
o Secretes enzymes.
o Manufactures and secretes digestive enzymes.
o The tubules join up to make the pancreatic duct.
o Enzymes are released in a fluid. The enzymes in the fluid are: Amylase,
Trypsinogen and Lipase.
o Also contained in the fluid is sodium hydrogencarbonate.…read more


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