b5

Homeostasis

regulation of internal conditions of an organism or a cell to maintain optimum conditions for cell activity in response to internal or external changes

examples of internal/external changes

temperature, blood glucose concentration, water levels

examples of receptors

nose, tongue, ears, eyes, skin

examples of coordination centres

spinal cord, brain, pancreas

examples of effectors

muscles, glands

synapse

connection between neurones. nerve signals transferred by neurotransmitters, chemicals that diffuse across the gap to stimulate the next neurone

reaction time practical

student holds ruler above volunteer’s thumb, student releases ruler without notice, volunteer catches and records measurement, use a chart to convert distance to time, repeat and calculate a mean

reflex arc

stimuli detected by receptors, sensory neurone carries impulse to spinal cord, impulse is transferred to relay neurone in spinal cord, conveys impulse to motor neurone, effector produces a response

pupil

gap allowing light to pass through

cornea

transparent so light can pass through, refracts light rays with the lens to focus on the retina

accommodation for a near object

ciliary muscles contract and suspensory ligaments loosen to give a smaller diameter. the lens becomes thicker and more curved in shape and light rays are refracted more than usual to focus on the retina

accommodation for a far object

ciliary muscles relax and suspensory ligament tighten to give a larger diameter, the lens becomes thinner and less curved, light rays are refracted a little and focus on the retina

hyperopia

long sightedness, when the eyeball is short or lens can’t be thickened enough, so light rays focus behind the retina

what lens is used for hyperopia

a convex lens, it refracts light rays more (further inwards)

myopia

eyeball is long, light rays focus in front of the retina

what lens is used for myopia

a concave lens, refracts light rays outwards

other treatments for eye conditions

hard and soft contact lenses, laser surgery to change the shape of the cornea, or a replacement lens in the eye

sclera

white, protective outer layer of the eye

adaptions in bright light

circular muscles contract, radial muscles relax, constricting the pupil

adaptions in dim light

circular muscles relax, radial muscles contract, pupil dilates

optic nerve

carries all generated impulses to the brain

iris

coloured part of the eye that controls pupil size

lens

refracts light with the cornea to focus on the retina

retina

contains light receptors

the brain

made of billions of interconnected neurones, controls complex behaviour

cerebral cortex

responsible for vision, language, memory and reasoning

medulla oblongata

controls subconscious and involuntary actions eg breathing

cerebellum

coordinates movement and balance

how can regions of the brain be mapped

studying patients with brain damage (damage in certain areas can show what that area does, eg vision), electrical stimulation of the brain, mri scanning techniques to produce detailed images of the brain

cone cells

allow us to see colour and fine detail, work best in bright light, not very sensitive in dim lighting, concentrated in the fovea

rod cells

detect light intensity, but not colour, help with vision in dim lighting, found mostly in peripheral parts of the retina, do not give sharp images

why is the brain hard to study

it is delicate, complex and behind a skull

thermoregulatory centre

part of the brain, contains blood temperature receptors, connected to temperature receptors in the skin

adaptions for when body temperature is too high

blood vessels dilate (vasodilation), more blood near the skin surface, more heat energy transfer to the surroundings by radiation, sweat glands produce sweat, water in the sweat evaporates and transfers heat energy away

adaptions for when body temperature is too low

blood vessels constrict (vasoconstriction), less blood near the skin surface, less heat energy transfer to the surroundings, sweat glands produce less sweat, muscles contract rapidly (shivering), releasing heat energy through respiration

when there are low levels of water outside the body cell

water leaves cells by osmosis (and vice versa)

ways we lose water that the body cannot control

water vapour in exhaled air and sweat (water, ions and urea)

formation of urea

if there are excess amino acids from protein digestion, the liver will convert them into ammonia (deamination). ammonia is toxic, so it is very quickly converted into urea, which is combined with water and leaves the body in urine

filtration in the kidneys

glucose, ions, water, and urea are filtered into kidney tubules from capillaries. move along the tubule, all glucose is reabsorbed, some ions reabsorbed, some water reabsorbed, no urea reabsorbed. what’s left in the tubules becomes urine and leaves the body

selective reabsorption in the kidneys

all glucose is reabsorbed by active transport, along with some ions, some water by osmosis

what happens when blood is too concentrated (low water levels)

the hormone ADH is secreted from the pituitary gland, this increases the permeability of kidney tubules, so more water is reabsorbed into the blood (negative feedback system)

dialysis

dialysis fluid with no urea and an ideal concentration of solutes enters a dialysis machine. the patient’s blood in the tube tends to have a high concentration of urea, so urea and excess ions diffuse out of the blood into the dialysis fluid across a partially permeable membrane until equilibrium is reached

benefits of kidney transplant compared to dialysis

no build up of toxins in the blood between sessions, no risk of infection from needles when using dialysis, no risk of clots from dialysis

human endocrine system

made of glands that secrete chemicals called hormones into the bloodstream

key glands in the endocrine system

pituitary (base of the brain), thyroid (base of the neck), pancreas, adrenal glands, ovaries (female), testes (male)

pituitary gland

‘master gland’ that secretes several hormones into the blood. these hormones in turn act on other glands to stimulate other hormones to be released to bring about effects

the pancreas monitors

blood glucose concentration

insulin

produced by the pancreas when blood glucose concentration is too high. moves glucose into cells so it is removed from the blood. in the liver and muscles it converts glucose into glycogen to be stored for later use

glucagon

secreted by pancreas when fall in blood glucose concentration is detected. converts glycogen back into glucose

type 1 diabetes

pancreas does not produce enough insulin, treated with insulin injections and low sugar meals

type 2 diabetes

insulin produced but cells do not respond to it. treated with low carb low sugar diet and exercise

testosterone

stimulates sperm production

fsh

causes the maturing of an egg in the ovary, released by the pituitary gland, stimulates oestrogen production

luteinising hormone (lh)

stimulates the releases of an egg, released by pituitary gland, inhibits (lowers) oestrogen production

oestrogen

stimulates the build up of uterus lining, inhibits fsh, released by ovaries, stimulates lh

progesterone

maintains lining of the uterus with lh, inhibits fsh and lh production

oral contraceptives

hormones that inhibits fsh production so no eggs mature

injection, implant or skin patch of slow release progesterone

inhibit the maturation and release of eggs for a number of months or years

fertility drugs

contains fsh and lh to mature and release eggs

in vitro fertilisation (ivf)

fsh and lh given to mature several eggs, eggs are extracted, eggs are fertilised in the lab, eggs develop into embryos, one or two inserted into mother’s uterus

risks of ivf

emotionally and physically stressful, low success rates, can lead to multiple births

negative feedback

where the response is opposite to the change

adrenaline

released in times of fear or stress, increases heart rate to deliver more blood to brain and muscles to prepare for fight or flight response, released by adrenal glands

thyroxine

stimulates the basal metabolic rate (respiration and building and breakdown of molecules), secreted by thyroid gland, important for growth and development

what organ detects thyroxine levels?

brain

positive phototropism

growth towards source of light (shown in the shoot)

negative geotropism

growth away from gravity (shown in shoot)

auxin

coordinates phototropism and geotropism in roots and shoots

high concentration of auxin in shoots

stimulates growth

high concentration of auxin in roots

inhibits growth

how does a shoot bend towards the light

auxin is produced at the tip of the shoot, light causes it to move to the shade side of the shoot, more growth on the shaded side

why does the root bend downwards in plants

auxin is moved to the lower side of the root by gravity, growth is inhibited on the lower side, so the root bends downwards towards water and mineral ions

gibberellins

initiates seed germination (growth), promotes plant flowering and increases fruit size

ethene

controls cell division and ripening of fruits in plants

uses of plant hormones

auxins as weed killers, rooting powders (encourages growth of roots), promoting plant growth in tissue culture, using ethene to control ripening of fruit during storage and transport