FREE NEET Biology Practice MCQ Test: Plant Growth And Development Exercise 3 Questions Answers With Detailed Explanations [PDF]

Answer: (d)

Ethylene promotes root growth and root hair formation. In low concentration, ethylene is used for initiation of roots and also of lateral roots.

Answer: (d)

When continous red light is given the level of $P_r$ decreases as most of it is converted to $P_{fr}$ form. When the concentration of $P_r$ reaches below a critical value, it starts synthesis of more phytochromes in the Pr form so that there is an equilibrium between synthesis and destruction of $P_r$ form.

Answer: (c)

Auxin bioassay is a quantitative test as it measures concentration of auxin to produce the effect and the amount of the effect. Avena curvature is based upon experiments of Went (1928). 10° curvature is produced by auxin concentration of 150 mg/litre at 25°C and 90% relative humidity. The test can measure auxin upto 300 mg/litre. Auxin from a shoot tip or any other plant organ is allowed to diffuse in a standard size agar block (generally 2 × 2 × 1 mm). Auxin can also be dissolved directly in agar. 15– 30 mm long oat coleoptile grown in dark is held vertically over water. 1 mm tip of coleoptile is removed without injuring the primary leaf. After 3 hours a second decapitation is carried out for a distance of 4 mm. Primary leaf is now pulled loose and agar block supported against it at the tip of decapitated coleoptile. After 90–110 minutes, the coleoptile is found to have bent. The curvature is measured. It can also be photographed and the curvature known from shadow graph.

Answer: (c)

Answer: (a)

Answer: (b)

Answer: (b)

Abscisic acid is a growth inhibiting phytohormone. It induces senescence in leaves by promoting the degradation of chlorophyll and proteins.

Answer: (b)

Seed dormancy is defined as a state in which seeds are prevented from germinating even under environmental conditions, normally favourable for germination. These conditions are a complex combination of water, light, temperature, gasses, mechanical restrictions, seed coats, and hormone structures.

Answer: (c)

Answer: (d)

The effect of photoperiods or daily duration of light hours (and dark periods) on the growth and development of plants, especially flowering, is called photoperiodism. Also refer to answer 67.

Answer: (c)

Zinc is essential for the synthesis of tryptophan - a precursor of auxins.

Answer: (c)

Answer: (b)

The rate of growth can be measured by an increase in size or area of an organ of the plant like leaf, flower, fruit etc. in a unit time. The rate of growth is also called efficiency index.

Answer: (b)

Answer: (a)

Short long day plants require short photoperiod for initiation of flowering and long photoperiod for blossoming, eg, Tripholium repent. Long short day plants require long photoperiod for initiation of flowering and short photoperiod for blossoming, eg, Bryophyllum, Cestrum. Intermediate plants flower within a definite range of photoperiod, eg, wild kidney beans.

Answer: (a)

Answer: (b)

Avena curvature test is a test based on the experiments of Went (1928) which can measure auxin upto 300 mg/litre. Indole 3-acetic acid (IAA) is a universal natural auxin and Avena curvature test serves as an accurate bioassay for this plant hormone.

Answer: (b)

Answer: (a)

Answer: (a)

The major physiological function of cytokinin is to enhance cell division. In tissue culture the undifferentiated mass of cells formed in the culture tubes is called callus.

The callus may remain in the undifferentiated condition or differentiation may take place in this. If it is differentiated, then root and shoot may be formed. Skoog and miller had reported that cytokinins induce shoot formation and auxins induce root formation (figure).

Fig. : The experiment to demonstrate the effect of auxins and cytokinins on the growth and the differentiation of tissues in culture.

Later however it was proved experimentally that

1. High cytokinins/auxin ratio - Differentiation of shoot.
2. Low cytokinins/auxin ratio-Differentiation of root.
3. Intermediate cytokinins/auxin ratio - Differentiation of both root and shoot.
4. Intermediate cytokinins/low auxin - Callus formation.