Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents are called:
- (a)Carcinogens
- (b)Metastasis
- (c)Allergy
- (d)AIDS
Correct — A, Carcinogens.
The stem is a straight definition. The agents that induce the transformation of normal cells into cancerous neoplastic cells are called carcinogens, and the definition is deliberately wide enough to hold three kinds of agent at once.
Ionising radiation such as X-rays and gamma rays, and non-ionising ultraviolet radiation, are the physical carcinogens. Constituents of tobacco smoke are the standard chemical example. Oncogenic viruses, which carry viral oncogenes, are the biological ones.
A carcinogen is the cause, not the cancer. Once the transformation has happened, the cell escapes the normal restraint on its division and piles up as a tumour — that later stage carries its own vocabulary, which option (b) is drawn from; (c) and (d) come from the immune-system portion of the same chapter.
- (b)Metastasis — Metastasis is something a malignant tumour does after cells have already turned cancerous. Cells sloughed off the primary tumour travel through the blood or lymph, lodge at distant sites and start fresh tumours there.
So it answers a question about how cancer spreads to new sites in the body, not one about what triggers the change in a normal cell.
- (c)Allergy — Allergy is an exaggerated response of the immune system to a substance that is otherwise harmless — an allergen such as pollen, dust mites or animal dander. Mast cells release chemicals including histamine, producing sneezing, watery eyes or breathlessness.
It is the right answer to a question on hypersensitivity of the immune system to allergens, which is a different part of the same health topic.
- (d)AIDS — AIDS is Acquired Immuno Deficiency Syndrome, caused by the human immunodeficiency virus (HIV), a retrovirus that damages helper T-lymphocytes and leaves the body open to infections it would otherwise resist.
It is the right answer to a question about the disease HIV causes. Grammatically it also fails the stem, which asks for the name of a class of agents, not the name of a disease.
A carcinogen is any agent capable of converting a normal cell into a cancerous, neoplastic one. The category is defined by what the agent does, not by what it is made of, so radiation, chemicals and viruses all sit inside it.
What changes in the cell is its control over its own division. Normal cells in culture typically stop dividing when they touch their neighbours — contact inhibition — while transformed cells carry on and accumulate as a mass of tissue called a tumour.
Normal cells also carry proto-oncogenes, or cellular oncogenes. When these are activated, the cell can be pushed into that uncontrolled state, which is the route by which many carcinogens act.
Cancer belongs to the human health and disease portion of general science, and this sentence follows the standard NCERT Class XII Biology wording closely enough that the answer is a recall of one word.
Within that material each limb of the three-way split has a stock example — ionising and ultraviolet radiation, constituents of tobacco smoke, and oncogenic viruses — which is why the stem can name physical, chemical and biological agents in a single line.
- Carcinogens are the physical, chemical or biological agents that induce transformation of a normal cell into a cancerous neoplastic cell.
- Ionising radiation such as X-rays and gamma rays, and non-ionising ultraviolet radiation, act as physical carcinogens.
- Chemical carcinogens include constituents of tobacco smoke, exposure to which is linked with lung cancer.
- Biological carcinogens include oncogenic viruses, which carry genes known as viral oncogenes.
- Normal cells in culture typically show contact inhibition; cancerous cells lose it and keep dividing to form a mass of cells.
- A benign tumour stays confined to its site of origin; a malignant tumour grows rapidly and invades surrounding tissue.
- Metastasis is the spread of cells from a malignant tumour through the blood (and lymph) to distant sites, where new tumours form.
- Normal cells carry proto-oncogenes, also called cellular oncogenes, whose activation can lead to oncogenic transformation.
The keyed option names an agent; the other three name a process, an immune response and a disease.
- Reading the stem for the topic rather than the question: it names a disease process but asks what the causative agents are called.
- Treating metastasis as a cause — it is the spread of already-malignant cells, which comes after the transformation, not before it.
- Assuming a carcinogen has to be a chemical, when the stem itself lists physical and biological agents alongside chemical ones.
- Blurring carcinogen with oncogene: the carcinogen is the agent acting on the cell, while a cellular oncogene is a gene already present inside it.
- Reaching for AIDS because a virus is involved; a virus can be a biological carcinogen, but AIDS is the name of a disease, not of a class of agents.
As a one-line definition item like this one, where the stem is a textbook sentence and the work is matching a single term to it.
It can also be put the other way round, with the term given and its definition to be picked, or as a classification item asking which of X-rays, tobacco smoke and an oncogenic virus is the physical, chemical or biological carcinogen.
Several cancer terms can equally sit in one option set, so that carcinogen, tumour, benign, malignant and metastasis have to be kept apart by meaning rather than by association.
UPSC_2010_GS1_Q902010Same subject, opposite end of it. That item is about treating cancerous tumours and describes the cyberknife as a robotic, image-guided system delivering an extremely precise dose of radiation — but it is a negative-format question, 'which one of the following statements is not correct?', so what it keys is the statement that the tool maps the spread of a tumour in the body, not those descriptions of it. This one asks instead what the agents causing the malignant change are called: the UPSC item needs familiarity with a named technology, whereas this needs only the textbook definition.
NDA_GAT_2021_I_Q722021Both stems open with the transformation of one kind of cell into another, and both are answered by a single term. The biology is unrelated: there it is normal plant development, meristematic cells becoming permanent tissue through cell differentiation, whereas here it is the pathological conversion of a normal cell into a neoplastic one. A reminder that 'transformation' takes its meaning from the sentence around it.
- practice — not a real PYQ
The spread of cells from a malignant tumour through the blood (and lymph) to distant sites in the body, where they form new tumours, is called:
- (a)Metastasis
- (b)Mutation
- (c)Metamorphosis
- (d)Mitosis
Answera — Metastasis is precisely this: malignant cells break away from the primary tumour, travel in the blood or lymph and establish secondary tumours elsewhere.Mutation is a change in the DNA sequence, not a movement of cells. Metamorphosis is the developmental change from larva to adult in certain animals. Mitosis is ordinary cell division producing two identical daughter cells.
- practice — not a real PYQ
Which one of the following is a physical carcinogen?
- (a)Ionising radiation such as X-rays and gamma rays
- (b)Tobacco smoke
- (c)An oncogenic virus
- (d)A cellular oncogene
Answera — X-rays and gamma rays are ionising radiation, the standard example of a physical carcinogen.Tobacco smoke is the chemical example and an oncogenic virus the biological one. A cellular oncogene is a gene already present inside the cell, so it is not an external agent acting on the cell at all.
- practice — not a real PYQ
A tumour that remains confined to its site of origin and does not invade the surrounding tissue is described as:
- (a)Malignant
- (b)Benign
- (c)Metastatic
- (d)Carcinogenic
Answerb — A benign tumour stays where it arose and does not spread into neighbouring tissue.A malignant tumour grows rapidly and invades surrounding tissue. 'Metastatic' describes tumour cells that have already travelled to a distant site. 'Carcinogenic' describes an agent that causes cancer, so it says nothing about how a tumour behaves.