Question

Which of the following is not a plant hormone?
A. Phytochrome
B. Florigen
C. GA
D. IAA

Answer 1

Hint: Plant hormones are signal molecules, these are produced inside plant bodies which occur in extremely low concentrations. Plant hormones control all aspects of plants from plant growth and development to reproductive development which includes embryogenesis, the regulation of organ size, pathogen defense, stress tolerance. These are produced in the stem, buds, and root tips

Complete answer: Phytochromes are photoreceptors in plants and some other organisms like bacteria, and fungi used to detect light. They are sensitive to red-colored light. There are two types of receptors that are activated by the far-red region of the visible spectrum and these activated receptors are in Type I, and Type II receptors are activated by a red light.
-Florigen is also called flowering hormone. It is a molecule that is responsible for starting and controlling the flowering process in plants. It is produced in the leaves. It affects mostly in shoot apical meristem of buds and in growing tips. It is known to be graft-transmissible.
-Gibberellic acid (GA) is a hormone found in plants, which helps in plant growth and development. It is commonly used in agricultural products to increase crop yields.
-Indoleacetic acid (IAA) is a molecule that is synthesized or produced by plants and in few microbes. IAA plays an important role in roots and shoots development. The hormone moves from one part of the plant to another part by a designated importer like AUX1 and efflux pumps.
Hence, the correct option is (A)-Phytochrome.

Note: The five classes of compounds comprising abscisic acid, auxin, cytokinins, ethylene, and gibberellins could account for most or all of the growth regulatory effects of plant hormones. Ethylene is considered a rare type of plant hormone because it is a gas. That means it can move through the air, and it helps in ripening an apple which causes another apple to ripen, or even over-ripen.