Q.Bt cotton is not:

Step 1 — How the Bt toxin actually works (this is the whole question).

Bacillus thuringiensis forms protein crystals containing the Cry protein, which exists as an inactive protoxin. When an insect eats it:

1. The insect's midgut is alkaline ($\text{pH} > 9.5$), which solubilises the crystal.
2. The protoxin is then converted into the active toxin.
3. The active toxin binds to specific receptors on the midgut epithelium, punching pores in the cells, which swell, lyse and kill the insect.

Every one of these three steps is insect-specific. That is exactly why the toxin is safe for humans and other animals — our stomachs are acidic, so the crystal is never solubilised, and we lack the midgut receptor.

Step 2 — Classify the four organisms.

Step 3 — Conclude.

The armyworm, cotton bollworm and tobacco budworm are all lepidopteran insects, and NCERT names them explicitly as targets of the cryIAc/cryIIAb genes. The tapeworm is an endoparasitic flatworm: it lives in the host's intestine, has no alkaline insect midgut and no Cry receptor, so the Bt protein has no effect on it.

ANSWER: C

Step 1 — The three layers of a blood-vessel wall

Both arteries and veins are built of the same three coats, from inside out:

Step 2 — Apply the pressure argument

Arteries receive blood ejected from the ventricles under high, pulsatile pressure. To absorb and smooth that surge, they need a thick, muscular, elastic tunica media.

Veins collect blood from capillaries and return it to the heart at low pressure (venous return relies on skeletal-muscle pumping, respiratory pump and valves, not on wall recoil). With no high pressure to contain, the muscular/elastic layer is not needed in bulk — so in veins the tunica media is comparatively thin. This is exactly why a vein has a larger lumen and collapses when empty, whereas an artery holds its shape.

Step 3 — Check the distractors

• (A) Tunica intima — it is a single endothelial layer in both vessel types, so it is not the layer that differs.
• (B) Tunica externa — in veins this fibrous coat is relatively well developed (proportionally it is the largest layer of a vein), not thin.
• (C) Both media and externa — only the media is the thinned layer, so this over-reaches.
• (D) Tunica media — correct. ✓

ANSWER: D

Step 1 — Recall the architecture of a myofibril

Each muscle fibre contains many myofibrils. A myofibril shows alternating light and dark bands:

• I-band (light) — contains only thin (actin) filaments; it is bisected by the Z-line.
• A-band (dark) — contains the thick (myosin) filaments; its centre carries the lighter H-zone, bisected by the M-line.

Step 2 — Define the functional (contractile) unit

The sarcomere is the portion of the myofibril between two successive Z-lines. It contains one full A-band flanked by two half I-bands. This is the smallest repeating assembly that contains everything needed to contract: anchored thin filaments (Z-line), overlapping thick filaments (A-band) and the cross-bridge machinery.

Step 3 — Why the sliding-filament model makes the Z-line the boundary

During contraction, myosin heads form cross-bridges and pull the actin filaments towards the centre of the A-band. The thin filaments are attached to the Z-lines, so the Z-lines are dragged inward:

Because the shortening is measured between the Z-lines, that span is by definition the functional unit.

Step 4 — Eliminate the other options

• (B) Between two M-lines — an M-line sits at the centre of each A-band; the span between two M-lines is a sarcomere-length region but it is not the standard definition, and it is not anchored to actin, so it is not the unit that shortens by anchor displacement.
• (C) Centre of the H-zone — this is merely the location of the M-line, a single plane, not a unit.
• (D) Centre of the I-band — this is where the Z-line lies; it is a boundary, not a unit.

ANSWER: A

Step 1 — What MTP is

MTP = Medical Termination of Pregnancy, the intentional/voluntary termination of a pregnancy before full term. It is not a contraceptive method — it is a remedial measure.

Step 2 — The legislation

The Government of India legalised MTP in 1971, but attached strict regulations to it. The reason was twofold:

1. A very large number of unsafe, illegal abortions were being performed, endangering women's lives; and
2. The procedure was liable to misuse — most notoriously for illegal female foeticide after sex determination of the foetus.

Step 3 — The conditions attached

• MTP is considered relatively safe up to 12 weeks (first trimester); terminations after 12 weeks up to 20 weeks are much riskier and require stricter clearance (in the NCERT text, the approval of two doctors).
• MTPs are legally allowed on grounds such as risk to the mother's life/health, contraceptive failure, foetal abnormality, or pregnancy from rape.
• A large fraction of MTPs are performed illegally by unqualified quacks, which remains a major health hazard — hence the emphasis on the regulated nature of the law.

Step 4 — Eliminate the other options

(A) 1951 and (B) 1961 predate the Act; (D) 2001 is far too late (by then the MTP Act had already been in force for three decades; 2001 is closer to the era of the PNDT amendments against sex determination).

ANSWER: C

Step 1 — Classify the four enzymes by what they physically do to DNA.

• Nucleases cut phosphodiester bonds. They come in two kinds:
  • Exonucleases remove nucleotides from the ends of the DNA.
  • Endonucleases make cuts at specific positions within the DNA.
• Ligases join two DNA fragments by sealing the phosphodiester backbone.
• Polymerases synthesise new DNA on a template.

Step 2 — Ask what "cleave a plasmid" requires.

A plasmid is a small, circular, extra-chromosomal DNA molecule. A circle has no free ends. Therefore:

• An exonuclease literally cannot start on an intact circular plasmid — there is no terminus to attack. ✗ (C)
• To linearise/open the plasmid so that a foreign gene can be inserted, the cut must be made inside the molecule → an endonuclease. ✓ (B)

Step 3 — The specific enzyme used in practice.

In rDNA technology the enzyme used is a restriction endonuclease. Each such enzyme:

1. inspects the DNA and binds at a specific palindromic nucleotide sequence (e.g. EcoRI: $5'\text{-GAATTC-}3' / 3'\text{-CTTAAG-}5'$),
2. cuts each strand a little away from the centre, between the same two bases on both strands,
3. leaves single-stranded overhangs — sticky ends.

Because the same enzyme cuts both the plasmid vector and the source DNA, both fragments carry complementary sticky ends that base-pair with each other — after which DNA ligase seals them (which is why (A) is the next step, not this one).

Step 4 — Eliminate the remainder.

• (A) Ligase — joins, does not cut; it acts after the endonuclease. ✗
• (C) Exonuclease — removes nucleotides from ends; cannot open a circle. ✗
• (D) Polymerase — synthesises DNA; no cleaving activity. ✗

ANSWER: B

Step 1 — Identify the molecule that treats emphysema.

Among the products obtainable by genetic engineering, the textbook list of human proteins reads: insulin (diabetes), $\alpha$-1 antitrypsin (emphysema), factor VIII (haemophilia), $\alpha$-interferon (viral infections/cancer) and $\alpha$-lactalbumin (a milk protein). The molecule paired with emphysema is unambiguously $\alpha$-1 antitrypsin. That leaves options (A) and (C) — both name antitrypsin — and the question then turns on how it is described.

Step 2 — The biology of why it works.

Emphysema is the progressive destruction of the alveolar walls of the lung. The enzyme neutrophil elastase digests elastin in lung tissue; $\alpha$-1 antitrypsin is a protease inhibitor — a plasma protein — that neutralises this elastase and thereby protects the alveoli. A hereditary deficiency of $\alpha$-1 antitrypsin leaves the elastase unopposed, the alveolar walls are destroyed, and emphysema results. Administering the (recombinant/purified) protein restores the missing inhibitor. Note that it works by inhibiting an enzyme, which is exactly what a protease-inhibitor protein does — it does not act on a receptor as a signalling molecule, so it cannot be a hormone.

Step 3 — Distinguish (A) from (C) — the actual discriminator.

• (A) "Human Hormone-$\alpha$-Antitrypsin" — the molecule is correct, but its classification is wrong. A hormone is a chemical messenger secreted by an endocrine gland into the blood to act on a distant target. $\alpha$-1 antitrypsin is a protease inhibitor protein, not a signalling hormone. ✗
• (C) "Human protein-$\alpha$-Antitrypsin" — correct molecule and correct classification: it is a human protein. ✓

Step 4 — Eliminate the rest.

• (B) Human-$\alpha$-Interferon — used against viral infections and cancers, not emphysema. ✗
• (D) Human-$\alpha$-Lactalbumin — a milk protein (transgenic cow Rosie produced human-protein-enriched milk containing human $\alpha$-lactalbumin); it is a nutritional protein, no role in emphysema. ✗

ANSWER: C

Step 1 — Define the two terms

• Exon — the expressed sequence; it appears in the mature mRNA and is translated.
• Intron — the intervening sequence; it is transcribed but removed during splicing and never appears in mature mRNA.

Step 2 — What "monocistronic but split" means

• Monocistronic → one eukaryotic mRNA codes for one polypeptide (unlike prokaryotic polycistronic mRNA, e.g. the lac operon, which codes for several).
• Split → the coding information of that one gene is not in one continuous block; it is interrupted.

Step 3 — The processing that follows

The hnRNA additionally receives capping (methyl guanosine triphosphate at the 5′ end) and tailing (poly-A at the 3′ end) before it is exported for translation.

Step 4 — Eliminate the other options

• (A) "Introns are interrupted with Mutons" — a muton is the smallest unit of DNA that can undergo mutation; it has nothing to do with gene architecture. Nonsense distractor.
• (B) "they contain Exons only" — if a gene had only exons it would be continuous, not split. This describes a prokaryotic gene.
• (C) "they contain Introns only" — impossible; a gene with no exons would encode no protein.

ANSWER: D

Step 1 — The historical sequence of virus discovery

The discovery of viruses came from work on tobacco mosaic disease, and each worker in the options contributed a different step:

Step 2 — Match the term to the worker

The question asks specifically who gave the concept of Contagium vivum fluidum. That Latin phrase is Beijerinck's coinage. It captured the crucial idea that the agent was living (it multiplied inside the host) yet behaved like a fluid (it was not retained by a filter, so it was not a visible cellular organism).

Step 3 — Eliminate

• (A) Ivanowsky — filterability, but no such term.
• (B) Stanley — crystallisation, 37 years later.
• (D) Whittaker — five-kingdom classification, irrelevant here.

ANSWER: C

The question asks for a plant that is both a source of a drug and native to America. The key is to connect each plant to its geographical origin and the drug it yields. Many medicinal and psychoactive plants have been spread globally by humans, but their native ranges are specific. America here refers to the Americas (North and South America).

Let’s examine each option:

1. Papaver somniferum (opium poppy) – This is the source of morphine, codeine, and heroin. It is native to the eastern Mediterranean region and western Asia, not America. It was introduced elsewhere later.

2. Erythroxylum coca – This shrub is the source of cocaine. It is native to the eastern slopes of the Andes in South America (Peru, Bolivia, Colombia). Indigenous peoples have used its leaves for centuries. This matches the requirement perfectly.

3. Cannabis sativa – Source of marijuana (THC) and hemp fiber. Its native range is debated but is generally considered to be Central Asia or the Indian subcontinent. It is not native to the Americas.

4. Atropa belladonna (deadly nightshade) – Source of atropine and other tropane alkaloids. It is native to Europe, North Africa, and western Asia. Not native to America.

Step 1 — Read the parts of the axoneme.

A cilium/flagellum is a 9 + 2 array enclosed by the plasma membrane:

• 9 peripheral doublets — pairs of microtubules arranged in a ring.
• 2 central microtubules — the central pair, wrapped in a proteinaceous central sheath.

Step 2 — Distinguish the two kinds of cross-link (this is the whole question).

The question asks specifically for the part that connects the peripheral microtubules to the central sheath — that is the radial spoke, and the figure labels exactly those inward-radiating lines as "Radial spoke".

Step 3 — Eliminate the others.

• (A) Plasma membrane — the outer boundary; it connects nothing internally.
• (B) Interdoublet bridge — connects doublet to doublet, i.e. peripheral to peripheral. This is the trap option.
• (C) Central microtubule — it is one of the things being connected, not the connector.

ANSWER: D

The key here is to understand what "advantage" means in the context of genetically modified crops. An advantage is a benefit — something that improves farming, the environment, or human well-being. The question tests whether you can spot the one statement that describes a disadvantage or a false claim.

Let’s examine each option carefully.

1. Option (A): Reduces the reliance on chemical pesticides.

   This is a well-known advantage. Many GM crops are engineered to be pest-resistant (e.g., Bt cotton produces a protein toxic to certain insects). This means farmers need to spray fewer chemical pesticides, which saves money and reduces environmental harm. So this is an advantage.

2. Option (B): Increases the post harvest losses.

   "Post harvest losses" refer to the spoilage or damage of crops after they are harvested — during storage, transport, or handling. GM crops are often modified to have longer shelf life, resist bruising, or tolerate better storage conditions (e.g., Flavr Savr tomato). So they decrease post harvest losses, not increase them. This statement is the opposite of an advantage — it is a disadvantage. Therefore, this is the correct answer.

3. Option (C): Increases efficiency of mineral usage in plants.

   Some GM crops are designed to use minerals (like nitrogen or phosphorus) more efficiently. This means they can grow well even in poorer soils, reducing the need for fertilizers. That is clearly an advantage — it lowers costs and environmental pollution.

4. Option (D): Enhances the nutritional value of food.

   This is a classic advantage. For example, "Golden Rice" is genetically modified to produce beta-carotene (a source of vitamin A), helping to prevent blindness in malnourished populations. So this is an advantage.

Step 1 — What defines a retrovirus.

A retrovirus is an RNA virus that reverses the usual flow of information: instead of DNA → RNA, it goes RNA → DNA, using the enzyme reverse transcriptase. HIV is the standard example.

Step 2 — The replication cycle (as in NCERT).

1. The virus attaches to a host cell (in HIV, a helper T-lymphocyte / macrophage) and its envelope fuses with the cell membrane.
2. The viral RNA genome enters the host cell. ← this is the step the question asks about
3. Inside the cell, reverse transcriptase copies the viral RNA into complementary DNA (cDNA).
4. That viral DNA is integrated into the host cell's DNA (as a provirus).
5. The infected cell then transcribes and translates viral genes, producing new virus particles.

Step 3 — Eliminate the distractors.

• (A) Viral protein: capsid/envelope proteins are not what is delivered as the genome.
• (C) Viral DNA: the virus does not carry DNA — DNA is made inside the host from the RNA. This is the commonest error.
• (D) The reverse transcriptase enzyme is packaged within the virion along with the RNA; it is not what is "introduced" as the genetic material, and the option's loose phrasing ("transcriptase") does not describe the defining event.

Conclusion. What enters the host cell during retroviral replication is the viral RNA.

ANSWER: B