Topic 5 - Homeostasis and Response Flashcards Preview

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Flashcards in Topic 5 - Homeostasis and Response Deck (236):

why do the conditions in your body need to be kept steady?

your cells need the right conditions in order to function properly, including conditions for enzyme activity. even if the external environment changes


what is homeostasis?

the regulation of the conditions inside your body (and cells) to maintain a stable internal environment in response to changes in internal and external conditions


what regulates your internal environment?

automatic control systems, including nervous and hormonal communication systems


what are examples of things your body has control systems to maintain?

body temperature
blood glucose
water content


what 3 main components are all control systems made up of?

coordination centres


how do your automatic control systems keep your internal environment stable?

using a mechanism called negative feedback


what is negative feedback?

when the level of something gets too high or too low your body uses negative feedback to bring it back to normal


process of negative feedback when the stimulus level is too high:

1. receptor detects stimulus - level is too high.
2. 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


process of negative feedback when the stimulus level is too low:

1. receptor detects a stimulus - level is too 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 increases


why does negative feedback keep happening?

the effectors will just carry on producing the responses for as long as they're stimulated by the coordination centre. this can cause the opposite problem - making the level change too much(away from ideal). the receptor detects the level is too different and negative feedback starts again


what is the nervous system made up of?

central nervous system
sensory neurones
motor neurones


what is the CNS?

in vertebrates this consists of the brain and spinal chord only. in mammals, the CNS is connected to the body by sensory nuerones and motor neurones


what are sensory neurones?

the neurones that carry information as electrical impulses from the receptors to the CNS


what are motor neurones?

the neurones that carry electrical impulses from the CNS to effectors


what are effectors?

all your muscles and glands, which respond to nervous impulses


what are receptors?

the cells that detect stimuli. there are many different types, like taste receptors in the tongue.


what can receptors form?

parts of larger, complex organs,e.g. the retina of the eye is covered in light receptor cells


what do effectors do?

they respond to nervous impulses and bring about a change. muscles and glands respond in different ways. muscles contract in response to a nervous impulse, whereas glands secrete hormones


what does the CNS do?

it receives information from the receptors and then coordinates a response. the response is carried out by effectors


example of the CNS coordinating a response:

a bird sees a cat (stimulus)
the receptors in the birds eyes are stimulated. sensory neurones carry the info from receptors to the CNS
the CNS decides what to do
The CNS sends info to the muscles in the wings (effectors) along motor neurones. the muscles contract


what is a synapse?

the connection between 2 neurones


what happens inside synapses?

the nerve signal is transferred by chemicals which diffuse across the gap. these chemicals then set off a new electrical impulse in the next neurone


what are reflexes?

rapid, automatic responses to certain stimuli that don't involve the conscious part of the brain.


what happens if someone shines a bright light in your eye?

your pupils automatically get smaller so less light gets in your eye, this stops them getting damaged


what happens if you get a shock?

your body releases the hormone adrenaline automatically


what is a reflex arc?

the passage of information in a reflex (from receptor to effector)


where do the relay neurones in a reflex arc go through?

the spinal cord or through an unconscious part of the brain


Describe a reflex arc:

impulses are sent along a sensory neurone to a synapse which triggers chemicals to be released, these chemicals cause impulses to be sent along the relay neurone in the CNS the same thing happens in the synapse between the relay and motor neurones. they then go to the effectors which carry out the response


why is a reflex quicker then a regular response?

we don't have to think about the response (which takes time)


what is the reaction time?

the time it takes to respond to a stimulus - its often less than a second


what can a reaction time be affected by?

factors like age, gender or drugs


what is caffeine?

a drug that can speed up a person's reaction time.


how do you conduct an experiment for measuring reaction time?

have a person sat with their arm on the edge of a table.
hold a ruler vertically at the 0 mark between their thumb and finger. then drop it without warning.
the other person should try to catch the ruler as quickly as possible.
the further down the ruler it is caught the slower the reaction time.
repeat several times and calculate the mean distance the ruler fell by.


what are the control variables for measuring reaction time?

the same person to catch the ruler each time
the same hand catching the ruler
ruler dropped from the same height
person being tested shouldn't have anything to affect their reaction time before


what can be used to measure reaction time?

simple computer tests e.g. clicking the mouse, or pressing a key as soon as they see a stimulus on the screen


why might a computer be better at measuring reaction time?

they give a more precise reaction time because they remove the possibility of human error.
they can record in milliseconds to give a more accurate measurement.
remove the possibility that the person being tested may be able to predict when to respond from the other persons body language


what is the brain made of?

its made up of billions of interconnected neurones


what does the brain do?

it's in charge of all of our complex behaviours. it controls and coordinates everything you do


what are the different parts of the brain?

cerebral cortex
spinal cord


what is the cerebral cortex?

this is the outer wrinkly bit. it's responsible for things like consciousness, intelligence, memory and language


what does the medulla do?

it controls unconscious activities (things you don't think about doing) like breathing and your heartbeat


what does the cerebellum do?

responsible for muscle coordination


what are scientists that study the brain called?



what are the 3 methods to study the brain?

studying patients with brain damage
electrically stimulating the brain
MRI scans


studying patients with brain damage:

if a small part of the brain has been damaged, the effect this has on the patient can tell you a lot about what the damaged part of the brain does.


electrically stimulating the brain:

the brain can be electrically stimulated by pushing a tiny electrode into the tissue and giving it a small zap of electricity. by observing what stimulating different parts of the brain does, it's possible to get an idea of what those parts do.


example of studying patients with brain damage to map the brain:

if an area at the back of the brain is damaged and the patient is blind, that part is responsible for vision


example of electrically stimulating the brain:

when a certain part of the brain (known as the motor area) is stimulated, it causes muscle contraction and movement.


MRI scans:

a magnetic resonance imaging scanner is a big tube-like machine that can produce a very detailed picture of the brains structures. scientists use it to find out what areas of the brain are active when people are doing things like listening to music or trying to recall a memory


how has studying the brain helped people?

knowledge of how the brain works has led to the development of treatments for disorders of the nervous system. e.g. electrical stimulation can help reduce muscle tremors


how can studying the brain have consequences?

the brain is incredibly complex and delicate - the investigation of brain function and any treatment of brain damage or disease is difficult. it also carries risks, such as physical damage to the brain or increased problems with brain function


what are all of the different parts of the eye?

ciliary muscles
optic nerve
suspensory ligaments


what is the sclera?

the tough, supporting wall of the eye


what is the cornea?

the transparent outer layer found at the front of the eye. it refracts light into the eye


what does the iris do?

it contains muscles that allow it to control the diameter of the pupil and therefore how much much light enters the eye


what does the lens do?

it focuses the light onto the retina


what is the retina?

which contains receptor cells sensitive to light intensity and colour


what controls the shape of the lens?

the ciliary muscles and suspensory ligaments


what does the optic nerve do?

it carries impulses from the receptors on the retina to the brain


what does the iris do when there is bright light?

when light receptors in the eye detect very bright light, a reflex is triggered to make the pupil smaller. the circular muscles contract and the radial muscles relax. this reduces the amount of light that can enter the eye


what does the iris do when there is dim light?

the radial muscles contract and the circular muscles relax, which makes the pupil wider


what is accommodation?

when the eye focuses light on the retina by changing the shape of the lens


what does the eye do when looking at near objects?

the ciliary muscles contract, which slackens the suspensory ligaments
the lens becomes fat (more curved)
this increases the amount by which it refracts light


what does the eye do when looking at distant objects?

the ciliary muscles relax, which allows the suspensory ligaments to pull fight.
this makes the lens go thin (less curved)
so it refracts light by a smaller amount


why are some people long-sighted?

their lens is the wrong shape and doesn't refract light enough. so the images of near objects are brought into focus behind the retina


how can long-sightedness be resolved?

you can use glasses with a convex lens to correct it. the lens refracts the light rays s they focus on the retina


what is the medical term for long-sightedness?



why are some people short-sighted?

their lens is the wrong shape and refracts light too much or the eyeball is too long. images of distant objects are brought into focus in front of the retina


how can short-sightedness be corrected?

you can use glasses with a concave lens, so that the light rays focus on the retina


what is the medical term for short-sightedness?



what are the different treatments for eye defects?

contact lenses
laser eye surgery
replacement lens surgery


what are contact lenses?

thin lenses that sit n the surface of the eye and are shaped to compensate for the fault in focusing.


why do people like contact lenses?

they're lightweight and almost invisible, they're more convenient than glasses for activities like sports


what are the 2 main types of contact lenses?

hard lenses
soft lenses


what are the differences between hard and soft lenses?

soft lenses are generally more comfortable but have a higher risk of eye infections than hard lenses


how does laser eye surgery work?

a laser can be used to vaporise tissue, changing the shape of the cornea. so it changes how strongly it refracts light. the surgeon can precisely control how much the laser takes off to completely correct the vision


how can laser eye surgery improve short sight?

it slims the cornea down, making it less powerful


how can laser eye surgery improve long sight?

it changes the shape of the cornea so that it's more powerful


what are the complications of laser eye surgery?

infection or the eye reacting in a way that makes your vision worse than before


what is replacement eye surgery?

where the natural lens of the eye is removed and an artificial lens, made of clear plastic, is inserted in its place.


why does replacement eye surgery have higher risks?

it involves working inside the eye so it has higher risk than laser eye surgery. the retina could get damaged and that could lead to sight loss


what does the body do to keep the core body temperature constant?

it has to balance the amount of energy gained and lost


how does the thermoregulatory centre detect body temperature?

there are receptors that are sensitive to the temperature of the blood flowing through the brain. it also receives impulses from the temperature receptors in the skin giving info about skin temperature


what does the thermoregulatory system do when you warm up?

temperature receptors detect core body temp is too high
thermoregulatory centre acts as coordination centre - it receives info from receptors and triggers effectors automatically
effectors e.g. sweat glands produce a response and counteract the change


what does the thermoregulatory system do when you cool down?

detect core body temp is too low
thermoregulatory centre acts as coordination centre - it receives info from receptors and triggers effectors automatically
effectors e.g. muscles produce a response and counteract the change


how can effectors work antagonistically?

e.g. one effector heats and another cool- they'll work at the same time to achieve a very precise temperature. this allows a more sensitive response


what do your effectors do when you're too hot?

sweat is produced by sweat glands and evaporates from the skin. this transfers energy to the environment.
vasodilation happens which helps transfer energy from the skin to the environment
hair erector muscles relax


what is vasodilation?

blood vessels supplying the skin with blood, dilate so more blood flows close to the surface of the skin.


what do your effectors do when you're too cold?

hairs stand up on end
no sweat is produced
vasoconstriction happens
you shiver (your muscles contract automatically) this needs respiration, which transfers some energy to warm the body


what is vasoconstriction?

when blood vessels supplying skin capillaries constrict to close off the skin's blood supply


what are hormones?

chemical molecules released directly into the blood. they tend to have relatively long-lasting effects


how are hormones carried around the body?

they are carried in the blood to other parts of the body, but only affect particular organs (target organs)


what do hormones control?

they control things in organs and cells that need constant adjustment


where are hormones produced?

they are produced in and secreted by various glands, called endocrine glands. these glands make up the endocrine system


what are some examples of glands in the endocrine system?

the pituitary gland
adrenal gland
the pancreas


what does the pituitary gland do?

it produces many hormones that regulate body conditions. it is sometimes called the 'master gland' because these hormones act on other glands, directing them to release hormones that bring about change


what does the thyroid do?

it produces thyroxine, which is involved in regulating things like the rate of metabolism, heart rate and temperature


what does the adrenal gland do?

it produces adrenaline, which is used to prepare the body for a 'fight or flight' response


what does the pancreas so?

it produces insulin, which is used to regulate the blood glucose level


what do the ovaries do?

produce oestrogen, which is involved in the menstrual cycle


what do the testes do?

produce testosterone, which controls puberty and sperm production in males


how are nerves and hormones different?

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


how do you know a response is nervous?

if the response is really quick, info needs to be passed to effectors really quickly so its not good using hormones to carry the message - they're too slow


how do you know a response is hormonal?

if a response lasts for a long time, e.g. adrenaline when you get a shock. you can tell its hormonal because you feel wobbly for a while afterwards


what happens when you eat carbohydrate? (metabolism)

it puts glucose into the blood from the gut. the level of glucose in the blood must be kept steady


how do we remove glucose from the blood?

normal metabolism of cells removes glucose from the blood
vigorous exercise remove much more glucose from the blood


what happens to excess glucose in the body?

it can be stored as glycogen in the liver and in the muscles


how are changes to the level of glucose in the blood monitored?

changes are monitored and controlled by the pancreas, using the hormones insulin and glucagon, in a negative feedback cycle


what does the body do when the blood glucose level is too high?

insulin is secreted by the pancreas.
glucose moves from the blood into the liver and muscle cells.
insulin makes the liver turn glucose into glycogen


what does the body do when the blood glucose level is too low?

the pancreas secretes glucagon.
glucagon makes the liver turn glycogen into glucose and glucose is released into the blood by the liver


what is diabetes?

a condition that affects your ability to control your blood sugar level


what are the 2 types of diabetes?

type 1 diabetes
type 2 diabetes


what is type 1 diabetes?

where the pancreas produces little or no insulin. this means a person's blood glucose level can rise to a level that can kill them.


what treatment do people with type 1 diabetes need?

insulin therapy


what is insulin therapy?

this involves several injections of insulin throughout the day, most likely at meal times. this makes sure that glucose is removed from the blood quickly once the food has been digested, stopping the level getting too high


what determines how much insulin someone should get injected into them?

a persons diet and how active they are.


what else do people with type 1 diabetes need to do other than insulin therapy?

they need to think about limiting the intake of food rich in simple carbohydrates and taking regular exercise


what is type 2 diabetes?

where a person becomes resistant to their own insulin (their body cells don't respond properly to the hormone). this can cause a person's blood sugar level to rise to a dangerous level


what increases chances of type 2 diabetes?

being overweight can increase the chance as obesity is a major risk factor in the development of the disease


how can type 2 diabetes be controlled?

by eating a carbohydrate-controlled diet and getting regular exercise


what is filtration in the kidneys?

the kidneys make urine by taking waste products out of your blood. substances are filtered out of the blood as it passes through the kidneys.


what is selective reabsorption?

when useful substances like glucose, some ions and the right amount of water are absorbed back into the blood


what substances are removed from the body in urine?



what does the body do to protein (which can't be stored)?

proteins (and amino acids) can't be stored in the body. so excess amino acids are converted into fats and carbohydrates (which can be stored) this happens in the liver and involves a process called deamination


what is a waste product of converting proteins to fats and carbohydrates?



what happens to ammonia in the body?

ammonia is toxic so it's converted to urea in the liver. urea is then transported to the kidney's where it's filtered out of the blood and excreted from the body in urine.


how is urea excreted from the body other than urine?

a small unregulated amount of urea is also lost from the skin in sweat


how do we get ions in our body?

ions like sodium are taken into the body in food and then are absorbed into the blood.


what happens if the ion or water content of the body is wrong?

this could upset the balance between ions and water, meaning too much or too little water is taken into cells by osmosis. having the wrong amount can damage cells or mean they don't work as well as normal


how are ions removed from the body?

ions are lost in sweat but this amount is not regulated, so the right balance of ions in the body must be maintained by the kidneys.


how is the ion content regulated by the kidneys?

the right amount of ions is reabsorbed into the blood after filtration and the rest is removed from the body in urine.


how do we lose water from our body's?

through the skin in sweat
from the lungs when breathing out
but this isn't controlled


how do we control the water content of our bodies?

we can't control it through sweat or breathing so it is balanced by the amount we consume and the amount removed by the kidneys in urine


what controls the concentration of urine?

a hormone called anti-diuretic hormone (ADH) which is released into the bloodstream by the pituitary gland


how does the body know when to release ADH?

the brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed


what happens in the body when the water content increases?

a receptor in the brain detects that the water content is too high
the coordination centre in the brain receives the info and coordinates a response
the pituitary gland releases less ADH, so less water is reabsorbed from the kidney tubules


what happens in the body when the water content decreases?

a receptor in the brain detects that the water content is too low
the coordination centre in the brain receives the info and coordinates a response
the pituitary gland releases more ADH, so more water is reabsorbed from the kidney tubules


what happens when 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 the body.


how are people with kidney failure kept alive?

by having dialysis treatment - where medicines do the job of the kidneys
or have a kidney transplant


why do people need to have dialysis?

they need to be treated regularly to keep the concentrations of dissolved substances in the blood at normal levels, and to remove waste substances


what happens in a dialysis machine?

the person's blood flows between partially permeable membranes, surrounded by dialysis fluid. it's permeable to things like ions and waste substances, but not big molecules like proteins.


how does dialysis fluid work?

it has the same concentration of dissolved ions and glucose as healthy blood. useful dissolved ions and glucose won't be lost from the blood during dialysis, only waste materials and excess ions and glucose diffuse across the barrier


how often do people need dialysis treatment?

they often have to have them 3 times a week and each session lasts for 3-4 hours


what are the disadvantages of dialysis?

it can cause blood clots or infections,
it isn't pleasant
it's expensive for the NHS


what is an advantage of dialysis?

it can buy valuable time until a donor organ is found


what is the only cure for kidney failure?

to get a kidney transplant


where do kidneys come from for transplants?

healthy kidneys are transplanted from people who have died suddenly, who are on the organ donor register or have a donor card
or living people can donate 1 of their kidneys but this carries a risk for the donater


what are the disadvantages of kidney transplants?

the donor kidney could be rejected by the patients immune system. they are given drugs to stop this from happening
there are long waiting lists


what are the advantages of kidney transplants?

they are cheaper in the long run than dialysis and can put an end to the hours patients have to spend on dialysis


what hormones do release at puberty?

your body starts releasing sex hormones that trigger off secondary sexual characteristics (e.g. facial hair, breasts) and eggs to mature in women


what are the main reproductive hormones in men?

testosterone, which is produced in the testes and stimulates sperm production


what are the main reproductive hormones in women?

oestrogen, which is produced by ovaries. as well as bringing about physical changes, oestrogen is also involved in the menstrual cycle


what is stage 1 of the menstrual cycle?

day 1 - menstruation starts. the uterus lining breaks down for about 4 days


what is stage 2 of the menstrual cycle?

from day 4 to 14 the uterus lining builds up again, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg


what is stage 3 of the menstrual cycle?

an egg develops and is released from the ovary at day 14 - this is called ovulation


what is stage 4 of the menstrual cycle?

the wall is maintained for about 14 days until day 28. if no fertilised egg has landed on the uterus wall by day 28, the spongy lining starts to break down and the whole cycle starts again


which 4 hormones control the menstrual cycle?



what does FSH stand for?

follicle-stimulating hormone


what does LH stand for?

luteinising hormone


where is FSH produced?

the pituitary gland


where is LH produced?

the pituitary gland


where is oestrogen produced?



where is progesterone produced?



what does FSH do?

causes an egg to mature in one of the ovaries, in a structure called a follicle
stimulates the ovaries to produce oestrogen


what does oestrogen do?

causes the lining of the uterus to grow
stimulates the release of LH and inhibits release of FSH


what does LH do?

stimulates the release of an egg at day 14 (ovulation)


what does progesterone do?

maintains the lining of the uterus during the 2nd half of the cycle. when the level of progesterone falls, the lining breaks down
inhibits release of LH and FSH


how can oestrogen be used as a method of contraception?

if it is taken every day to keep the level permanently high, it inhibits the production of FSH, so egg development and production stop


how can progesterone be a contraceptive?

it stimulates the production of thick mucus which prevents any sperm getting through and reaching the egg


what is the pill?

an oral contraceptive containing oestrogen and progesterone (a.k.a. the combined oral contraceptive pill)


advantages of the pill:

over 99% effective at preventing pregnancy


disadvantages of the pill:

can cause side effects like headaches and nausea and doesn't prevent against STI's


what other pill other than the combined pill is there?

the progesterone only pill. it has fewer side effects than the pill and is just as effective


what is the contraceptive patch?

a small 5 by 5 cm patch containing oestrogen and progesterone that sticks to the skin. it lasts for 1 week


what is the contraceptive implant?

an implant inserted under the skin that releases a constant amount of progesterone. it can last for 3 years


what does a contraceptive implant do?

it stops ovaries releasing eggs, makes it hard for sperm to swim to the egg and stops any fertilised egg implanting in the uterus


what is an intrauterine device (IUD)?

a T-shaped device that is inserted into the uterus to kill sperm and prevent implantation of a fertilised egg.


what are the 2 types of IUD?

plastic IUD
copper IUD


what does a plastic IUD do?

they release progesterone


what do copper IUD's do?

they prevent sperm surviving in the uterus


what are the non- hormonal forms of contraception?



which methods of contraception use hormones?

contraceptive patch
contraceptive implant
contraceptive injection


what are non-hormonal methods of contraception designed for?

stopping sperm getting to the egg


how do condoms work?

they are worn over the penis or inside the vagina during intercourse to prevent the sperm entering the vagina. condoms are the only contraception that protect against STI's


what is a diaphragm?

a shallow plastic cup that fits over the cervix to form a barrier. it has to be used with spermicide (that disables or kills sperm)


how effective is spermicide?

spermicide can be used alone as a form of contraception but it is not as effective (70-80%)


what are the more drastic ways to avoid pregnancy?

'natural' methods


what is sterilisation?

it involves cutting or tying the fallopian tubes in a female, or sperm ducts in a male. this is permanent but there's a chance the tubes rejoin


what is the 'natural' method of contraception?

not having sexual intercourse on the days when a woman is most fertile. this is good for people who think other ways are unnatural, but it's not very effective


what is abstinence?

not having intercourse at all


how are some women infertile?

their FSH levels are too low to cause their eggs to mature, so no eggs are released and the women can't get pregnant


how can fertility be cured?

FSH and LH can be given in a fertility drug to stimulate ovulation


what are the advantages of the fertility drug?

it helps a lot of women to get pregnant when previously they couldn't


what are the disadvantages of the fertility drug?

it doesn't always work - some women may have to do it many times, which is expensive
too many eggs could be stimulated, resulting in unexpected multiple pregnancies


how else can a woman have children if drugs don't work?

she can use IVF


what does IVF stand for?

in vitro fertilisation


what does IVF involve?

collecting eggs from the women's ovaries and fertilising them in a lab using the mans sperm
the fertilised eggs are grown into embryos in a laboratory incubator
once they are tiny balls of cells 1 or 2 are transferred to the womans uterus to improve chances of pregnancy


what technique CAN IVF treatment involve?

intra-cytoplasmic sperm injection (ICSI), where the sperm is injected directly into an egg. its useful if the man has a low sperm count


what is done before IVF?

FSH and LH are given before egg collection to stimulate several eggs to mature


advantages of IVF:

fertility treatment can give an infertile couple a child - a pretty obvious benefit


disadvantages of IVF:

multiple births can happen if more than one embryo grows into a baby
there is a low success rate (26%)
emotionally stressful
physically stressful if they have a bad reaction to the hormones


what increases the success rate of IVF?

specialised micro-tools that have been developed to use on the eggs and sperm under the microscope. the development of time-lapse imaging means growth can be continuously monitored to identify which are most likely to result in a successful pregnancy


why do some people disagree with IVF?

unused embryos are destroyed so some people think it unethical because it is potential life
genetic testing could lead to preferred characteristics like gender or eye colur


where is adrenaline released?

in the thyroxine glands, above the kidneys


why is adrenaline released?

in response to stressful or scary situations, your brain detects fear or stress and sends nervous impulses to the adrenal glands, which secrete adrenaline


how does adrenaline get your body 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 increase heart rate


how does your body control the levels of hormones in the blood?

using negative feedback systems. when the body detects that the the level of a substance has gone above or below the normal level, it triggers a response to bring the level back to normal again


where is thyroxine produced?

the thyroid gland in the neck (from iodine and amino acids)


what is the basal metabolic rate?

the speed at which chemical reactions in the body occur while the body is at rest


what does thyroxine do?

regulates basal metabolic rate
stimulates protein synthesis for growth and development


what stimulates the release of thyroxine?

the thyroid stimulating hormone (TSH) which is released in the pituitary gland


how does negative feedback keep the amount of thyroxine in the blood at the right level?

when the level of thyroxine is too high the secretion of TSH is inhibited. this reduces the amount of thyroxine released, so the level falls back to normal


what is auxin?

a plant hormone that controls growth near the tips of shoots and roots


what does auxin do?

controls the growth of a plant in response to light (phototropism) and gravity (gravitopism or geotropism)


where is auxin in the plant?

its produced in the tips and moves backwards to stimulate the cell elongation process which occurs in the cells just behind the tips


what happens if the top of a shoot is removed?

no auxin is available and the shoot may stop growing


what does extra auxin do?

promotes growth in the shoot but inhibits growth in the root


what happens when a shoot tip is exposed to light?

more auxin accumulates on the side thats in the shade than the side thats in the light.
this makes the cells elongate faster on the shaded side so the shoot grows towards the light


what happens when a shoot grows sideways?

gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side. so the lower side grows faster, bending the shoot upwards


what happens when a root grows sideways?

it will have more auxin on its lower side. in roots auxin inhibits growth so the cells on top will elongate faster and the roots bend downwards


how do you investigate the effect of light on growth?

put 10 cress seeds in 3 petri dishes with moist filter paper labelled A, B and C
shine light on 1 from above and 2 from different sides.
leave them in the dark and you will see they grow towards the light


what are different control variables for the investigation of the effect of light on growth?

number of seeds
type of seeds
light intensity


what are the different ways auxin can be used?

killing weeds
growing from cuttings with root powder
growing cells in tissue culture


how can auxins be used for weed killer?

most weeds are broad-leaved, selective weedkillers are made with auxins to only affect plants with broad leaves.
they disrupt their normal growth patterns, which soon kills them


how can auxins help to grow plants from cuttings?

if you stick cuttings in the soil they won't grow. if you add rooting powder (containing auxins) they will produce roots rapidly and start growing as new plants. this means lots of clones can be produced quickly


how can auxins help grow cells in tissue culture?

tissue culture can be used to grow clones of a plant from a few of its cells. auxins need to be added to the growth medium (with nutrients) to stimulate the cells to divide to form both roots and shoots


what is gibberellin?

a type of plant hormone that stimulates seed germination, stem growth and flowering


what can gibberellin be used for?

controlling dormancy
inducing flowering
growing larger fruit


what is dormancy?

when lots of seeds go through certain conditions (e.g. periods of cold or dryness) to cause germination


why is gibberellin used to alter dormancy?

it makes plants germinate at times of the year they normally wouldn't. it also makes sure all the seeds in a batch germinate at the same time


how can gibberellin induce flowering?

some plants require certain conditions to flower (longer days low temperatures). when treated with gibberellin they will flower without any changes in the environment. they can also be used to grow bigger flowers


how can gibberellin induce flowering?

seedless varieties of fruit often don'y grow as large, but gibberellin helps them grow to the same size as normal


what is produced by ageing parts of plants?

ethene, some fruit also produce ethene as it ripens


what does ethene do in plants?

it influences the growth of the plant by controlling cell division.
it also stimulates enzymes that cause fruit to ripen


how is ethene commercially used for plants>

to speed up the ripening of fruit. either on the plant or during transport. this means fruit can be picked when unripe so firmer and harder to damage


how can ripening be delayed while the fruit is being stored?

adding chemicals that block ethene's effect on the fruit or reduce the amount of ethene that the fruit can produce. some chemicals can react with ethene to remove it from the air