BiologyICSE Class 9 · Health and Hygiene

Modes of Transmission, Body Defences and Health Organisations (ICSE Class 9 Biology)

Updated 17 October 2026 · Fact-checked

Diseases are infectious or non-infectious, congenital or acquired, and spread by air, water, food, contact, vectors and blood. The body defends itself by skin, mucus, tears, saliva and stomach acid (local defences), by white blood cells and antibodies, and through vaccination; the Red Cross and the WHO work for health care.

Notice that germs leave an infected person by five different routes, and each route has its own typical diseases.

Illustration drawn for QuestionBuddy.

Understand Modes of Transmission, Body Defences and Health Organisations

1. Types of disease. *Infectious* (communicable) diseases pass from one person to another, such as cholera and chicken pox; *non-infectious* ones do not, such as diabetes. *Congenital* diseases are present at birth; *acquired* diseases develop later (infectious, deficiency, degenerative, allergic).

2. Modes of transmission.

*Air* (droplets): tuberculosis, common cold.
*Water and food*: cholera, typhoid, hepatitis A.
*Direct contact*: ringworm, scabies.
*Vectors*: mosquitoes (malaria, filariasis), houseflies carrying germs to food.
*Blood and body fluids*: AIDS, hepatitis B.

A *carrier* shows no symptoms but spreads the germs.

3. Aids to health and local defences.

*Skin* is a barrier; *mucus* in the nose traps germs; *cilia* sweep them away.
*Tears and saliva* contain lysozyme which kills bacteria; *stomach acid* destroys germs in food.
Personal and community hygiene: clean water, safe disposal of waste, vaccination.

4. Immunity. White blood cells engulf germs (phagocytes) and lymphocytes make *antibodies*. *Vaccination* introduces weakened or killed germs so that antibodies and memory cells are made in advance; *active* immunity is made by the body, *passive* is given ready-made antibodies (as in a serum).

5. Health organisations. The *Red Cross* gives relief in disasters and wars, organises blood donation and first aid. The *WHO* (World Health Organization), a specialised agency of the United Nations, works for international health standards and for control of diseases.

Modes of Transmission, Body Defences and Health Organisations: key facts

Modes: Air
Water and food
Contact
Vector
Blood
Local defence: Skin
Mucus and cilia
Tears and saliva (lysozyme)
Stomach acid
Immunity: Active: own antibodies after vaccine | Passive: ready-made antibodies
Organisations: Red Cross: relief, blood donation | WHO: global health, UN agency

Modes of Transmission, Body Defences and Health Organisations in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

A crowded bus

Suppose a student with a cough travels in a crowded bus and three days later two classmates develop similar symptoms.

Which mode of transmission is likely and how can it be limited?

Try it first, then show the solutionSolution

Coughing sends droplets into the air.
Cover the mouth and nose, avoid crowds, vaccinate where possible.

Answer: Air-borne droplets; cover the mouth and wash hands.

Memory hook: Cough into your elbow.

Tricks to remember Modes of Transmission, Body Defences and Health Organisations

Short memory aids. Say each one aloud once, then use it on a question the same day.

AWCVB
Air, Water/food, Contact, Vector, Blood.
Use it when: Modes of transmission.
Lyso = dissolve
Lysozyme dissolves bacteria in tears.
Use it when: Local defences.

Modes of Transmission, Body Defences and Health Organisations: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Define · 2 marks · Short answerBoard level

Define a carrier and give one example of a disease it may spread. [2]

Try it first, then show the solutionSolution

A carrier harbours the germ without showing symptoms.
It can spread typhoid.

Answer: A person who has germs but no symptoms; typhoid is an example.

Example 2: Local defences · 4 marks · Short answerBoard level

Name four local defences of the body against germs. [4]

Try it first, then show the solutionSolution

Skin.
Mucus and cilia.
Tears and saliva.
Stomach acid.

Answer: Skin, mucus with cilia, lysozyme in tears and saliva, stomach acid.

Example 3: Vaccine action · 3 marks · Short answerHarder board level

Explain how a vaccine protects a child from measles later. [3]

Try it first, then show the solutionSolution

It contains weakened or killed germs.
The body makes antibodies and memory cells.
On real infection the response is quick and strong.

Answer: Memory cells and antibodies from the vaccine act fast on later exposure.

Example 4: Vaccine versus serum · 4 marks · Long answerHarder board level

A person bitten by a rabid animal is given ready-made antibodies at once, while a child gets a scheduled vaccine. Explain the difference in the immunity given. [4]

Try it first, then show the solutionSolution

Ready-made antibodies give passive immunity.
It works immediately but lasts a short time.
A vaccine gives active immunity.
It takes time but lasts long due to memory cells.

Answer: Passive immunity: quick, short; active immunity: slow, long.

Example 5: Case: the outbreak · 5 marks · Case-basedHOTS / competency

Case. In a hostel, a cook who has no symptoms is found to carry typhoid bacteria. (i) What is he called? [1] (ii) How could the disease spread? [1] (iii) Suggest two controls. [2] (iv) Which organisation could assist in a wider outbreak? [1]

Try it first, then show the solutionSolution

(i) A carrier.
(ii) Through food and water.
(iii) Hygiene, treatment, screening of food handlers.
(iv) WHO.

Answer: (i) Carrier (ii) Contaminated food (iii) Hygiene and treatment (iv) WHO.

Where students lose marks in Modes of Transmission, Body Defences and Health Organisations

The slips examiners see most often, and what to write instead.

Mistake: Writing that carriers are always ill
Symptoms are assumed.
Do this: A carrier may show no symptoms.
Usually costs: 1 mark.
Mistake: Mixing active and passive immunity
Both give antibodies.
Do this: Active: body makes; passive: given.
Usually costs: 1 mark.
Mistake: Naming WHO as an Indian body
Origin is confused.
Do this: WHO is a UN agency.
Usually costs: 1 mark.

Exam tips

Give an example with every mode of transmission.
Link prevention to the mode.
State the mechanism in vaccination answers.
Use a table for active versus passive immunity.

Practice questions on Modes of Transmission, Body Defences and Health Organisations

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Lysozyme is found in:
(a) gastric juice
(b) tears
(c) bile
(d) urine
Hint
Eye.
Answer
(b) tears.
Q2 · 2 marks · Very short answerBoard level
Name two non-infectious diseases. [2]
Hint
Not spread.
Answer
Diabetes and cancer (for example).
Q3 · 2 marks · Very short answerBoard level
State two functions of the Red Cross. [2]
Hint
Relief.
Answer
Relief in disasters and blood donation (also first aid).
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Tears protect the eyes from infection.
Reason (R): Tears contain lysozyme.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Enzyme.
Answer
(a).
Q5 · 3 marks · Short answerHarder board level
Distinguish between active and passive immunity. [3]
Hint
Source of antibodies.
Answer
Active: the body makes antibodies after a vaccine or infection, lasting long; passive: antibodies are given ready-made, acting quickly but briefly.
Q6 · 2 marks · Very short answerBoard level
Why does a person with a cold covering the nose and mouth when sneezing help others? [2]
Hint
Droplets.
Answer
It stops droplets carrying germs from spreading in the air.
Q7 · 3 marks · Short answerHarder board level
Explain why house flies must be kept away from food. [3]
Hint
Mechanical carriers.
Answer
Flies sit on faeces and waste, pick up germs and deposit them on food, spreading diseases like cholera and typhoid.
Q8 · 3 marks · Short answerHarder board level
Explain the role of mucus and cilia in the windpipe in preventing lung infection. [3]
Hint
Trap and sweep.
Answer
Mucus traps dust and germs and cilia sweep them to the throat to be swallowed or coughed out.
Q9 · 4 marks · Case-basedHOTS / competency
Case. Two children are given the same vaccine; one later gets mild disease and the other none. A parent asks if the vaccine failed. (i) Give a reason it may still be useful. [2] (ii) Suggest what the doctor can do. [2]
Hint
Severity.
Answer
(i) The vaccine can reduce severity even if it does not stop all infection. (ii) Review the schedule and give booster doses if required.
Q10 · 4 marks · Case-basedHOTS / competency
Case. After an earthquake, a team arrives with first aid, blood donation camps and health advisers. (i) Name the organisation known for relief and blood donation. [1] (ii) Name the UN agency that advises on health standards. [1] (iii) Why is clean water urgent in such places? [2]
Hint
Water-borne.
Answer
(i) Red Cross. (ii) WHO. (iii) Contaminated water causes cholera and typhoid.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What are antibodies?Show answer
Proteins made by lymphocytes against germs.
2.What is a vector?Show answer
An organism that carries a disease agent.
3.Which UN agency works for world health?Show answer
WHO.
4.Enzyme in tears?Show answer
Lysozyme.
5.Active immunity example?Show answer
Vaccination.

Modes of Transmission, Body Defences and Health Organisations: frequently asked questions

Is diabetes infectious?

No.

What is a booster dose?

A repeat vaccine dose to maintain immunity.

Who runs blood donation camps?

The Red Cross among others.