Topic 5 homeostasis and response

Why do conditions need to be stable?, Whats homeostasis, what are automatic control systems & give 4 examples, what are all automatic system made up of & what do they do?

Why do conditions need to be stable?, Whats homeostasis, what are automatic control systems & give 4 examples, what are all automatic system made up of & what do they do?

• conditions in body need to be kept stable even when external environment changes because cells need right conditions to function properly & enzyme action

• Homeostasis → regulation of condition inside body (& cells) to maintain a stable internal environment in response to changes in both internal & external conditions

• have loads automatic control systems to regulate internal environment → nervous & hormonal communication systems ( are control systems that maintain body temperature, blood glucose level, water content)

• all automatic control systems made up of 3 main components, work together to maintain steady condition (receptors, coordination centres - brain & spinal cord, effectors

How does negative feedback (automatic) work when the stimulus level is too high?, when the stimulus is too low? how may a loop occur?

1. receptor detects a stimulus level is too high

2. coordination centre receives & processes information then organises a response

3. effector produces response which counteracts change & restores optimum level (level decreases)

1. Receptor detects a stimulus level is too low

2. coordination centre receives & processes information then organises a response

3. effector produces response which counteracts change & restores optimum level (level increases)

   (effectors carry on producing responses for as long as they’re stimulated by coordination centre → may cause opposite problem making level too much and process repeats)

What are the 4 parts of the nervous system and what are their functions?

1. Central nervous system (CNS) → in vertebrates (animals w backbones) this consists of brain & spinal cord only. In mammals, CNS is connected to body by sensory neurones & motor neurones

2. Sensory neurones → carry information as electrical impulses from receptors to CNS

3. motor neurones → carry electrical impulses from CNS to effectors

4. effectors → all muscles & glands which respond to nervous imuplses

What are receptors & where are they found, how can they form part of complex organs (example), whats function of effectors & where are they found?

• Receptors → detect stimuli, can be taste receptors on tongue/ sound receptors in ears

• Receptors can form part of larger complex organs (retina of eye is covered in light receptor cells)

• effectors → respond to nervous impulses & bring about change

• can be muscles & glands, muscles contract in response to nervous impulse whilst glands secrete hormones

Example how central nervous system coordinates the response

• bird spots cat skulking towards it out of corner of its eye (stimulus)

• Receptors in birds eye are stimulated, sensory neurones carry information from receptors to CNS

• CNS decides what to do about it

• CNS send information to muscles in birds wings (effectors) along motor neurones, muscles contract & bird flies away safely

whats synapses, how is a nerve signal transferred across neuron & what happens after

• Synapses → connection between 2 neurones

• nerve signal is transferred by chemicals which diffuse (move) across the gap

• these chemicals the set off new electrical signal in next neuron

what are reflexes, give 2 examples, whats a reflex arc?

• reflexes → rapid, automatic responses to certain stimuli that don’t involve conscious part of brain (reduce changes getting injured)

• example → someone shines bright light into eye, pupils automatically get smaller so less light gets in eye (stops it getting damaged)

• example → get a shock, body releases adrenaline (hormone) automatically

• reflex arc→ passage of information in reflex (receptor → effector)

How does a reflex work step by step

1. neurones in reflex arcs go through spinal cord/ unconscious part of brain

2. when stimulus (painful bee sting) detected by receptors, impulses sent along sensory neurone to relay neurone in CNS

3. When impulse reaches a synapse between sensory neurone & relay neurone, trigger chemicals to be released (cause impulses to be sent along relay neurone)

4. when impulses reach a synapse between relay neurone & motor neurone, same thing happens. Chemicals are released & cause impulses to be sent along motor neurone

5. impulses travel along motor neurone to effector (usually muscle)

6. muscle contracts & moves hand away from bee

7. don’t have to think about response (takes time) = quicker than normal responses

What is reaction time? what can affect it?

• reaction time → time it takes to respond to stimulus (often less than second)

• can be affected by age, gender, drugs

measure the affect pf caffeine on reaction time

1. person being tested should sit with arm resting on edge of table (should stop them moving arm up & down during test)

2. hold ruler vertically between their thumb & forefinger. make sure zero end of ruler is at level with their thumb & forefinger. Then let go without giving any warning

3. Person being tested should try catch the ruler as quickly as they can (as soon as see it fall)

4. reaction time is measured by number on ruler where its caught. Number should be read from top of thumb. The further down its caught (higher the number) = slower their reaction time

5. repeat test several times then calculate mean distance the ruler fell

6. person being tested should have a caffeinated drink (300ml cola). After 10 mins, repeat steps 1-5

7. need to control any variable to make sure its a fair test. Use same person to catch ruler each time & person should always use same hand, ruler should be dropped from same height, should make sure person being tested has not had any caffeine/ something that affects reaction time before start of experiment

8. too much caffeine can cause unpleasent side effects, so person being tested should avoid drinking any more caffeine for rest of the day after experiment is completed

How can computers be used to measure reaction time

• person being tested has to click mouse/ press key as soon as they see stimulus on screen (box change colour)

• computers can give more precise reaction time because they remove human error from measurement

• as computer records reaction time in milliseconds , can also give accurate measurement

• using computer also removes possibility that person can predict when to respond, using ruler test catcher may learn to anticipate drop by reading testers body language

4 parts of central nervous system & functions

1. cerebral cortex → outer wrinkly bit. Its responsible for things like consciousness, intelligence, memory & language

2. medulla → bottom part around spinal cord. Controls unconscious activities like breathing & heartbeat

3. Cerebrum → bottom right flower shaped ball. Responsible for muscle coordination

4. Spinal cord → line connecting brain to spine

how do you study the brain by studying patients with brain damage

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

how do you study the brain by electrically stimulating the brain

• the brain can be electrically stimulated by pushing a tiny electrode into the tissue & giving it a small zap of electricity

• By observing what stimulating different parts of the brain, its possible to get an idea of what those parts do

How do you study the brain by using MRI scans

• a magnetic resonance image (MRI) scanner is a big fancy 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/ trying to recall a memory

what did knowledge of the brain lead to & give an example, the brain is complex & delicate this means…, what does it carry a risk of

• knowledge of how the brain works has led to the development of treatments for disorders of the nervous system, example → electrical stimulation of brain can help reduce muscle tremors caused by nervous system disorders such as Parkinson’s disease

• the brain is incredibly complex & delicate, investigation of brain function & any treatment of brain damage or disease is difficult. Also carries risk, such as physical damage to the brain/ increased problems with brain function (difficulties w speech)

what are the 7 parts of they eye & their functions

• Sclera → tough, supporting wall of the eye

• Cornea → transparent outer layer found at the front of eye, it refracts (bends) light into the eye

• Iris → contains muscles that allow it to control diameter of the pupil (hole in middle) & therefore how much light enters the eye

• Lens → focuses the light onto the retina

• Retina → contains receptor cells sensitive to light intensity & colour

• Ciliary muscles & suspensory ligaments → control shape of lens

• Optic nerve → carries impulses from receptors on retina to brain

What happens when light receptors detect a very bright light? dim light?

• light receptors in eye detect very bright light → reflex is triggered that makes pupil smaller. circular muscles in iris contract & radial muscles relax = reduces amount of light that enters the eye

• opposite process happens in dim light → radial muscles contract & circular muscles relax, making pupil wider

Explain what happens in order to look at near objects, look at distant objects

• to look at near objects:

  1. ciliary muscles contract, which slackens suspensory ligaments

  2. lens becomes fat (more curved)

  3. this increases the amount by which it refracts light

• to look at distant objects:

  1. ciliary muscles relax, which allows suspensory ligaments to pull tight

  2. this makes the lens go thin (less curved)

  3. so it refracts light by a smaller amount

why people are short sighted, where does image appear, how to fix it, whats the medical term

• Long-sighted people are unable to focus on near objects:

  1. occurs when lens is the wrong shape & doesn’t refract (bend) light enough or the eyeball is too short

  2. images of near objects are brought into focus behind the retina

  3. you can use glasses with a convex lens (lens which curves outwards) to correct it. The lens refracts the light rays so they focus on the retina

  4. medical terma for long-sightedness → hyperopia

why does short-sightedness occur, images are?, how to fix it, medical term?

• short-sighted people are unable to focus on distant objects:

  1. occurs when lens is wrong shape & refracts light too much or the eyeball is too long

  2. images of distant objects are brought into focus in front of the retina

  3. you can use glasses with concave lens (lens which curves inwards) to correct it, so that light rays focus on the retina

  4. medical term for short-sightedness → myopia

how do contact lenses work?, 2 pros, 2 main types, con

• contact lenses → thin lenses that sit on the surface of the eye & are shaped to compensate for fault in focusing

• Pros → popular because they’re lightweight & almost invisible, more convenient than glasses for activities like sports

• 2 main types → hard lenses & soft lenses

• con → soft lenses are more comfortable but have a higher risk of eye infections than hard lenses

how does laser eye surgery work?, Pro, Con

• laser eye surgery → can sometimes correct bad eyesight, laser can be used to vaporise tissue, changing shape of the cornea (& so changing how strongly it refracts light into eye), surgeon can precisely control how much tissue laser takes off completely correcting the vision

• pros → changing shape so that its more powerful will improve long sight

• Con → like all surgical procedures theres a risk of complications (infection/ eye reacting in a way that makes your vision worse)

how does replacement lens surgery work?, pro, con

• replacement lens surgery → natural lens of eye is removed & an artificial lens, made of clear plastic is inserted in its place

• pros → sometimes long-sightedness may be more effectively treated by replacing lens of the eye (rather than altering shape of cornea w laser eye surgery)

• cons → as it involves working inside the eye, replacing a lens carries higher risks than laser eye surgery including possibly damage to retina (could lead to loss of sight)

describe what the thermoregulatory centre does when temp is too high & too low?

1. temperature receptors detect core body temp is too high

2. thermoregulatory centre acts as coordination centre (receives info from temp receptors & triggers effectors automatically)

3. effects (sweat glands) produce response & counteract change

   1. temp receptors detect core body temp is too low

   2. thermoregulatory centre acts as coordination centre (receives info from temp receptors & triggers effectors automatically)

   3. effectors (muscles) produce response & counteract change

What does the body do when we’re too hot?

• sweat produced by sweat glands & evaporates from skin. Transfers energy to environment

• blood vessels supplying skin dilate so more energy flows close to the surface of skin → vasodilation, helps transfer energy from skin to environment

What does the body do when you’re too cold?

• hairs stand up to trap an insulating layer of air

• no sweat is produced

• blood vessel supplying skin capillaries constrict to close off skin’s blood supply → Vasoconstriction

• when you’re cold you shiver too (muscles contract automatically), this needs respiration which transfers some energy to warm the body

what are hormones & how are they transported, what are they produced/secreted by & what do they make up, what kind of effects do they have?

• hormones → chemical molecules released directly into blood, carried in blood to other parts of body, but only affect particular cells in particular organs (target organs). Hormones controls things in organs & cells that need constant adjustment

• are produced in (& secreted by) various gland (endocrine glands), make up endocrine system

• tend to have relatively long-lasting effects

what are the 6 glands in the endocrine system & their functions?

• pituitary gland/ master gland (connected to brain) → produces many hormones that regulate body conditions, these hormones act on other glands directing them to release hormones to bring about change

• Ovaries (females only) → produce oestrogen, which is involved in the menstrual cycle

• testes (males only) → produce testosterone, which controls puberty & sperm production in males

• thyroid (neck) → produces thyroxine, involved in regulating things like rate of metabolism, heart rate & temp

• adrenal gland (on top kidneys) → produces adrenaline, used to prepare body for ‘fight or flight’ response

• pancreas (between kidneys) → produces insulin, used to regulate blood glucose level

differences between hormones & nerves

• nerves → very fast action, act for a very short time, act on a precise area

• hormones → slower action, act for a long time, act in a more general way

what does eating carbohydrates do, what does normal metabolism do, what does vigorous exercise do?, what can excess glucose be stored as, what does the pancreas do?

• eating foods containing carbohydrates puts glucose (type sugar) into blood from gut

• normal metabolism of cells removes glucose from blood

• vigorous exercise removes much more glucose from blood

• excess glucose can be stored as glycogen in liver & muscles

• level in glucose must be kept steady, changes are monitored & controlled by pancreas

What happens when blood glucose level is too high

• blood w too much glucose → insulin secreted by pancreas → too much glucose → insulin → glucose removes from blood into liver & muscle cells → blood glucose reduced → insulin makes liver turn glucose into glycogen

what happens when theres too little glucose in blood

• blood w too little glucose → glucagon secreted by pancreas → to little glucose → glucagon → glucose released into blood by liver → blood glucose increased → glucagon makes liver turn glycogen into glucose

what type 1 diabetes, how to treat it, pro, con

• Type 1 diabetes → pancreas doesn’t produce enough insulin/ any = persons blood glucose level can rise to a level that can kill them.

• Need insulin therapy - involves several injections of insulin throughout day (likely mealtimes), makes sure glucose is removed from blood quickly once food has been digested, stopping level getting too high

• pro → effective treatment

• con → amount of insulin that needs to be injected depends on the persons diet & how active they are

what is type 2 diabetes, 2 cons, pro

• type 2 diabetes → when person becomes resistant to their own insulin (produce it but body don’t respond properly to the hormone)

• con → can cause persons blood sugar to rise to a dangerous level, being overweight can increase chance of developing type 2 diabetes = obesity major risk factor

• pro → can br controlled by carbohydrate-controlled diet & getting regular exercise

how do kidneys make urine, what is filtration, what is selective reabsorption, what are the substances in urea?

• kidneys make urine by by taking waste products (& other unwanted substances) out of blood

• substances are filtered out of blood as it passes through kidneys → filtration

• useful substances like glucose, some ions & right amount of water are then absorbed back into blood → selective reabsorption

• substances removed from body in urine are urea, ions, water

What happens to proteins when they can’t be stored, what is ammonia produced as, what is ammonia converted to

1. proteins (& amino acids they’re broken down into) can’t be stored by body = any excess amino acids r converted into fats & carbohydrates which can be stored. This occurs in lover & involves process called deamination

2. ammonia is produced as a waste product from this process

3. Ammonia is toxic so its converted to urea in liver. Urea is then transported to the kidneys, where its filtered out of the blood & excreted from body in urine

How are ions taken into the body, what happens if ion/ water content in body is wrong, How are some ions lost & what do we have to do because of this

1. Ions (sodium) are taken into body by food & then absorbed into blood

2. if ion(or water) content of body is wrong, could upset balance between ions & water = too much/little water drawn into cells by osmosis → having wrong amount of water can damage cells/ mean don’t work as well as normal

3. some ions lost in sweat, this amount is not regulated so right balance of ions in body must be maintained by kidneys. Right amount of ions is reabsorbed into blood after filtration & rest is removed from body in urine

what does the body constantly do with water, where do we lose it, how do we balance it if we cant control how much we lose

1. body has to constantly balance water coming in against water going out

2. lose water from skin in sweat & from lungs when breathing out

3. cant control how much we lose in these ways, so amount of water is balanced by amount we consume & amount removed in kidneys in urine

Explain what happens when water content is too high & too low

• If water content is too high:

  1. a receptor in brain detects that water content is too high

  2. coordination centre in brain receives info & coordinates a response

  3. pituitary gland releases less ADH, so less water is reabsorbed from kidney tubules

• if water content is too low:

  1. receptor in brain detects water content is too low

  2. coordination centre in brain receives the info& coordinates a response

  3. pituitary gland releases more ADH, so more water is reabsorbed from kidney tubules

     (example of negative feedback)

what happens if kidneys don’t work properly, how can we keep people with kidney failure alive

• if kidneys don’t work properly, waste substance builds up in blood & you lose your ability to control levels of ions & water in body, eventually results in death

• people w kidney failure can be kept alive by having dialysis treatment (machines do job of kidneys) or can have kidney transplant

How does a dialysis machine work, explain the cons and pros

1. dialysis has to be done regularly to keep concentrations of dissolved substances in blood at normal levels, & to remove waste substances

2. in dialysis machine persons blood flows between partially permeable membranes surrounded by dialysis fluid. permeable to things like ions & waste substances but not big molecules (like in kidneys)

3. dialysis fluid has same concentration of dissolved ions & glucose as healthy blood

4. means useful dissolved ions & glucose won’t be lost from blood during dialysis

5. only waste substances (urea) & excess ions & water diffuse across barrier

6. many patients w kidney failure have to have dialysis sessions 3x week, each session takes 3-4 hours

7. dialysis may cause blood clots/ infections

8. being on dialysis machine is not pleasant experience & its expensive for NHS to run

9. dialysis can buy a patient w kidney failure valuable time until donor organ is found

what the cure for kidney failure, who can it be received from, risks, pros &cons

1. at moment only cure for kidney failure is to have kidney transplant

2. healthy kidneys are usually transplanted from people who have died suddenly

3. person who died has to be on organ donor register/ carry donor card (provided relatives agree too)

4. kidneys can also be transplanted from people who r still alive (have 2) but theres small risk to person donating kidney

5. theres also risk that donor kidney can be rejected by patients immune system. Patient is treated w drugs to prevent this but can still happen

6. transplants are cheaper (in long run) than dialysis & can put an end to hours patients have to spend on dialysis but there are long waiting lists for kidneys

What happens at puberty in women & men?

• at puberty body starts releasing sex hormones that trigger off secondary sexual characteristics (development facial hair in men & breasts in women) & cause eggs to mature in women

• In men → main reproductive hormone = testosterone, produced by testes & stimulates sperm production

• in women → main reproductive hormone = oestrogen, produced by ovaries. Bring about physical changes and involved in menstrual cycle

What are the 4 stages of the menstrual cycle and explain them

• Stage 1 → Day 1 -menstruation starts. Uterus lining breaks down for about 4 days

• Stage 2 → Uterus lining builds up again. From day 4–14, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg

• stage 3 → An egg develops & is released from ovary at day 14 → ovulation

• stage 4 → wall is maintained for about 14 days until day 28. If no fertilised egg has landed on uterus wall by day 28, spongy lining starts to break down & whole cycle starts again

What are the 4 hormones involved in the menstrual cycle, where are they produced, what do they cause & what do they stimulate

1. FSH (follicle-stimulating hormone) → produced in pituitary gland, causes an egg to mature in one of ovaries in structure called a follicle, stimulates ovaries to produce oestrogen

2. Oestrogen → produced in ovaries, causes lining of uterus to grow, stimulates release of LH (causes release of egg) & inhibits release of FSH

3. LH (luteinising hormone) → produced by pituitary gland, stimulates release of an egg at day 14 (ovulation)

4. Progesterone → produced in ovaries by remains of follicle after ovulation, maintains lining of uterus during second half of cycle when level of progesterone falls the lining breaks down, inhibits release of LH & FSH

how can hormones be used to reduce fertility, how are they taken, give side effects & effectiveness

1. Oestrogen can be used to prevent release of an egg - can be used as method of contraception

2. if oestrogen is taken every day to keep level of it permanently high, it inhibits production of FSH & after while egg development & production stop & stay stopped

3. progesterone reduces fertility by stimulating production of thick mucus which prevents any sperm getting through & reaching egg

4. The pill is an oral contraceptive containing oestrogen & progesterone (combined oral contraceptive pill)

5. over 99% effective at preventing pregnancy but can cause side effects like headaches & nausea & doesnt protect against sexually transmitted diseases

6. theres a progesterone-only pill → fewer side effects than pill & just as effective

what are the other contraceptive hormonal methods and how do they work

• contraceptive patch contains oestrogen & progesterone (same as combined pill), its a small (5cmx5cm) patch thats stuck to skin, each patch lasts 1 week

• contraceptive implant → inserted under skin of arm, releases continuous amount of progesterone which stops ovaries releasing eggs, makes it hard for sperm to swim to egg & stops any fertilised egg implanting in uterus, can last for 3 years

• contraceptive injection → contains progesterone, each dose lasts 2-3 months

• an intrauterine (IUD) → T-shaped device thats inserted into uterus to kill sperm & prevent implantation of fertilised egg. 2 main types → plastic IUDs that release progesterone & Copper IUDs that prevent sperm surving in uterus

what are the 4 non-hormonal contraceptives and how do they work?

1. non-hormonal forms of contraception r designed to stop sperm from getting to egg

2. condoms → worn over penis during intercourse to prevent sperm entering vagina. Also female condoms → worn inside vagina. Condoms r only form contraception that will protect against sexually transmitted diseases

3. diaphragm → shallow plastic cup that fits over cervix (entrance to uterus) to form a barrier. Has to be used w spermicide (substance that disables/ kills spem)

4. spermicide can be used alone as form of contraception but not as effective (only about 70-80%)

what are the 3 other way to avoid pregnancy and explain how they work

• sterilisation → involves cutting/ tying fallopian tubes (connect ovaries to uterus) in female, sperm duct (tube between testes & penis) in male. Permanent procedure, small chance that tubes can rejoin

• ‘natural’ methods → pregnancy may be avoided by finding out when in menstrual cycle woman is most fertile & avoiding sexual intercourse on those days. popular w people who think hormonal & barrier methods r unnatural, not very effective

• abstinence → only way to be completely sure that sperm & egg don’t meet is to not have intercourse

what happens if women have low FSH, what hormones could we give to help, pro & 2 cons

• some women have levels of FSH (follicle-stimulating hormone) that are too low to cause their eggs to mature, means no eggs are released & women can’t get pregnant

• hormones FSH & LH can be given to women in fertility drug to stimulate ovulation

• pros → helps lots of women get pregnant when they couldn’t before

• cons → doesn’t always work - some women may have to do it many times = can be expensive, too many eggs could be stimulated resulting in unexpected multiple pregnancies (twins, triplets, ect)

How does IVF work, pro & 3 cons

1. IVF involves collecting eggs from woman’s ovaries & fertilising them in a lab using man’s sperm

2. IVF treatment can also involve a technique called intra-cytoplasmic sperm injection (ICSI), where sperm is injected directly into an egg. Useful if man has a very low sperm count

3. fertilised eggs are then grown into embryos in a laboratory incubator

4. once embryos are tiny balls of cells, 1/ 2of them are transferred to womans uterus to improve chance of pregnancy

5. FSH & LH are given before egg collection to stimulate several eggs to mature (more than 1 egg can be collected)

• pro → fertility treatment can give an infertile couple a child

• cons → multiple births can happen if more han 1 embryo grows into a baby (risky for mother & babies - higher risk of miscarriage, stillbirth), success rate of IVF is low - avg in UK is ~ 26% - makes process incredibly stressful & often upsetting especially if ends in multiple failures, process is also physically stressful for women - some have a strong reaction to hormones (abdominal pain, vomiting, dehydration)

How have advances in microscopic techniques helped improve IVF give 3 things

• Advances in microscopic techniques have helped to improve techniques (& therefore success rate) of IVF

• specialised micro-tools have been developed to use eggs & sperm under microscope, also used to remove single cells from embryo for genetic testing (to check its healthy)

• development of time-lapse imaging (using microscope & camera built into incubator) means growth of embryos can be continuously monitored to help identify those that r most likely to result in successful pregnancy

Why are some people against IVF 2 things

1. process of IVF results in unused embryos that are eventually destroyed because of this some people think its unethical because each embryo is a potential human life

2. the genetic testing of embryos before implantation also raises ethical issues as some pple think could lead to selection of preferred characteristics (gender, eye colour)

where is adrenaline released from, why is it released, what does it get the body ready for

• adrenaline is a hormone released from adrenal glands (just above kidneys)

• adrenaline is released in response to stressful/ scary situations - brain detects fear/ stress & sends nervous impulses to adrenal glands, which respond by secreting adrenaline

• gets body read for ‘fight or flight’ by triggering mechanisms that increase supply of oxygen & glucose to cells in brain & muscles (increases heart rate)

where is thyroxine released from, what are the 2 important roles it has, what is released in response to, what does the negative feedback system do

• thyroxine is a hormone released by thyroid gland which is in neck (from iodine & amino acids)

• plays an important role in regulating basal metabolism rate → speed at which chemical reactions in body occur while body is at rest, also plays important part for loads of processes in body such as stimulating protein synthesis for growth & development

• thyroxine is released in response to thyroid stimulating hormone (TSH) which is released from pituitary gland

• negative feedback system keeps amount thyroxine in blood at right levels - level of thyroxine in blood too high = secretion of TSH from pituitary gland is inhibited

whats an auxin, how does it control growth of plant, where is it produced, what happens if tip is removed, what does extra auxin do

• auxin → plant hormone that controls growth near tips of shoots & roots

• control growth of plant in response to light (phototropism) & gravity (gravitropism/ geotropism)

• auxin produced in tips & moves backwards to stimulate cell elongation (enlargement) process which occurs in cells just behind tips

• if tip of shoot is removed, no auxin is available & shoot may stop growing

• extra auxin promotes growth in shoot but inhibits growth in root - producing desired effect

how does a shoot grow towards light

• when shoot tip is exposed to light more auxin accumulates on other side thats in shade than the side thats in light

• makes cells grow (elongate) faster on shaded side so shoot bends towards light

explain how shoots grow away from gravity & roots grow towards gravity

• when shoot is growing sideways, gravity produces an unequal distribution of auxin in tip, w more auxin on lower side

• causes lower side to grow faster, bending shoot upwards

• root growing sideways will also have more auxin on its lower side

• but in a root the extra auxin inhibits growth = means the cells on top elongate faster & root bends downwards

How can you investigate the effect of light on growth of cress seeds? (investigate plant growth response)

1. put 10 cress seeds into 3 different petri dishes, each lined w moist filter paper (remember to label dishes)

2. shine a light onto one of dishes from above & 2 of dishes from different directions

3. leave your cress seeds alone for 1 week until you can observe their responses & you’ll find the seedlings grow towards the light

4. need to control all the control variables so you know growth response of cress seeds is due to light

5 control variables & how to control them from the investigation of the effect of light on growth of cress seeds? (investigate plant growth response)

• number of seeds → use same number of seeds in each dish

• type of seed → use seeds that all come from the same packet

• temperature → keep petri dishes in place where temp us stable

• water → use measuring cylinder to add same amount of water

• light intensity → keep distance between bulb & dish the same

how are auxins used to kill weeds, grow plants from cuttings with rooting powder, growing cells in tissue culture

• killing weeds → most weeds growing in fields of crops/ lawn r broad-leaved whilst grasses & cereals have narrow leaves. selective weedkillers have been developed using auxins, only affect broad-leaved plants. Totally disrupt their normal growth patterns which soon kill them & leave grass & crops untouched

• growing from cuttings w rooting powder → cutting is a part of plant that has been cut off it like end of branch w few leaves on it. Normally if stick cuttings in soil they wont grow, but if add rooting powder (contains auxins) will produce roots rapidly & start growing as new plants. Enables growers to produce lots of clones of really good plant very quickly

• growing cells in tissue culture → tissue cultures can be used to grow clones of a plant from few of its cells. To do this hormones such as auxins need to be added to growth medium (along w nutrients) to stimulate cells to divide to from both roots & shoots

whats gibberellin, hows it used in controlling dormancy, inducing flowering, growing larger fruit

• gibberellin is another plant growth hormone, it stimulates seed germination, stem growth, flowering. Its uses include:

  1. controlling dormancy → lots seeds wont germinate until they’ve been through certain conditions (period cold/ dryness) → dormancy. Seeds can be treated w gibberellin to alter dormancy & make them germinate at times of year that they wouldn’t normally. Also helps make sure all seeds in batch germinate at same time

  2. inducing flowering → some plants require certain conditions to flower like longer days/ low temp. If plants r treated w gibberellin they will flower w/out any change in their environment. Can also be used grow bigger flowers

  3. growing larger fruit → seedless variations of fruit often don’t grow as large as seeded fruit. if gibberellin is added to fruits they will grow larger to match normal types

whats ethene & 2 things it does, how is it used commercially, what does that mean, 3 ways ripening can be delayed

• ethene is a gas produced by aging parts of plant, it influences growth of plant by controlling cell division, also stimulates enzymes that cause fruit to ripen

• commercially can be used to speed up ripening of fruits (while still on plant or during transport to shops)

• means fruit can be picked while its still unripe (firmer & less easily damaged), gas is then added to fruit on way to supermarket so it’ll be perfect just as reaches shelves

• ripening can be delayed while fruit in storage by adding chemicals that block ethene’s effect on fruit/ reduce amount ethene that fruit can produce. Alternatively some chemicals can be used that react w ethene to remove it from air