MODULE 1 UNIT 1

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Define Homeostasis
Maintenance of the internal environment in a constant state despite external changes.
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Describe negative feedback.
Optimum condition > change away from optimum > receptor detects change > communiction system informs effector > effector reacts to reverse change > return to optimum conditions
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Define positive feedback
A process that increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis.
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What is an ectotherm?
An organism that relies on external sourses of heat to regulate its body temperature.
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Name advantages of being an ectotherm
Ectotherms use less food in respiration so can survive with long periods of time without food. A greater proportion of the energy obtained from food can be used for growth.
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Describe some disadvantages of being an ectotherm.
Less active in cooler temperatures and may need to warm up in the morning before they can be active which makes them vunerable, e.g lizzards. Ectotherms must survive on energy stores over winter without eating.
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Describe some adaptations of an ectotherm and how it helps to regulate temperature.
Ectotherms can hide in burrows to reduce heat absorption by keeping out of the sun. Ectotherms can increase breathing movements to evaporate more water.
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Give three examples of ectotherms.
Lizzards, snakes and locusts
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What is meant by an endotherm?
An organism that can use internal sourses of heat, such as heat generated from metabolism in the liver, to maintain its body temperature.
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What part of the brain in endotherms monitors blood temperature?
Hypothalamus
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Describe what happens in an endotherm when there is a rise in core temperature.
Thermoregulatory centre in hypothalamus detects change > nervous system and hormonal system carry signals to skin, liver and muscles > less heat generated and more lost >temperature falls
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Describe what happens in an endotherm when there is a fall in core temperature?
Thermoregulatory centre in hypothalamus detects change > nervous system and hormonal system carry signals to skin, liver and muscles > more heat generated and less heat lost > temp rises
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What happens to sweat glands in the skin if core body temp is too high?
Secrete more sweat onto skin > water in sweat evaporates, using heat from blood supply latent heat of vaporisation
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Explain how vasodilation helps to increases heat loss
Vasodilation allows more blood into capillaries near the skin surface, more heat can be radiated from the skin, which, in pale skinned people may look red
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Explain how the liver can help us to warm up.
The liver increases the rate of metabolism, therefore respiration generates more heat, which is transferred to the blood.
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The peripheral temp receptors in the skin monitor the temperature in the...
extremities.
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What are the advantages to being an endotherm?
Fairly constant body temperature despite external conditions, activity possible when external temperatures are cool, ability to inhabit colder parts of planet
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What energy changes are detected by muscle spindles?
Length of muscle fibres
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What energy changes are detetced by Pacinian corpuscles in the skin?
Pressure on skin
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Which receptors detect the presence of soluble chemicals?
Taste buds in the tongue, hard palate, epiglottis and the first part of the oesophagus
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Which receptors detect the presence of volatile chemicals?
Olfactory cells lining the inner surface in the nasal cavity.
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What are sensory receptors?
Energy transducers that convert one form of energy to another (usually a nerve impulse).
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Define depolarisation.
The loss of polarisation across the membrane. It refers to the period when sodium ions are entering the cell making the inside less negative with respect to the outside.
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What is a polarised membrane?
A membrane which has a potential difference across it . This is the resting potential.
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What are the similarities between a motor and sensory neurone?
They both have an axon coated with fatty myelin sheath, this is made from Schwann cells.
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What are the differences between a sensory and motor neurone?
In a motor neurone the cell body is in the CNS at the end of the neurone, but in sensory the cell body is not in CNS and is in the middle of the neurone. A motor neurone has a longer axon than a sensory.
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Describe how the resting potential is set up.
Sodium/potassium ion pumps use ATP to pump 2K+ ions into the cell and 3Na+ ions out of the cell. This means the inside of the cell will me more negative, making the membrane polarised.
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Define resting potential.
The potential difference across the neurone cell membrane while the neurone is at rest. It is about -60mV inside the cell compared with the outside.
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What is an endocrine gland?
A gland that secretes hormones directly into the blood. Have no ducts.
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What is an exocrine gland?
A gland that secretes molecules into a duct that carries the molecules to where they are used.
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What are the two types hormones?
Protein and peptide hormones, and derivatives of amino acids. Steroid hormones.
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Outline the action of adrenaline.
Adrenaline receptor on the outside cell surface membrane complementary to adrenaline. Adrenaline(the first messenger) activates the enzyme adenyl cyclase. The adenyl cyclase converts ATP to cyclic AMP (cAMP- 2nd messenger) -causes effect inside cell.
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Define: first messenger
The first messenger is the hormone that transmits a signal around the body.
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What is the role of the adrenal cortex?
The adrenal cortex uses cholesterol to produce steroid hormones.
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What are the names and functions of the steroid hormones produced by the adrenal cortex.
Mineralcorticoids help to control the concentrations of sodium and potassium in the blood. Glucocorticoids help to control the metabolism of carbohydrates and proteins in the liver.
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Name a few effects of adrenaline in the body.
Relax smooth muscle in bronchioles. Increases stroke volume of heart. Increases heart rate. Causes vasoconstriction to raise BP. Stimulates glycogenolysis. Dilates pupils. Causes erect body hair.
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Outline the exocrine function of the pancreas.
Pancreatic cells surrounding small tubules secrete digestive enzymes. The tubules join to make up the pancreatic duct, which carries fluid containing enzymes such as amylase, trypsinogen and lipase, into the first part of the small intestine.
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Why might 'pancrearic fluid' contain sodium hydrogencarbonate?
So that the fluid is alkaline. This helps to neutralise the contents of the digestive system that have just left the acid environment of the stomach.
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Outline the endocrine function of the pancreas.
The endocrine function is to secrete hormones insulin and glucagon directly into the blood. Alpha cells produce glucagon, and Beta cells produce Insulin. A and B cells make up Islets of Langerhanss.
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Outline what happens if blood glucose rises too high.
It is detected by B-cells in the Islets of Langerhans, which then secrete insulin. The insulin is detected by receptors on hepatocytes and muscle cells. The hepatocytes and muscle cells remove glucose from blood and convert glucose to glycogen.
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What effects does insulin have on a cell?
More glucose channels are placed into the plasma membrane. More glucose enters the cell. Glucose in the cell is converted to glycogen for storage (glycogenesis). More glucose is converted to fats. More glucose is used in respiration.
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Whats effects does glucagon have on a cell?
Conversion of glycogen to glucose (glycogenolysis). Use of more fatty acids in respiration. The production of glucose by conversion from amino acids and fats ( gluconeogensis)
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Outline what happens if blood glucose falls too low.
It is detected by alpha cells in the islets of langerhans. The alpha cells secrete glucagon into the blood. Glucagon is detected by receptors on hepatocytes which then convert glycogen to glucose and release glucose into the blood.
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What is type I diabetes?
Type I diabetes is a disease where the body can no longer make sufficient insulin and cannot store excess glucose as glycogen.
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What are the causes of type I diabetes?
It is thought to be caused as a the result of an autoimmune response in which the body's own immune system attacks the B-cells and destroys them. It may also be caused by a viral attack.
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How can type I diabetes be treated?
With insulin injections. Blood glucose concentration must be monitered and the correct dose of insulin must be given.
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What is type II diabetes?
'Non-insulin dependent diabetes'. A person with type II can still produce insulin, however their responsiveness to insulin has declined.
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What are the causes of type II diabetes?
The specific receptors on the surface of liver and muscle cells decline with ageing and the cells lose their ability to respond to the insulin in the blood. The levels of insulin secreted may also decline.
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How is type II diabetes treated?
Type II is treated by controlling diet carefully. This may be supplemented by insulin injections or other drugs that slow down the absorption of glucose from the digestive system.
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What is meant by myogenic muscle?
Myogenic muscle tissue initiates its own contractions.
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How does movement of limbs increase heart rate?
Stretch receptors in muscles send impulses to the medulla oblongata, which then sends impulses down the accelerator nerve which secretes noradrenaline to increase the HR.
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How do levels of CO2 affect heart rate?
Exercise = more CO2, this reduces the pH of the blood.The change is detected by chemoreceptors in the carotid arteries, aorta and brain. The chemoreceptors send impulses to the MO which sends impulses down the accelerator nerve to SAN increase HR.
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How might heart rate be reduced?
When heart rate is high the BP high, this is detected by baroreceptors in the walls of the carotid sinus,impulses are sent to the medulla oblongata which then sends impulses down the vagus nerve which secretes acytlcholine to decrease heart rate.
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What is the role of acetylcholinesterase?
Acetylcholinesterase hydrolyses the acetylcholine to ethanoic acid and choline. This stops the transmission of signals so that the synapse does not continue to produce action potentials in the postsynaptic neuron.
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What is a neurotransmitter?
A chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone.
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What is meant by saltatory conduction?
Jumping condction. It refers to the way that the action potential appears ti jump from one node of ranvier to the next.
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What is a generator potential?
A small depolarisation caused by sodium ions entering the cell.
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What is temporal summation?
Several successive action potentials in a pre synaptic neurone. The release of many vesicles of acetylcholine over a short period of time will enable the postsynaptic generator potentials to combine together to produce an action potential.
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What is spatial summation?
Several presynaptic neurones may each contribute to producing an action potential in the post synaptic neurone. Several presynaptic neurones each release a small number of vesicles into one synapse.
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Card 2

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Describe negative feedback.

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Optimum condition > change away from optimum > receptor detects change > communiction system informs effector > effector reacts to reverse change > return to optimum conditions

Card 3

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Define positive feedback

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Card 4

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What is an ectotherm?

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Card 5

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Name advantages of being an ectotherm

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