Diet And Metabolic Rate


  • In order to keep healthy people should eat a balanced diet which conatins different kinds of nutrients such as: carbohydrates, fats, protein for energy and small amounts of vitamins and mineral ions for keeping healthy. Having an unbalaced diet can lead to someone becoming malnourished or suffer from a deficiency disease.
  • To lose body mass(weight), people may go on a slimming diet where they choose to eat less. Another way of losing body mass is to do more exercise, these two methods both lead to the more energy being used up forcing the body to raid its fat stores as more energy is needed.
  • Metabolic rate is the rate at which chemical reactions take place in your cells.
  • The greater proportion of muscle to fat, the higher the metabolic rate is likely to be and can also increase through exercise.
  • Factors that can affect your meatbolics rate is the genes you inherit from your parents.
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Diet And Cholesterol


  • A high level of cholestreol kn the blood can increase the risk of developing plaque in walls of arteries. Sometimes, a clot blocks one of tye arteries that take oxygenated blood to the heart muscle. This can lead to a heart attack as the heart cannot beat properly.
  • Eating saturated fats which are mainly found in animal produscts can raise blood cholesterol levels, however unsaturated fats that are found in plants can lower blood cholesterol levels.
  • Some people's bodies are better than others at keeping low levels of cholesterol in their blood due to the genes they have inherited.
  • LDL cholesterol is bad and can cause heart attacks.
  • HDL cholesterol is good and can protect again heart disease by helping to remove cholesterol from the walls of blood vessels.
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Pathogens And Infections


  • Microorganisms that causes diseases are called pathogens.
  • Bacteria can reproduce rapidly inside the body. The may produce toxins that are harmful and make us feel ill.
  • Viruses reproduce inside a body cell and destroys it when it bursts out, which then invade other cells.
  • An epidemic occurs hwen a wide spread of people are affected by the disease. a pandemic is where a disease affects a whole country or goes worldwide.
  • A doctor called Semmelweis used evidence from the death rate of women to work out that they were dying because the doctors were transferring bacteria to them from the dead bodies. He made all the doctors wash their hands in chlorine water inbetween each patient, within a short time the death rate plummeted very quickly.
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Phagocytosis And Lymphocyte


  • A phagocyte moves towards a bacterium and then pushes a sleeve of cytoplasm outward to surround the bacterium. The bacterium is then enclosed in a vacuole inside to be killed and then digested by enzymes. This activity is called phagocytosis.
  • Lymphocytes produce chemicals called anibodies. The antibodies group round and stick to the pathogen. This may ill it directly, or stick to other pathogens in clumos so that the phagocytes can destroy them directly.
  •  Some lymphocytes make antitoxins that can stick to the toxins given off by the bacteria and destroy them.
  •  Both antibodies and antitoxins are very specific- each kind only works against a particular pathogen or toxin.
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  • Antibiotic such as penicillin and streptomycin are drugs that kill bacteria inside your body, without killing your own cells. 
  • Antibiotics do not all work eqaully well against all the kinds of bacteria.
  • To find the best antibiotics to kill a bacterium, bacteria are spread on to a jelly. Paper discs soaked in different antibiotics are placed on the jelly and the antibiotics diffuse out. If the anitbiotic killes the bacteria, they do not grow around the disc.
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Antibiotic Resistance


  • Bacteria do not become resistant to antibiotics on purpose. It happens by natural selection.
  • As new antibiotic-resistant strains of bacteria emerge, there is a need to develop new antibiotics to kill them.
  • To reduce the chance of new strains from forming, it is important to reduce the use of antibiotics. Whenever antibiotics are used, it gives an advantage to any mutant bacterium that happens to be resistant to them. If they are not used, then a mutant bacterium does not have any advantage; it is no more likely to reproduce than any other bacterium.
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  • Children in the UK are given the MMR vaccination which makes them immune to the diseases: Measles, Mumps and Rubella.
  • A small amount of dead or inactive viruses that cause the diseases are injected into the blood. The white blood cells attack them just as they would attack living pathogens. This allows them to remember the antibody, so the child is now immune to the disease without having to suffer the symptoms first.
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Nerves And Hormones


  • Nerves contain special cells called nerve cells, which transmit impulses to and from the brain and spinal cord(CNS). Glands secrete chemicals called hormones into the blood. The bloodstream carries the hormones around the body.
  • Most hormones only affect a few organs. These are called tehir target organs.
  • An example of a hormone is adrenaline, which affects the heart, breathing muscle, eyes and digestive system.
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  • Information is carried in the nervous system as electrical impulses. The cells that transmit these impulses are called neurones.
  • The neurones that transmit impulses from receptors to the CNS are sensory neurones.
  • The neurones that transmit impulses from the CNS  to the effectors are called motor neurones.
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Reflex Arc

A refelx arc is a pathway taken by a nerve impulse as it passes from a receptor, through the central nervous system, and finally to an effector.

1) When you stand on a pin, a receptor picks up the stimulus.

2) A sensory neurone carries an impulse towards the spinal cord.

3) The leg muscle contracts and pulls your foot away.


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Impulse Pathway


  • It takes a nerve impulse only a fraction of a second to go along this route which is why reflex actions are so quick.
  • The gaps between the neurones are called synapses.
  • Electrical impulses cannot jump across synapses. When an impulses gets to an end of a neurone, it causes synapses. When and impulse gets to the end of a neurone, it causes a chemical to be secreted. The chemical diffuses across the gap and starts an electrical impulse along the next neurone.
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Hormones And The Menstrual Cycle


At the start of the menstrual cycle, the pituary gland secretes FSH. This causes an egg to mature in one of the woman's ovaries and also stimulate the ovary to secrete oestrogen.

Oestrogen makes the inner lining of the uterus grow thicker. Hight level of oestrogen stops the production of FSH being secreted.

LH stimulates the release of eggs from the ovary.

As the level of FSH drops, the ovary stops secreting oestrogen. This cuts of the inhibition of FSH secretion, so the cycle starts all over again.

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  • IVF stands for 'In Vitro Fertilisation'.
  • The woman is given hormones, such as FSH, to make her ovaries produce several eggs.
  • The eggs are removed and are mixed with her partner's sperm for fertilisation to occur.
  • One of The Embryos is chosen and placed in the woman's usterus. It should hopefully sink into the uterus lining and develop as a fetus.
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Dangers of drugs


  • Recreatinal drug use is when people take drugs because it makes them feel different.
  • Many recreational drugs are legal but still can be harmful to humans, such as alcahol.
  • Some recreational drugs are illegal because they can be a great danger to people, an example is cannabis- may cause mental illness.
  • A drug addiction can have dangerous long-term affects. Over time, the lungs, brain and liver can be seriously damages due to the excessive use.
  • If someone os addicted to a drug, they may suffer from very unpleasant withdrawal symptoms if they stop taking it.
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Drug Trials


A drug trial, on a potential new medicine, contains three stages:

1) The drug is tested in a laboratory on human cells or tissues to find out if it toxic. It may also be tested on live animals.

2) Human volunteers are given different doses, to find out what the highest dose that can be taken safely. Any side-effects are recorded.

3)In clinical trials, the drug is tested on its target illness. It is given to people who have the illness, to see if it makes them better. Some patients are given placebos which do not contain the drug. Neither the patient nor their doctor kniws whether they have a placebo or the real drug(double-blind trial). This helps determine whether the drug really works.

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  • Organisms may have to compete for resources if they are in short supply. For example, plants compete for light- the ones that grow tallest win the competition.
  • The individuals best at competeing are the most likely to survive. Those not good at getting resources are the most likely to die.
  • If there are not enough females to go around, then males will compete for a mate.
  • Animals may also compete for territory.
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Living In Difficult Climates


Plants that live in dry places usually have:

>long, wide-spread roots- the roots grow deep into the soil, to reach water

>small or no leaves- the smaller the leaf surface area, the less the amount of water evaporating away

>tissues that can store water

Animals that live in dry places must be able to manage without much water. For example, the camels' stomachs can hold over 20 litres of water, they can drink very quickly, store water as fat in their humps , and they produce very little urine.

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