O Level Revision : Integrated Science - Science in Community - Health

In order for mankind to be productive people should be healthy. Complete health combines the physical, mental and social well-being of an individual. Maintaining good health involves eating a balanced diet. A balanced diet provides all the nutrients required by the body in the right proportions. Different nutrients may be required in different proportions according to the age, sex and activity of the individual. Sick people may also need special diets. There are a number of diseases that are caused by malnutrition due to wrong, excessive eating and undernourishment.


  • Caring of  teeth is an important part of maintaining good health.
  • Harmful substances such as alcohol, tobacco, marijuana, mandrax and cannabis are bad for health.
  • Food should be preserved to prevent the growth of micro-organisms that cause decay and make food toxic.
  • Pathogens cause people to get sick.
  • Good  hygiene is an essential tool for disease prevention.
  • The spread of diseases can be controlled by chemical and cultural methods.
  • The body has defence mechanisms to prevent attack from diseases.
  • HIV damages the body’s ability to fight diseases.

 Health and well-being

Definition: Health is a state of complete physical, mental and social wellbeing, not merely the absence of disease (World Health Organisation definition).

Physical health

  1. Eating a balanced diet. b)   Regular exercise.
  2. Immunization against disease.
  3. Having sufficient
  4. Cleaning teeth regularly

Mental health

  1. Absence of depression.
  2. Reduced stress factors.
  3. Not overworking.
  4. Having sufficient
  5. Coping with the world around

Social health

  1. Decent accommodation.
  2. Clean water and sanitation.
  3. Sufficient clothing and food.
  4. Access to education.
  5. Access to health care

Components of health

  • Social health is a result of a functional family unit as well as a functional community.
  • Health can be achieved at personal level and at community level.
  • Personal or individual health is achieved through:
    • eating balanced diet
    • personal hygiene
    • eating clean food
    • drinking clean water
    • regular exercise.
  • Community health is achieved through provision of proper sewage disposal, availability of clinics, drugs and health personnel as well as clean water for drinking.


Components of a balanced diet





Energy source

maize, potato, cereals


Body building and repair

meat, eggs, fish


Energy store

nuts, meat fat, margarine


Calcium and phosphorous are used for teeth and bone formation.

Iron is used for red blood  cells formation, etc.

Iodine is important for prevention of goitre.

sea weed, milk, vegetables


Protection against disease

fruits, vegetables



Prevents constipation and aids peristalsis movements

vegetables, fruits


Solvent, hydrolysis of food in gut, transport medium

water, succulent food (fruits)


  • In the laboratory, food samples can be tested for the presence of carbohydrates in the form of starch and glucose, proteins and fats.
  • Some foods may contain more than one nutrient.
  • Food tests are easier to conduct when food is in liquid form.


Food tests

Food can be analysed to find the presence of starch, protein, fat and reducing sugar.

A summary of food tests

Test for



Positive test


Iodine solution

Add a few drops of iodine solution to food sample

Brown  to  blue- black



a) Albustix


Insert albustix strip


Yellow to green

b) Biuret test (potassium hydroxide

+ copper sulphate)

Add solution to food sample

A  purple/violet colour


a) Paper

Smear some food onto a test paper

Spot   be com e s translucent (a see through)

b) Ethanol emulsion

Add drops of ethanol to food sample, shake vigorously

Cloudy   w hite emulsion



a) Clinistix

Insert clinistix into food sample solution

Pink to purple




Ad d   Be ne di c t ’ s

Blue → green → yellow → brick red



Solution and heat in a

water bath


The importance of a balanced diet

  • A balanced diet must have a balance of both quantity and quality of food to ensure that the individual gets the right amount of nutrients.
  • A balance of quantity is when one gets the correct amounts of each nutrient in the diet.
  • A balance of quality is when one eats a diet containing the foods that ensure the supply of all the required nutrients.
  • A balanced diet is important as it prevents deficiency diseases.
  • Different people have different nutritional needs (energy requirement) depending on differences in age, sex,  activities and different metabolic rates.

Comparison of nutrition requirements of people of different occupations



Special needs


Manual workers e.g. builders

-hard work

-requires a lot of energy

-diet rich in carbohydrates

Sedentary workers e.g. nurses

-non-manual work but requires a lot of thinking

- requires little energy

-small quantities of fats and carbohydrates

-moderate amounts of proteins vitamins C and D


-rapid growth, little activity

-body building  and bone development

-a lot of proteins, calcium in breast milk

Nursing / breastfeeding mothers

-little activity

-provide for infant’s

development of bones/ teeth, red blood cell formation and protection against diseases.

-a lot of calcium, iron, and vitamins C and D


It is the feeding of an infant or young child with breast milk directly from female human breasts rather than using infant formula.

Advantages of breast feeding

  1. Antibodies are contained in the mother’s milk hence the baby is protected against diseases.
  2. Breast fed babies are rarely constipated due to the digestibility of breast milk.
  3. It enhances the bond between mother and child.
  4. The chances of breast cancer to the mother are reduced.
  5. Breast milk contains balanced nutrients for the baby.
  6. The mother’s milk is always available, clean and has the right temperature.
  7. Unlike bottle feeding, breast feeding promotes optimum brain development rate of babies.
  8. Child spacing in mothers is increased (breastfeeding acts as a natural contraceptive).
  9. Breast feeding is more economical than formula/bottle feeding.
  10. Breast feeding promotes better visual response to babies.


Malnutrition is a condition that results from eating a diet in which certain nutrients are lacking (undernourishment), in excess (overnourishment), or in the wrong proportions.

  • Marasmus, kwashiorkor, obesity anaemia and goitre are typical examples of malnutrition.
  • Marasmus – it is also referred to as dry malnutrition, caused by not eating enough of any kind of food (starvation). Symptoms include small body size, very thin, tissue and muscle wasting, dry skin, loose skin folds hanging over the buttocks and armpit. Eating more food particularly energy giving foods helps curb the disease.
  • Kwashiorkor – also called wet malnutrition, caused by a deficiency of dietary protein (lack of proteins in the diet). Symptoms include swollen abdomen, swollen limbs, brownish hair colour, skin depigmentation and stunted growth.
  • Obesity – caused by eating excessive fat in the diet, as well as other foods in excess. Obesity may eventually cause heart disease. Regular physical exercises and reducing the intake of high energy foods are very important in correcting the disease.
  • Other deficiency diseases include goitre (lack of iodine) and anaemia (lack of iron).
  • Lack of vitamin A results in poor night vision and blindness while lack of calcium results in poor bone and teeth formation.

Dental decay

  • Dental or tooth decay is caused by the action of bacteria. It is the destruction of the hard tissues of the teeth (enamel, cementum and dentine).
  • Bacteria produce acid when they ferment food debris accumulated on the tooth surface.
  • Tooth decay can be best described by understanding the structure of a tooth

Structure of a tooth  

  • The dentine is the main substance of teeth. The dentine is protected by a thin layer called enamel. The pulp inside the tooth contains nerves and arterioles (blood vessels).

Causes of tooth decay

  • Well refined sugar in the diet and other sweet, sticky foods like chocolates and sweets are the main causes of tooth decay.
  • The bacteria in the plaque ferments the sugar left on the teeth to produce acids which corrodes the enamel of the tooth, then the dentine through to the pulp.
  • Severe toothache is then experienced once the decay reaches the nerves. At this stage, teeth may require extraction.

Care of tooth

The following habits and practices help prevent tooth decay:

  • Brush your teeth at least twice a day with fluoride-containing toothpaste. Preferably, brush after each meal and especially before going to bed.
  • Clean between your teeth daily with dental floss or interdental cleaners.
  • Eat nutritious and balanced meals and limit snacks. Avoid carbohydrates such as candy, chocolates, sweets, pretzels and chips, which can remain on the tooth surface. If sticky foods are eaten, brush your teeth soon afterwards.
  • Check with your dentist about use of supplementary fluoride, which strengthens your teeth.

  • Ask your dentist about dental sealants (a plastic protective coating) applied to the chewing surfaces of your back teeth (molars) to protect them from decay.
  • Drink fluoridated water. At least a pint of fluoridated water each day is needed to protect children from tooth decay.
  • Visit your dentist regularly for professional cleaning and oral exam.
  • Where toothpaste is unavailable or unaffordable, make your own toothpaste powder by mixing salt with bicarbonate of soda in equal amounts. This is equally effective as synthetic toothpaste.

 Substance use and abuse


  • Tobacco contains a drug called nicotine which causes addiction in smokers. Addicts have to smoke regularly to avoid the discomfort of withdrawal effects.
  • The following are effects of smoking on health:
    • Lung cancer - begins with coughing, chest pains and then spitting blood/mucus.
    • Bronchitis - a viral disease characterised by a noisy cough, typical in heavy smokers.
    • Emphysema - characterised by a ‘whistling’ noise in the chest when breathing
    • Stomach ulcers.
    • Heart attack - heart rate is increaed as nicotine narrows the coronary arteries.
    • Stroke - brain cells and blood supply to the brain are affected by nicotine.
  • Non-smokers can however, suffer from the above health conditions due to passive smoking.
  • This refers to inhaling of cigarette smoke from smokers in confined areas like offices, buses or gatherings.


Excessive consumption of alcohol results in the following effects:

  • cirrhosis of the liver.
  • cardiovascular disease e.g. stroke, heart attack.
  • destruction of nerve tissues.
  • loss of memory.
  • distorted judgement e.g. in driving which leads to accidents.
  • results in Vitamin B deficiency.
  • increased the risk of cancer.
  • anaemia.
  • high blood pressure.
  • a weakened immune system.

Mandrax and cannabis

  • These are drugs which are extracted or made from parts of the plant called Indian hemp (Cannabis sativa), locally known as “mbanje” or “marijuana”.
  • These drugs cause the following effects:

•     lung cancer

•     heart and muscle damage

•      slowed reactions

•     hallucinations

•     imprecise co-ordination



Sniffing of organic solvents like ethanol, phenol as well as glue has the following effects:

  • liver and kidney damage.                   •     heart and muscle damage.
  • suffocation.                                         •     unconsciousness and vomitting.
  • uninhibited negative social behaviour.
  • slowed reactions.

Food preservation

  • Food preservation is the process of treating or handling food to stop or slow down food spoilage, loss of quality and deterioration of edibility or nutritional value.
  • Food preservation allows for longer food storage.
  • This usually involves preventing the growth of bacteria.

Optimum conditions for growth of micro-organisms

(i)   warmth             (ii)  moisture            (iii) air

  • Preserving food thus hinges on removing at least one of the conditions necessary for growth of microorganisms.
  • The following experiment is used to show that warmth, moisture and oxygen are needed for growth of microorganisms.

To demonstrate the conditions required for the growth of micro-organisms


Four petri dishes with lids, 4 slices of bread, small container

of silica gel, a small container of alkaline pyrogallol, refrigerator


Set up four petri dishes:






dry bread

room temperature drying agent

moist bread refrigerator

moist bread

room temperature alkaline pyrogallol

moist bread

room temperature

Demonstrating conditions for microbial growth

Set up A:   bread with drying agent in small container at room temperature (no moisture).

Set up B:   moist bread with water in small container placed in refrigerator (low temperature). Set up C:   moist bread with alkaline pyrogallol in small container at room temperature (no oxygen). Set up D:   moist bread with water room temperature (control).


Mould grows on bread in set up D as all conditions (moisture, warmth and air) are present.

Food preservation

Summary of different methods of food preservation and how they limit growth of micro-organisms






Reducing temperatures of food to around 4°C

Slows down growth and reproduction of micro- organisms

Meat, fruit, vegetables


Draws  moisture  from  foods  by osmosis

Kills organisms that spoil food

Meats, fish



Draws  moisture  from  foods  by osmosis

Kills organisms that spoil food

Fruits & jams


Food exposed to smoke from burning plants e.g. wood

Antibacterial and antifungal compounds found in smoke kill microorganisms

Meat, fish


Food placed in vinegar, brine, alcohol or vegetable oil

Liquids used are edible but inhibit growth of or kill bacteria and other micro organisms

Cucumbers, fish, fruit, peppers


Involves cooking food and sealing in sterile containers

Cooking kills microorganisms,

Meats, beans, fruits, vegetables

sealing in sterile cans prevents

micro-organisms from entering and excludes oxygen for the growth of the micro- organisms


  • A disease/illness is an abnormal condition affecting the body of an organism.
  • There are four main types of diseases.

Pathogenic diseases

  • Caused by other organisms
  • Disease causing organismsare called pathogens
  • Associated with bacteria, viruses, protozoa, fungi etc

Deficiency diseases

Caused by the lack of one or more nutrients

Genetic Diseases

Caused by a malfunctioning of a part of the body

  • Pathogens are disease causing organisms. They include bacteria, viruses and protozoa and flukes.
  • There are different methods of transmission of pathogens.

Methods of transmitting pathogens



Method of transmission




Examples of diseases




Tiny water droplets in exhaled air.


Influenza(flu), colds, mumps tuberculosis, pneumonia, measles




By physical contact (direct or indirect) e.g. sharing towels, sexual intercourse, etc


Measles, ringworm, tetanus, sexually transmitted diseases, leprosy, chicken pox


Contaminated food and water


Pathogens enter drinking water or food e.g. from sewage directly into water or food or carried by flies etc.


Bilharzia, cholera, dysentery, typhoid




Carried by other organisms such as insects e.g. mosquitoes, tsetse flies


Malaria, sleeping sickness


Causes, transmission, symptoms and treatment of cholera




contaminated water or food


diarrhoea, fever, sunken eyes, body shrinks

Treatment of cholera

1.  seek medical advice

2.  use oral rehydration solution (ORS)

3. antibiotics that kill the bacteria are used for treatment



Causative agent of cholera (Vibro cholerae)


  • Hygiene is a basic factor in the prevention of diseases.
  • Three levels of hygiene can be identified namely

(i)   personal hygiene (ii)  domestic hygiene (iii) community hygiene

Levels of hygiene


Personal hygiene involves:

Domestic hygiene involves:

Community hygiene involves:

• washing hands after using the


• washing hands before handling


• regular bathing

• using clean utensils for food


• eating warm food

• covering food to exclude


• ensuring that food eaten raw is

thoroughly cleaned

• using proper toilet facilities

• correct waste disposal

• protecting sources of drinking

water or purifying water

• vaccination

• using proper sewage disposal


• using proper rubbish disposal




Life cycle of the female anopheles mosquito

Life cycle of the female anopheles mosquito


Life cycle of the plasmodium

  • red blood cells are attacked
  • plasmodium spores passing to blood stream after mosquito bite
  • red blood cells rapture
  • spores become male
  • and female gametes spores and toxins pour into blood stream

 Life cycle of plasmodium

Different methods of controlling malaria are illustrated in 

  • Destroying the pathogen with drugs
  • Preventing the breeding of mosquitos
  • Preventing mosquito bites

 Methods of controlling malaria

  1. Mosquito control:

This depends on understanding the life cycle of the mosquito to enable control at various stages.

  • Drain water logged areas
  • Spraying mosquito breeding places with suitable chemicals
  • Cutting tall grass around homes
  • Applying oil on water surfaces
  1. Correct use of chloroquine:
  • Effective drugs for treatment of malaria are recommended by medical personnel.
  • Plasmodium has developed resistance to some of the drugs used to treat malaria.
  • Coartimeta is now being used in place of chloroquine.
  • It is important that patients take the full course of malaria treatment even after they begin to feel better.
  1. Correct use of prophylactic drugs:
  • These are drugs used to prevent/protect people against malaria.
  • Prophylactic drugs are taken before, during and after exposure.
  1. Avoiding mosquito bites:
  • Sleeping under a net.
  • Wearing long clothes (that cover the skin).
  • Use of repellents.

Defence systems

The body has various natural defence mechanisms against pathogens

  • Ears
  • Mouth
  • Eyes
  • Nose
  • Skin
  • Stomach
  • Vagina and anus
  • Foot sole

Defence mechanisms by the body

Defence mechanisms by the body against pathogens.


Body part

Defence mechanism


Tears clean eyes and contain antibiotics that prevent eye infetion


Wax traps pathogens and dust


Mucus trap dust and pathogens


Saliva neutralises acid produced by the fermentation of plaque


It is a physical barrier against pathogens


Stomach acids destroy bacteria in food preventing poisoning


White blood cells destroy pathogens

Blood produces antibodies and it also clots, creating a barrier to prevent pathogens from entering the body

Vagina and anus

They secrete acidic mucus that destroy bacteria

Foot sole

Has a thicker skin for more protection against penetration by disease causing organisms


  • It is the state of having sufficient biological defences to avoid infection, disease, or other unwanted biological invasion.
  • It is the capability of the body to protect itself against diseases or toxins by the action of antibodies.





























Types of immunity

Active immunity


  • Active immunity is the type of immunity developed in an organism by the organism’s production of antibodies in response to an exposure to either:
    • an antigen or pathogen (disease causing organism) leading to natural active immunity.
    • a vaccine leading to artificial active immunity.
  • Active immunity is generally long term.



  • Vaccination is the introduction of attenuated (weakened) pathogens into the body for the purpose of developing immunity (since pathogens are artificially introduced),  active immunity.
  •  Vaccination is carried out for child killer diseases such as:
    • Tetanus                                                         •     Diphtheria
    • Pertussis (whooping cough)                         •     Tuberculosis
    • Measles                                                        •     Polio
    • Meningitis                                                    •     Pneumonia bacteremia

Acquisition of immunity in infants (Passive immunity)

  • Antibodies are passed on to the child from the mother to the unborn baby via the placenta.
  • This gives the child an ability to fight off infection in their first few months of life.
  • The child also receives antibodies through breast milk.
  • Passive immunity is short lived unlike active immunity.

Effect of human immuno-deficiency virus (HIV) on the body

  •  HIV causes inability to resist infection hence one suffers from opportunistic infections e.g.
    • TB                     •     Shingles                •     Diarrhoea              •     Pneumonia
    • Hepatitis.
  •  Parts of the body are affected as follows:

(i)   Mouth – thrush (white patches in mouth) (ii)  Skin     – shingles (herpes zoster) skin sores (iii) Brain   – dementia e.g. forgetfulness

(iv) Weight – weight loss

  • HIV leads to the destruction of the immune system.
  • Eventually HIV infection leads AIDS to the death of  the infected person.