Q.Write any two biochemical/molecular diagnostic procedures for early detection of viral infection. Explain the principle of any one of them.
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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 — Sewage Composition Hazards
Let’s start with something you already know. Imagine the water that goes down your kitchen sink after washing dishes, or the flush from a toilet. That water doesn’t just vanish — it carries everything we rinse, flush, or pour away. That mixture is called sewage.
Now, sewage is not just “dirty water.” It is a complex, living soup. And because it comes from homes, hospitals, factories, and streets, its composition is both predictable and dangerous. Understanding its hazards means understanding what is in that soup and why it cannot be ignored.
What is sewage made of?
Sewage contains three broad categories of material:
- Organic matter — human waste (faeces and urine), food scraps, paper, oils, and detergents. These are biodegradable but require oxygen to break down.
- Inorganic matter — salts, metals, sand, and grit. These do not rot easily.
- Pathogens — disease-causing microorganisms like bacteria, viruses, and parasites. This is the most dangerous part.
The key hazard of sewage is not just that it smells bad — it is that untreated sewage is a direct carrier of waterborne diseases such as cholera, typhoid, dysentery, and hepatitis. These diseases spread when sewage contaminates drinking water or food.
Why does composition matter for hazards?
The hazard depends on what is in the sewage and how much of it there is. For example:
- High organic content means bacteria will multiply rapidly, using up oxygen in water bodies. This kills fish and creates foul-smelling, dead zones in rivers.
- High pathogen load means even a small leak into a well can cause an epidemic.
- Industrial sewage adds toxic chemicals (acids, heavy metals, dyes) that poison soil and groundwater for decades.
In India, untreated sewage is the single biggest source of pollution in rivers like the Ganga and Yamuna. The NCERT textbook highlights that over 80% of the water supplied to Indian cities returns as sewage — and most of it is discharged without treatment.
The three main hazards at a glance
- Health hazard — Direct contact or ingestion causes disease. Sewage workers, children playing near drains, and communities using contaminated wells are most at risk.
- Environmental hazard — Organic waste depletes oxygen in water (eutrophication). Chemicals kill aquatic life. Groundwater gets polluted.
- Aesthetic and social hazard — Stagnant sewage breeds mosquitoes (malaria, dengue), produces unbearable odour, and lowers property values. It also spreads stigma and inequality — poor neighbourhoods often lack proper sewerage.
A real-world connection …
Part (a)
Two molecular/biochemical diagnostic procedures for early detection of viral infection: PCR (Polymerase Chain Reaction) and ELISA (Enzyme-Linked Immuno-Sorbent Assay).
Principle of PCR: the very low amount of the pathogen's nucleic acid (DNA/RNA) present in the early stage is amplified into millions of copies by repeated cycles of denaturation, primer annealing and extension. This lets the virus be detected long before symptoms appear, when its numbers are still very low. …
- PCR and ELISA detect viral infection early; PCR amplifies tiny amounts of the virus's nucleic acid so it is detectable before symptoms.
- Secondary sewage treatment uses aerobic microbes (flocs) in an aeration tank to lower BOD, then a settling tank collects the activated sludge; part is recycled and the rest anaerobically digested.
Part (a)
Serious diseases are hard to treat if detected late, so early, sensitive molecular/biochemical methods are used. Two such procedures are:
- PCR (Polymerase Chain Reaction) — detects the pathogen's genetic material.
- ELISA (Enzyme-Linked Immuno-Sorbent Assay) — detects the pathogen or the antibodies against it. …
Showing the 12 most recent of 31 on this concept.
- 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.What is primary sludge?
›Reveal solutionSolution
In sewage treatment, primary sludge refers to the settled solid organic matter removed by physical settling in the primary treatment stage, before the wastewater proceeds to biological (secondary) treatment.
Raw sewage first undergoes primary treatment, which is essentially physical: it passes through filters to remove large floating debris, then through a grit chamber (settling of sand/grit), and finally into a primary settling/sedimentation tank. Here, the heavier, particulate suspended solids (faecal matter and other organic debris) settle down under gravity to form primary sludge, while the floating material (scum) is skimmed off separately. The clarified supernatant liquid (called effluent) is then passed on to secondary treatmen …
- CBSE 2025Set ANNUAL1 markQ.Differentiate between primary sludge and activated sludge by giving one point.
›Reveal solutionSolution
Primary sludge is settled solid waste from physical treatment; activated sludge is a microbial floc formed during aerobic biological treatment.
Sewage (waste water) treatment happens in stages:
- Primary treatment (physical): the sewage passes through filters and settling tanks. Heavier solid particles simply settle down under gravity, forming primary sludge, while the floating debris is removed by skimming. This is purely a physical, non-biological separation step.
- Secondary treatment (biological): the effluent from primary treatment is passed into large aeration tanks and constantly agitated and aerated. This allows aerobic micro-organisms (bacteria, protozoa, etc., collectively called "activated sludge") to grow vigorously, forming flocs, and to consume/oxidise the remaining organic matter in the effluent, reducing its BOD (biochemical oxygen demand). …
- CBSE 2024Set GG1 markQ.What is sewage?
›Reveal solutionSolution
Sewage is the municipal waste water full of organic matter and microbes.
Concept. Large amounts of waste water are generated every day in cities and towns. This municipal waste water, called sewage, is carried through sewers and contains human excreta, domestic and industrial liquid waste, a high load of organic matter, and many microbes, several of which are pathogenic.
…
- 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 ANNUAL1 markMCQQ.The organism which causes disease in plants and animals is called(a) vector(b) pathogen(c) insect(d) worm
›Reveal solutionSolution
A pathogen is any disease-causing organism, whereas a vector is merely the carrier that transmits the pathogen from one host to another.
A pathogen is any organism (bacterium, virus, fungus, protozoan, or helminth) capable of causing disease in a host organism, whether plant or animal. A vector (a), such as the female Anopheles mosquito for malaria, is an intermediate organism that transmits the pathogen from an inf …
- CBSE 2023Set ANNUAL1 markMCQQ.Which of the following diseases is caused by a DNA Virus?(a) AIDS(b) Measles(c) Mumps(d) Chicken pox
›Reveal solutionSolution
Chicken pox is caused by Varicella-zoster virus, a double-stranded DNA virus; the other three listed diseases are all caused by RNA viruses.
Let's classify each disease by its causative virus's genome:
- AIDS (a) is caused by HIV, a retrovirus with an RNA genome (reverse-transcribed into DNA inside the host cell).
- Measles (b) is caused by the measles morbillivirus, an RNA virus. …
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