Biology Revision


Diet and Exercise

A balanced diet contains the correct proportions of each food type. If the diet is unbalanced a person can become malnourished.

Different people need different amounts of energy because the metabolic rate varies from person to person.

Metabolic rate means the speed of chemical reactions in cells.

Exercise increases the metabolic rate. The proportion of muscle to fat in your body and inherited factors can also affect your metabolic rate.

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Weight Problems

If the energy intake in is the same as the energy you use then your mass will stay the same. If your energy intake is greater you become overweight and obese.

Long-term obesity can lead to Type 2 diabetes (high blood sugar).

The problem of obesity can be reduced by eating less carbohydrate and doing more exercise.

It is unhealthy to have too much food and too little food. People who are underweight find it difficult to walk because of the lack of vitamins and minerals.

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Inheritance, Exercise and Health

Your metabolic rate can be affected by the genes you inherit from your parents.

There are two types of cholesterol- bad cholesterol which can lead to heart disease and good cholesterol which you need for your cell membranes and to make vital substances.

Foods rich in saturated fat can also increase cholesterol levels.

Exercise increases your metabollic rate and lowers high cholesterol levels.

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Pathogens and Disease

Pathogens cause infectious diseases and are tiny microorganisms-usually bacteria or viruses.

When bacteria or viruses enter the body they quickly reproduce and produce toxins that make you feel ill.

Viruses are much smaller than bacteria and reproduce inside cells.

Semmelweiss realised that infection can be transferred from person to person in a hospital and washing your hands can prevent this.

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Defence Mechanisms

The skin prevents pathogens from entering the body.

Pathogens are also trapped by mucus and killed by stomach acids.

White blood cells that are part of the immune system, ingest pathogens, produce antibodies and antitoxins to destroy pathogens.

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Using Drugs To Treat Disease

Antibiotics kill infective bacteria. Penicillin is an example of an antibiotic.

The antibiotic was first discovered by Alexander Fleming in 1928.

Viruses are difficult to kill as they reproduce inside cells.

Some medicines releave the syptoms of the disease but don't kill the pathogen.

Antibiotics cannot destroy viruses.

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Growing And Investigating Bacteria

Bacteria can be grown on agar jelly.

You have to sterilise the equipment before using it-heat up the inoculating loop using a bunsen burner to get rid of unwanted bacteria.

The air contains microorganisms so to keep the bacteria culture pure, the microorganisms in the air must be killed or prevented from entering the culture.

Uncontaminated cultures can be used to investigate the effect of antibiotics and disinfectants on the bacteria.

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Changing Pathogens

Some pathogens, mainly viruses can mutate, which causes disease to spread quickly as not many people are immune to these changed pathogens.

Diseases that spread in a country result in an epidemic. Diseases that spread from country to country result in a pandemic.

Mutations of pathogens produce new strains, some of which are resistant to antibiotics. The antibiotics kill the pathogens that haven't mutated so aren't resistant. The mutated pathogens then multiply and a resistant strain develops (natural selection). Antibiotics should not be used for mild infections to try and slow the rate of mutation and resistant strains.

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Vaccines are made of a dead or inactive form of a pathogen. A vaccine causes white blood cells to produce antibodies which makes the person immune as if that virus ever enters their body the white blood cells will recognise antigen on the pathogens and destroy it.

MMR is a vaccine given for measles, mumps and rubella.

Vaccines protect against bacterial and viral pathogens.

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How Do We Deal With Disease?

People in a society need to be vaccinated in order to protect the from serious diseases. Vaccines can cause side effects.

Advantages of a vaccine:

Protects the individual and society from serious diseases which may cause death.


The antibiotics kill the non resitant pathogens which allow the resistant ones to survive and multiply causing strains of resistant pathogens.

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Responding To Change

The nervous system has receptors to detect stimuli. Receptors are found in sense organs such as the eyes or the nose. For example, light stimulates receptors in the eye that send an electrical impulse to the brain which responds.

Sensory neurons carry impulses to the brain and spinal cord (CNS).

Motor neurons carry impulses from the CNS to effector organs such as muscles.

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Reflex Actions

Stimulus-Receptor-Sensory Neuron-CNS-Relay Neuron-Motor Neuron-Response

Receptor to effector is called reflex arc.

The gap between to neurons is called a synapse. Chemicals transmit the impulse across the gap

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Hormones And The Menstrual Cycle

Three hormones involved:

FSH made by the pituitary gland and causes egg to mature and oestrogen to be produced.

Oestrogen made by ovaries and stops more FSH being produced, causes LH to be produced and makes womb lining develop.

LH made by the pituitary gland and causes the mature egg to be released from the ovary (ovulation).

The menstrual cycle takes 28 days with ovulation about 14 days into the cycle.

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The Artificial Control Of Fertility

The contraceptive pill may contain oestrogen and progesterone to stop FSH so no eggs mature. If a woman cannot produce mature eggs FSH and LH are given known as fertility treatment.

1. Fertility drugs make lots of eggs mature at same time.

2. Eggs collected and put in petri dish.

3. Sample of semen (sperm) collected.

4. Eggs and sperm mixed in dish.

5. Eggs checked if fertilised and early embryos developing properly.

6. When formed tiny balls of cells, 1 or 2 of embryos placed in uterus to develop.

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Controlling Conditions

The body carefully controls its internal environment and the nervous system and hormones help to do this. Homeostasis means keeping a constant internal environment.

Internal conditions that are controlled include:

Water content, ion content, temperature and blood sugar level.

Water leaves the body via breathing out, sweat and excess water is lost in urine produced by the kidneys. We also lose ions in sweat and urine.

Temperature must be constant otherwise enzymes will not function properly.

Sugar in blood is the energy source for cells. The level of sugar in blood is controlled by the pancreas.

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Hormones And The Control Of Plant Growth

Plants are sensitive to light, gravity and moisture.

Phototropism-shoots grow towards light

Gravi/geotropism-roots grow towards gravity

Hydrotropism-grows towards moisture

Negative/Positive tropism-away/towards stimulus

Auxin controls these responses.

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Using Hormones

Women use hormones to prevent/help them get pregnant. Taking hormones for a long time can lead to side effects.

Plant hormones are use dto kill unwanted plants, encourage roots to grow and encourage fruit to ripen. If used incorrectly they can cause damage to the environment.

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Developing New Medicines

Substances are tested to see if they might cure a disease or relieve syptoms.

Tests in laboratories on organs, cells and tissues, on animals, healthy human volunteers and then on patients.

Placebos don't contain drug so half of the patients have placebo and don't know. This is to see if the drug actually has an effect on the patients.

A double-blind trial means neither the doctor nor the patient know if it is a dummy drug or the real thing.

Drugs must be tested to deem they are safe and have no harmful side effects such as the sleeping pill (thalidomide) which caused morning sickness in pregnant women.

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How Effective Are Medicines?

Statins lower the amount of bad cholesterol in the blood. Statin is given daily to the elderly and has meant heart disease and strokes have gone down by 40%.

Herbs are also used as a drug as a medicine. To find out if herbs work better than normal medicines you would have to use a double blind trial.

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Useful drugs are made from natural substances for a long time.

You have to test a drug over a long period of time to make sure there are no bad side effects.

Recreational drugs are used for pleasure such as heroin or cocaine.

If you stop taking addictive drugs you will suffer from withdrawal symptoms.

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Legal and Illegal Drugs

Medicinal drugs control disease or help people suffering and are only available by prescription from a doctor.

Recreational drugs are used for pleasure and affect the brain and nervous system. They also have affects on the heart and the circulatory system. They are very easy to become addicted to.

Nicotine and caffeine are legal drugs used recreationally.

Cannabis and heroin are illegal drugs used recreationally.

Some drugs used medicinally can be used illegally like stimulants used by sports people.

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Does Cannabis Lead To Hard Drugs?

Cannabis can cause mental illness and teenagers risk getting depression from taking it.

It is an illegal drug sold by dealers which brings the buyer into contact with other drugs such as heroin.

Not all cannabis users go on to take hard drugs.

Nearly all heroin users previously smoked cannabis.

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Drugs in Sport

Steroids are used to build up muscle mass and other drugs are used to increase stamina.

The drugs are very expensive and gives and unfair advantage to those who can afford them.

The drugs can harm the body permanently and can lead to death.

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Adapt And Survive

Plants need light, carbon dioxide, water, oxygen and nutrients to survive.

Animals need food from other organisms, water and oxygen.

Special features of organisms are called adaptations. They allow them to survive in extreme conditions such as high temperature, salt levels and high pressure.

Plants are adapted to obtain light by photosynthesis. Animals mouthparts are adapted to their diet.

Extremophiles are microorganisms which are adapted to living in conditions where enzymes don't work because they would denature.

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Adaption In Animals

Animals in cold climates have thick fur and blubber to keep warm. Some are white in winter for camouflage so are not easily seen.

Animals in hot climates conserve water and keep cool. Some have large surface areas like on the ear to keep them cool.

Bigger animals have a smaller surface area compared to volume. So, they conserve energy more easily but find it more difficult to cool down.

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Adaptations In Plants

Plants need light, water, space and nutrients to survive.

They lose water as water vapour through holes in the leaves called stomata.

An extensive root system collects more water.

Small waxy leaves conserve water as well as a swollen stem to store water.

Plants develop thorns, poisonous chemicals and bright colours to warn animals off to prevent themselves from being eaten.

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Competition In Animals

Animals compete for water, space, mates and breeding sites.

Predators compete with their prey as they want to eat them.

Predators and prey use camouflage for their own advantage.

Prey compete with each other to escape predators and for food.

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Competition In Plants

Plants compete for water, nutrients and light.

Some plants use animals to spread their fruits and seeds and others use the wind or min-explosions to spread their seeds.

Large root systems are one adaptation to collect more water than other plants.

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How Do You Survive?

Fig wasps have special shaped heads for getting into fig tree flowers and ovipositors to allow them to place eggs deep inside the flower. 

The star nosed mole lives underground and is almost blind but is sensitive to touch and smell.

Venus fly traps have sweet sickly nectar and bright red colouring inside to attract insects.

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Measuring Environmental Change

Non living factors which might change in the environment are temperature, rainfall, light and oxygen levels.

Living factors which might change are new predators, diseases and new plants.

Lichen indicate the level of air pollution. The more lichen the cleaner the air. They are an indicator species.

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The Impact Of Change

Changes in the environment affect the distribution of living organisms.

Sometimes it is difficult to find what the change is.

Birds may fly North if the climate is getting warmer. The fall in the bee population may have been caused by chemical sprays used by farmers, a disease and possibly changes in flower patterns due to climate change.

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