homeostasis and response gcse biology

what is homeostasis?

maintaining a stable internal environment

what is negative feedback?

a response to a change in the body that counteracts or opposes the initial change

what are the components of automatic control systems?

receptors, coordination centers, effectors

what are the components of the nervous system?

CNS (consists of the brain and spinal cord only)

sensory neurones - carry information as electrical impulses from receptors to the CNS

motor neurones - carry electrical impulses from the CNS to effectors

effectors - muscles and glands which respond to nervous impulses

what is a synapse and how does it work?

- a gap between two neurones

- transfers the electrical signal between two neurones by converting it to a chemical signal which diffuses across the gap

- then converts it back into a new electrical signal in the next neurone

what is the reflex arc?

- neurones in the reflex arc go through the spinal cord or an unconscious part of the brain

- a stimulus is detected by receptors

- impulses are sent along a sensory neurone to the CNS

- when the impulse reaches a synapse chemicals are released which causes impulses to be sent along the relay neurone

- when this impulse reaches another synapse the same thing happens and causes impulses to be sent along the motor neurone

- this takes these impulses to the effector eg a muscle which contracts

what is the investigating reaction time required practical?

- hold a ruler between your thumb and finger making sure the zero is in line with them

- have someone let go of the ruler and as quickly as you can grab onto the ruler

- measure the distance that the ruler fell

- repeat the test several times to calculate the mean distance

- drink a caffeinated drink and wait ten minutes then repeat the experiment

what happens to your body when you are too hot?

- thermoreceptors detect body temp is too high

- thermoregulatory centre acts as a coordination centre

- effectors produce a response: hairs lie flat, sweat is produced and evaporates from the skin transferring energy to the environment, vasodilation occurs to transfer more energy to the environment

what happens to your body when you are too cold?

- thermoreceptors detect your body temp is too high

- thermoregulatory centre acts as a coordination centre

- effectors produce a response: hairs stand up to trap insulating layer of air, no sweat is produced, vasoconstriction occurs, shivering happens which needs respiration which transfers energy to warm the body

what are hormones?

- chemical molecules released directly into the blood

- they only affect target organs

- they are produced by endocrine glands

- they have long lasting effects

what is the pituitary gland?

- master gland

- it produces many hormones and often these hormones act on other glands, directing them to release hormones

what is the thyroid?

- gland in the throat

- produces thyroxine which regulates rate of metabolism, heart rate, and body temperature

what is the adrenal gland?

- produces adrenaline for fight or flight

what are the ovaries?

- produce oestrogen

what is the pancreas?

- gland behind the stomach that produces insulin

what are the testes?

- produce testosterone which controls puberty and sperm production

what's the difference between nerves and hormones?

- nerves are fast, hormones are slow

- nerves act for a short time, hormones act for a long time

- nerves act on a precise area, hormones act in a general area

which gland monitors blood glucose?

pancreas

what happens if blood sugar is too high?

- pancreas releases insulin into bloodstream

- insulin binds to receptors on certain cells (liver and muscle)

- tells them to absorb some of the glucose in your bloodstream

- glucose molecules are combined together to form glycogen

what happens if blood sugar is too low?

- pancreas releases glucagon into the bloodstream

- glucagon travels around body and binds to liver cells

- breaks down glycogen into glucose and releases them into the bloodstream

what is type 1 diabetes and how can it be treated?

- the pancreas doesn't produce enough insulin

- means blood glucose can rise to a fatal level

- treated with insulin injections, the amount of insulin is based on diet and exercise

what is type 2 diabetes and how is it treated?

- a person becomes resistant to their own insulin

- controlled by eating a carbohydrate controlled diet and exercising (when you exercise your muscles absorb more glucose from the blood)

what do the kidneys do?

filter blood and produce urine

what substances are removed from the body in urine?

urea - ammonia is produced during deamination (proteins can't be stored, so any excess amino acids are converted into fats and carbohydrates which can be stored). ammonia is toxic so it's converted to urea in the liver

ions - if the wrong balance of ions is in the body, the water to ion balance will be off meaning cells will either take in too little or too much water, so they won't work as well as normal. the kidneys decide how many ions go into the body and how many are lost in urine

water - the body constantly loses water eg from sweating and breathing out. the kidneys control how much water is lost in urine to maintain the balance.

what controls the concentration of urine?

hormone called 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

how does a dialysis machine work?

- the blood flows between partially permeable membranes surrounded by dialysis fluid. the membranes are permeable to small molecules eg ions and waste substances but not big molecules like proteins

- dialysis fluid has the same concentration of ions and glucose as healthy blood

- this means useful dissolved ions and glucose won't be lost from the blood during dialysis

what are advantages and disadvantages of dialysis?

advantages:

- saves lives

- can provide valuable time until a donor is found

disadvantages:

- takes up time in someone's life

- may cause blood clots or infections

- it's unpleasant for the patient

- it's expensive for the NHS

what are the advantages and disadvantages of kidney transplant?

advantages:

- no need to control diet

- no sessions required, more freedom

- cheaper in the long run

disadvantages:

- surgery carries risks

- not always organs available

- kidney can be rejected

what are the four stages of the menstrual cycle?

- stage 1: day 1 menstruation starts and the uterus lining breaks down for 4 days

- stage 2: day 4-14 uterus lining builds up again into a thick spongy layer full of blood vessels

- stage 3: day 14 ovulation

- stage 4: day 14-28 the wall is maintained. if no egg is released the cycle starts again

what does FSH stand for and what does it do?

- follicle stimulating hormone

- produced in the pituitary gland

- causes an egg to mature in one of the ovaries

- stimulates the ovaries to produce oestrogen

what is oestrogen?

- hormone produced in the ovaries

- causes the lining of the uterus to grow

- stimulates the release of LH and inhibits the release of FSH

what is LH and what does it do?

- luteinising hormone

- produced by the pituitary gland

- stimulates the release of an egg to

what does progesterone do?

- produced in the ovaries

- maintains the lining of the uterus during the second half of the cycle

- inhibits the release of LH and FSH

how do hormones reduce fertility?

- taking oestrogen inhibits the production of FSH which stops egg development

- taking progesterone produced thick mucus which prevents sperm getting to the egg

what are some examples of hormonal contraceptives?

- a contraceptive patch that is stuck to the skin. lasts a week.

- the implant releases progesterone under the skin. lasts 3 years.

- contraceptive injection contains progesterone. lasts 2-3 months.

- IUD inserted into the uterus to kill sperm and prevent implantation of a fertilized egg. plastic ones release progesterone, copper ones prevent sperm surviving

what are some examples of non-hormonal contraceptives?

- condoms prevent sperm entering as well as STDs

- a diaphragm along with spermicide forms a barrier and kills any sperm that gets past

what are some other methods of contraception?

- sterilisation: cutting/tying the fallopian tubes or sperm duct

- natural methods: tracking a woman's fertility cycle

- abstinence

how can hormones increase fertility?

- some women have low FSH levels so their eggs don't mature and aren't released

- giving FSH and LH stimulates ovulation

what are the pros and cons of using hormones to increase fertility?

- pros: helps many women get pregnant

- cons: doesn't always work, expensive, could result in twins or triplets if too many eggs are stimulated

how does IVF work?

- eggs are collected from the woman's ovaries and fertilised in a lab using the man's sperm

- fertilised eggs are grown into embryos in an incubator

- once they have developed into tiny balls of cells, 1-2 are implanted into the woman's uterus

what are the pros and cons of IVF?

- pros: gives an infertile couple a child

- cons: high chance of multiple births is risky for the mother and the baby, success rate is low making it stressful, some women have physical reactions to the hormones given to stimulate egg maturity eg abdominal pain and vomiting

what is adrenaline?

- hormone released by adrenal glands when brain sends nervous impulses

- increases heart rate, breathing rate, and blood glucose concentration

what is thyroxine?

- regulates metabolism and stimulates protein synthesis

- it's released in response to to thyroid stimulating hormone, which is released from the pituitary gland

what are the main parts of the brain and what does each one do?

- cerebral cortex: consciousness, intelligence, memory, language

- medulla: unconscious activities eg breathing and heartbeat

- cerebellum: muscle coordination

- spinal chord

how can the brain be studied?

- studying patients with brain damage

- electrically stimulating the brain to observe which parts control which part of the body

- MRI scans

what is the sclera?

tough supporting wall of the eye

what is the cornea?

transparent outer layer at the front of the eye, refracts light into the eye

what is the iris?

coloured part of the eye. contains muscles that control the diameter of the pupil and therefore how much light enters the eye

what is the lens?

refracts light to focus it into the retina

what is the retina?

covers back of eye, contains receptor cells that are sensitive to light and colour

what is the optic nerve?

the nerve that carries neural impulses from the eye to the brain

what does the iris do if it's too bright?

- circular muscles contract

- radial muscles relax

- this makes the iris smaller and reduces the amount of light that can enter the eye

what does the iris do if it's too dark?

- circular muscles relax

- radial muscles contract

- makes pupil bigger and increases amount of light that enters the eye

what happens to the lens when looking at near objects?

- ciliary muscles contract

- suspensory ligaments slacken

- lens becomes fatter

- increases the amount that light refracts by

what happens to the lens when looking at near objects?

- ciliary muscles relax

- suspensory ligaments pull tight

- lens goes thin and flatter

- light is refracted by a smaller amount

what causes long sightedness?

when the light is focused behind the retina. either the eyeball is too short or the lens is the wrong shape and doesn't refract enough. wear concave lenses to help.

what is auxin and what does it do?

- plant hormone that controls the growth of tips of roots and shoots in response to light or gravity

- promotes growth in shoots, inhibits growth in roots

why do shoots grow towards light?

- auxin accumulates on the shaded side, so cells grow faster on this side

- this makes the shoot grow towards the light

why do shoots grow away from gravity?

- when a shoot grows sideways auxin accumulates on the lower side

- this means the lower side grows faster, so the shoot points upwards

why do roots grow towards gravity?

- auxin accumulates on the lower side

- this means the lower side grows slower so the root bends downwards

what are commercial uses of auxin?

- killing weeds: selective weed killers attack broad leaves plants such as weeds using auxin to disrupt their growth pattern which kills them

- growing from cuttings: auxin is added to rooting powder to make a cutting produce roots rapidly and start growing new plants (clones) quickly

- growing cells in tissue culture: add auxin to the growth medium along with nutrients to stimulate the cells to divide

what are commercial uses of gibberellin?

- controlling dormancy: makes seeds germinate at certain times of year and all at the same time

- induces flowering: plants will flower without necessary environmental conditions. also creates bigger flowers

- growing larger fruit: gibberellin is added to seedless fruit to make them grow as big as seeded fruit

what are commercial uses of ethene?

- ethene influences the growth of the plant and stimulates enzymes that cause fruit to ripen

- fruit can be picked underripe then transported and added ethene once at the shops so it will be shelf ripe