(a) (i) Name and explain the property present in normal cells but is lost in cancer cells. (ii) All normal hum

Question

Q. (a)

(i) Name and explain the property present in normal cells but is lost in cancer cells.

(ii) All normal human cells have genes that may become cancerous under certain conditions. Name them and explain how.

(iii) State the role of the following techniques in detection and diagnosis of cancer:

(1) Biopsy and Histopathology

(2) Magnetic Resonance Imaging

(OR)

(b) Large quantities of sewage are generated every day in cities as well as in towns and are treated in Sewage Treatment Plants (STPs) to make them less polluting. Given below is the flow diagram of stages of STP. Study the flow diagram and answer the questions that follow: [Flow diagram: 'Primary effluent passed into large aeration tanks' → 'Effluent passed into settling tanks to form sediment'.]

(i)

(1) Why is primary effluent passed into large aeration tanks?

(2) What is the 'sediment' formed, referred to as? Mention its significance.

(3) Explain the final step in the settling tank before the treated effluent is released into water bodies.

(ii) Name any two organisms commonly used as biofertilisers, belonging to different kingdoms. Write how each one acts as a biofertiliser.

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Part (a)Concept understanding — Cancer Cell Biology

Imagine a city where every cell is a citizen with a specific job. Skin cells form the outer wall, stomach cells digest food, nerve cells carry messages. Each citizen follows a strict rulebook: grow when needed, stop when the job is done, and eventually die to make room for younger replacements. This orderly cycle is what keeps the city healthy.

Now, what happens if one citizen suddenly stops listening to the rules? It starts growing uncontrollably, refuses to die, and begins crowding out its neighbours. Worse, it might break through the city walls and travel to a different district, setting up a new colony there. That rogue citizen is a cancer cell. Cancer cell biology is the study of how normal, well-behaved cells turn into these rebellious, destructive ones.

The core idea: a breakdown of cellular discipline

Every cell in your body contains a complete set of instructions — your DNA. Think of DNA as the city's master blueprint and rulebook. Inside that blueprint are specific genes that act like traffic lights: some tell the cell to grow (these are called proto-oncogenes), and others tell it to stop growing or to self-destruct when damaged (these are called tumour suppressor genes).

Cancer begins when these traffic lights break. A proto-oncogene might get stuck on green, so the cell grows non-stop. Or a tumour suppressor gene might get stuck on red, so the cell never gets the signal to stop or die. Usually, a single broken light isn't enough — the cell has backup systems. But over years, multiple lights break, and the cell loses all control.

Important

Cancer is not one disease but a collection of diseases. All cancers share one fundamental property: uncontrolled cell division caused by accumulated damage to the DNA. The type of cancer depends on which original cell type went rogue (e.g., lung cells → lung cancer, skin cells → skin cancer).

How a normal cell becomes cancerous: a step-by-step intuition

Initiation — A cell's DNA gets damaged by something (a chemical in cigarette smoke, UV radiation from the sun, a random copying error during cell division). This damage is a mutation. One mutation alone rarely causes cancer, but it's the first crack in the rulebook.
Promotion — The damaged cell is now slightly more prone to grow. If it encounters more damaging agents (promoters), it accumulates more mutations. Each mutation pushes it further from normal behaviour.
Progression — After several mutations, the cell now divides rapidly, ignores signals to stop, and refuses to die. It forms a mass of cells called a tumour. Not all tumours are cancerous — benign tumours stay in one place and don't invade neighbours. Malignant tumours are the dangerous ones: they invade nearby tissues and can break off to travel through blood or lymph vessels.
Metastasis — This is the most dangerous step. A few cancer cells detach from the original tumour, travel through the bloodstream or lymphatic system, and settle in a distant organ (like the liver, lungs, or brain). There, they start a new tumour. This spread is what makes cancer so hard to treat.

Why does this matter for you?

You don't need to memorise gene names or pathways. What matters is understanding the logic behind prevention and treatment:

Prevention works because most cancers take years to develop. Avoiding known DNA-damaging agents (tobacco, excessive sun, certain viruses like HPV) reduces the chance of those first mutations.
Early detection works because a small, localised tumour can often be surgically removed before it metastasises. …

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.

Important

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.

Note

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 …

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Part (a): Cancer cells lose contact inhibition; proto-oncogenes (c-onc) activated to oncogenes cause uncontrolled division; biopsy/histopathology (tissue exam) and MRI (imaging) detect cancer.

Part (b): In an STP, aeration lets aerobic microbes lower the BOD; the sediment (activated sludge) is recycled and digested anaerobically to biogas; biofertilisers Rhizobium (Monera, N-fixation) and Glomus (Fungi, mycorrhiza) enrich the soil.

Part (a) Cancer biology and detection

Property lost in cancer cells — contact inhibition. Normal cells show contact inhibition: contact with neighbouring cells inhibits their uncontrolled growth, keeping tissues orderly. Cancer cells have lost contact inhibition, so they continue to divide, pile up and form tumours.
Genes that can become cancerous — proto-oncogenes. All normal cells contain cellular oncogenes (c-onc) or proto-oncogenes, which normally regulate cell growth and division. When activated by oncogenic agents (carcinogens) — physical (ionising radiation), chemical, or biological (oncogenic viruses carrying viral oncogenes, v-onc) — these proto-oncogenes are converted into active oncogenes. Their products cause the cell to divide in an uncontrolled, unregulated manner, producing cancer.
Detection and diagnosis.

Biopsy and Histopathology: a small piece of the suspected tissue is cut into thin sections, stained and examined under the microscope by a pathologist. Malignant tissue shows abnormal cells, increased mitotic figures, and loss of the normal tissue architecture — this confirms cancer and its type/grade. (Blood cancers are detected by counting blood cells too.) …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

Showing the 12 most recent of 25 on this concept.

CBSE 2026Set ANNUAL1 markMCQ
$Q. Contact inhibition is a property related to$
(a) Normal cells
(b) Cancerous cells
(c) Hepatic cells
(d) Macrophages
›Reveal solutionSolution

Contact inhibition means normal cells stop dividing and moving once they come into contact with neighbouring cells; cancer cells characteristically lose this property.

Normal cells show contact inhibition — when growing in a culture or tissue, a normal cell stops proliferating and migrating once it touches surrounding cells, which keeps tissue growth orderly and confined.

…

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CBSE 2026Set ANNUAL1 mark
$Q. Name one substance which is used for cancer immunotherapy.$
›Reveal solutionSolution

Interferons, natural antiviral signalling proteins, are also used therapeutically to stimulate the immune system against cancer.

Interferons are proteins naturally secreted by virus-infected cells to help protect neighbouring, uninfected cells from viral infection, but they also have immune-modulating properties that make them useful in cancer immunotherapy — recombinant interferons are used clinically to stimulate the patient's immune system to more effectively recognise and destroy cancer cells (e.g., in the treatment of certain leuk …

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CBSE 2025Set 57/6/11 markMCQ
$Q. A characteristic property that distinguishes a malignant tumor from a benign tumor is : (A) Metamorphosis (B) Metastasis (C) Metabolism (D) Metagenesis$
›Reveal solutionSolution

Metastasis — the ability to invade surrounding tissues and spread to distant body sites — is the defining characteristic that separates malignant tumors from benign ones.

When we talk about tumors, we're really talking about two fundamentally different kinds of abnormal cell growth. Both benign and malignant tumors arise from uncontrolled cell division, but what happens next determines whether a tumor remains a localized nuisance or becomes a life-threatening disease.

Benign tumors are, in a sense, well-behaved troublemakers. They grow slowly, remain confined within a capsule of connective tissue, and stay exactly where they started. A benign tumor in your liver stays in your liver. It might press on nearby structures and cause problems through sheer size, but it doesn't invade the surrounding tissue or send rogue cells traveling through your body. Surgical removal usually cures the problem completely because the tumor has clear boundaries.

Malignant tumors — cancers — are an entirely different story. The cells in a malignant tumor lose the normal restraints that keep cells in their proper place. They acquire the ability to break through the basement membrane that normally acts as a barrier, invade neighboring tissues, and most critically, enter the bloodstream or lymphatic system. Once in circulation, these cancer cells can establish secondary tumors at distant sites. A lung cancer cell might travel to the brain, bone, or liver and start a new colony there. This process of spreading from the original site to distant organs is called metastasis, and it's the hallmark of malignancy.

Important

Metastasis is not just spreading — it's a multi-step process requiring cancer cells to detach, survive in circulation, invade new tissue, and establish growth at a distant site. Benign tumors never metastasize. …

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CBSE 2025Set F1 markMCQ
$Q. By which of the following methods do cancer cells divide?$
(a) Mitosis
(b) Amitosis
(c) Meiosis
(d) None of these
›Reveal solutionSolution

Cancer cells multiply by uncontrolled mitosis.

Cancer arises when normal cells lose the control over cell division (contact inhibition and cell-cycle checkpoints). Such transformed cells proliferate rapidly and continuously by mitosis, forming a mass called a tumour. This uncontrolled mitotic division and the ability to invade other tissues (metastasis) ar …

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CBSE 2025Set ANNUAL1 mark
$Q. What is primary sludge?$
›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 …

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CBSE 2025Set ANNUAL1 mark
$Q. The ability of malignant tumors to spread to distant sites in the body through the blood is called _________.$
›Reveal solutionSolution
Metastasis is the defining feature of malignant (cancerous) tumours: cells break away, invade blood/lymph vessels, and establish new secondary tumours elsewhere in the body.

Tumours are of two types:

Benign tumours remain confined to their original site and do not spread to other parts of the body; they cause limited damage. …
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CBSE 2025Set ANNUAL1 mark
$Q. Differentiate between primary sludge and activated sludge by giving one point.$
›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). …
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CBSE 2025Set ZOOLOGY1 markMCQ
$Q. Which gene is involved in cancer?$
(i) Supplementary gene
(ii) Operon gene
(iii) Oncogene
(iv) Complementary gene
›Reveal solutionSolution

Oncogenes (activated forms of cellular proto-oncogenes) cause cancer by promoting uncontrolled cell division.

Normal cells contain proto-oncogenes that regulate normal cell growth and division. When these become altered (by mutation, viral action, etc.) they turn into oncogenes (cellular oncogenes, c-onc), which drive uncontrolled, unregulated cell proliferation, forming tumours — i.e., cancer. Certain oncogenic viruses also carry viral oncogenes (v-onc).

…

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CBSE 2024Set GG1 mark
$Q. What is sewage?$
›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.

…

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CBSE 2024Set E1 markMCQ
$Q. Which of the following is a non-infectious disease?$
(a) AIDS
(b) Malaria
(c) Cancer
(d) Typhoid
›Reveal solutionSolution
Cancer is a non-infectious disease; AIDS, malaria and typhoid are all infectious (pathogen-caused).

Diseases are broadly infectious or non-infectious:

AIDS (HIV virus), malaria (Plasmodium) and typhoid (Salmonella typhi) are all caused by pathogens and can be transmitted between people — INFECTIOUS diseases. …
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CBSE 2024Set D1 mark
$Q. Write True or False: Genes that cause cancer are called oncogenes.$
›Reveal solutionSolution

The statement is True — genes capable of transforming a normal cell into a cancerous (malignant) cell are indeed called oncogenes.

Cancer arises when normal regulatory mechanisms that control cell growth and division break down, leading to uncontrolled proliferation. Certain genes, when activated, mutated, or overexpressed, drive this transformation — these are called oncogenes.

…

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CBSE 2024Set ANNUAL1 markMCQ
$Q. The spread of cancerous cells to distant places is called ____________.$
(a) Malignancy
(b) Metastasis
(c) Mutations
(d) Carcinogens
›Reveal solutionSolution
Metastasis is the spread of cancer cells from the primary tumour to distant parts of the body.

Cancer cells lose contact inhibition and divide uncontrollably, forming a primary tumour. Some tumour cells acquire the ability to invade the surrounding normal tissue, enter the blood or lymph, and travel to a distant site where they establish a new (secondary) tumour. This spread of cancerous cells to distant sites is called metastasis, and metastatic tumours are the most difficult to treat.

Malignancy is the general property of a tumour being cancerous/invasive. …
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Q.(a)

Part (a) Cancer biology and detection

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