Q.What is a carcinogen? Give an example each for Physical and Biological carcinogens.
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🔒 Start your 14-day free trial to unlock the full solution →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.
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
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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.
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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.
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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.
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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. …
A carcinogen is any agent that damages DNA and transforms normal cells into cancer cells, and such agents fall into physical, chemical and biological types. …
A carcinogen is a cancer-causing agent; example physical = ionising/UV radiation, biological = oncogenic viruses.
Carcinogen: An agent (physical, chemical or biological) that induces/causes cancer by damaging the DNA and transforming normal cells into cancer (neoplastic) cells.
- Physical carcinogen: Ionising radiations such as X-rays and gamma rays, and non-ionising UV radiation — they cause DNA damage leading to neoplastic transformation. …
Showing the 12 most recent of 17 on this concept.
- CBSE 2026Set ANNUAL1 markMCQQ.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 markQ.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 …
- CBSE 2025Set 57/6/11 markMCQQ.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.
ImportantMetastasis 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. …
- CBSE 2025Set F1 markMCQQ.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 …
- CBSE 2025Set ANNUAL1 markQ.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. …
- CBSE 2025Set ZOOLOGY1 markMCQQ.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 E1 markMCQQ.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. …
- CBSE 2024Set D1 markQ.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 markMCQQ.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. …
- CBSE 2024Set ANNUAL1 markMCQQ.The genes causing cancer are -(i) structural genes(ii) expressor genes(iii) oncogenes(iv) regulatory genes
›Reveal solutionSolution
Oncogenes are the genes responsible for triggering uncontrolled cell division (cancer).
Cancer-causing genes are called oncogenes. Some viruses carry oncogenes (viral oncogenes), and normal cells also possess counterparts of these genes called proto-oncogenes (cellular oncogenes/c-onc); when a proto-oncogene gets activated u …
- CBSE 2022Set HE2201 markMCQQ.Choose the correct answer: Disease caused by activation of Oncogens.(a) Tuberculosis(b) Asthma(c) Cholera(d) Cancer
›Reveal solutionSolution
Cancer arises when normal genes controlling cell division (proto-oncogenes) are converted into cancer-causing oncogenes.
Normal cells contain proto-oncogenes, genes that regulate cell growth and division under tight control. Mutation, chromosomal rearrangement, or activation by viruses can convert a proto-oncogene into an oncogene, which drives uncontrolled, unregulated cell proliferation — a hallmark of cancer. (Loss of function of tumour-suppressor genes, such as p53, similarly contributes …
- CBSE 2022Set ZOOLOGY1 markMCQQ.Which gene is involved in cancer?(i) Supplementary gene(ii) Operon gene(iii) Oncogene(iv) Complementary gene
›Reveal solutionSolution
Oncogenes are the genes that cause cancer by promoting uncontrolled cell proliferation.
Normal cells possess cellular genes called proto-oncogenes (c-onc) that regulate normal cell growth and division. When these are activated - by mutation, or by cancer-causing viruses carrying viral oncogenes (v-onc) - they become oncogenes, leading to transformation of a normal cell into a cancerous cell that divides uncontrollably. Supplementary and co …
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