Q.(a)
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 Start your 14-day free trial to unlock the full solution →Part (a)Concept understanding — Biology Disease Control
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 — 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
-
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. …
Concept: Life cycle of Plasmodium / malaria (a); tumours and cancer diagnostics (b).
Part (a)
(i) In the human body: When an infected female Anopheles bites, it injects sporozoites (the infective stage) with its saliva. These reach the liver, multiply, and then enter the red blood cells (RBCs), where they multiply asexually and rupture the RBCs, releasing a toxin (haemozoin) that causes the recurring high fever and chills. Some parasites in the RBCs form the sexual stages, the male and female gametocytes, which circulate in the blood ready to be picked up by a mosquito.
(ii) Two events inside the female Anopheles:
- Fertilization / fusion of gametes — the gametocytes taken up in the blood meal form gametes that fuse to form a zygote (which develops further in the gut wall). …
Part (a): In humans, Plasmodium sporozoites multiply in the liver, then in RBCs (releasing haemozoin → fever) and form gametocytes; inside the female Anopheles the two events are fertilization (gamete fusion → zygote) and sporogony (formation of sporozoites that reach the salivary glands).
Part (b): Malignant tumours invade tissues and metastasise, unlike localised benign tumours; cancer is detected by biopsy/histopathology, imaging (X-ray/CT/MRI) and antibody/molecular techniques.
Part (a) Life cycle of Plasmodium
(i) In the human body.
- A bite by an infected female Anopheles mosquito injects the infective sporozoites with the mosquito's saliva into the human blood.
- The sporozoites reach the liver cells and multiply there.
- They then enter the red blood cells (RBCs), where they multiply asexually, and the RBCs rupture, releasing more parasites and a toxic substance called haemozoin. Haemozoin is responsible for the characteristic recurring high fever and chills every 3–4 days.
- After several such cycles, some parasites within the RBCs develop into the sexual forms — male and female gametocytes, which circulate in the blood. These are the stages that continue the cycle when a mosquito bites the infected person.
(ii) Two events inside the female Anopheles.
When a female Anopheles bites an infected person, it sucks up blood containing gametocytes; inside the mosquito's gut:
- Fertilization (gametogony): the gametocytes mature into male and female gametes, which fuse to form a zygote (the zygote develops further in the wall of the mosquito's gut). …
Showing the 12 most recent of 40 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.
…
- 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 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 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 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.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).
…
- 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.
…
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.