Gcse Aqa Biology Unit 1

GCSE AQA BIOLOGYUNIT 1

B1a HUMAN BIOLOGY

1. Co-ordination and control

2. Healthy eating

3. Drug Abuse

4. Controlling disease

B1b EVOLUTION & ENVIRONMENT

5. Adaptation

6. Variation

7. Evolution

8. How people affect the planet

REVISION

1. The Nervous System

• N.S. uses electrical impulses to enable you to react to your surroundings + co-ordinate behaviour

• Sense organs contain receptor cells which detect stimuli

- receptors change stimulus energy into electrical impulses

• Neurones (nerve cells) transmit info (as electrical impulses) v.quickly to and from CNS

• CNS where info from receptors is sent + where reflexes and actions are co-ordinated.

• Effectors respond in diff. ways: - muscle contract- glands secrete hormones

• STIMLULUS RECEPTOR SENSORY NEURONE CNS (co-ordinator) MOTOR NEURONE EFFECTOR

Sensory Neurone:

Motor Neurone:

1. Reflexes• Reflex actions are automatic, rapid responses to

certain stimuli- reduce chances of injury because no

thinking about response: quicker: V.FAST• Route taken by info in a reflex is reflex arc

- bypasses conscious areas of brain (usually through spinal cord)

• STIMULUS RECEPTOR SENSORY NEURONE RELAY NEURONE MOTOR NEURONE EFFECTOR

• e.g. of reflex:- hand withdrawn from hot/sharp object- shock hormone adrenaline released - bright light pupils get smaller- breathing/ moving food through gut

The Reflex arc in detail

1. Synapses

• Impulse arrives at synapse

• Sacs release chemicals called neurotransmitters

• Chemicals diffuse across gap (synapse)

• Chemicals arrive at receptor sites on next neurone

• This triggers a new electrical impulse.

1. Hormones• Hormones are chemical messengers, secreted

by special glands, that are transported in the blood to activate target organs/cells

• Pituitary gland LH, FSHOvaries oestrogenPancreas insulinTestes testosteroneAdrenal gland adrenalineThyroid gland

Nerves Hormones

v.fast message

Slower message

Act for short time

Act for long time

Precise area More general way

Electrical message

Chemical message

1. The Menstrual Cycle• Stage 1: bleeding starts. Uterus lining breaks down for

about 4 days. [At the same time, a new egg begins to mature in ovary]

• Stage 2: lining of uterus builds up again (from day 4-14) into thick layer ready to receive a fertilised egg

• Stage 3: mature egg is released from ovary: ovulation. • Stage 4: lining is maintained for about 14 days, until day

28. If no fertilisation by day 28 lining starts to break down.

1. The menstrual cycle’s controlled by hormones

• FSHcauses egg to develop/mature in one of ovariesstimulates ovaries to produce oestrogenproduced in the pituitary gland

• Oestrogencauses lining of uterus to thicken and growstimulates production of LH & inhibits production of FSHproduced in ovaries

• LHstimulates ovulation produced in pituitary gland

1. Hormones used in contraception...

Oral contraceptives (contraceptive pills) prevent release of eggs from ovaries.

• BECAUSE.. They contain oestrogen, which (when taken everyday to keep levels high) inhibits the production of FSH so no eggs can mature, and thus prevents pregnancy.

• Only a doctor can prescribe; ensures as little risk as possible.ADVANTAGES• Over 99% effective @ preventing pregnancy• Has helped to make families smaller (dev. world) less

poverty because people have fewer mouths to feed• China help control population• Can reduce risk of some types of cancerDISADVANTAGES• Can cause side effects; headaches, nausea, irreg. period• Can also cause blood clots, high BP, heart attacks, stroke• Must be taken regularly, if forgotten, body’s own hormones

can take over v.quickly. Could result in unexpected pregnancy.

• Doesn’t protect against STI’s• Ethical issues: religious groups conception = denying life

(so forbidden).

1. Fertility treatment

• FSH can be taken by women who do not produce enough (so can’t get pregnant as eggs cannot mature) to stimulate ovaries to produce oestrogen, which stimulates production of LH, so ovulation can occur

ADVANTAGES• Helps women get pregnant when they couldn’tDISADVANTAGES• Doesn’t always work• Too many eggs could be stimulated, could result in

multiple pregnancies.

1. IVF- ‘in vitro fertilisation’1. Fertility drugs (hormone; FSH) are used to make lots of

eggs mature at the same time, so they can be collected.

2. Once eggs are collected, they’re placed in a special solution in a petri dish.

3. A sample of a man’s semen is collected, and mixed with the eggs in the petri dish.

4. Eggs are checked to make sure they have been fertilised and early embryos are developing properly

5. When the fertilised eggs have formed tiny balls of cells, 1 or 2 of the tiny embryos are placed in the uterus of the mother.

• Some women have v.strong reactions to hormones used (abdominal pain, dehydration, vomiting)

• Ethical implications SPARE EMBRYOs designer babies

1. Controlling Conditions• Homeostasis is the result of the coordination of the N.S.,

hormones and body organs.• Humans need to maintain a constant internal environment

by balancing inputs with outputs• Water content need to keep a balance with

water you drink+ produce in respiration with water lost in urine, sweat and breathing.

• Body Temp get rid of excess body heat when hot, but retain heat when environment is cold.

Controlling water and ions• Water and salt lost in urine (made in kidneys). • Kidneys can change amount of salt and water lost in urine,

depending on body conditions. • Some ions lost in sweat.• Sports drinks (usually contain electrolytes and

carbohydrates).The electrolytes (e.g. sodium) replace those lost in sweat, while the carbohydrates can give an energy boost.

• BUT claims about sports drinks need to be looked at carefully.

1.Controlling ConditionsControlling Temperature• Vital core body temp kept @ 37C• Temp enzymes work best at• Sweat cool down• Shiver warm up

Controlling blood sugar• Digest food sugar passes into blood• Levels would be v.high after meal….but low

again few hours after.• BUT conc. of glucose in blood kept constant by

insulin hormone made in pancreas.

N.S. v.important in coordinating responses to temp.

2. Healthy Eating• Balanced diet; right balance of different foods you need

and right amount of energy.• Diet not balanced= malnourished too fat/too

thin/deficiency • Carbs. provide energy• Fats provide energy + insulation, energy store• Protein growth + repair• Vitamins various functions (e.g. Vit.C prevents scurvy)• Minerals various functions (e.g. iron to make

haemoglobin)• Water constant supply needed to replace water lostEnergy and Nutrient needs vary in diff. people…Energy and Nutrient needs vary in diff. people…• Age children+teens need more protein for growth

old people need more calcium to protect against degenerative bone diseases such as osteoporosis

• Gender females need more iron to replace that lost in menstrual blood

• Physical activity active people more protein for muscle development & more carbs. for energy.

-simple sugars like glucose-fatty acids + glycerol-amino

acids

diseases

2. Metabolic Rate• Amount of energy you need also depends on ‘resting

metabolic rate’• Energy is needed to fuel chemical reactions in body. Speed

at which these reactions occur is called metabolic rate.• Metabolic rate varies from person to person.• Muscle needs more energy than fatty tissue• So people with a higher proportion of muscle to fat in their

bodies will have a higher metabolic rate. e.g. men tend to have a higher metabolic rate than woman

• [metabolic rate can be boosted with regular exercise because it builds muscle]

• Metabolic rate also affected by amount of physical activity and possibly genetic factors inherited from parents.

The less exercise you do, the less food you need

2.Weight Problems• BMI used as a guide to indicate under/over weight• BMI = Body mass ÷ (height)²

In developed countries problem of too much food;• Obesity too much sugary/fatty food & too little exercise.

or because of underactive thyroid gland (uncommon)

Increases risk of diabetes, arthritis, high BP, coronary heart disease

Losing weight…• Reduce energy intake (cut back on amount of food)• Increase amount of energy you use up (more exercise)• Doing both is best way to lose weight effectively

Slimming groups the wish to make a profit may lead to exaggerated claims for the method or product.

look for scientific evidence…must not contain bias from experimenter [see p33 CGP health claims]

2. Weight Problems

• In developing countries there may be a lack of food;Starvation can become v.thin + muscles waste away

weak immune system; reduced resistance to infection

females; irregular/completely stopped periods

Same symptoms can be seen with people with anorexia nervosa

2.Cholesterol• Made in liver, transported in blood• Needed to make cell membranes & sex + stress hormones• High cholesterol level = increased risk of heart disease.

because blood vessels get clogged with fatty cholesterol deposits (can even block them entirely heart attack)

• Liver (controls amount of cholesterol in blood) makes new cholesterol and removes it from blood

• The amount liver makes depends on amount of fat in your diet (and inherited factors that cant be changed)

Cholesterol is carried around the body attached to proteins. Combination of cholesterol and protein called lipoprotein.• Low-density lipoproteins (LDLs) carry fat to cells: ‘bad’

cholesterol; raised levels of LDLs increase risk of heart disease b’coz excess LDLs can cause build up of C in arteries

• High-density lipoproteins (HDLs) carry cholesterol to liver for removal from the body: ‘good cholesterol’

• Balance of HDLs to LDLs is v.important

2..Cholesterol• Level of cholesterol in body affected by amount and type of

fat in diet;– Saturated Fats- raise blood cholesterol levels. Found in

animal fats; meat, butter, cheese– Mono-unsaturated Fats- seem to reduce overall blood

cholesterol + improve balance between HDLs and LDLs. Found in olive oil, olives, peanuts, many margarines

– Polyunsaturated Fats- seem to be even better at reducing overall blood cholesterol + improving balance between HDLs and LDLs (than mono-unsaturates). Found in corn oil, sunflower oil, many margarines and oily fish

2. SALT• Too much salt can cause high BP • Particular problem for about 30% of the UK population

who need to carefully monitor how much salt they eat• High BP can damage heart and kidney, and can crease

risk of heart disease or a stroke• Processed foods often contain a high proportion of fat +

salt

3. STATINS

• Evidence that drugs called statins lower blood cholesterol and significantly lower the risk of heart disease in diabetic patients

• Original research done by government scientists with no connection to manufacturers. Sample was v.big 6000 patients

• Compared 2 groups of patients (those who had statins, those who hadn’t). Other studies have backed up these findings.so control groups were used + results were reproducible

3. Drugs• Drugs alter the chemical reactions in the body so people

may become dependant or addicted to them and suffer withdrawal symptoms without them

• Drugs can be medically useful (e.g. antibiotics penicillin)• Many drugs derived from natural substances have been

known to indigenous peoples for many years• Tolerance develops with some drugs; the body gets used

to having it and so you need a higher dose to give the same effect. (this can happen with legal and illegal drugs)

• Alcohol, tobacco (nicotine) and illegal drugs may harm your body.

• Smoking cannabis may cause psychological problems• Hard drugs such as cocaine and heroin are v.addictive

and can cause serious health problems (some from the drug itself, but others from the lifestyle may turn to crime, not eat properly, STDs & HIV/AIDS)

3. DrugsWhich class a drug is in depends on how dangerous it is;• CLASS A

– Heroin, LSD, ecstasy, cocaine• CLASS B

– Amphetamines (but class A if prepared for injection), cannabis

• CLASS C– Anabolic steroids, tranquilisers

CANNABIS…Many scientists have looked at whether cannabis causes brain damage and mental health probs. or leads to further drug taking. The results vary and are sometime open to diff. interpretations.

Until more evidence is found…no one’s sure.

The overall impact of legal drugs on health is much greater than the impact of illegal drugs bcoz more ppl use them

3. How drugs affect you…• Many drugs affect nervous system; this can affect

behaviour which can be potentially dangerous (either for druggie or others)

• E.g. driving or operation machinery• Some drugs can affect people judgement ‘losing their

inhibitions’ = relaxing more / taking more risks• Drug abuse can affect immune system- increase risk

infection• Depressants [e.g. alcohol, barbiturates, solvents] ;

decrease the activity of the brain. This slows down the response of the N.S. causing slow reactions + poor judgement of speed and distance.

• Stimulants [nicotine, ecstasy, caffeine]; increase activity of brain. Make you feel alert and awake.

• Some people use recreational drugs (like caffeine, nicotine, alcohol) to help them cope with everyday life.

• Other people might use other recreational drugs for excitement or escape.

• Some drugs are taken to enhance performance in sport

3. Alcohol

• Absorbed through the gut and into your bloodstream carried to the brain from there it affects the N.S.

• Reduces activity of the N.S.- slowing your reactions. Can make you fee less inhibited- helps you socialise and relax

• Too much leads to impaired judgement, poor balance + coordination, lack of self control, unconsciousness

• Alcohol in excess causes dehydration, which damages brain cells, a noticeable drop in brain function. And too much drinking causes severe damage to the liver liver disease.

• Alcohol abuse over many years (alcoholics) can cirrhosis of liver (destroys liver tissue) they can also get liver cancer.

• Social costs; linked to violent crime, domestic assaults etc.• Costs to NHS are huge, but v.small related to crime (police

time, damages) and the economy (lost working days) that may be caused by alcohol.

3.Smoking• Tobacco smoke contains carbon monoxide- this combines

irreversibly with haemoglobin so the blood carries less oxygen. Pregnant women; can deprive foetus of oxygen born underweight/stillborn/premature

• Tobacco smoke contains carcinogens (e.g. tar); chemicals that can lead to cancer. Lung cancer more common in smokers than non-smoker

• Incidence rate and mortality rate of lung cancer are similar; means lung cancer kills most who get it

• Smoking can cause heart disease (+ diseased blood vessels) [leading to heart attacks+strokes], damage to lungs [leading to emphysema + bronchitis

• Tar in cigarettes damages cilia in your lungs and windpipes (the cilia and mucus catch dust and bacteria before it reaches the lungs) chest infections are more likely

• Tar builds up in lungs (makes it more likely for people to get bronchitis) also the build up can lead 2 delicate air sacs in the lung breaking down emphysema.

• Tobacco contains nicotine with is v.addictive

See p 55 smoking and pregnant.

3.Lung Cancer & Smoking• In the first half of the 20th century it was noticed that lung

cancer and the popularity of smoking increased together. And studies found that far more smokers than non-smokers got lung cancer

• But it was just a statistical correlation at that time it didn’t prove that smoking caused lung cancer. Some people argued that there was some other factor (e.g. a person’s genes) with both caused lung cancer and also made them more likely to smoke.

• Later research eventually disproved these claims now even the tobacco industry had had to admit that smoking does increase the risk of lung cancer

3. Drug testing

• When new medicines are developed they have to be tested and trialled extensively before being used.

• Drugs are tested to see if they are effective, safe (must not be toxic or have unexpected side effects), stable (medicine can be used in normal conditions and stored), and successfully taken into and removed from your body (body must be able to remove the medicine once it has done its work).

• Thorough testing procedure;– Computer models simulate human response to a drug.

Identifies promising drugs to be tested @ next stage (not accurate because not live organism)

– Then drugs are tested on human tissue in the lab.– Next step is to test on live animals (Brit. Law 2 dif. live

mammals)

– After drug has been tested on animals it’s tested on human volunteers in a clinical trial to help determine if there are any side effects.

3.Clinical Trials• Involve 2 groups;

– One group given new drug, other group given a placebo. So that scientists can see the difference the drug makes and allows them to see the placebo effect

• Clinical trials are blind; patient doesn’t know what they’re getting

• Or they are double blind; neither doctor nor patient knows.

Developing new drugs is expensive;• New drugs can take many years to develop and test

before they are at a stage where they can be put to use• Most potential drugs are rejected during trials• All of this adds to the cost of coming up with a new drug

that can be used safely on humans

Pathogens• Micro-organisms that cause disease are known as

pathogens.

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