B1.1 Keeping Healthy


B1.1.1 A Healthy Diet

A healthy diet contains the right amounts and proportions of nutrients and energy that the body needs to stay healthy

Food contains:

  • Carbohydrates, fats and proteins
  • Used to release energy, and provide nutrients to build cells
  • Mineral ions and vitamins
  • Needed in small amounts so cells can wok properly

People who do not have balanced diets may become malnourished, this can result in:

  • Becoming very underweight
  • Becoming very overweight
  • Conditions sucha s type 2 diabetes
  • Deficiency diseases caused by too little of a nutrient
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B1.1.1 Controlling Mass

Energy is expended during exercise- the balance between energy taken in with food and energy expended affects your mass:

  • More energy expended in exercise than gained in food = body loses mass
  • More energy gained in food than expended in exercise = body gains mass

Metabolic rate

The rate at which all the chemical reactions are carried out in the body.

Metabolic rate is affected by many factors:

  • The proportion of muscle to fat in your body
  • How much exercise you do
  • Some inherited factors (in your genes)

A man usually has a higher metabolic rate than a woman of the same mass- males usually have bigger muscles, and muscle cells use most energy.

A person who exercises regularly is more likely to stay healthy than a person who doesn't. Inherited factors can affect health- for example, some people have genes that give them a higher blood cholesterol level than other people with the same diet.

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B1.1.2 Pathogens and Infection

Pathogens- microorganisms that cause disease. When pathogens infect us, they can reproduce very rapidly- large numbers of pathogens can make us ill.


  • Much smaller than our cells
  • Release toxins that make us feel ill
  • Some invade and destroy body cells


  • Much smaller than bacteria
  • Take over the body cell's DNA
  • Cause the invaded cell to produce toxins
  • Damage the cell in which they reproduce
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B1.1.2 The Immune System

The immune system helps protect the body against pathogens.

White blood cells

  • Some ingest and destroy pathogens
  • Some produce chemical antibodies that attatch to pathogens and destroy them
  • Some produce antitoxins that destroy toxins made by pathogens


Antibodies produced by a white blood cell are specific for one particular kind of pathogen, hence can only destroy this type. This leads to immunity:

  1. At the first infection, white blood cells respond to the infection by making antibodies
  2. By the second infection, the immune system "remembers" how to attack that pathogen
  3. White blood cells release more antibodies more quickly, so the pathogens are destroyed before you even feel ill- you are immune!

Semmelweis (infection topic)

  • Doctor in mid 1800s- many women died of infection soon after childbirth
  • Realised that doctors might transfew infection between patients on their hands
  • Insisted doctors wash their hands before examining each patient
  • Death rates fell rapidly in wards where doctors washed their hands
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B1.1.2 Treating Diseases

Some medicines (namely painkillers) only treat symptoms of disease (the result of the disease) and do not kill pathogens. 


  • An example is penicillin
  • Kill bacterial pathogens in the body
  • Cannot be used to kill viral pathogens- they live and reproduce inside cells. It is difficult to develop drugs that kill viruses without also damaging the body's tissues
  • Specific bacteria killed by specific antibiotics
  • Deaths from bacterial diseases have greatly decreased where antibiotics are used

Overuse and inappropriate use of antibiotics can increase the development of antibiotic resistant strains of bacteria:

  • Strains of bacteria such as MRSA can develop antibiotic resistance
  • Mutations produce new, antibiotic-resistant strains of bacteria
  • In natural selection, non-resistant bacteria die when antibiotics are used, but the new strain survives and reproduces
  • The population of resistant bacteria increases- needs a new antibiotic to treat it
  • New strain will spread rapidly as there is no effective treatment and people are not immune
  • Now, antibiotics are not used to treat non-serious infections, so that the rate of development of resistant strains is slowed down
  • Antibiotic-resistant strains of bactera means new antibiotics must be developed
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B1.1.2 Immunisation


  • MMR- given to children to immunise them against measles, mumps and rubella
  • Vaccine contains a small amount of a dead or inactive form of the pathogen
  • Vaccine causes white blood cells to make antibodies, as it would if the body was infected by live pathogens
  • If the live pathogen later infects you, your immune system remembers how to destroy it, and responds quickly so you don't fall ill. You are immune!

Mutations of pathogens

  1. Mutations produces new strain of pathogen
  2. Antibodies against the old strain may not recognise the new one
  3. People who were vaccinated against the old strain are not immune to the new one
  4. The new strain may spread rapidly, causing an epidemic (when many people catch a disease at the same time) or a pandemic (when many people in many places have the same disease at the same time)
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B1.1.2 Cultures

The action of disinfectants and antibiotics can be studied using cultures of microorganisms. Microorganisms grow in a culture medium. More than one medium are referred to as media.

To do this:

  • Sterilise petri dish (by autoclaving or heating to a high temperature) and culture media (by heating to a high temperature) to kill unwanetd microorganisms
  • Sterilise inoculating loops (used to transfer microorganisms to the growth medium) by passing them through a flame, to kill unwanted microorganisms
  • Seal petri dish (using adhesive tape) to prevent microorganisms from the air contaminating the culture

In school laboratories, cultures incubated at a maximum temp of 25 c, as this greatly reduces the likelihood of groth of pathogens that might be harmful to humans. In industrial conditions, higher temperatures can produce more rapid growth. 

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