Communication and Homeostasis

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What is a stimulus?
A change in the environment that causes a response.
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What is a response?
A change in behaviour or physiology as a result of a change in the environment.
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What is the environment of cells in animals?
The tissue fluid which they are bathed/surrounded in.
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How does carbon dioxide build up disrupt enzyme action?
It changes the pH of the environment around cells.
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What is the composition of the tissue fluid maintained by?
The blood as it removes toxins in the tissue fluid.
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How are multicellular organisms more efficient than single-celled organisms?
Because their cells can be differentiated and therefore specialised to perform certain functions.
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What 5 things does a good communication system do?
Cover the whole body. Enable cells to communcate. Enable specific communication. Enable rapid communcation. Enable short and long term responses.
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What is cell signalling?
The way cells communicate by releasing a chemical that will be detected and form a response.
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What 2 major systems use cell signalling?
The neuronal system and the hormonal system.
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What is the neuronal system?
An interconnected network of neurones that signal to each other across synapse junctions.
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What is the hormonal system?
Uses the blood to transport signals in the form of hormones which will have been released by cells in an endocrine organ.
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What is homeostasis?
The maintenance of the internal environment in a constant state despite external changes.
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What is negative feedback?
The process that brings about a reversal of any change in conditions of the internal environment so that it is returned to a steady state or optimum position (its original condition).
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What pathway is involved in negative feedback?
Stimulus > receptor > cell signalling > effector > response.
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What are sensory receptors?
Internal receptors that monitor conditions in the body that detect changes and are stimulated by this to send a message.
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What are effector cells?
Cells that bring about a response that reverses changes detected by sensory receptor cells.
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What is positive feedback?
A process that increases any change detected by the receptors. It tends to be harmful.
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What are 2 examples of positive feedback?
When the body gets too cold. When the cervix is dilated during pregnancy.
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What hormone is release to incrase uterine contractions and stretch the cervix?
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What is an endotherm?
An organism that can control production and loss of heat to maintain their body temperature.
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What is an ectotherm?
An organism that relies on external sources of heat and behavioural activities to regulate their body temperature.
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What are 3 advantages of being an ectotherm?
Use less food in respiration. Able to survive long periods without food. Energy from food can be used for growth.
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What are 2 disadvantages of being an ectotherm?
Less active in cooler temperatures which requires them to warm up so they are at greater risk of predation. May have to store sufficient energy for winter if they are not capable of activity.
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What does an ectotherm do in cold or hot weather to absorb/lose heat?
Change its behaviour or physiology.
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What are 3 advantages of being an endotherm?
Maintaining a fairly constant body temperature. Can be active in cool temperatures. Can inhabit colder parts of the planet.
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What are 3 disadvantages of being an endotherm?
Most energy intake is to maintain body temperature. Require more food than ectotherms. Require more/extra food for growth.
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What 6 body components are used in temperature regulation in endotherms?
Sweat glands, lungs/mouth/nose, hairs, arterioles, hepatocytes, skeletal muscles.
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What monitors the blood temperature and core body temperature in endotherms?
The thermoregulatory centre in the hypothalamus of the brain.
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Why are sensory receptors energy transducers?
Because they convert one form of energy to another.
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What does a sensory receptor convert a stimulus into?
A nerve impulse which is a form of electical energy.
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What specialised channel proteins to neurones contain?
Those specific to either sodium or potassium ions.
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What type of sodium or potassium channels are in neurones?
Gated channel proteins.
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How many sodium ions are pumped out and how many potassium ions are pumped in?
3 sodium ions out for every 2 potassium ions in.
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What is transported out and in of a sodium/potassium ion pump?
Sodium ions out. Potassium ions in.
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What is a polarised membrane?
One that has a potential difference across it. It is at resting potential.
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What is depolarisation?
The loss of polarisation across the membrane. Caused by sodiumions entering the cell making it less negative with respect to the outside.
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What is a generator potential?
A small depolarisation caused by sodium ions entering thecell.
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What is an action potential?
When the threshold level is reached so enough sodium ions enter the cell so that the membrane is depolarised to +40mV.
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Where do sensory neurones carry action potentials from/to?
From a sensory receptor to the central nervous system (CNS).
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Where do motor neurones carry action potentials from/to?
From the central nervous system (CNS) to an effector.
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What do relay neurones connect?
Sensory and motor neurones.
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What is the myelin sheath?
A series of Schwann cells (that meet at nodes of Ranvier) that insulates the neurone from electrical activity in nearby cells.
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Where is the cell body of a motor neurone located?
In the central nervous system.
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Where is the cell body of a sensory neurone located?
Just outside the central nervous system.
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What connects both sensory and motor neurones to other neurones?
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What is the resting potential?
The potential difference across the neurone cell membrane while it is at rest. It is at around -60mV inside compared to the outside.
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What are voltage-gated channels?
Channels in the cell membrane that allow passage of charged particles or ions. Their gate can open and close in response to changes in the potential difference across the membrane.
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Are gated sodium ion channels open or closed at rest?
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What is the threshold potential?
A potential difference across the membrane of about -50mV which causes an action potential once it is reached.
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What is repolarisation?
When potassium ions diffuse out of the cell bringing the potential difference back to being more negative inside.
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What happens to the cell when it is hyperpolarised?
When the potential differents overshoots slightly (is even more negative).
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What is the refractory period?
A short time after each action potential where the cell membrane cannot reach another action potential.
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What are local currents?
The flow of ions along a neurone which is caused by an increase in concentration at one point and causes diffusion away from the region of high concentration.
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What is saltatory conduction?
The way that the action potential appears to jump from one node of Ranvier to the next.
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Do myelinated or non-myelinated neurone conduct action potentials quicker?
Myelinated neurones.
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What is a neurotransmitter?
A chemical that diffuses across the synaptic cleft to transmit a signal to the postsynaptic neurone.
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What are cholinergic synapses?
Ones that use acetylcholine as their neurotransmitter.
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What is the swelling at the end of the presynaptic neurone called?
The synaptic knob.
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What do specialised sodium ion channels in the postsynaptic membrane consist of?
5 polypeptide molecules. 2 with a special receptor site specific to acetylcholine to open the channels.
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How is acetylcholine released?
By exocytosis.
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What is acetylcholinesterase?
An enzyme in the synaptic cleft used to break down acetylcholine.
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How does acetylcholinesterase break down acetylcholine?
By hydrolising it to ethanoic acid and choline.
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How are ethanoic acid and choline recycled to acetylcholine?
By using ATP from respiration.
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What is summation?
The way that several small potential changes can combine to produce one larger change in potential difference across the membrane.
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Does the presynaptic or postsynaptic knob contain vesicles and why?
The presynaptic knob to ensure signals are transmitted in the correct direction.
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What is acclimatisation?
Where repeated stimulation causes the synapse to be fatigued so that the nervous system no longer responds to the stimulus.
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How does the brain determine the intensity of a stimulus?
By the frequency of the signals arriving. Higher frequency means more intense stimulus.
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What is a hormone?
Molecules released by the endocrine glands directly into the blood acting as messengers to carry a message to a target organ or tissue.
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What is an exocrine gland?
One that secretes molecules into a duct that carries molecules to where they are used.
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What is an example of exocrine glands?
The salivary glands.
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What are the 2 types of hormones?
Protein/peptide/derivatives of amino acids. And steroid.
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How are steroid hormones different to protein hormones?
They can pass through the membrane of a cell to have a direct effect on the DNA.
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What type of protein is adrenaline?
An amino acid derivative.
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What is adenyl cyclase?
An enzyme associated with receptors for hormones (such as adrenaline) on the inside of the cell surface membrane.
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In the action of adrenaline, what are the first and second messengers?
First is the adrenaline molecule. Second is cyclic AMP (cAMP).
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What does cyclic AMP (cAMP) do inside a cell?
Activates enzyme action to cause the desired effect.
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Where are the adrenal glands?
Just above the kidneys.
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What do the adrenal medulla's cells do?
Manufacture and released adrenaline in response to stress or shock.
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What does the adrenal cortex do?
Uses cholesterol to produce steroid hormones.
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What are mineralocorticoids and what is an example?
Steroid hormones that help control concentrations of sodium and potassium in the blood. An example is aldosterone.
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What are glucocorticoids and what is an example?
Steroid hormones that help control the metabolism of carbohydrates and proteins in the liver. An example is cortisol.
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What is the exocrine function of the pancreas?
To manufacture and release digestive enzymes.
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What is the pancreatic duct?
A tube that collects all the secretions from the exocrine cells in the pancreas and carries the fluid to the small intestine.
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Fluid in the pancreatic duct contains which 3 enzymes?
Amylase, trypsinogen and lipase.
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What does sodium hydrogencarbonate in the pancreatic duct fluid do?
Neutralises the contents of the digestive system that have been in the acidic stomach environment.
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What type of cells are in the islets of Langerhans?
Alpha (a) cells and beta (b) cells.
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What do alpha cells manufacture and secrete?
Hormone glucagon.
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What do beta cells manufacture and secrete?
Hormone insulin.
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Which cell type detects a high blood glucose concentration?
The beta cells in the islets of Langerhans.
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Which cell type detects a low blood glucose concentration?
The alpha cells in the islets of Langerhans.
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What is diabetes mellitus?
A disease in which blood glucose concentrations cannot be controlled effectively.
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What is hyperglycaemia?
When blood glucose concentration is too high.
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How can type I diabetes be treated?
Using insulin injections and monitoring blood glucose concentrations.
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How can type II diabetes be treated?
Careful control of diet. May be supplemented by insulin injections.
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What does myogenic mean?
Muscle tissue that can initiate its own contractions, like the heart muscle.
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What is the sinoatrial node? (SAN)
The pacemaker in the right atrium wall that generates an impulse to initiate the contraction of heart chambers.
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What is the medulla oblongata?
A part of the brain that coordinates unconscious functions such as heart rate and breathing.
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What is in the medulla oblongata?
The cardiovascular centre.
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What does the accelerator nerve between the medulla oblongata and SAN do?
Send signals to the SAN to increase the heart rate.
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What does the vagus nerve between the medulla oblongata and SAN do?
Send signals to the SAN to decrease the heart rate.
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What receptors detect the movement of the limbs?
Stretch receptors in the muscles.
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What is change in pH of blood plasma detected by?
Chemoreceptors in carotid arteries, aorta and brain.
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What is blood pressure monitored by?
Stretch receptors in the walls of the carotid sinus in the carotid artery.
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What is a response?


A change in behaviour or physiology as a result of a change in the environment.

Card 3


What is the environment of cells in animals?


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Card 4


How does carbon dioxide build up disrupt enzyme action?


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Card 5


What is the composition of the tissue fluid maintained by?


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