Consider the following statements and choose the correct answer using the codes given below :
Assertion (A): Heartwood is less susceptible to fungus and contains less moisture than sapwood.
Reason (R): Heartwood stores secondary metabolites and have tylosis.

Question

Consider the following statements and choose the correct answer using the codes given below : 
Assertion (A): Heartwood is less susceptible to fungus and contains less moisture than sapwood. 
Reason (R): Heartwood stores secondary metabolites and have tylosis.

Accepted Answer

The correct option is 1: Both A and R are true and R is the correct explanation of A.

The correct option is 1: Both A and R are true and R is the correct explanation of A

This option is correct because both the Assertion (A) and the Reason (R) are factually true statements in the study of plant anatomy, and furthermore, Reason (R) provides the direct causal explanation for the condition stated in Assertion (A). Heartwood, or *duramen*, is the central, older part of the secondary xylem that has ceased to conduct water. This transition is marked by the accumulation of organic substances, which are the secondary metabolites, and the formation of tyloses. These secondary metabolites, such as resins, tannins, gums, and essential oils, act as a defense mechanism, making the heartwood chemically hostile to invading fungi and insects, thereby increasing its durability and resistance to decay. Simultaneously, the formation of tyloses (balloon-like outgrowths of parenchyma cells) physically plugs the tracheary elements, and the subsequent death of cells leads to the desiccation of the tissue, resulting in significantly lower moisture content compared to the functional sapwood. Therefore, the storing of these protective chemicals and the physical occlusion of water-conducting elements (tylosis) directly explains why heartwood is less susceptible to fungal attack and contains less moisture.

The incorrect option is 2: Both A and R are true but R is not the correct explanation of A

While it is true that both statements are correct, this option is incorrect because the Reason *is* the explanation for the Assertion. The defining characteristics of heartwood listed in the Reason—the presence of secondary metabolites and tylosis—are precisely the biological mechanisms that confer resistance to decay (less susceptible to fungus) and reduce water content (less moisture), as mentioned in the Assertion. Had the Reason been a separate, correct fact about heartwood (e.g., "Heartwood is also known as duramen") that did not explain its properties, this option would be correct. However, in this case, the Reason provides a direct cause-and-effect relationship for the Assertion, making it the correct explanation.

The incorrect option is 3: A is true but R is false

This option is incorrect because the Reason (R) is a scientifically sound statement. Heartwood formation is fundamentally defined by the processes it describes. Secondary metabolites (defensive compounds like tannins and resins) and tyloses are hallmark features of heartwood; they are deposited and formed as the sapwood converts into heartwood. The Assertion (A) is definitely true, as heartwood's durability and low moisture content are its main advantages for commercial use, but since the Reason (R) is also factually correct, the premise of this option fails.

The incorrect option is 4: A is false but R is true

This option is incorrect because the Assertion (A) is a correct statement. Heartwood is indeed less vulnerable to biotic agents like fungi and has a markedly lower moisture level than the outer, functional sapwood. The Reason (R) is also true, as discussed previously, but since the Assertion is not false, selecting this option would be based on an incorrect evaluation of the Heartwood's known properties. Heartwood's utility in timber and construction is a direct result of its superior resistance to pests and water, which proves the Assertion's truth.