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54 Cards in this Set
- Front
- Back
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What is homeostasis? |
-the maintenance of a constant internal environment -it involves control systems that keep your internal environment roughly constant(within certain limits) -this means your internal environment is kept in a state of dynamic equilibrium |
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Why is it important to keep your internal environment constant? |
-it is vital for cells to function normally and to stop them from being damaged |
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Why is homeostasis particularly important? |
-it is important to maintain the right core body temperature and blood pH -this is because temperature and pH affect enzyme activity, and enzymes control the rate of metabolic reactions -its also important to maintain the right blood glucose concentration bc cells need glucose for energy and blood glucose conc affects the water potential of blood |
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How is the rate of metabolic reactions affected by temperature? |
-the rate increases when the temperature is increased -more heat means more KE, so molecules move faster -this makes more substrate molecules more likely to collide with the enzymes' active sites -the energy of these collisions also increases, which means each collision is more likely to result in a reaction |
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What happens if the temperature gets too high? |
-the reaction essentially stops -the rise in temperature makes the enzyme's molecules vibrate more -if the temperature goes above a certain level, this vibration breaks some of the hydrogen bonds that hold the enzymes in its 3D shape -the active site changes shape and the enzyme and substrate no longer fit together -at this point, the enzyme is denatured-it no longer functions as a catalyst |
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What happens if the temperature is too low? |
-If body temperature is too low enzyme activity is reduced, slowing the rate of metabolic reactions -the highest rate of enzyme activity happens at their optimum |
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What happens if blood pH is too high or too low? |
-enzymes become denatured -the hydrogen bonds that hold them in their 3D shape are affected so the shape of the enzyme's active site is changed and no longer works as a catalyst -the highest rate of enzyme activity happens at their optimum pH |
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What happens when blood glucose concentration is too high? |
-the water potential of blood is reduced to a point where water molecules diffuse out of cells into the blood by osmosis -this can cause cells to shrivel up and die |
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What happens if blood glucose concentration is too low? |
-cells are unable to carry out normal activities because there isn't enough glucose for respiration to provide energy |
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What is negative feedback? |
-homeostasis involve receptors, a communication system and effector -receptors detect when a level is too high or too low, and the information's communicated via the nervous system or the hormonal system to effectors -the effectors respond to counteract the change-bringing the level back to normal -the mechanism that restores the level to normal is called negative feedback mechanism |
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Give the negative feedback mechanism |
normal level->level changes from normal->receptors detect change->communication via nervous or hormonal system->effectors respond->level brought back to normal |
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How far will the negative feedback go?
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-negative feedback only works within certain limits though-if the change is too big then the effectors may not be able to counteract it |
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What does multiple negative feedback mechanisms mean
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-this is because having more than one mechanism gives more control over changes in your internal environment then just having one negative feedback mechanism |
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What does having multiple negative feedback mechanisms enable you to do/
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-if you only had one negative feedback mechanism, all you could do would be turn it on or turn it off -you'd only be able to actively change a level in one direction so it returns to normal -only one negative feedback mechanism means a slower response and less control |
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What is positive feedback? |
-the effectors respond to further increase the level away from the normal level |
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Give the positive feedback mechanism
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normal level->normal level changes->receptors detect change->communication via nervous or hormonal system->effectors respond->change amplified->normal level changes again |
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Why isn't positive feedback involved in homeostasis? |
-positive feedback is useful to rapidly activate processes in the body |
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How is positive feedback involved when a homeostatic system breaks down?
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-positive feedback can also happen when a homeostatic system breaks down -eg -hypothermia is low body temperature -it happens when heat is lost from the body quicker than it can be produced -as body temperature falls the brain doesn't work properly and shivering stops-this makes the body temperature fall even more -positive feedback takes body temperature further away from the normal level, and it continues to decrease unless action is taken |
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What are ectotherms?
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-this means the internal temperature of ectotherms depends on the external temperature |
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What is their metabolic rate like?
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-they generate v little heat themselves -this means that the activity level of ectotherms depends on the external temp too-they're more active at higher temps and less active at lower temps |
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What are endotherms? |
-this means that, compared to ectotherms, the internal temperature of endotherms is less affected by the external temperature |
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What is the metabolic rate of endotherms like? |
-they generate a lot more heat from metabolic reactions -this means that the activity level of endotherms is largely independent of the external temperature-they can be active at any temperature-within certain limits |
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Describe the body's mechanisms to lose heat
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1-sweating-more sweat is secreted from sweat glands when the body is too hot. The water in sweat evaporates from the surface of the skin and takes heat from the body. The skin is cooled 2-hairs lie flat-mammals have a layer of hair that provides insulation by trapping air. When it is hot, erector pili muscles relax so the hairs lie flat. Less air is trapped, so the skin is less insulated and heat can be lost more easily 3-vasodilation-when it's hot, arterioles near the surface of the skin dilate. More blood flows through the capillaries in the surface layers of the dermis. This means that more heat is lost from the skin by radiation and the temperature is lowered |
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Describe the body's mechanisms to produce heat |
2-hormones-the body releases adrenaline and thyroxine. These increase metabolism and so more heat is produced |
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Describe the body's mechanisms to conserve heat |
1-much less sweat-less sweat is secreted from sweat glands when it's cold, reducing the amount of heat loss 2-hairs stand up-erector pili muscles contract when it's cold, which make the hairs stand up. This traps more air and so prevents heat loss 3-vasoconstriction-when it is cold, arterioles near the surface of the skin constrict so less blood flows through the capillaries in the surface layers of the dermis. This reduces heat loss |
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How is body temperature in mammals maintained at a constant level? |
-the hypothalamus receives info about both internal and external temperature from thermoreceptors |
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How do these thermoreceptors interact with the hypothalamus?
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-info about external temperature comes from thermoreceptors in the skin that detect skin temperature -thermoreceptors send impulses along sensory neurones to the hypothalamus, which sends impulses along motor neurones to effectors. These neurones are part of the autonomic nervous system, so it's all done unconsciously. The effectors respond to restore the body temperature back to normal |
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What happens when the thermoreceptors detect body temperature is too high? |
-effectors respond to increase heat loss from the body and to reduce the amount of heat loss from the body and to reduce the amount of heat that's produced by the body -body temp then returns to normal |
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What happens when the thermoreceptors detect body temperature is too low?
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-effectors respond to produce more heat (eg. adrenaline and thyroxine are released to produce more heat) and to conserve it -body temperature then returns to normal |
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Why does blood glucose conc have to be carefully controlled? |
-the conc of blood is normally around 90mg per 100cm^3 of blood -it is monitored by cells in the pancreas -blood glucose conc rises after eating food containing carbohydrate -it falls after exercise, as more glucose is used in respiration to release energy |
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How does the hormonal system control blood glucose conc?
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-using two hormones called insulin and glucagon which are both secreted by clusters of cells in the pancreas called the islets of Langerhans |
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What do the islets of Langerhans contain? |
-beta cells secrete insulin into the blood -alpha cells secrete glucagon into the blood -insulin and glucagon act on effectors, which respond to restore the blood glucose conc to the normal level |
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What does insulin do? |
-it binds to specific receptors on the cell membranes of liver cells and muscle cells and increases the permeability of cell membranes to glucose, so the cells take up more glucose |
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What else do insulin do, in regards to enzymes? |
-liver and muscle cells are able to store glycogen in their cytoplasm, as an energy source -the process of forming glycogen from glucose is called glycogenesis -insulin also increases the rate of respiration of glucose, especially in muscle cells |
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What does glucagon do? |
-it binds to specific receptors on the cell membranes of liver cells and activates enzymes that break down glycogen into glucose-the process of breaking down glycogen is called glycogenolysis -glucagon also promotes the formation of glucose from glycerol and amino acids-the process of forming glucose from non-carbohydrates is called gluconeogenesis -glucagon also decreases the rate of respiration of glucose in cells |
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How do negative feedback mechanisms restore the glucose concentration to normal when there has been a rise in glucose concentration? |
-insulin then binds to receptors on liver and muscle cells (the effectors) -the liver and muscle cells respond to decrease the blood glucose concentration eg. glycogenesis is activated -blood glucose conc then returns to normal |
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How do negative feedback mechanisms restore the glucose concentration to normal when there has been a fall in glucose concentration?
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-when the pancreas detects blood glucose is too low, the alpha cells secrete glucagon and the beta cells stop secreting insulin -glucagon then binds to receptors on liver cells (the effectors) -the liver cells respond to increase the blood glucose concentration eg. glycogenolysis is activated -blood glucose conc returns to normal |
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What is adrenaline?
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-it is a hormone that is secreted from your adrenal glands (found just above your kidneys) -it is secreted when there's a low concentration of glucose in your blood, when you're stressed and when you're exercising -andrenaline binds to receptors in the cell membrane of liver cells and does various things to increase blood glucose concentration |
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How does adrenaline increase blood glucose concentration? |
-it activated glycogenolysis-the breakdown of glycogen to glucose -it inhibits glycogenesis-the synthesis of glycogen from glucose -it also activates glucagon secretion and inhibits insulin secretion, which increases glucose concentration -adrenaline gets the body ready for action by making more glucose available for muscles to respire |
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What can both adrenaline and glucagon do?
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-activate glycogenolysis inside a cell even though they bind to receptors on the outside of the cell |
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How do they do this? |
-the second messenger activates other enzymes in the cell to bring about a response |
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How do adrenaline and glucagon activate glycogenolysis? |
-activated adenylate cyclase converts ATP into a chemical called cyclic AMP (cAMP), which is a second messenger -cAMP activates a cascade that break down glycogen into glucose (glycogenlysis) |
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Give the summary of blood glucose control |
GLYCOGENOLYSIS=converts glycogen to glucose, is activated by glucagon and adrenaline GLUCONEOGENESIS=converts glycerol/amino acids to glucose, is activated by glucagon |
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What does type I diabetes involve? |
-after eating, the blood glucose level rises and stays high-this is hyperglycaemia and can result in death if it is left untreated -the kidneys can't reabsorb all this glucose, so some of its excreted in the urine -type I diabetes can be treated by regular injections of insulin -but this has to be carefully controlled bc too much can produce a dangerous drop in blood glucose levels-this is called hypoglycaemia -eating regularly and controlling simple carbohydrate intake (sugars) helps avoid a sudden rise in glucose |
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What does type II diabetes involve?
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-it occurs when the beta cells don't produce enough insulin or when the body's cells don't respond properly to insulin -cells don't respond properly because the insulin receptors on their membranes don't work properly, so the cells don't take up enough glucose -this means the blood glucose concentration is higher than normal -it can be treated by controlling simple carbohydrate intake and losing weight -glucose-lowering tablets can be taken if diet and weight loss can't control it |
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What is the human menstrual cycle?
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-it is a cycle of physiological changes in which the female body prepares for reproduction |
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What does the menstrual cycle involve?
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-ovulation-an egg being released -the uterus lining becoming thicker so that a fertilised egg can implant -a structure called a corpus luteum developing from the remains of the follicle if there is no fertilisation, the uterus lining breaks down and leaves the body through the vagina-this is known as menstruation, which marks the end of one cycle and the start of another |
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What is the menstrual cycle controlled by?
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-4 different hormones |
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What are these 4 hormones and what do they do? |
-luteinising hormone (LH)-stimulates ovulation and stimulates the corpus luteum to develop -oestrogen-stimulates the uterus lining to thicken -progesterone-maintains the thick uterus lining, ready for implantation of an embryo -FSH and LH are secreted by the anterior pituitary gland in the brain -oestrogen and progesterone are secreted by the ovaries |
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What is stage 1 of the menstrual cycle?
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-a high FSH conc in the blood stimulates follicle development -the follicle releases oestrogen -FSH stimulates the ovaries to release oestrogen -this causes the conc of oestrogen in the blood to rise, which stimulates the uterus lining to thicken -oestrogen inhibits FSH being released from the anterior pituitary gland |
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So, what happens after FSH has stimulated follicle development?
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-this makes sure that no more follicles develop |
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What is stage 2? |
-oestrogen conc rises to a high level -when oestrogen conc is high it no longer inhibits FSH release -instead it stimulates the anterior pituitary gland to release FSH and LH -in turn, LH stimulates the ovaries to release more oestrogen -oestrogen further stimulates the anterior pituitary gland to release more LH, and so on -this causes a surge in LH conc (it rapidly increases) which stimulates ovulation-the follicle ruptures and the egg is released -so a high oestrogen conc triggers a positive feedback mechanism, LH also stimulates the ruptured follicle to turn into a corpus luteum |
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What is stage 3?
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-the corpus luteum releases progesterone, so progesterone con rises -progesterone inhibits the release of FSH and LH from the anterior pituitary gland, so the concs of these fall -the uterus lining is maintained by progesterone -so negative feedback makes sure that no more follicles develop when the corpus luteum is developing |
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What happens if no embryo implants?
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-when progesterone stops being released. FSH and LH concs increase because they're no longer inhibited by progesterone -also the uterus lining isn't maintained so it breaks down-menstruation happens and the cycle starts again |
