F. W. Went in 1928 used tip of Avena coleoptile. He removed the tip of Avena coleoptile and placed in on the agar agar block for the definite measured amount of time. Then this agar agar block was placed asymmetrically on the stump, this showed a positive curvature. 

I.A.A. is auxin. The precursor of auxin is tryptophan and Zn.

Presumptive pathways of IAA biosynthesis from tryptophan:

Avena curvature helps in determining the biological activity of IAA.
Avena curvature is performed as follows:

• The shoot tip of a plant is removed and placed on an agar block so that the auxin diffuses into the agar.
• The agar piece is cut after some time and is placed on one side of the coleoptile of the plant from where the shoot tip was obtained.
• An angle of curvature is obtained.

Hence, option B is correct.

Th first naturally occurring auxin i.e., Indole 3-acetic acid was isolated by Kogl and Haagen-Smit from human urine.

The plant hormone auxin is used for agriculture and horticulture.

• During the process of plant propagation, auxin is used to initiate rooting in stem cutting.
• Auxin performs the role of promoting flowering in the plant.
• Abscission of older mature fruits and leaves is regulated by the hormone auxin.
• It also prevents leaves and fruits from dropping at the early stage. The growing apical buds in most higher plants inhibit the growth of auxiliary buds. This phenomenon is called apical dominance.

Therefore, the correct answer is option D.

Stem elongation is a kind of growth of stem.

Auxin and Gibberellin are known as growth hormones of plants. Therefore, stem elongation is affected by hormones Auxin and Gibberellin.

Auxins are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action. In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance.

The apical bud produces an auxin hormone that inhibits the growth of the lateral buds further down on the stem towards the axillary bud.

• Auxin is a plant hormone that is involved in various growth and developmental processes of plants. It stimulates the induction of rooting in stem cuttings.
• Bougainvillea plants are primarily propagated by stem cuttings. Hence, induction of rooting in stem cutting would be most beneficial in Bougainvillea.

Thus, the correct answer is option D.

2,4-dichlorophenoxyacetic acid is a herbicide class, which is a synthetic auxin. Hence it is not a naturally occurring plant hormone.

It is absorbed through the leaves and is translocated to the plant meristems resulting in stem curling, leaf withering, and finally plant death.

Seedless fruits like grapes and papaya are called Parthenocarpic fruits. These fruits are developed from unfertilized ovaries.
Plant hormones like auxins induce parthenocarpy.
Example: Tomatoes.

Due to a reduction in photosynthesis, this may trigger the abscission of leaves (separation of leaves) and this abscission layer is produced when auxin content falls below a minimum causing leaf or other plant part to fall off.

• A chemical substance produced in one part of body and regulates the activity of other parts is called as hormones.
• Plant hormones are produced in the stem, bud and root tips and control the plant growth, formation of flowers, stems, leaves, development, and ripening of fruit, etc.
• Auxins are specialized hormones which acts on the tip.

Thus, the correct answer is option B.

IAA is actually a type of Auxin hormone so it helps in nodule formation.

Auxanometer is a simple instrument to measure growth of a plant. Most common type of auxanometer is arc auxanometer, which measures growth as the increase in length of axis. This increase can be caused due to increase in mass of protoplasm (cell division) or simply by absorption of water (increase in length or surface of existing cells).

• Apical dominance: In many plants, the apical bud grows and the lower axillary buds are suppressed. Removal of apical bud results in the growth of lower buds.
• The auxin (IAA) of the terminal bud inhibits the growth of lateral buds. This phenomenon is known as apical dominance.
• This property of auxins has found use in agriculture. Sprouting of lateral buds (eyes) of the potato tuber is checked by applying synthetic auxin (NAA).

Parthenocarpy (literally meaning "virgin fruit") is the natural or artificially induced production of fruit without fertilization of ovules, which makes the fruit seedless. 

It may also produce apparently seedless fruit, but the seeds are actually aborted while they are still small. 

Most of the auxins in plants are believed to be produced by apical shoot meristem.
This auxin then suppresses the growth of lateral buds, the phenomenon is called as apical dominance.
Auxins like IAA and indole butyric acid (IBA) have been isolated from plants.

Hence, option C is correct.

Different concentrations of IAA appear to have differing effects on root growth.
These effects may vary from one species to another but generally, at low concentrations, IAA stimulates root growth while at higher concentrations it inhibits root growth.

As the most important site of auxin synthesis is shoot tips, they frequently migrate in the downward direction. They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action.

Hence, option A is correct.

Auxin causes growth of the coleoptile of wheat, maize, and other cereals. The tip of the coleoptile produces auxin. Therefore, coleoptile shows rapid growth.
When the tip is removed, the growth of the coleoptile stump stops. Auxin causes growth of the coleoptile by cell elongation. It also causes growth in stem by cell elongation.

In plants, growth can refer to change in size, it is restricted to meristematic regions of the plant and cannot be reversed.

Turgor pressure is the water pressure maintained by osmosis.
It is also known as the driving force for cell extension, any general theory of plant growth requires quantitative information on the relationship between steady irreversible growth rate and turgor pressure.
At constant turgor pressure, growth is irreversible.

The climatic factors include rainfall and water, light, temperature, relative humidity, air, and wind. They are abiotic components, including topography of  the soil and the environmental factors that influence plant growth and development.

trans-zeatin riboside is the most abundant type of cytokinin found in coconut water (Table 2). trans-zeatin is normally used to induce plantlet regeneration from callus in plant tissue culture. Based on experimental data, trans-zeatin plays a key role in the G₂-M transition of tobacco cells.

Phases Of Plant Growth

1. Meristematic Phase

• The cells in the root and shoot apex of a plant are constantly dividing. They represent the meristematic phase of growth.
• The cells in these regions have large nuclei and are rich in protoplasm and their cell walls are thin and contain cellulose.

2. Elongation Phase

• The cells in the zone just after the meristematic region represent the phase of elongation.
• The characteristics of cells in this zone are cell enlargement, increased vacuole formation and new cell wall deposition.

3. Maturation Phase

• Just close to the phase of elongation, but away from the apex lies the phase of maturation.
• The cells in this region reach their maximum size with respect to their protoplasm and cell wall thickening.

Phases of Plant Growth:

The existence of first plant growth hormone came from the work of Jensen and Darwin. They found that bending movement of coleoptile of canary grass was due to exposure of tip to unilateral light. Boysen-Jenson found that the tip produces a chemical which was later named auxin.

Auxins were first isolated from human urine. The term auxin is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth-regulating properties.

Cytokinins have specific effects on cytokinesis and were discovered as kinetin from the autoclaved herring sperm DNA.
Kinetin does not occur naturally in plants. Search for natural substances with cytokinin-like activities led to the isolation of zeatin from corn kernels (corn germ oil) and coconut milk.

Hence option C is correct.

Zinc is an essential micronutrient required for the growth and development of plants. It is involved in the synthesis of indoleacetic acid (IAA), which is a natural auxin.

The function of zinc is to activate the enzyme tryptophan synthetase which is responsible for auxin biosynthesis from tryptophan.

For a plant organ to bend in response to a stimulus, differential growth of cells on either side of the organ is required.

Example: For the stem of a plant to bend toward a light source, cells on the shaded side of the stem near the shoot tip must elongate faster than cells on the lighted side.