Q.(a) Name the causative agents of pneumonia and common cold.
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Biology Disease Control — A First Look
Think of your body as a city. Every day, germs (bacteria, viruses, fungi, parasites) try to enter — through the air you breathe, the food you eat, a cut on your skin. Most of the time, your body's defence systems stop them before you even notice. That's immunity, your natural security force.
But sometimes the invaders break through. You get a fever, a cough, an infection. Now you need disease control — the set of actions that stop the illness from spreading and help you recover.
What exactly is disease control?
In biology, disease control means reducing the incidence (new cases), prevalence (total cases), or transmission of a disease. It's not about wiping out every germ — that's impossible. It's about keeping the disease at a level where it no longer threatens public health.
The NCERT textbook divides disease control into two broad approaches:
1. Preventive measures — stopping the disease before it starts
These are actions taken by individuals, communities, and governments to block the entry of pathogens.
- Vaccination — training your immune system to recognise a germ before it attacks. This is the single most powerful tool in disease control.
- Sanitation and hygiene — clean drinking water, proper sewage disposal, handwashing. Many diseases (cholera, typhoid, hepatitis A) spread through contaminated water or food.
- Vector control — killing or avoiding the organisms that carry disease. Mosquito nets, insect repellents, draining stagnant water — these control malaria, dengue, chikungunya.
- Quarantine and isolation — separating sick people from healthy ones during outbreaks. You saw this during COVID-19.
Prevention is always better than cure. Once a disease spreads in a population, controlling it becomes exponentially harder and more expensive. That's why governments invest heavily in vaccination drives and public sanitation.
2. Curative measures — treating the disease once it occurs
Even with the best prevention, some people will fall ill. Curative measures aim to:
- Reduce the severity of the illness (e.g., antibiotics for bacterial infections, antiviral drugs for flu)
- Shorten the duration of the illness
- Prevent complications and death
- Stop the patient from infecting others
The key point: treatment alone cannot control a disease in a population. If you only treat sick people without preventing new infections, the disease keeps circulating.
Why does disease control matter for society?
A single outbreak can paralyse a city. Schools close, hospitals overflow, businesses shut down. The economic cost is enormous. That's why disease control is not just a medical issue — it's a public health issue.
The NCERT textbook emphasises that disease control requires community participation. No matter how good the doctors or vaccines are, if people refuse to vaccinate their children or ignore hygiene, the disease will keep spreading. …
Part (b)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).
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.
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 …
Part (a)
- Causative agents: Pneumonia is caused by the bacteria Streptococcus pneumoniae (and Haemophilus influenzae); the common cold is caused by Rhino viruses.
- Difference in symptoms: Pneumonia affects the alveoli of the lungs — high fever, chills, cough with thick sputum, chest pain and difficulty in breathing; lips and finger-nails may turn grey to bluish. The common cold affects only the upper respiratory tract — nasal congestion and discharge, sneezing, sore throat, hoarseness, tiredness; the lungs are not involved. …
Part (a): Pneumonia (bacterial — Streptococcus pneumoniae) is a deep lung infection with fever, sputum-cough and breathlessness, whereas the common cold (viral — Rhino viruses) is a mild upper-airway illness with sneezing and congestion; both share cough and fever. Part (b): Malaria is caused by Plasmodium and carried by the female Anopheles mosquito, giving recurring chill-and-fever; Aedes mosquitoes transmit dengue and chikungunya.
Part (a)
Both are respiratory infections but differ in the pathogen and the depth of the airway they attack.
Causative agents. Pneumonia is caused chiefly by the bacterium Streptococcus pneumoniae (also Haemophilus influenzae). The common cold is caused by Rhino viruses, which infect the nose and respiratory passage.
Difference in symptoms. In pneumonia the infection reaches the alveoli, which fill with fluid, so the patient has fever, chills, cough with sputum, chest pain and marked difficulty in breathing; in severe cases the lips and finger nails turn grey to bluish from poor oxygenation. The common cold is confined to the upper respiratory tract (nose and throat) and causes nasal congestion and discharge, sneezing, sore throat, hoarseness and tiredness — the lungs are not affected and breathing is not seriously impaired. …
Showing the 12 most recent of 37 on this concept.
- CBSE 2026Set A1 markMCQQ.Which of the following diseases is/are transmitted by insect vectors?(a) Typhoid(b) Malaria(c) Filaria(d) Both (B) and (C)
›Reveal solutionSolution
Malaria and filariasis are insect (mosquito) transmitted; typhoid is spread by contaminated food and water.
Malaria is transmitted by the female Anopheles mosquito, and filariasis (elephantiasis) is transmitted by the female Culex mosquito — both are insect vectors. Typhoid, caused by Salmonella typhi, is transmitted through food and water contaminated with …
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: Virus infected cells secrete proteins are called ______.
›Reveal solutionSolution
Proteins secreted by virus-infected cells are called interferons.
When a cell is infected by a virus, it secretes a group of protective proteins called interferons. These interferons diffuse to the surrounding, still-healthy cells and make them resistant to viral infection, thereby limiting the spread o …
- CBSE 2026Set ANNUAL1 markMCQQ.Haemozoin is released as a result of –(a) Rupture of liver cells(b) Rupture of red blood cells(c) Multiplication of sporozoites(d) Replication in macrophages
›Reveal solutionSolution
Haemozoin, the toxic malarial pigment, is liberated when parasitised red blood cells rupture, causing the characteristic recurring chills and fever.
When a female Anopheles mosquito bites, Plasmodium sporozoites enter the human liver, multiply, and then invade red blood cells. Inside the RBCs the parasite digests haemoglobin and multiplies. When the infected RBCs burst to release the next generation of parasites, they also release a to …
- CBSE 2026Set ANNUAL1 markQ._________ test is performed to confirm typhoid.
›Reveal solutionSolution
The blank is the Widal test — the diagnostic test that detects antibodies against Salmonella typhi to confirm typhoid fever.
In the CBSE/NCERT Human Health and Disease chapter, typhoid is caused by Salmonella typhi, spread through contaminated food and water. It is confirmed by the **Widal te …
- CBSE 2025Set A1 markQ.Write True / False: All microbes are not pathogenic.
›Reveal solutionSolution
The statement is True: most microbes are non-pathogenic and many are beneficial to humans.
Microbes (bacteria, fungi, protozoa, viruses, archaea) are extremely diverse, and only a small proportion of them are pathogens capable of causing disease in humans, plants or animals. The overwhelming majority of microbes play beneficial or neutral roles — decomposing organic matter, fixing nitrogen, fermenting food and beverages (curd, bread, alcoholic drinks), pro …
- CBSE 2025Set ANNUAL1 markQ.Name two diseases whose spread can be controlled by the eradication of Aedes mosquito.
›Reveal solutionSolution
The Aedes mosquito is the vector for several viral diseases, notably dengue and chikungunya, so controlling its population directly limits their spread.
The Aedes mosquito acts as the vector transmitting several important viral diseases to humans, including dengue fever and chikungunya (it can also transmit Zika virus and yellow fever). Since these viral diseases spread only through the bite of an infected Aedes mosquito, eliminating its breeding sites (stagnant/clean standing water) and controlling its population is an …
- CBSE 2024Set 57/2/11 markMCQQ.The vector for dengue fever is : (A) Female Aedes mosquito (B) Female Anopheles mosquito (C) Male Aedes mosquito (D) Female Culex mosquito
›Reveal solutionSolution
Dengue fever is transmitted by the bite of an infected female Aedes mosquito (primarily Aedes aegypti), which requires a blood meal for egg development. The answer is (A).
Why vectors matter in disease transmission
A vector is an organism that transmits a pathogen from one host to another without suffering from the disease itself. For many viral diseases, mosquitoes serve as vectors because the pathogen replicates in the mosquito's body and is passed on when the mosquito feeds on blood.
The key biological detail: only female mosquitoes bite and feed on blood. Males feed on plant nectar and do not require blood meals. Females need the protein from blood to develop their eggs, which is why they are the disease vectors.
Identifying the dengue vector
Different mosquito genera transmit different diseases, and this specificity is crucial for public health control measures.
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Aedes mosquitoes are the primary vectors for dengue fever. The species Aedes aegypti (and to a lesser extent Aedes albopictus) transmit the dengue virus when an infected female bites a human. These mosquitoes are recognizable by their distinctive black-and-white striped legs and body, and they typically bite during the day, especially in the early morning and before dusk.
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Anopheles mosquitoes transmit malaria, not dengue. The Plasmodium parasite that causes malaria requires Anopheles as its vector. …
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- CBSE 2024Set GG1 markMCQQ.The vector of Dengue (Break bone) fever is:(a) Anopheles(b) Culex(c) Aedes(d) None of these
›Reveal solutionSolution
Dengue is spread by the Aedes mosquito, so the answer is (c).
Concept. Many diseases have a specific insect vector. Matching the pathogen to its vector is important: malaria — Anopheles; filariasis — Culex; dengue and chikungunya — Aedes.
…
- CBSE 2024Set ANNUAL1 markMCQQ.Bacterial disease is(a) Diphtheria(b) Malaria(c) Amoebiasis(d) Ascariasis
›Reveal solutionSolution
Diphtheria is bacterial; malaria and amoebiasis are protozoan diseases and ascariasis is a helminth (roundworm) disease.
Diphtheria is caused by the bacterium Corynebacterium diphtheriae. In contrast, malaria is caused by the protozoan Plasmodium (transmitted by female Anopheles mosquito), amoebiasis is caused by the protozoan Entamoeba histolytica, and **asc …
- CBSE 2024Set ANNUAL1 markMCQQ.Choose the pair of viral diseases from the following sets :(a) Ringworm, AIDS(b) Common Cold, AIDS(c) Dysentery, Common Cold(d) Typhoid, Tuberculosis
›Reveal solutionSolution
Both Common Cold and AIDS are caused by viruses.
Common Cold is caused by Rhinoviruses (a group of viruses), and AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human Immunodeficiency Virus (HIV), a retrovirus. Checking the other pairs: Ringworm is fungal (not viral); Dysentery is caused by bacteria/protozoa (Entamoeba histolytica for amoebiasis, or bacteria); Typhoid is caused by the bacterium Salmonel …
- CBSE 2024Set ANNUAL1 markMCQQ.Choose the incorrectly matched pair -(i) Mumps - Paramyxovirus(ii) Typhoid - Salmonella typhi(iii) Cholera - E. Coli(iv) Pneumonia - Diplococcus pneumoniae
›Reveal solutionSolution
Cholera is caused by the bacterium Vibrio cholerae, so pairing it with E. coli is incorrect.
Checking each pair against the actual causative organism:
- Mumps – Paramyxovirus: correct.
- Typhoid – Salmonella typhi: correct.
- Cholera – E. Coli: incorrect — cholera is caused by Vibrio cholerae, a comma-shaped bacterium, not by Escherichia coli. …
- CBSE 2023Set TERM21 markMCQQ.A disease which can easily transmit from one person to another is called(a) Non-infectious disease(b) Infectious disease(c) Viral disease(d) Bacterial disease
›Reveal solutionSolution
A disease that spreads from an infected person to a healthy person is called an infectious (communicable) disease.
Diseases are broadly grouped into non-infectious (e.g. cancer, allergies) and infectious diseases. Infectious diseases are caused by pathogens such as bacteria, viruses, fungi, protozoans and helminths, and these pathogens can be transmitted from an infected host to a healthy person directly (contact, air, water) or through vectors, which is why such diseases are also called …
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