The following table shows certain diseases, their causative organisms and symptoms. Fill the gaps. (i) Disease

NCERT Exemplar · Q47

Q. The following table shows certain diseases, their causative organisms and symptoms. Fill the gaps.

(i) Disease: Ascariasis; Causative organism: Ascaris; Symptoms: ____

(ii) Disease: ____; Causative organism: Trichophyton; Symptoms: Appearance of dry, scaly lesions on various parts of the body

(iii) Disease: Typhoid; Causative organism: ____; Symptoms: High fever, weakness, headache, stomach pain, constipation.

(iv) Disease: Pneumonia; Causative organism: Streptococcus pneumoniae; Symptoms: ____

(v) Disease: ____; Causative organism: Rhino viruses; Symptoms: Nasal congestion and discharge, sorethroat, cough, headache

(vi) Disease: Filariasis; Causative organism: ____; Symptoms: Inflammation in lower limbs

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Concept understanding — Disease Transmission Modes

Let’s begin with something you already know. When someone in your family catches a cold, you instinctively avoid sharing their glass or sitting too close. That instinct is your brain recognising that something — a disease — can travel from one person to another. The how of that travel is what we call disease transmission modes.

In everyday language, a transmission mode is simply the route a germ takes to leave an infected person and reach a healthy one. Think of it as the germ’s travel plan. If the germ cannot travel, it cannot cause new infections. So understanding these routes is the first step in stopping outbreaks — whether it’s a common flu or a more serious epidemic.

The two big families: Direct and Indirect transmission

The NCERT textbook (Class XII, Biology, Chapter 8 — Human Health and Disease) divides transmission into two main categories. This is the standard classification you need to remember.

1. Direct Transmission — The germ moves straight from the infected person to the healthy person, with no intermediate object or living being involved. This can happen through:

Physical contact: Touching, shaking hands, kissing, or sexual contact. Diseases like the common cold, scabies, and sexually transmitted infections (e.g., syphilis, HIV) spread this way.
Droplet infection: When an infected person coughs, sneezes, or even talks, tiny droplets of saliva or mucus fly out. If you are within about a metre, you can inhale them. This is how influenza, the common cold, and COVID-19 spread.
Direct exposure to infected tissue or blood: For example, a needle-stick injury in a hospital, or a mother passing an infection to her baby during pregnancy (congenital transmission).

Note

Direct transmission is often the easiest to interrupt. Simple actions — like maintaining distance, wearing a mask, or washing hands — break the chain because the germ has no vehicle to ride on.

2. Indirect Transmission — Here, the germ needs a middleman to reach a new host. The middleman can be:

A vehicle: This is a non-living thing that carries the germ. Common vehicles include:
- Air: Dust particles or droplet nuclei (the dried remnants of droplets) can float for hours. Measles and tuberculosis spread through air.
- Water: Contaminated drinking water spreads cholera, typhoid, and hepatitis A.
- Food: Improperly cooked or stored food can carry salmonella or E. coli.
- Fomites: Inanimate objects like door handles, towels, syringes, or surgical instruments. Hepatitis B can spread through contaminated needles.
A vector: This is a living organism — usually an insect or animal — that carries the germ from one host to another. The vector itself is not infected (or is only incidentally infected). Classic examples:
- Mosquitoes: Female Anopheles mosquito transmits malaria; Aedes mosquito transmits dengue and chikungunya.
- Fleas: Rat fleas transmit the plague bacterium.
- Ticks: Spread Lyme disease.

Important

The key difference between a vehicle and a vector is that a vehicle is non-living, while a vector is a living creature. Both are intermediate agents — the germ does not jump directly from person to person.

Why this matters beyond biology

For a commerce or humanities student, the importance of transmission modes is not just medical — it is social and economic. Think about it:

If a disease spreads through water (like cholera), the solution is not a vaccine alone — it is clean water supply, sanitation infrastructure, and public awareness campaigns. That is a government policy and budget issue.
If a disease spreads through vectors (like malaria), the solution involves mosquito nets, insecticide spraying, and urban planning to eliminate stagnant water. That is a logistics and community management problem.
If a disease spreads through direct contact (like HIV), the solution involves education, behaviour change, and stigma reduction — which is a social science challenge.

In short, the mode of transmission determines the type of intervention needed. That is why public health officials always ask: “How is this disease spreading?” before they decide what to do.

A quick summary for revision …

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This table links diseases to their causative organisms and symptoms, and the gaps are filled using NCERT Class 12 Biology (Chapter 8: Human Health and Diseases) as the sole source.

Let’s walk through each row one by one, because understanding why a particular symptom or organism belongs there is far more useful than just memorising the answer.

(i) Ascariasis – Causative organism: Ascaris – Symptoms: ____

Ascaris is a roundworm (a helminth) that lives in the human intestine. The infection, ascariasis, happens when you ingest its eggs through contaminated food or water. Inside the gut, the larvae hatch, burrow through the intestinal wall, travel via the bloodstream to the lungs, and then get coughed up and swallowed back into the intestine, where they mature into adult worms. That journey causes real trouble. The textbook lists the classic symptoms as internal bleeding, muscular pain, fever, anaemia, and blockage of the intestinal passage. So the gap here is filled with those specific signs.

Note

Notice that ascariasis is a helminthic disease, not a bacterial or viral one. The NCERT groups it under "diseases caused by worms" alongside filariasis.

(ii) Disease: ____ – Causative organism: Trichophyton – Symptoms: Appearance of dry, scaly lesions on various parts of the body

Trichophyton is a fungus. It belongs to a group of fungi called dermatophytes, which infect the skin, hair, and nails. The disease it causes is a type of ringworm. The NCERT explicitly names ringworm as the disease caused by Trichophyton (along with Microsporum and Epidermophyton). The symptoms given — dry, scaly lesions — are textbook ringworm. So the disease name is Ringworm.

Important

Ringworm is not caused by a worm. It is a fungal infection. The name comes from the circular, ring-like shape of the rash, not the organism.

(iii) Disease: Typhoid – Causative organism: ____ – Symptoms: High fever, weakness, headache, stomach pain, constipation

Typhoid is a classic bacterial disease. The causative organism is Salmonella typhi, a bacterium that enters the body through contaminated food or water. The NCERT is very clear: typhoid is caused by Salmonella typhi. The symptoms listed — high fever (which can last for weeks), weakness, headache, stomach pain, and constipation — are exactly what the textbook describes. So the gap is Salmonella typhi.

(iv) Disease: Pneumonia – Causative organism: Streptococcus pneumoniae – Symptoms: ____

Pneumonia is an infection of the alveoli (air sacs) of the lungs. Streptococcus pneumoniae is a bacterium that causes this. The NCERT lists the symptoms as fever, chills, cough, and headache. In severe cases, the alveoli fill with fluid, leading to difficulty breathing. The key point is that the infection is in the lungs, so respiratory symptoms dominate. The gap is filled with fever, chills, cough, and headache. …

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Q.The following table shows certain diseases, their causative organisms and symptoms. Fill the gaps.

Concept understanding — Disease Transmission Modes

The two big families: Direct and Indirect transmission

Why this matters beyond biology

A quick summary for revision …

Method: Classify by Pathogen Type First, Then Derive the Symptom Pattern

Q.The following table shows certain diseases, their causative organisms and symptoms. Fill the gaps.

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