F214-Communication, Homeostasis and Energy
Module 1-Communication and Homeostasis
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
Cells need to communicate to ensure that the different parts of the body work
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
o Interconnected network of neurones that signal to each other across
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
d. Define the terms negative feedback, positive feedback and homeostasis
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.
o Process that increases the change detected by the receptors.
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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
1. Sensory receptor
Internal receptor to monitor conditions inside the body.
If a change is detected they will be stimulated to send a message.
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.
evaporates from moist Spread out limbs to
areas using latent heat increase surface area to
from the blood. lose heat from.
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
o Carry the action potential from a sensory receptor to the Central
o Surrounded by the myelin sheath which is made up of Schwann cells. The
gaps where the cells meet are known as the nodes of Ranvier.
Describe and explain how the resting potential is established and maintained
When the neurone is not transmitting an action potential it is said to be at rest.
The neurone is not actively transporting ions across its cell surface membrane.
It is about -60mV inside the cell compared to the outside.
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.
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.
In the peripheral nervous system In the Central Nervous System and
carrying impulses from sensory in the nerves controlling the organs
receptors to the Central Nervous with no conscious control.
System or from the Central Action potential moves in a wave.
Nervous System to the effector. Carry signals over a short distance.
Action potential moves via
Carry signals over a longer
i. Describe the structure of a cholinergic synapse
Cholinergic synapse=A synapse that uses acetylcholine as the neurotransmitter.
Allow several presynaptic neurones to converge into one postsynaptic neurone
to allow signals from different parts of the nervous system to create the same
Allow one presynaptic membrane to diverge into several postsynaptic neurones
to allow one signal to be passed to several parts of the body.
Ensure that signals are transmitted in the right direction.
To filter out unwanted low level signals.
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
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.
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.
o This is at the Islets of Langerhans which is split up into and cells.
cells secrete glucagon.
cells secrete insulin.