F214 Biology 0CR

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Communication, Homeostasis & Energy
Communication & Homeostasis
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 co-ordinate the activities of different organs.
Organisms need to respond to external stimuli, e.g. temperature, oxygen concentration and levels of
sunlight. These may be over time, e.g. winter fur to summer fur, or quickly, e.g. changing size of pupils.
Internal environments change too- the build up of carbon dioxide as a result of respiration changes the pH
of the tissue fluid, and therefore inhibits enzyme activity. Multicellular organisms need to coordinate
different organs, so this requires a good communication system which will:
· Cover the whole body
· Enable cells to communicate with each other
· Enable specific communication
· Enable rapid communication
· Enable both short and long-term responses.
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.
Define the terms negative feedback, positive feedback and homeostasis.
Negative feedback- A process in which any change in a parameter brings about the reversal of that change
so that the parameter is kept fairly constant.
Positive feedback- A process in which any change in a parameter brings about an increase in that change
Homeostasis- The maintenance of a constant internal environment despite external changes
Explain the principles of homeostasis in terms of receptors, effectors and negative feedback.
Any change is detected by receptors, the communication system transmits a message from the receptor to
the effector and, through negative feedback, the effectors reverse the change.
Describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms
and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and
To maintain a constant core body temperature, ectotherms have physiological and behavioural responses;
The horned lizard expands its ribcage and the frilled lizard uses its frill to expand its surface
area to absorb more heat from the sun
Locusts increase their abdominal breathing movements to increase water loss when hot
Snakes expose their body to the sun so more heat is absorbed
Locusts orientate their body towards the sun to expose a larger surface area & so more
heat is absorbed. By orientating their body away from the sun, more heat is lost.
Lizards hide in burrows to prevent heat absorption by staying out of the sun.
To maintain a constant core body temperature, endotherms have physiological and behavioural
Sweat glands
When hot they secrete sweat onto the skin. Water evaporates using heat from the
blood to supply latent heat of vaporisation.
When cold, less sweat is secreted, less water evaporates and so less loss of latent heat
Lungs, nose and mouth
When hot, panting increases water evaporation from lungs, tongue and moist
surfaces. Loss of latent heat as above.
When cold, no panting, less water evaporates, no loss of latent heat.
Hairs on skin
When hot, the hairs lie flat, providing little insulation, meaning heat can be lost
through convection and radiation.
When cold, hairs raise to trap a layer of air, insulating the skin and reducing heat
Arterioles leading to capillaries in skin
Hot- vasodilatation allows more blood to capillaries near skin surface, so heat can
be radiated from skin
Cold- vasoconstriction reduced the flow of blood through the capillaries near skin,
so less heat is radiated
Liver cells
Alex McCourt Jan 2010

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Communication, Homeostasis & Energy
Hot- reduce rate of metabolism so less heat is generated from exergonic reactions
e.g. respiration.
Cold- increased rate of metabolism so more heat is generated. Respiration
generates more heat which is transferred to the blood.…read more

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Communication, Homeostasis & Energy
Describe and explain how an action potential is transmitted in a myelinated neurone, with reference to the roles of
voltage-gated sodium ion and potassium ion channels.
The myelin sheath is an insulating layer of fatty material which Na and K ions cannot pass through. Between
the Schwann cells are gaps- called the Nodes of Ranvier, which contain Voltage-gated Sodium and Potassium
ion channels, allowing ionic exchange to occur. The action potential `jumps' from one node to the next-
Saltatory conduction.…read more

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Communication, Homeostasis & Energy
Outline the role of neurotransmitters in the transmission of action potentials.
A neurotransmitter is a chemical that diffuses across the cleft of the synapse to transmit a signal to the
postsynaptic neurone. They cause the generation of a new action potential in the postsynaptic neurone. In
cholinergic synapses the neurotransmitter is acetylcholine. It is stored in vesicles in the synaptic knob, and
when the action potential arrives, the voltage gated sodium ion channels open, so calcium ions diffuse out.…read more

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Communication, Homeostasis & Energy
Describe, with the aid of diagrams and photographs, the histology of the pancreas, and outline its role as an endocrine
and exocrine gland.
The cells surrounding exocrine gland of the pancreas secretes digestive enzymes into the pancreatic duct,
which then goes onto the small intestine. This is the majority of the pancreas.
The exocrine cells- the Islets of Langerhans- consist of and cells. The cells manufacture and secrete
glucagon, whereas the cells manufacture and secrete insulin.…read more

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Communication, Homeostasis & Energy
Discuss the use of insulin produced by genetically modified bacteria, and the potential use of stem cells, to treat diabetes
GM bacteria:
· Exact copy of human insulin.
o Faster acting.
o More effective.
· Less chance of developing tolerance.
· Less chance of rejection.
· Cheaper.
· More adaptable to demand.
· Less likely to have moral objections.
Stem cells
· Could be used to produce new cells.…read more

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Communication, Homeostasis & Energy
Define the term excretion.
Excretion: The removal of metabolic wastes from the body
Explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body.
Carbon dioxide must be removed as, when it dissolves in water is produces hydrogencarbonate ions. These
ions compete with oxygen for space on the haemoglobin. This causes a reduction in oxygen transport.
Carbon dioxide can also combine directly with haemoglobin to form carbaminohaemoglobin, which has a
low affinity for oxygen.…read more

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Communication, Homeostasis & Energy
Describe and explain the production of urine, with reference to the processes of ultrafiltration and selective
reabsorbtion.…read more

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Communication, Homeostasis & Energy
Outline the problems that arise from kidney failure and discuss the use of renal dialysis and transplants for the
treatment of kidney failure.
· Unable to remove excess water & waste products from the body
o E.g. urea & excess salts
· Inability to regulate urea and salt levels
· Death
Waste, excess fluids and salts are removed from the body by passing the blood over a dialysis membrane.…read more

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Communication, Homeostasis & Energy
Define the terms autotroph and heterotroph.
Autotroph-organisms that use light or chemical energy and inorganic molecules to synthesise complex
organic molecules.
Heterotroph- organisms that ingest and digest complex organic molecules releasing the chemical potential
energy stored in them.
State that light energy is used during photosynthesis to produce complex organic molecules.
Explain how respiration in plants and animals depends upon the products of photosynthesis.…read more


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