biology, physics and chemistry



Homeostasis is how an organism maintains a stable internal environment so that the millions of cells can function properly 

Three examples of homeostasis; correct water levels, constant temperature, correct glucose levels in blood.

Water (osmoregulation)

      not enough water, urinate less, urine more concentrated – dark yellow

      enough water, urinate more often, urine more dilute – pale yellow

Body temperature (thermoregulation)

Skin is largest organ and important in maintaining body temperature. Has receptors providing information on skin temperature

37 deg C optimum for human enzymes so body temp must remain close to this.

Hypothalamus in brain has receptors sensitive to blood temperature

Negative feedback;

Too hot – vasodilation (veins dilate) – blood flows through capillaries near skin surface so can cool down. Sweat – evaporating water removes heat. Oily sebum from sebaceous glands help sweat to spread. Erector muscles make hairs lie flat.

Too cold – vasoconstriction (veins constrict) – blood flow through superficial capillaries restricted – less heat lost so body kept warm. Muscles shiver so energy released in cells. Erector muscles cause hairs to stand up to insulate. Oily sebum from sebaceous glands help waterproof skin.

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Nervous system

Brain – co-ordinates body actions.

      frontal lobe (mental functions)

      cerebral hemisphere (numerical computation, language, emotions)

      medulla (automatic actions e.g. heartbeat, breathing)

      cerebellum (movement and balance)


Carry electrical signals or impulses

Elongated to connect parts of body – elongated bits covered by insulating myelin sheath to increase speed of impulses – have branched endings so can act on many muscle fibres or connect with other neurones

Elongated parts carrying impulses away from cell body = axons

Elongated parts carrying impulses to body = dendrons

      sensory neurones – take impulses from stimulated receptors in sense organs to the CNS

      relay neurones – in the CNS – pass impulses from sensory neurones to motor neurones

      motor neurones – impulses from CNS to muscles or glands 


Gap between neurones – they don’t touch – from neurone a goes via a chemical transmitter (neurotransmitter) to neurone b and then is destroyed or removed.

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Pathway of an impulse;

Receptor in sense organ (stimulus) produces and impulse

Sensory neurone conducts impulse to relay neurone in CNS via synapse (neurotransmitter)

Relay neurone passes impulse on to motor neurone (synapse)

Motor neurone passes impulse on to muscle (or gland) - effectors

Muscle contracts = movement. 

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Investigating skin sensitivity

      Skin covered in receptors(detect touch, temperature pressure and pain)

      Receptors vary in distance apart

      Lips and fingertips very sensitive to touch meaning receptors are close together.

      Test distance by gently touching to points and moving them closer to until you can only feel one.

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Voluntary and reflex responses

      Voluntary- we have complete control over ( walking, speaking and picking things up

      Involuntary(reflexes)- responses we have no control over (blinking and moving part of your body away from pain) 

Reflex arcs

      Kick in when a conscious reaction is to slow to protect the body, reflex action speeds the response time by skipping out the brain. (via spinal cord)

1.     Receptor is stimulated by sharp pin

2.     Causing impulses to pass along a sensory neurone into the  spinal cord

3.     The sensory neurone synapses with relay neurone

4.     The relay neurone synapses with the motor neurone bypassing the brain and sending impulses down the motor neurone

5.     To the muscles causing them to contract in response to the pain from the sharp drawing pin.

Investigating human responses to external stimuli

      Iris reflex – shine a torch into some ones eye and see how the pupil becomes smaller.

      Temperature control- either cool or warm you’re partners skin and see there response

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Hormones and coordination

      Hormones are chemical messages produced by endocrine glands, they coordinate the way which parts of the body function (transported through blood stream)

      The adrenal glands above the kidney make adrenaline

      The pituitary gland in the brain produces a growth hormone FSH- follicle stimulating hormone and LH- luteinising hormone

      In males testes produce testosterone

      In females the ovaries produce oestrogen and progesterone

      The pancreas produces insulin.


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Control of blood glucose

The body needs controlled quantities of glucose for respiration different parts of the body work together to monitor and control blood glucose levels

·      If the blood glucose concentration is too high

·      The pancreas releases insulin

·      Glucose from the blood is then converted to insoluble glycogen in the liver

·      And is removed from the blood

·      The blood glucose level returns to normal

·      If the blood glucose level is to low

·      The pancreas releases glucagon

·      Insoluble glycogen from the liver is then converts to glucose

·      And removed from the blood

·      The blood glucose concentration returns to normal

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·      Diabetes is a condition were the amount of glucose  in the blood is too high

·      Type 1 = cannot produce insulin

·      Type 2 = resistant to insulin

·      The main symptoms are:

·      Urinating more often

·      Becoming more thirsty

·      Increased tiredness

·      Weight loss

·      Blurred vision

Treatment of diabetes


·      Diabetes cannot be cured

·      Diabetics need to lead healthy lifestyles

·      Type 1 diabetics need to inject insulin 

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How drugs affect you

Drugs are chemical substances that affect you’re central nervous system causing changes in you’re behaviour. Many drugs are medicines e.g painkillers antibiotics.

·      Stimulant – speeds up transmission across synapses – you’re reaction times become faster – keep you awake making you physically exhausted

·      Depressant – slow down transmission across synapses – make you drowsy – addictive

·      Painkillers – prevent transmission across synapses – make you drowsy impair vision – felling dizzy itchy

·      Hallucinogens – block pathways in sensory parts of the brain – distort sense perception – make you scared confused easily upset


Paracetamol is a commonly used painkiller and anti-inflammatory, which helps lower body temperature, deadly if overdosed (liver failure)

Cannabis and opiates

Cannabis comes from cannabis plants opiates. Opiates are drugs that come from poppy plants. Both cannabis and opiates are able to relieve pain especially for the terminally ill.

·      They are both illegal

·      People looking into making cannabis legal

Solvents alcohol and tobacco

Solvents alcohol and tobacco can have major mental and physical effects on the body

·      Solvents are depressants that give off different vapours – Physical effects: damage lungs, liver, brain and kidneys. Mental effects: increase reaction times, cause hallucinations and alter behaviour and personality.

·      Alcohol is a depressant that contains the chemical ethanol – Physical effects: short-term use can blurred vision long-term use can lead to damage to the brain and liver (cirrhosis). The liver removes alcohol from the body excess use can lead to unconsciousness, brain damage, coma and death. Mental effects – increase reaction times by slowing down the synapses, can cause depression and can lead to loss of inhibitions and self-control.


Tobacco contain tar and nicotine and produces carbon monoxide when smoked – carbon monoxide is absorbed by haemoglobin in red blood better than oxygen long term use can lead to: emphysema ( alveoli walls break down), build up of mucus cilia stop moving, bronchitis, damage to circulatory system, cancer and increased heart rate and blood pressure and blood pressure because of nicotine narrowing blood vessels 

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The tar in cigarette smoke contains carcinogens (chemical that cause cancer).

These cause cells to mutate and divide uncontrollably, which can form cancerous tumours.

Smoking and poor health 

Studies show that smoking shows a direct correlation with poor health especially with lung cancer

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Plant hormones

·      Plants are sensitive to light and gravity (shoots grow towards the light and roots towards the light/phototropic and gravitropic)

·      The two most important hormones are called auxins and gibberellins: auxins promote cell elongation and gibberellins promote cell elongation and encourage flowering, breaking seed dormancy and can be used to force seedless fruit to develop.


Hormones in solution travel down towards the lower sides of shoots and roots;

·      In the shoots, auxins increase growth in the lower region, which makes the shoot bend upwards.

·      In the roots, the hormones slow down the growth in the lower region, which makes the root bend downwards.


in shoots, light causes auxins to accumulate on the shaded part of the stem , which causes growth on that side and means that the plant grows towards the light.

Commercial uses of plant hormones

·      Gardeners often apply selective weed killers (with a hormone that kills everything but grass) to their lawns.

·      You can place stem cuttings in rooting powder to promote formation of roots so you cake make many identical plants from on original.

·      Fruit gets sprayed with unpollinated flowers with gibberellins so they make fruit faster.

·      Supermarket use ethene to ripen up ripened fruit.

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Meg Ancrum


what unit is this is it biology 1 or 2 ?? :)

Meg Ancrum


what unit is this is it biology 1 or 2 ?? :)

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