Tag: life processes: control and coordination

• Auxins- play a key role in tropism (controlling the direction of plant growth). 

The gibberellins are plant growth hormones which enhance the longitudinal growth of stem when applied to the intact plant. Gibberellins produce extraordinary elongation of stems and leaf sheaths in intact plants. The elongation of the stem is caused due to cell division and cell elongation induced by gibberellic acid. Thus option D is the correct answer.

The directional growth of organisms in response to light is called phototropism. In plants, aerial shoots usually grow towards the light. The phototropic response is controlled by auxin.

• Ethylene is a gaseous hormone, which stimulates transverse or isodiametric growth but retards the longitudinal one. 
• It is a gas that forms through the break down of methionine, which is in all cells. 
• It has very limited solubility in water and does not accumulate within the cell but diffuses out of the cell and escapes out of the plant.
• Thus, the correct option is D.

• There are various plants which are used in the process of bioremediation. 
• The plants are capable of taking up the toxic constituents and accumulating them in the plant body. 
• The plant Gibberella fusarium can take up the toxic material like cyanide. 
• The cyanide is reduced by this plant and converted to a non-toxic form. 
• Thus, the correct answer is option C. 

• Abscisic acid is a carotenoid-derived plant hormone known to regulate critical functions in growth, development and responses to environmental stress.
• It plays a key role in the regulation of stomatal closure by regulating ion channel activities and water exchanges across the plasma membrane of guard cells.
• It increases the influx of calcium ions and efflux of potassium ions, which results in the closure of stomata.
• So, the correct option is D.

Abscisic acid is the plant growth hormone which is responsible for inhibiting growth. The hormone causes inhibition in the growth of the roots and shoots. The hormone also causes abscission which is the falling of the leaves, fruits and flowers. The hormone suppresses all the processes in the plants during unfavourable conditions. 

Auxin is a plant hormone that plays important role in plant growth. It stimulates stem elongation by increasing permeability of cells which in turn increases uptake of water by cells. It also enhances plasticity of cell walls which results in cell enlargement. It also increases the respiration rate.

Leaf abscission is a detachment or fall of older leaves.It occurs at the base of the petiole. When auxin is applied to the base of petiole of young leaf, the abscission is greatly suppressed. Also, it is observed that the intact leaf does not fall off because it synthesizes auxin.

Auxin is a plant hormone which is involved in various physiological processes. It is present on the tip of the stem and helps in phototropic movement in response to light. It also maintains apical dominance where there is more growth on the stem tip and growth of lateral bud is inhibited. Auxin along with cytokinin and gibberellin helps in the process of parthenocarpy. It does not cause bolting. It does not influence flowering in the plant.