The plant hormone used to destroy weeds in a field is: 
2, 4-D, widely used to kill dicotyledonous weeds, does not affect mature monocotyledonous plants.
They help to initiate rooting in stem cuttings, an application widely used for plant propagation. Auxins promote flowering e.g. in pineapples. They help to prevent fruit and leaf drop at early stages but promote the abscission of older mature leaves and fruits.
In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance. Removal of shoot tips (decapitation) usually results in the growth of lateral buds (Figure 15.11). It is widely applied in tea plantations, hedge-making. Can you explain why?
The process of growth is maximum during : 
Period of growth characterized by the number of cells increasing at an exponential rate.
It takes very long time for pineapple plants to produce flowers. Which combination of hormones can be applied to artificially induce flowering in pineapple plants throughout the year to increase yield? 
Synthetic auxins like NAA and 2, 4-D are often employed for inducing flowering in pineapple, Ethylene also stimulates Powering in pineapple and related plants. Hence, both auxin and ethylene can be applied artificially to induce flowering in pineapple plants throughout the year to increase yield.
The pineapple which under natural conditions is difficult to blossom has been made to produce fruits throughout the year by application of [NEET Kar. 2013]
Plants which are difficult to flower can be made to do so by spraying them with 2, 4, –D (2, 4 – dichlorophenoxy acetic acid) and NAA (napthalene acetic acid) which are synthetic auxins, e.g., litchi, pineapple.
During seed germination its stored food is mobilized [NEET 2013]
Gibberellins stimulate the synthesis of α-amylase and proteases enzyme in germinating grains of cereals. They are involved in the conversion of starch into sugar. The proteases convert an inactive β-amylase to the active form. The active β-amylase and α-amylase together digest starch to glucose which is mobilized to meet the metabolic demands of embryo.
Which one of the following is not used for ex-situ plant conservation ? [NEET 2013]
Shifting or Jhum cultivation contributes to deforestation. Ex-situ conservation is a biodiversity conservation method in which threatened animals and plants are taken out of their natural habitat and placed in protected and carring environment zoological parks, botanical gardens, wildlife safari parks, seed banks and gene banks.
Vernalization stimulates flowering in [2012M]
Carrot is a biennial plant which flowers in the second season. Vernalization is the subjection of seeds or seedlings to low temperature in order to hasten plant development and flowering. Vernalization is commonly used for crop plants such as winter rye and is possible because the seeds and buds of many plants require cold in order to break dormancy. Winter cereals are therefore sown in the autumn for flowering the following year. However, if germinating seeds are artificially vernalized they can be sown in the spring for flowering the same year. Biennial plants, such as carrot (Daucus carota), will remain in their non - flowering rosette form until subjected to cold treatment.
Which one of the following generally acts as an antagonist to gibberellins? [2012M]
Gibberellins & ABA are antagonistic with each other. ABA counteracts many effects of gibberellins like induction of hydrolases and alpha- amylases in barley seedlings.
Through their effect on plant growth regulators, what do the temperature and light control in the plants? [2012M]
Flowering is induced by light and temperature.
Coiling of garden pea tendrils around any support is an example of: 
The coiling of garden pea tendrils around any support is an example of thigmotropism. Thigmotropism is the growth movement in response to touch. The stems and tendrils of the climbers are positively thigmotrophic in their response.
Phototropic curvature is the result of uneven distribution of: 
Phototrophic curvature is the result of uneven distribution of auxin. The experiments conducted by Charles Darwin concluded that the tip of coleoptile of canary grass contain auxin that causes the bending of the entire coleoptile towards the light source.
Which one of the following acids is a derivative of carotenoids ? 
Abscisic acid (ABA), also known as abscisin II and dormin, is a plant hormone. It functions in many plant developmental processes, includsing bud dormancy. Abscisic acid is a derivative of carotenoids. It was called “abscisin II” originally because it was thought to play a major role in abscission of fruits. At about the same time another group was calling it “dormin” because they thought it had a major role in bud dormancy. The name abscisic acid (ABA) was coined by a compromise between the two groups.
One of the synthetic auxin is: 
NAA is a synthetic auxins. Some of the most widely used weed killers are synthetic auxins. Synthetic auxin analogs include 1–naphthaleneacetic acid (NAA), 2, 4-dichlorophenoxy acetic acid (2,4-D) and 2,4,5-trichlorophenoxy acetic acid (2,4,5- T).
Senescence as an active developmental cellular process in the growth and functioning of a flowering plant, is indicated in 
Senescence is not confined only to whole plant,it may be limited to a particular organ such as leaf and flower or cells such as phloem and xylem. Abscission is natural shedding of leaves,foliage branches,fruits floral parts etc. According to Leopold (1967) abscission is a senescence phenomenon. Senescence as an active developmental cellular process in the growth and functioning of a flowering plant,is indicated in leaf abscission.
So, the correct answer is 'Leaf abscission.'
“Foolish seedling’’ disease of rice led to the discovery of 
The effect of gibberellins had been known in Japan since early 1800 where certain rice plants were found to suffer from bakane or bakanae (foolish seedling) disease. Such rice plants were thin, pale green, spindle-shaped, longer by 50% than the healthy plants, and were sterile.
Which one of the following pairs, is not correctly matched? 
Gibberllic acid stimulates cell growth of leaves and stem causing their expansion, elongation respectively and leaf fall is controlled by ABA.
Opening of floral buds into flowers, is a type of 
Opening of floral buds into flowers, is a type of autonomic movement of water which is due to epinasty.
How does pruning help in making the hedge dense?
When an apical bud is present on a plant, it suppresses the growth of axillary buds, this is called apical dominance. When in pruning apical bud is cut off the axillary buds start growing & hedge become dense
Treatment of seed at low temperature under moist conditions to break its dormancy is called 
Treatment of seed at low temperature under moist conditions to break dormancy is called stratification.
An enzyme that can stimulate germination of barley seeds is 
a-amylase enzyme stimulates the germination of barley seed.
Cell elongation in internodal regions of the green plants takes place due to 
Gibberellins induces elongation of internodes.
One set of a plant was grown at 12 hours day and 12 hours night period cycles and it flowered while in the other set night phase was interrupted by flash of light and it did not produce flower. Under which one of the following categories will you place this plant?
Short day plants require long uninterrupted dark period for flowering. They will not produce flower if night was interrupted by flash of light.
Anthesis is a phenomenon which refers to 
Anthesis is the period during which a flower is fully open and functional. It may also refer to the onset of that period
Plants deficient of element zinc, show its effect on the biosynthesis of plant growth hormone 
Zinc is one of the component of Auxin.
Differentiation of shoot is controlled by 
Ratio of cytokinins to auxins controls differentiation. If both of these are present in equal quantities, the cells divide but fail to differentiate. If there is more cytokinin than auxin, shoot buds develop. If there is more auxin than cytokinin, roots develop.