Name any two physiological barriers that provide innate immunity. OR Select two disease resistant crop varieti

Question 88 of 117

Q. Name any two physiological barriers that provide innate immunity.

(OR)

Select two disease resistant crop varieties from the list of crop varieties given below : Himgiri, Pusa Gaurav, Pusa Komal, Pusa A-4

CBSECBSE Class XII Board 2019Subjective· 1mImportance★★★★★

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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.

Important

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 — Biofertilizers Biopesticides

Imagine you have a garden. You want your plants to grow strong and healthy, and you also want to keep pests away. There are two main ways to do this: one is with harsh chemicals (chemical fertilizers and pesticides), and the other is with living things or natural substances. Biofertilizers and biopesticides are the second way — they are nature’s own tools for farming.

Let’s start with biofertilizers. Think of them as "living manure." A chemical fertilizer is like giving a plant a direct shot of nutrients — it works fast but can burn the soil over time. A biofertilizer, on the other hand, is a preparation containing live microorganisms (like bacteria, fungi, or algae) that help the plant get nutrients from the soil or air. For example, certain bacteria can take nitrogen from the air and convert it into a form the plant can use. The plant doesn’t get fed directly; instead, the biofertilizer helps the soil become richer and more fertile naturally.

Note

The NCERT textbook (Class 12 Biology, Chapter 10) defines biofertilizers as organisms that enrich the nutrient quality of the soil. The main examples are Rhizobium (a bacterium that lives in root nodules of legumes and fixes nitrogen), Azospirillum and Azotobacter (free-living nitrogen-fixing bacteria), and blue-green algae (like Anabaena) which also fix nitrogen.

Now, biopesticides. These are living organisms or natural substances that control pests — insects, fungi, weeds, etc. — without using synthetic chemicals. Instead of spraying a poison that kills everything (good and bad bugs alike), a biopesticide might use a specific bacterium that only harms a particular caterpillar, or a fungus that attacks a weed. The most famous example is Bacillus thuringiensis (often called Bt), a bacterium that produces a protein toxic to certain insect larvae but harmless to humans, animals, and most other insects.

Important

The key difference between chemical and biological agents: Biofertilizers and biopesticides are renewable, eco-friendly, and do not leave toxic residues in the soil or water. They are a cornerstone of sustainable agriculture — farming that can continue for generations without destroying the land.

Why does this matter for a commerce or humanities student? Because agriculture is not just about biology — it’s about economics, policy, and human health. Chemical fertilizers and pesticides are expensive to produce, can pollute groundwater, and their overuse leads to "superpests" that become resistant. Biofertilizers and biopesticides are often cheaper in the long run, safer for farm workers, and help maintain soil health. Governments around the world (including India) promote them through subsidies and organic farming schemes. Understanding them helps you see why "organic" food costs more, why some farmers switch to natural methods, and how environmental regulations work.

Here’s a quick summary of the main types you should know (from NCERT):

Biofertilizers:
- Rhizobium (symbiotic with legumes) …

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Part (a): Two physiological barriers of innate immunity are stomach acid (low pH) and lysozyme in tears/saliva.

Part (b): From the given list, the disease-resistant crop varieties are Himgiri (wheat) and Pusa Komal (cowpea).

Part (a)

Concept-first idea: Innate immunity is the non-specific, present-from-birth defence, and its physiological barriers are internal body conditions that make survival difficult for microbes (distinct from physical barriers like skin).

Two physiological barriers:

Acid in the stomach (HCl, low pH) — the strongly acidic stomach environment kills most microbes that are swallowed.
Lysozyme — present in tears, saliva and other secretions, this enzyme digests bacterial cell walls. …

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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 64 on this concept.

CBSE 2026Set A1 markMCQ
$Q. Which of the following cyanobacteria fixes atmospheric nitrogen?$
(a) Nostoc
(b) Anabaena
(c) Oscillatoria
(d) All of these
›Reveal solutionSolution

All the listed cyanobacteria are nitrogen fixers; the correct option is (d).

Cyanobacteria (blue-green algae) are autotrophic aquatic and terrestrial microbes that can fix atmospheric nitrogen and are used as biofertilizers, especially in paddy fields. Nostoc, Anabaena and Oscillatoria are all exa …

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CBSE 2026Set A1 markMCQ
$Q. With the help of what are butterfly caterpillars controlled?$
(a) Pseudomonas
(b) Trichoderma
(c) Bacillus thuringiensis
(d) Baculovirus
›Reveal solutionSolution

Bacillus thuringiensis is used to control butterfly caterpillars; the correct option is (c).

Bacillus thuringiensis (Bt) is a bacterium used as a biocontrol agent against insect pests. Dried Bt spores are mixed with water and sprayed onto crops. When eaten by the larvae (caterpillars) of butterflies and moths, the toxin (crystal protein) is released in their gut and kills them, while being harmless to other …

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CBSE 2026Set ANNUAL1 markMCQ
$Q. Microbes (micro-organism) found in the form of biofertilizer is$
(a) Agrobacterium
(b) Bacillus thuringiensis
(c) Baculoviruses
(d) Rhizobium
›Reveal solutionSolution

Biofertilisers are living organisms that enrich soil nutrient quality; Rhizobium (a symbiotic N2-fixer in legume root nodules) is a classic bacterial biofertiliser.

Rhizobium lives symbiotically in the root nodules of leguminous plants and fixes atmospheric nitrogen into a usable form, enriching soil fertility - hence it is used as a biofertiliser. Agrobacterium is used as …

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CBSE 2026Set ANNUAL1 mark
$Q. Which fungus is used as biological control in the treatment of plant diseases?$
›Reveal solutionSolution

Trichoderma species are free-living fungi widely used as biological control agents to protect plant roots from fungal pathogens.

Trichoderma is a genus of free-living fungi commonly found in root ecosystems, and several species act as effective biocontrol agents against a number of plant pathogens, reducing the need for chemical fungicides. This is one of th …

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CBSE 2026Set ANNUAL1 markMCQ
$Q. Cyanobacteria are useful biofertilizers in the field of$
(a) Wheat
(b) Paddy
(c) Maize
(d) Sugarcane
›Reveal solutionSolution

Cyanobacteria (blue-green algae) are nitrogen-fixing biofertilizers especially valuable in flooded paddy fields.

Cyanobacteria such as Nostoc, Anabaena, and Oscillatoria are photosynthetic, nitrogen-fixing prokaryotes that enrich soil with organic matter and fix atmospheric nitrogen into forms plants can use, increasing soil fertility.

…

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CBSE 2026Set ANNUAL1 markMCQ
$Q. Which bacterial species acts as an bio-insecticide ?$
(a) LAB
(b) Bacillus thuringiensis
(c) Acetobacter aceti
(d) Streptococcus
›Reveal solutionSolution

Bacillus thuringiensis (Bt) produces crystal (Cry) proteins toxic to insect larvae and is widely used as a biological insecticide.

Bacillus thuringiensis forms proteinaceous crystals during a particular phase of its growth that contain a toxic insecticidal protein. When ingested by an insect larva, the toxin is activated in the alkaline gut environment, damaging the gut lining and killing the insect — this is used commercially as Bt-based bio-insecticide (dried spore-crystal formulations) and is also the …

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CBSE 2026Set ANNUAL1 markMCQ
$Q. Assertion (A): Rhizobium leguminosorum is a symbiotic bacterium found in the root nodules of leguminous plants. Reason (R): This bacterium has the ability to fix atmospheric sulphur into sulphur dioxide.$
(a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Assertion is false but Reason is true.
›Reveal solutionSolution

Rhizobium leguminosorum is indeed a symbiotic bacterium in leguminous root nodules (Assertion true), but it fixes atmospheric NITROGEN into ammonia — not sulphur into sulphur dioxide (Reason false).

Assertion: Rhizobium species live symbiotically in the root nodules of leguminous plants (like pea, gram, beans) — true; this is a classic example of a biofertilizer relationship.

…

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CBSE 2026Set ANNUAL1 mark
$Q. Fill in the blank: Virus infected cells secrete proteins are called ______.$
›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 …

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CBSE 2026Set ANNUAL1 markMCQ
$Q. Haemozoin is released as a result of -$
(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 …

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CBSE 2026Set ANNUAL1 markMCQ
$Q. Which one of the following is commonly found in root ecosystem and control several plant pathogens?$
(a) Rhizobium
(b) Bacillus thuringiensis
(c) Trichoderma
(d) Azospirillum
›Reveal solutionSolution

Trichoderma is a soil fungus of the root ecosystem used as a biocontrol agent against many plant pathogens.

Biocontrol agents are living organisms used to control plant diseases and pests instead of chemicals. Trichoderma species are free-living fungi very common in the root ecosystems (rhizosphere) and are effective biocontrol agents against several soil-borne plant pathogens.

…

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CBSE 2026Set ANNUAL1 mark
$Q._________ test is performed to confirm typhoid.$
›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 …

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CBSE 2025Set X11 mark
$Q. Members of genus ____________ form mycorrhiza and absorb phosphorous from soil and supply it to the plant.$
›Reveal solutionSolution

Members of the genus Glomus form mycorrhiza and supply phosphorus to plants.

Many members of the fungal genus Glomus form a symbiotic association (mycorrhiza) with the roots of higher plants. The fungal partner absorbs phosphorus from the soil and passes it to the plant; the association al …
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Q.Name any two physiological barriers that provide innate immunity.

Part (a)

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