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homeostasis & response (controlling fertility (hormones (the pill…
homeostasis & response
the brain
part of the central nervous system made up of billions of interconnected neurones.
in charge of complex behaviours - controls + coordinates
- cerebral cortex - outer layer responsible for things like consciousness, intelligence, memory and language.
- medulla - controls unconscious activities e.g. breathing, heartbeat
- cerebellum - responsible for muscle coordination
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knowledge of brain has led to treatment for disorders of the nervous system e.g. electrical stimulation can reduce muscle tremors (due to e.g. Parkinson's disease)
but the brain is complex & delicate so investigation & treatment can be difficult & carries risks e.g. physical damage or increased problems w/ brain function.
the eye
- the sclera - tough, supporting wall
- the cornea - transparent outer layer at front of eye that refracts light onto eye
- the iris contains muscles that control the diameter of the pupil & therefore how much light enters the eye
- the lens focuses the light onto the retina. lens shape controlled by ciliary muscles & suspensory ligaments
- retina - contains receptor cells sensitive to light intensity & colour
- the optic nerve carries impulses from the receptors on the retina to the brain
iris reflex
(bright light damages the retina)
when light receptors detect a bright light, a reflex makes the pupil smaller. the circular muscles contract & the radial muscles relax, reducing the amount of light that enters the eye.
dim light - radial muscles contract & circular muscles relax, making the pupil wider/dilate.
focusing on objects
NEAR
- ciliary muscles tighten/contract
- lens becomes fat (more curved)
increasing amount by which it refracts light
DISTANT
- ciliary muscles relax, allowing suspensory ligaments to pull tight
- lens becomes thin (less curved)
so it refracts light less
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the endocrine system
hormones are chemical molecules released directly into the blood, carried to target organs and cells. they control things in organs & cells that need constant adjustment
produced by endocrine glands & have long-lasting effects
ovaries (females):
produce oestrogen, involved in menstrual cycle
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thyroid:
produces thyroxine, involved in regulating e.g. rate of metabolism, heart rate, temperature
adrenal gland:
produces adrenaline, prepares body for 'fight or flight' response
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the pituitary gland produces hormones that regulate body conditions - 'master gland' as these hormones act on other glands, directing them to release hormones that bring about change.
nerves: very fast action, act for a short time, act on a precise area
hormones have slower action, act for a long time & in a more general way
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the kidneys
- make urine by taking waste products & unwanted substances out of blood.
- substances filtered out of blood as it passes through kidneys - filtration
- glucose, some ions, right amount of water absorbed back into blood (useful substances) - selective reabsorption
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control of concentration of urine:
- controlled by anti-diuretic hormone (ADH), released into bloodstream by pituitary gland
- brain monitors water content of blood & instructs pituitary gland to release ADH into blood according to how much is needed
controlled by negative feedback:
- receptors in brain detects water content too high :arrow_right: coordination centre receives info. & coordinates a response :arrow_right: pituitary gland releases less ADH so less water absorbed from kidney tubules :arrow_right: water content decreases
- content too low :arrow_right: more ADH so more water reabsorbed from kidney tubules
kidney failure
waste substances build up in blood & you lose ability to control the level of ions & water in body --> death
dialysis machines filter the blood & has to be done regularly to keep the concentrations of dissolved substances in the blood at normal levels & to remove waste substances
- blood flows between partially permeable membranes, surrounded by dialysis fluid --> permeable to (excess) ions & water & waste substances (e.g. urea) but not big molecules like proteins
- dialysis fluid has same conc. of dissolved ions & glucose as healthy blood so useful dissolved ions & glucose aren't lost from blood during dialysis.
- 3 times a week, 3-4 hours
- may cause blood clots or infections
- not a pleasant experience & is expensive for NHS to run
- buys patient valuable time until a donor organ is found
kidney transplants = cure
from those ppl who have died suddenly, have to be on organ donor register or carry a donor card (+ relatives agree)
can be transplanted from people who are still alive (two kidneys) but small risk to donor
risk that donor kidney is rejected by patient's immune system - treated w/ drugs to prevent this.
transplants cheaper than dialysis (in long term) + put an end to hours spent on dialysis but there are long waiting lists
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controlling fertility
condoms worn over penis during intercourse to prevent sperm entering vagina, only form of contraception that protects against STDs
female condom worn inside vagina
diaphragm shallow plastic cup fits over cervix to form a barrier & has to be used w/ spermicide (substance that disables or kills sperm)
spermicide can be used alone but isn't as effective, only 70-80%
hormones
the pill (combined oral contraceptive pill) contains oestrogen, progesterone. over 99% effective at preventing pregnancy but can cause side effects e.g. headaches, nausea & doesn't protect against STDs
progesterone-only pill - fewer side effects & just as effective
- oestrogen can prevent the release of an egg & if taken everyday to keep the level of it permanently high, it inhibits the production of FSH so egg development & production stops.
- progesterone reduces fertility by stimulating the production of thick mucus which prevents any sperm getting through and reaching an egg.
contraceptive patch contains oestrogen & progesterone (small 5x5cm) patch stuck to skin, lasts one week.
contraceptive implant implanted under skin of arm, releases a continuous amount of progesterone, stopping the ovaries from releasing eggs, makes it hard for sperm to swim to egg & stops any fertilised egg implanting in the uterus - lasts for 3 years.
contraceptive injection contains progesterone, each dose lasts 2-3 months
intrauterine device (IUD) T-shaped device inserted into uterus to kill sperm & prevent implantation of a fertilised egg. plastic IUDs release progesterone & copper IUDs prevent sperm surviving in the uterus
sterilisation involves cutting or tying the Fallopian tubes or sperm duct (between testes & penis).
permanent procedure - very small chance tubes can rejoin.
'natural' methods - find out when in menstrual cycle woman is most fertile & avoiding sexual intercourse on those days. popular w/ ppl who think hormonal & barrier methods are unnatural, not very effective.
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adrenaline & thyroxine
thyroxine released by thyroid gland (neck) & regulates the basal metabolic rate (speed at which chemical reactions in body occur while body is at rest).
stimulates protein synthesis for growth & development & released in response to thyroid stimulating hormone (TSH), released from pituitary gland.
negative feedback system keeps amount of thyroxine in blood at correct level - when level too high, secretions of TSH inhibited, reducing amount of thyroxine released by thyroid gland, so level falls
adrenaline is released by the adrenal glands (above kidneys) in response to stressful or scary situations - brain detects fear or stress & sends nervous impulses to adrenal glands, respond by secreting adrenaline.
prepares body for 'fight or flight' by triggering mechanisms that increase supply of oxygen & glucose to cells in brain & muscles e.g. increases heart rate.
plant hormones
when shoot tip exposed to light, more auxin accumulates on side in shade so cells grow (elongate) faster on shaded side so shoot bends towards light
- auxin controls growth near tips of shoots & roots & controls growth of plant in response to light (phototropism) & gravity (geotropism).
- produced in tips & moves backwards to stimulate cell elongation (enlargement) process which occurs in cells just behind tips.
- if tip of shoot removed, no auxin available so shoot may stop growing.
- extra auxin promotes growth in shoot but inhibits growth in root
- when a shoot is growing sideways, gravity produces an unequal distribution of auxin in tip, more auxin on lower side so lower side grows faster, bending shoot upwards.
- root growing sideways also has more auxin on lower side but the extra auxin inhibits growth so cells on top elongate faster & root bends downwards
investigating plant growth responses:
effect of light on growth of cress seeds:
- put 10 cress seeds into 3 different Petri dishes, lined w/ moist filter paper, label.
- shine a light onto one of dishes from above & two dishes from different directions.
- leave for a week until their responses can be observed --> grow towards light
growth response is due to light if all other variables controlled:
- number of seeds - use same number in each dish
- type of seed - same packet
- temperature - keep Petri dishes in place where temp. is stable (away from heat sources & draughts)
- water - use measuring cylinder to add same amount
- light intensity - keep distance between bulb & dish same
effect of gravity: place 4 seedlings on damp cotton wool in a Petri dish, each w/ roots pointing in a different direction. store dish vertically for a few days in dark --> roots grow downwards
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gibberellin stimulates seed germination, stem growth & flowering.
inducing flowering some plants require certain conditions to flower e.g. longer days, low temperatures but if they are treated w/ gibberellin, they flower without any change in their environment. can be used to grow bigger flowers.
controlling dormancy - many seeds won't germinate until they've been through certain conditions (e.g. a period of cold or dryness) - dormancy. seeds can be treated w/ gibberellin to alter dormancy & make them germinate at times of the year when they wouldn't normally. helps to make sure all the seeds in a batch germinate at same time.
growing larger fruit seedless varieties of fruit do not grow as large as seeded fruit but if gibberellin is aded, they grow larger to match their normal types.
ethene is a gas produced by ageing parts of a plant which influences the growth of the plant by controlling cell division & stimulating enzymes that cause fruit to ripen.
- it can be used to speed up the ripening of fruits - whilst still on plant or during transport to shops.
:arrow_right_hook: fruit can be picked while it is still unripe (firmer & less easily damaged). the gas is then added on its way to the supermarket.
- ripening can be delayed while the fruit is in storage by adding chemicals that block ethene's effect or reduce amount of ethene that the fruit can produce. some chemicals can be used that react w/ ethene to remove it from the air.