Q.For Questions number 13 to 16, two statements are given – one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : The meristems are grown 'in vitro' to obtain virus-free plants from an infected plant. Reason (R) : If the plant is infected with a virus, the roots and the stems are free of virus.

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. …