AQA GCSE Biology 1A

AQA Biology GCSE

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Diet and Metabolic Rate

CARBOHYDRATES- release energy

FATS- keep warm-release energy

PROTEIN- growth-cell repair- cell replacement

FIBRE-everything moving smoothly through your digestive system

VITAMINS and MINERAL IONS- to keep skin, bones,blood, everything healthy

METABOLISM-chemical reactions

METABOLIC RATE- speed at which they occur



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Factors Affecting Health

* Unbalanced Diet

* MALNOURISHED- badly out of balance-fat or thin

* Eating TOO much-obesity

* Too much SATURATED FAT- increase blood cholestral level

* Too much SALT- high BP and heart problems

* Eating TOO LITTLE- slow growth, fatigue, poor resistance to infection, and irregular periods

* DEFICIENCY DISEASES- lack of vitamins or minerals

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Bacteria: very small, reproduce rapidly, DAMAGING CELLS + PRODUCING TOXINS

* Viruses: not cells, tiny! REPLICATE themselves by invading your cells and using the cells' machinery to produce many copies of themselves.

* cell bursts-releases all the new viruses

* cell damage- makes you feel ill.


* SKIN. HAIR. MUCUS-stop microorganisms getting inside your body

* PLATELETS - help blood clot quickly to seal wounds


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Fighting Disease

The body’s first line of defence is called passive immunity, which means preventing the pathogen from entering in the first place. If a pathogen manages to get into the body, the second line of defence takes over. This is called active immunity. The white blood cells have key functions in this.

White blood cells can:

  • ingest pathogens and destroy them
  • produce antibodies to destroy pathogens
  • produce antitoxins that neutralise the toxins released by pathogens

* White Blood Cells- control for microbes

* 3 lines of attack- 1) Consuming them- whit blood cells ENGULF foreign cells and digest them

                              2) Producing Antibodies- whit blood cell comes across a foreign antigen, they will start to produce proteins called antibodies to lock on to and kill the invading cells. Antibodies are then produced rapidly and carried around the body to kill all similar bacteria or viruses.

                             3) Producing Antitoxins- counter toxins produced by the invading bacteria.

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People can be immunised against a pathogen through vaccination. Different vaccines are needed for different pathogens.

Vaccination involves putting a small amount of an inactive form of a pathogen into the body. Vaccines can contain:

  • live pathogens treated to make them harmless
  • harmless fragments of the pathogen
  • toxins produced by pathogens
  • dead pathogens

These all act as antigens. When injected into the body, they stimulate white blood cells to produce antibodies to fight the pathogen.

The vaccine contains only a weakened or harmless version of a pathogen, which means that the vaccinated person is in no danger of developing the disease.

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Some common diseases like influenza (flu) and the common cold are caused by viruses. These mutate quickly, and this changes their surface proteins. This makes it almost impossible to develop a permanent vaccine against them. A new flu vaccine has to be developed every year, after the strain has been analysed.

There is no vaccine for the common cold because the virus that causes it mutates far too quickly. By the time a vaccine could be developed, the virus would have changed its surface proteins. It would no longer be recognised by the antibodies.

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Fighting Disease-drugs

*Drugs are substances that change chemical reactions in the body.

*Medical drugs relieve disease and illness, and are extensively tested before being used.

*Recreational drugs such as alcohol and tobacco are taken by people because they like the effects they have on their bodies, but they may be addictive.

*Cannabis and heroin are illegal recreational drugs that are very addictive

*Drugs change the chemical processed in the body. People may become dependent on the drug or addicted to it, and may suffer withdrawal symptoms if they stop taking the drug.

*The alcohol in alcoholic drinks such as wines, beer and spirits is ethanol, which is a depressant, meaning that it slows down signals in the nerves and brain.

Alcohol is addictive. Long-term effects of alcohol include damage to the liver and brain, and it is often the cause of weight gain.

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Nicotine is the addictive substance in tobacco smoke. It reaches the brain within 20 seconds and creates a dependency so that smokers become addicted. Smoking increases the risks of:

  • heart disease and strokes
  • miscarriage, premature birth and low birth weight
  • lung cancer, mouth cancer and throat cancer.
  • below left: healthy lung
  • below right: unhealthy lung

the lung is pink ( lung is tinged yellow and has black tar deposits (

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Illegal Drugs

Ecstasy, cannabis and heroin are illegal recreational drugs. Using them can cause health problems.

Heroin and cocaine are very addictive. Like ecstasy, they can damage the heart and circulatory system. Cannabis smoke contains chemicals that cause mental illness in some people.

Injecting a drug using a needle and syringe that someone else has used may lead to a number of diseases from infected blood, including HIV and hepatitis.

Athletes are often under great pressure to perform well. Some drugs are capable of artificially improving their performance; these include:

  • stimulants – these boost heart rate and other body functions
  • anabolic steroids – these stimulate the growth of muscles.
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The Nervous System

The nervous system allows the body to respond to changes in the environment in a process usually coordinated by the brain. Reflex actions are extra-rapid responses to stimuli; this process also involves the nervous system but bypasses the brain.

Receptors are groups of specialised cells that can detect changes in the environment called stimuli. Receptors are often located in the sense organs, such as the ear, eye and skin.

Neurones are nerve cells that carry information as tiny electrical signals. There are three different types of neurones, each with a slightly different function:

  • sensory neurones carry signals from receptors to the spinal cord and brain
  • relay neurones carry messages from one part of the CNS to another
  • motor neurones carry signals from the CNS to effectors.

Where two neurones meet there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neurone releases the chemical into the gap. The chemical diffuses across the gap and makes the next neurone transmit an electrical signal.

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The Nervous System

a neurone has a 'head' at one end where the nucleus, cytoplasm, cell membrane and dendrite are. The axon is tail-like, with nerve endings at the end which look like branches. (

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The Nervous System

When a receptor is stimulated it sends a signal to the central nervous system, where the brain coordinates the response, but sometimes a very quick response is needed, one that does not involve the brain: this is a reflex action.

stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector

Reflex actions are rapid and happen without us thinking. (hot flame example! hand pulls away because of the heat)

Control in the Human Body

The internal environment of the body is controlled by the nervous system and hormones. The maintenance of a constant internal environment is called homeostasis.

Water content is controlled by water loss from:

  • the lungs - when we exhale
  • the skin - through sweating
  • passing urine - produced by the kidneys.
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Control in the Human Body

Ion levels are controlled to protect cells from too much water entering or leaving them. Ion content is controlled by the loss of ions from:

  • the skin - through sweating
  • passing urine - produced by the kidneys.

This is controlled to maintain the temperature at which enzymes work best. Body temperature is controlled by sweating, shivering, and controlling blood flow to the skin.

This is controlled to provide cells with a constant supply of energy. Blood sugar level is controlled by the release and storage of glucose controlled by insulin.

Hormones are chemicals secreted by glands in the body

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Control in the Human Body

Brain: contains a sensitive centre called the hypothalamus, which controls the Pituitary Gland

Adrenal Glands: produces adrenaline which prepares the body for rapid activity

Ovary: produces Oestrogen which causes changes at puberty and helps control the menstrual cycle

Testes: produces testosterone which causes puberty and stimulates sperm production

Pancreas: produces insulin which controls blood sugar levels

Thyroid gland: produces Thyroxine which controls the rate of metabolism

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Control in the Human Body

The menstrual cycle in women is a recurring monthly process in which the lining of the uterus (the womb) is prepared for pregnancy. If pregnancy does not happen, the lining is shed at menstruation.

Several hormones control this cycle, which includes controlling the release of an egg each month from an ovary, and changing the thickness of the uterus lining. These hormones are secreted by the ovaries and pituitary gland.

The hormone FSH is secreted by the pituitary gland. FSH makes two things happen:

  • it causes an egg to mature in an ovary
  • it stimulates the ovaries to release the hormone oestrogen.

The hormone oestrogen is secreted by the ovaries. Oestrogen makes two things happen:

  • it stops FSH being produced - so that only one egg matures in a cycle
  • it stimulates the pituitary gland to release luteinizing hormone (LH), which triggers ovulation (the release of the mature egg from the ovary).
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Control in the Human Body

Human fertility is controlled by hormones. This means that knowledge of hormones can be used to decide to increase, or reduce, the chances of fertilisation and pregnancy.

The oral contraceptive, commonly known as the pill, greatly reduces the chances of mature eggs being produced. It contains oestrogen or progesterone (another hormone). These hormones inhibit the production of FSH, which in turn stops eggs maturing in the ovaries.

Some women have difficulty becoming pregnant because they don't produce enough FSH to allow their eggs to mature. Fertility drugs contain FSH and LH, which stimulate eggs to mature in the ovary.

This increases the risk of complications in pregnancy and childbirth, and may lead to premature or underweight babies.

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Plants produce hormones and respond to external stimuli, growing towards sources of water and light, which they need to survive.

Plants need light and water for photosynthesis. Plant responses - called tropisms - help make sure that any growth is towards sources of light and water.

There are two main types of tropism:

  • positive tropism – the plant grows towards the stimulus
  • negative tropism – the plant grows away from the stimulus.
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