Q.From which part of, “Virus infected plant” healthy plants can be recovered? Name the technique involved.

The technique of growing meristems in culture — what we call meristem culture — is one of the most elegant applications of plant tissue culture. When a plant is infected with a virus, the virus spreads through most of the plant's tissues via the vascular system. However, the shoot apical meristem, the tiny dome of actively dividing cells at the very tip of a growing shoot, often remains virus-free. Why? Because meristematic cells divide so rapidly that the virus cannot keep up, and they lack the well-developed vascular connections that viruses use to travel. So by excising that tiny meristem tip and growing it on a sterile nutrient medium (in vitro), we can regenerate a whole plant that is free from the virus.

Now look at the assertion: "The meristems are grown 'in vitro' to obtain virus-free plants from an infected plant." This is exactly what the NCERT textbook describes. It is a standard, widely used method in horticulture and agriculture to produce healthy stock from diseased parent plants — for example, in potatoes, bananas, or sugarcane. …

The question tests two distinct concepts in plant tissue culture: the definition of totipotency and the technical requirements for in vitro culture. Understanding what totipotency actually means is crucial here.

Totipotency refers to the capacity of a single cell to divide and differentiate into all cell types of an organism, ultimately regenerating a complete, functional plant. This property is most famously demonstrated in plant cells, where a single somatic cell (say, from a leaf or root) can be cultured to produce an entire new plant with roots, stems, leaves, flowers — the works. The term comes from totus (Latin for "whole") + potency (power), emphasizing the ability to form the whole organism.

The assertion claims totipotency means generating "only a part of the plant," which is the exact opposite. Generating only a part — say, callus tissue, or roots alone, or shoots alone — would be examples of pluripotency or multipotency, not totipotency.

Now let's evaluate each statement:

1. Assertion (A): "To generate only a part of the plant from a cell is totipotency."

   This is false. Totipotency is the ability to regenerate the entire plant, not just a part. If a cell can only form a specific tissue or organ, it is not exhibiting totipotency.

2. Reason (R): "Suitable special nutrient media and sterile conditions are required in 'in vitro' conditions for the division of cells in explants."

   This is true. Tissue culture (in vitro culture) absolutely requires:

   • Nutrient media containing sugars, minerals, vitamins, and plant growth regulators (auxins, cytokinins) to support cell division and differentiation. …