39. Plants make several hormones that are important for growth and development. Some statements on plant hormones are given below:

    A. Auxin is produced primarily in the root apices

B.Cytokinins are a smaller group of related compounds

C.Gibberellins are a large group of related compounds defined not by their biological functions but by their structures.

D.Brassinosteroids are an important class of plant hormones, which control a broad spectrum of developmental reposes including pollen tube growth.
Which one of the following combination of the above statements is correct?
(1) A, B and C         (2) B, C and D

(3) A, C and  D       (4) A, B and D

Correct combination: (2) B, C and D

Explanation:

• (A) Auxin is produced primarily in the shoot apices and young leaves, not root apices, so statement A is incorrect.

• (B) Cytokinins are indeed a smaller group of related compounds that regulate cell division and differentiation.

• (C) Gibberellins are a large group of related compounds defined by their chemical structure, not solely by biological function.

• (D) Brassinosteroids constitute an important class of plant hormones controlling a wide range of developmental processes including pollen tube growth.

Option-wise:

• (1) A, B and C — incorrect due to wrong A.

• (2) B, C and D — correct.

• (3) A, C and D — incorrect due to wrong A.

• (4) A, B and D — incorrect due to wrong A.

  Plant hormones are diverse in function and origin. Auxin originates mainly in shoot tips, cytokinins regulate growth as smaller compound groups, gibberellins are classified structurally, and brassinosteroids play versatile roles in reproductive development such as pollen tube growth.