Topic 5 - Homeostasis and response

Question	Answer
What is homeostasis?	Homeostasis is the regulation if the conditions inside the body (and cells) to maintain a stable internal environment, in response to changes in both internal and external conditions.
How does negative feedback counteract changes if the level of something is too high/low?	1. receptor detects a stimulus - level is too high/low. 2. the coordination centre receives and processes the information, then organises a response. 3. effector produces a response which counteracts the change and restores the optimum level - the level decreases/increase. This automatic loop repeats regulating the body.
What are the four main parts of the nervous system?	1. central nervous system (CNS) - brain and spinal chord, connected to sensory and motor neurones. 2. sensory neurones - carry information as electrical impulses from receptors to the CNS. 3. motor neurones - carry electrical impulses from the CNS to effectors. 4. effectors - muscles and glands which respond to nervous impulses.
What are receptors?	Receptors are cells that detect stimuli, e.g. taste, sound, retina etc. Effectors respond to receptors e.g. muscles contracting, glands secreting.
What is the series of parts of the nervous system that triggers a response from a stimulus?	Stimulus-->receptor-->sensory neurone-->CNS-->motor nuerone-->effector-->response.
What are synapses?	The connection between two neurones. The nerve signal is transferred by chemicals which diffuse(move) across the gap. These chemicals trigger a new electrical signal in the next neurone.
What are reflexes?	Reflexes are rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain reducing the chances of being injured.For example, bright light in the eyes; pupil gets smaller, reducing damage. Shock; adrenaline hormone released The passage of information in a reflex (from the receptor to the effector) is a reflex arc.
Explain reflexes in terms of the reflex arc?	The neurones in reflex arcs go through the spinal chord or an unconscious part of the brain. When a stimulus is detected by receptors, impulses are sent along a sensory neurone to the CNS. When they reach a synapse between sensory and relay neurones, the chemical released causes the impulses to be sent along the relay. When they reach a relay-motor synapse the same thing happens and they are sent along the motor. The impulses travel along motor to an effector, which then contracts or secretes causing a reflex. As you don't have to think about the response, its quicker than normal responses.
Explain the investigation for reaction time?	1. person should sit with arm resting on edge of a table. 2. hold the ruler vertically between their thumb and forefinger. Make sure that the zero end is level with their thumb and finger. Let go without warning. 3. The person should catch the ruler as quickly as they can. The reaction time is measured by the number on the ruler where it's caught, further down, slower reaction time. 4. repeat multiple times and calculate a mean distance it fell.5. The person being tested should have a caffeinated drink and after 10 mins repeat steps 1-4.
How is reaction time measured by a computer?	Simple computer tests can be used to test reaction times (click the mouse), computers give a more precise reaction time because they remove human error from the measurement, also can record in milliseconds so can be more accurate, can no longer predict when to react (body language).
What is the function of the brain and name the different regions?	The brain is part of the CNS and is responsible for complex behaviours. Cerebral cortex (top front) - conciousness,intelligence, memory and language. Medulla (bottom front) - unconscious activities like breathing and your heartbeat. Cerebellum (middle back) - muscle coordination. Spinal chord (bottom)
What are the three methods to study the brain?	Studying patients with brain damage - if a small part of the brain is damaged, the effect can tell a lot about what the damaged part of the brain does. Electrical stimulating the brain - observing what stimulating different areas of the brain does, so can have an idea of what that part does. MRI scan (magnetic resonance imaging scanner - produces a very detailed picture of the brain's structures. Used to find which areas are active when doing things like listening or memory recall.
What are the parts of the eye?	Sclera - tough, supporting wall Cornea - transparent outer layer at front, it refracts light into the eye. Iris - has muscles that allow it to control the diameter of the pupil (hole in the middle) and therefore how much light gets in the eye. Lens - focuses light into the retina (contains receptor cells sensitive to light intensity and colour). Ciliary muscles and suspensory ligaments - the shape of the lens is controlled by these. Optic nerve - carries impulses from receptors on the retina to the brain.
What is the iris reflex?	1. when light receptors in the eye detect very bright light, a reflex is triggered, making the pupils smaller. The circular muscles contract and radial relax, reducing the amount of light entering the eye. 2. when dim light, radial contract and circular relax, widening the pupils.
Explain focusing to look at near objects?	1. ciliary muscles contract which slackens the suspensory ligaments. 2. the lens becomes fat (more curved). 3. this increases the amount by which it refracts light.
Explain focusing to look at distant objects?	1. the ciliary muscles relax, which allows the suspensory ligaments to pull tight. 2. this makes the lens go thin (less curved). 3. so it refracts light by a smaller amount.
Describe how people are long-sighted?	Long-sighted (hyperopia) people are unable to focus on near objects: 1. occurs when the lens is the wrong shape and doesn't refract the light enough or the eyeball is too short. 2. the images of near objects are bought into focus behind the retina. 3. you can use glass with a convex lens (curved outwards) to correct it. 4. the lens then refracts the light rays so they focus on the retina.
Describe how people are short-sighted?	Short-sighted (myopia) people are unable to focus on distant objects: 1. occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long. 2. the image of the distant objects are bought into focus in front of the retina. 3. you can use glasses with a concave (curved inwards) lens to correct it, light rays focus on the retina.
What temp should the inside of the body be?	About 37oC
What is the thermoregulatory centre?	The thermoregulatory centre in the brain contains receptors that are sensitive to the temperature of the blood that flows through the brain. Also receives impulses from temp receptor in the skin.
Explain how body temperature is regulated via negative feedback?	1. temperature receptors detect that core body temps are too high/low. 2. the thermoregulatory centre acts as a coordination centre - receives info from temp receptors and triggers effectors automatically. 3. effectors produce a response and counteract the change. The loop constantly cycles.
What is the function of antagonist effectors?	Effectors that oppose each other's actions, making a more sensitive response.
How does the body alter its temperature when it's too hot/cold?	too hot: 1. hairs lie flat/stand up to trap an insulating layer of air. 2. sweat is produced by sweat glands and evaporates from the skin, transferring energy to the environment/ no sweat produced. 3. The blood vessels supplying the skin dilate so more blood flows close to the surface of the skin - vasodilation, helps transfer energy to the environment/ blood vessels supplying skin capillaries constrict to close off the skin's blood supply - vasoconstriction. 4. when cold you shiver (muscles contract automatically), needs respiration, transferring some energy to warm the body.
What are hormones?	1. hormones are chemical molecules released directly into the blood and are carried in it to other parts of the body, but only affect particular cells in organs (target organs). 2. hormones control things in organs and cells that need constant adjustment. 3. produced/secreted by endocrine glands, making up your endocrine system. 4. they have long-lasting effects.
Name the six main endocrine glands?	Pituitary gland - produces many hormones that regulate body conditions, known as 'master gland' as it produces hormones that act on other glands, making them produce hormones that make changes. Thyroid - produces thyroxine, regulates things like rate of metabolism, heart rate and temperature. Adrenal gland - produces adrenaline, used for 'fight or flight' response. Pancreas - produces insulin, used to regulate blood glucose level. Ovaries - produces ostrogen, involved in mestrual cycle. Testes - produces testosterone, controls puberty and sperm production.
What is the difference between the way hormones and nerves carry messages?	Nerves - very fast action, act for a very short time, act on a very precise area. Hormones - slower action, act for a long time, act in a more general way. If the response is really quick, it's probably nervous. If a response lasts for a long time, it's probably hormonal.
How does the body control blood glucose levels?	1. eating foods containing carbohydrates puts glucose into the blood from the gut. 2. the normal metabolism of cells removes glucose from the blood but vigourous exercise removes much more glucose from the blood, excess glucose can be stored as glycogen in the liver and muscles. 3. the level of glucose in blood must be kept steady, changes are monitored and controlled by the pancreas, using the hormones insulin and glucagon, in a negative feedback cycle. Blood glucose level too high - insulin added. Blood glucose level too low - glucagon is added.
What are the two types of diabetes?	Diabetes is a condition that affects your ability to control your blood sugar level. Type 1 - pancreas produces little or no insulin, so blood sugar level can rise to a level that can kill them. Usually, need insulin therapy (insulin injections throughout the day), ensures glucose is removed from the blood quickly once the food has been digested, it's very effective. Also, think about limiting intake of food rich in carbohydrates and taking regular exercise. Type 2 - the person becomes resistant to their own insulin (still produces it but body cells don't respond properly to the hormone. This can also cause a person's blood sugar level to rise to a dangerous level. Overweight can increase the chance, controlled by eating a carbohydrate-controlled diet and getting regular exercise.
What are the functions of the kidneys?	The kidneys make urine by taking waste products (and other substances) out of your blood. Substances are filtered out of the blood as it passes through the kidneys, called filtration. Useful substances like glucose, some ions and the right amount of water are then absorbed back into the blood, called selective reabsorption.
What are the three main things removed from the body in urine?	1. urea - proteins cant be stored by the body so any excess amino acids are converted into fats and carbohydrates, which can be stored. Ammonia is produced as a waste product from this process but it's toxic so is converted to urea in the liver and filtered then excreted. 2. ions - ions such as sodium are taken into the body in food and absorbed into the blood. If the ion (or water) content of the body is wrong, this could upset the balance between the ions and water meaning too much/little water is drawn into the cells by osmosis. Having the wrong amount of water can damage cells or mean they don't work as well as normal. Some ions lost in sweat, but this amount is not regulated, so the right balance of ions in the body must be maintained by the kidneys. The right amount is reabsorbed after filtration and the rest is removed in the urine. 3. water - body has to constantly balance the water in against water out. We lose water from the skin in sweat and from the lungs when breathing out. But the amount we consume and the amount removed by the kidneys in urine is balanced.
What controls the concentration of urine?	The concentration of urine is controlled by a hormone called anti-diuretic hormone (ADH), which is released into the bloodstream by the pituitary gland. The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into blood according to how much is needed.
What happens if the water content is too high/low?	A receptor in the brain detects that water content is too high/low. The coordination centre in the brain receives the information and coordinates a response. The pituitary gland releases less/more ADH, so less/more water is reabsorbed from the kidney tubules, so water content decreases/increases.
What happens if the kidneys don't work properly?	If the kidneys don't work properly, waste substances build up in the blood and you lose your ability to control the levels of ions and water in your body, this results in death eventually. People with kidney failure can be kept alive by having dialysis treatment, machines do the job of kidneys or have a kidney transplant.
What is the job of a dialysis machine?	1. Dialysis has to be done regularly to keep the concentration of dissolved substances in the blood at normal levels, and to remove waste substances. 2. the person's blood flows through partially permeable membranes, surrounded by dialysis fluids. The membranes are permeable to things like ions and waste substances, but not big molecules like proteins. 3. dialysis fluid has the same conc of dissolved ions as the healthy blood, meaning useful dissolved ions and glucose won't be lost during dialysis, only waste (like urea) and excess ions and water diffuse across the barrier. 4. many patients with kidney failure have to have a dialysis session three times a week for 3-4 hours, also may cause blood clots or infections. Its expensive and unpleasant, but can buy a patient time until a donor organ is found
How can kidney transplant not work?	At the moment, the only cure for kidney failure is a kidney transplant. Kidneys taken from people who died suddenly, still alive with a small risk. Also, a risk that it will be rejected by the person's immune system, treated with drugs to prevent this but can still happen. Transplants are cheaper (in the long run) than dialysis and they can put an end to the hour's patients have to spend on dialysis, but there are long waiting lists for kidneys.
At puberty what do hormones do?	In puberty, your body releases sex hormones that trigger secondary sexual characteristics (facial hair/breasts) and cause eggs to mature in women. - in men, the main reproductive hormone is testosterone, produced in the testes and stimulates sperm production. - in women, the main reproductive hormone is oestrogen, it's produced by the ovaries. It brings about a physical change and is involved in the menstrual cycle.
Describe the four stages of the menstrual cycle?	stage 1 - day one menstruation starts, the uterus lining breaks down for about for days. stage 2 - the uterus lining builds up again, from day 4 to 14, into a thick spongey layer full of blood vessels, ready to receive a fertilised egg. stage 3 - an egg develops and is released from the ovary at day 14 - ovulation. stage 4 - the wall is then maintained for about 14 days until day 28. If no fertilised egg has landed on the uterus wall by day 28, the spongey lining starts to break down and the whole cycle starts again.
What is the follicle-stimulating hormone (FSH)?	1. Produced in the pituitary gland. 2. Causes an egg to mature in one of the ovaries, in a structure called a follicle. 3. Stimulates the ovaries to produce oestrogen.
What is oestrogen?	1. Produced in the ovaries. 2. Causing the lining of the uterus to grow. 3. Stimulated the release of LH (which causes the release of the egg) and inhibits release of FSH.
What is luteinising hormone (LH)?	1. Produced in the pituitary gland. 2. stimulates the release of an egg at day 14 - ovulation.
What is progesterone?	1. Produced in the ovaries by the remains of the follicle after ovulation. 2. Maintains the lining of the uterus during the second half of the cycle. When the progesterone levels fall, the lining breaks down. 3. Inhibits the release of LH and FSH.
How can hormones be used to reduce fertility?	Oestrogen can be used to prevent the release of an egg - contraception method. This is because if it taken every day then the level is permanently high and it inhibits the production of FSH and after a while egg development and production stop and stays stopped. Progesterone also reduces fertility, e.g. by stimulating the production of thick mucus which prevents any sperm getting through reaching an egg.
What is the pill?	The pill is an oral contraceptive containing oestrogen and progesterone. It's over 99% effective at preventing pregnancy but can have side effects like headaches and nausea and it doesn't protect against STDs.
Give examples of four other contraceptives that contain hormones?	1. contraceptive patch - oestrogen and progesterone, last a week at a time. 2. contraceptive implant - inserted under the skin, releases continuous amounts of progesterone, stopping ovulation and makes it hard for sperm to swim, stops eggs implanted in the uterus, lasts 3 years. 3. the contraceptive injection also contains progesterone, each dose lasts 2 to 3 months. 4. intrauterine device (UID) is a T-shaped device that is inserted into the uterus to kill sperm and prevent implantation of fertilised egg. Plastic (release progesterone) or copper (prevent sperm surviving).
Give some examples of barrier methods of contraception?	1. condoms - stop sperm and STDs 2. diaphragm - plastic cup over cervix with spermicide. 3. spermicide - used on its own not that effective.
Give some examples of the more extreme ways to avoid pregnancy?	Sterilisation - involves cutting or tying the fallopian tubes or sperm ducts, very small chance the tubes can rejoin. 'natural methods' - pregnancy may be avoided by avoiding sexual intercourse when the female is most fertile, not very effective. Abstinence - not having intercourse.
How can hormones be used to increase fertility?	1. some women have levels of FSH that are too low to cause their eggs to mature, so no eggs are released and they cant get pregnant. The hormones FSH and LH can be given a fertility drug to stimulate ovulation. pro; women who couldn't, can get pregnant. con; doesn't always work - some have to do lots which can be expensive. too many eggs could be stimulated resulting in multiple pregnancies.
What is IVF?	1. involves collecting eggs from the woman's ovaries and fertilising them in a lab using the man's sperm. 2. IVF can also involve injecting sperm directly into an egg - intra-cytoplasmic sperm injection (ICSI). 3. the fertilised eggs are then grown into embryos in a lab. 4. once they are tiny balls of cells, one or two of them are transferred to the woman's uterus to improve the chance of pregnancy. 5. FSH and LH are given before egg collection to stimulate several eggs to mature (so more than one egg can be collected).
What are the pros/cons of IVF?	pros; can give an infertile couple a child. cons; multiple births can happen, increased risk. Low success rate, in the UK its 26%. emotionally and physically stressful, some women have strong reactions to the hormones.
What has improved IVF?	Advances in microscopy techniques. Specialised micro-tools. Time-lapse imaging means constant monitoring.
Why are some against IVF?	Often unused embryos are destroyed potential human life. Genetic testing of embryos means people think people can select preferred characteristics.
What is the function of adrenaline?	Adrenaline is a hormone released by the adrenal glands (just above kidneys). Released in response to stressful situations - brain detects fear and sends impulses to these glands. The body gets ready for 'fight or flight' by triggering mechanisms that increase the supply of oxygen and glucose to cells in the brain and muscles, e.g. adrenaline increases heart rate.
What is a negative feedback system?	Your body can control the levels of hormones (and other substances) in the blood by using negative feedback system. When the body detects the level of substance is above/below the normal level it triggers a response to bring the level back to normal again.
How does thyroxine regulate metabolism?	1. thyroxine (a hormone released in thyroid gland in the neck), is important in regulating the basal metabolic rate (rate of metabolism at rest). Also important for many processes like protien synthesis for growth and development. 2. thyroxine is released in response to thyroid stimulating hormone (TSH), which is released from the pituitary gland. 3. a negative feedback system keeps the amount of thyroxine in the blood at the right level. Too high, secretion of TSH is inhibited, reducing the amount of thyroxine released, so blood falls back to normal.
What is Auxin?	Auxin is a plant growth hormone that controls growth near the tips of shoots and roots in response to light (phototropism) and gravity (geotropism). It's produced in the tips and moves backwards to stimulate the cell elongation (enlargement) process which occurs in the cells just behind the tips. If the tip of a shoot is removed it may stop growing (no auxin produced). extra auxin promotes growth in shoots but inhibits growth in the roots.
How do shoots grow towards the light?	When a shoot tip is exposed to light, more auxin accumulates on the side that's in the shade than the side that's in the light, so cells grow faster (elongate) on the shaded side so the shoot bends towards the light.
How do shoots grow away from gravity?	When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side. This causes the lower side to grow faster, bending the shoot upwards.
How do roots grow towards gravity?	A root growing sideways will also have more auxin on its lower side. But in a root extra auxin inhibits growth, so the cells on top elongate faster and the root bends downwards.
How would you investigate plant growth responses?	you can investigate the effect of light on the growth of cress seeds. 1. put 1o cress sees into three different Petri dishes, each lined with moist filter paper (label dishes). 2. shine a light onto one of your dishes from above and two of the dishes from different directions. 3. Leave your cress seeds alone for one week until you can observe their responses (they will grow towards the light). control variables; no. of seeds, type of seeds, temp, water, light intensity.
What are the three main uses of auxin?	1. killing weeds - most weeds are broad-leaved, and grass etc are narrow-leaved. Selective weedkillers have been developed using auxins, which only affect broad-leaved plants. They kill weeds and leave grass. 2. growing from cuttings with rooting powder - a cutting is part of a plant that has been cut off it, with rooting powder (contains auxins) cuttings will grow roots and rapidly start growing into new plants, allows clones quick and cheap. 3. growing cells in tissue culture - tissue culture can be used to grow clones of a plant from a few of its cells. To do this, hormones such as auxins need to be added to the growth medium (and nutrients) to stimulate the cells to divide to form shoots/roots.
What is Gibberellin?	It is another type of plant growth hormone that stimulates seed germination, stem growth and flowering.
What are the uses of Gibberellin?	1. controlling dormancy - lots of seeds won't germinate until they have been through certain conditions - dormancy, gibberellin makes them germinate at different times of the year (not like they normally do). 2. inducing flowering - certain conditions required to flower, low temps long days, but gibberellin causes them to flower without this change. 3. growing larger fruit - makes seedless and other fruits larger.
How does ethene stimulate the ripening of fruit?	ethene is a gas produced by ageing parts of a plant, it influences growth by controlling cell division. also, stimulate enzymes. Can be used to speed up the ripening of fruit. Fruit can be picked unripe then gas added so ripe for the shelf. Ripening can also be delayed by added chemicals in storage that stops ethenes effect.

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