Biotechnology in Agriculture

NCERT grounding

NCERT Class 12 Biology, Chapter 10 (Biotechnology and Its Applications), opens Section 10.1 with the line that anchors this entire subtopic: "Let us take a look at the three options that can be thought for increasing food production — (i) agro-chemical based agriculture; (ii) organic agriculture; and (iii) genetically engineered crop-based agriculture." After noting that the Green Revolution tripled food supply but still could not keep pace with population growth, NCERT pivots to genetically modified organisms (GMOs) as the way forward. The Bt-cotton and RNAi-tobacco examples that follow are the two pieces of agriculture biotechnology that NEET tests almost every year.

"Plants, bacteria, fungi and animals whose genes have been altered by manipulation are called Genetically Modified Organisms (GMO)."

NCERT Class 12 Biology · Chapter 10, §10.1

Three options for raising food output

The chapter lays out three mutually distinct routes to a larger food supply, and forces the student to weigh each against the constraints of cost, environmental damage and scalability. The Green Revolution lifted yields using improved varieties together with better management and large doses of agrochemicals (fertilisers and pesticides). For farmers in the developing world, agrochemicals are often too expensive, and conventional breeding cannot raise yields any further on existing varieties.

Tissue culture and somatic hybridisation extended what classical breeding could do — micropropagation produces somaclones from a single explant, meristem culture removes viral infections from banana, sugarcane and potato, and protoplast fusion yielded the "pomato" — but none of these strategies place a brand-new trait inside a crop. For a step-change in agricultural output NCERT points explicitly to genetically modified crops: transgenic plants engineered to carry a chosen, characterised gene from any biological source.

The line that NEET almost always paraphrases is that GM crops let the breeder transfer a single defined gene — including from a non-plant source — in one generation, whereas conventional crossing can only shuffle the existing alleles of two parents and even then drags hundreds of unwanted genes along with the trait of interest.

GM crops — the five canonical uses

NCERT enumerates five concrete benefits of genetic modification of crops, and a sixth "industrial" use bolted on at the end of the list. NEET treats this list as a fixed five-point set: match-the-column items, statement-correct questions, and "which of the following is NOT a benefit of GM crops" all rotate through the same five. Learn them in the NCERT order, with the canonical example NCERT cites for each.

Two of these uses are big enough that NCERT splits them off as their own worked examples. Reduced pesticide reliance is illustrated by Bt cotton, where the cry genes from Bacillus thuringiensis have been moved into the plant genome. Pest-resistance against nematodes is illustrated by RNA-interference in tobacco against Meloidogyne incognita. The next two sections develop each of these to NEET depth; the dedicated subtopic pages go further.

Bt toxin and cry genes

Bacillus thuringiensis is a soil-dwelling Gram-positive bacterium that, during sporulation, manufactures crystalline parasporal inclusion bodies. Each crystal is built almost entirely of an insecticidal protein. Different strains produce different crystal proteins, each insect-group specific — some toxic to lepidopterans (tobacco budworm, armyworm), some to coleopterans (beetles), and some to dipterans (flies, mosquitoes).

The reason the toxin does not kill the bacterium that makes it is one of NEET's favourite single-sentence questions: in the crystal, the toxin is an inactive protoxin. When a susceptible insect larva eats Bt-coated plant tissue, the larval midgut is strongly alkaline. The alkaline pH solubilises the crystal, and proteolytic enzymes cleave the protoxin into its active form. Activated toxin then binds receptors on midgut epithelial cells, perforates them with pores, and the larva dies of cell-swelling, lysis, septicaemia and starvation. The bacterium itself never exposes the inclusion to anything close to that pH.

The toxin proteins are coded by the family of cry genes — named because their products form crystals. NEET expects you to remember three specific mappings because NCERT names them explicitly:

RNAi against root-knot nematode

The second worked agriculture-biotech example in NCERT pivots from insect to nematode. Meloidogyne incognita, a root-knot nematode, parasitises tobacco roots and slashes yield. Conventional chemical nematicides are environmentally damaging, and breeding has not produced reliable resistance. Scientists instead engineered tobacco to exploit a cellular defence pathway that exists in every eukaryote: RNA interference (RNAi).

RNAi works by destroying or silencing a specific mRNA whenever a double-stranded RNA (dsRNA) complementary to that mRNA appears in the cell. Naturally this happens when an RNA virus infects the cell or when transposons replicate via an RNA intermediate. The engineered strategy hijacks the same machinery to silence a gene the plant wants turned off — in this case a transcript essential for the nematode parasite that is feeding on the plant.

Worked examples

Common confusion & NEET traps