31 Years NEET Previous Year Questions: Plant Growth & Development - 1 - NEET MCQ

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?

3. Log phase

Explanation: The log phase (also known as the exponential phase) is the stage of rapid growth in living organisms, where cells divide at a constant and maximum rate. This phase is marked by a high rate of metabolic activity and cell reproduction, leading to exponential growth.

In contrast:

• Senescence refers to the aging process, where growth slows down or stops.
• Dormancy is a period of suspended growth or inactivity.
• Lag phase is the initial phase of growth where cells are adjusting to their environment and growth is minimal.

Hence, the log phase is when growth is at its maximum.

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.

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.

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. 

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.

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.

Gibberellins & ABA are antagonistic with each other. ABA counteracts many effects of gibberellins like induction of hydrolases and alpha- amylases in barley seedlings.

Flowering is induced by light and temperature.

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.

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.

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.

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 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.'

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.

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 autonomic movement of water which is due to epinasty.

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

Stratification is a process used to simulate the natural conditions seeds experience in the wild before they germinate. Many seeds have a dormancy period during which they will not germinate, even under optimal conditions. This dormancy helps to ensure that the seeds do not germinate during unfavorable times, such as winter or droughts.

In the wild, seeds often go through a period of cold and moist conditions, which helps to break their dormancy. Stratification mimics this environmental process by subjecting the seeds to a period of cold, moist treatment. This can be done by placing the seeds in a moist medium (such as sand, peat moss, or a paper towel) and storing them in a refrigerator for a specified period, which can range from a few days to several months, depending on the species.

Once the stratification period is complete, the seeds can be removed from the cold environment and sown under normal growing conditions. This process helps to increase the germination rate and ensures that the seeds are ready to grow when the appropriate conditions are present.

a-amylase enzyme stimulates the germination of barley seed.

Gibberellins induces elongation of internodes.

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 the period during which a flower is fully open and functional. It may also refer to the onset of that period

 Zinc is one of the component of Auxin.

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.