1.1 A healthy diet contains the right balance of the different foods
you need. Carbohydrates, fats and proteins are used by the
body to release energy and to build cells. Mineral ions and
vitamins are needed in small amounts for healthy functioning
of the body.
1.1.1 A person is malnourished
if their diet is not balanced.
This may lead to a person
being overweight or
unbalanced diet may also
lead to deficiency diseases
or conditions such as Type
18.104.22.168 A person loses mass when the energy
content of the food taken in is less than
the amount of energy expended by the
body. Exercise increases the amount of
energy expended by the body.
22.214.171.124.1 The rate at which all the chemical reactions in the cells of the body are
carried out (the metabolic rate) varies with the amount of activity you do
and the proportion of muscle to fat in your body. Metabolic rate may be
affected by inherited factors.
126.96.36.199.1.1 Inherited factors also
affect our health; for
example cholesterol level.
188.8.131.52.1.1.1 People who exercise regularly are
usually healthier than people who
take little exercise.
2 B1.1.2 How Our Bodies Defend Themselves
Against Infectious Diseases
2.1 Microorganisms that cause infectious
disease are called pathogens.
2.1.1 Bacteria and viruses may reproduce rapidly
inside the body and may produce poisons
(toxins) that make us feel ill. Viruses
damage the cells in which they reproduce.
184.108.40.206 The body has different ways of
protecting itself against pathogens.
220.127.116.11.1 White blood cells help to defend against pathogens by: ingesting pathogens;
producing antibodies, which destroy particular bacteria or viruses; producing
antitoxins, which counteract the toxins released by the pathogens.
18.104.22.168.1.1 The immune system of the body produces specific antibodies to kill a particular
pathogen. This leads to immunity from that pathogen. In some cases, dead or inactivated
pathogens stimulate antibody production. If a large proportion of the population is
immune to a pathogen, the spread of the pathogen is very much reduced.
22.214.171.124.1.1.1 Semmelweis recognised the
importance of hand-washing
in the prevention of spreading
some infectious diseases. By
insisting that doctors washed
their hands before examining
patients, he greatly reduced
the number of deaths from
infectious diseases in his
126.96.36.199.188.8.131.52 Some medicines, including painkillers, help to relieve the
symptoms of infectious disease, but do not kill the pathogens.
184.108.40.206.220.127.116.11.1 Antibiotics, including penicillin, are medicines that help to cure
bacterial disease by killing infectious bacteria inside the body.
Antibiotics cannot be used to kill viral pathogens, which live and
reproduce inside cells. It is important that specific bacteria
should be treated by specific antibiotics. The use of antibiotics
has greatly reduced deaths from infectious bacterial diseases.
Overuse and inappropriate use of antibiotics has increased the
rate of development of antibiotic resistant strains of bacteria.
18.104.22.168.22.214.171.124.1.1 Many strains of bacteria, including MRSA, have developed resistance
to antibiotics as a result of natural selection. To prevent further
resistance arising it is important to avoid over-use of antibiotics.
126.96.36.199.188.8.131.52.1.1.1 Mutations of pathogens produce new strains. Antibiotics and vaccinations may no longer
be effective against a new resistant strain of the pathogen. The new strain will then spread
rapidly because people are not immune to it and there is no effective treatment.
184.108.40.206.220.127.116.11.18.104.22.168 Antibiotics kill individual pathogens of the non-resistant strain, individual resistant
pathogens survive and reproduce, so the population of the resistant strain increases and
now, antibiotics are not used to treat non-serious infections, such as mild throat
infections, so that the rate of development of resistant strains is slowed down.
22.214.171.124.126.96.36.199.188.8.131.52.1 The development of antibiotic-resistant strains of bacteria
necessitates the development of new antibiotics.
184.108.40.206.220.127.116.11.18.104.22.168.1.1 People can be immunised against a disease by introducing small quantities of dead or
inactive forms of the pathogen into the body (vaccination). Vaccines stimulate the white
blood cells to produce antibodies that destroy the pathogens. This makes the person
immune to future infections by the microorganism. The body can respond by rapidly
making the correct antibody, in the same way as if the person had previously had the
disease. MMR vaccine is used to protect children against measles, mumps and rubella.
22.214.171.124.126.96.36.199.188.8.131.52.1.1.1 Uncontaminated cultures of microorganisms are required for investigating the action of
disinfectants and antibiotics: petri dishes and culture media must be sterilised before use to kill
unwanted microorganisms; inoculating loops used to transfer microorganisms to the media must
be sterilised by passing them through a flame; the lid of the Petri dish should be secured with
adhesive tape to prevent microorganisms from the air contaminating the culture.
184.108.40.206.220.127.116.11.18.104.22.168.22.214.171.124 In school and college laboratories, cultures should be
incubated at a maximum temperature of 25 °C, which
greatly reduces the likelihood of growth of pathogens that
might be harmful to humans.
126.96.36.199.188.8.131.52.184.108.40.206.220.127.116.11.1 In industrial conditions higher temperatures
can produce more rapid growth.