NEET Previous Year Questions (2016-2024): Plant Growth & Development | Biology Class 11 PDF Download

2024

Q1: Auxin is used by gardeners to prepare weed-free lawns. But no damage is caused to grass as auxin     (NEEET 2024)
(a) promotes apical dominance.
(b) promotes abscission of mature leaves only.
(c) does not affect mature monocotyledonous plants.
(d) can help in cell division in grasses, to produce growth.
Ans: (c)
Auxin is a plant growth hormone primarily known for its role in stimulating plant growth by facilitating elongation of cells within shoots. Its effect varies depending on the plant species and its developmental stage. The given options can be assessed to understand why grass remains undamaged in lawns treated with auxin for weed control.

Option A: promotes apical dominance.
Apical dominance refers to the phenomenon where the main, central stem of the plant grows more dominantly than the side stems due to the concentration of auxin in the apex. This is not relevant to the selective action of auxin on weeds versus grass, because while it might affect growth patterns, it doesn’t relate directly to why weeds are eliminated and grass is not.

Option B: promotes abscission of mature leaves only.
Abscission is the process where parts of a plant, such as leaves or fruit, are shed. Auxin helps delay abscission by inhibiting the process. Thus, promoting abscission does not align with the characteristic actions of auxin. Additionally, this mechanism would not be selective for weeds over grass.

Option C: does not affect mature monocotyledonous plants.
Grasses are monocotyledonous plants, characterized by having one seed leaf, parallel leaf veins, and vascular bundles scattered in stem sections. It is known that the structure and growth patterns of monocots differ sufficiently from dicots; hence, many dicot-specific herbicides (including those based on auxin-like substances) do not affect monocots. Therefore, this option provides a plausible explanation why grass, a monocot, remains unaffected by a treatment intended for dicot weeds.

Option D: can help in cell division in grasses, to produce growth.
While auxin does promote cell division and growth in plants, this is a generalized action and does not explain why it would selectively not harm grass when used as a weed killer in lawns.

Based on the analysis above, the correct answer is Option C: does not affect mature monocotyledonous plants. This option directly addresses the differential effect of auxin on monocots versus dicots, aligning with the observed outcome that grass remains undamaged while dicot weeds are targeted.

Q2: Formation of interfascicular cambium from fully developed parenchyma cells is an example for    (NEET 2024)
(a) Differentiation
(b) Redifferentiation
(c) Dedifferentiation 
(d) Maturation
Ans: (c)
The process involved in the formation of interfascicular cambium from fully developed parenchyma cells is known as "dedifferentiation." This is because dedifferentiation refers to the phenomenon where mature, specialized cells revert to a more primitive, less specialized state. In plants, certain mature cells, such as parenchyma cells, can lose their specialized characteristics and revert to meristematic activity. This newly formed meristematic tissue can then differentiate into specialized tissues once again, in this case, forming interfascicular cambium.

In contrast, differentiation (Option A) is the process where cells develop from a less specialized form to a more specialized form. Redifferentiation (Option B) refers to the process where dedifferentiated cells become specialized again, but this is a subsequent step following dedifferentiation. Maturation (Option D) refers to the final stages of cell and tissue specialization, not the regression to a less developed state.

Therefore, the correct answer to the query is: Option C - Dedifferentiation

Q3: Spraying sugarcane crop with which of the following plant growth regulators, increases the length of stem, thus, increasing the yield?      (NEET 2024)
(a) Auxin 
(b) Gibberellin 
(c) Cytokinin 
(d) Abscisic acid
Ans: (b)
The correct answer to the question is Option B, Gibberellin. Gibberellins (GAs) are a group of plant hormones that play a crucial role in regulating various aspects of plant growth and development. One of the notable effects of gibberellins is their ability to promote stem elongation by stimulating cell division and elongation.
In the case of sugarcane, a crop that is valued for its stem (from which sucrose is extracted), applying gibberellin can increase the length of the stem, thereby potentially increasing the yield of the crop. This increase in stem length due to gibberellin application is primarily because gibberellins overcome the inhibitory effects of other hormones that suppress growth; they stimulate the cells in the stems to grow larger and divide more frequently.
While Auxin (Option A) and Cytokinins (Option C) also influence plant growth and have their specific uses, such as rooting and promoting cell division, respectively, they do not primarily target stem elongation to the extent gibberellins do. Abscisic acid (Option D) is generally involved in stress responses and the inhibition of growth, making it unsuitable for promoting stem elongation.
Therefore, to specifically enhance stem length and yield in sugarcane, gibberellins are the most effective plant growth regulators among the options given.

2023

Q1: Spraying of which of the following phytohormone on juvenile conifers helps hastening the maturity period, that leads early seed production?    (NEET 2023)
(a) Indole-3-butyric Acid
(b) Gibberellic Acid
(c) Zeatin
(d) Abscisic Acid
Ans: (b)
Gibberellic acid (GA) is a plant hormone that stimulates cell elongation, germination, and influences a variety of developmental processes, including maturation and seed production. In the forestry industry, it is often used to hasten the maturity period and stimulate early seed production in juvenile conifers.

Q2: Which hormone promotes internode/petiole elongation in deep water rice?     (NEET 2023)
(a) GA₃
(b) Kinetin
(c) Ethylene
(d) 2, 4-D
Ans: (c)
The hormone that promotes internode/petiole elongation in deep water rice is Ethylene.
Ethylene is a plant hormone that plays a critical role in growth and development, including responses to environmental stimuli. In the case of deep water rice, when the plants are submerged, the ethylene concentration increases and promotes rapid internodal elongation, which allows the plant to keep its leaves above the water surface.
So, the correct answer is Option C - Ethylene.

2022

Q1: Which one of the following plants does not show plasticity?     (NEET 2022 Phase 1)
(a) Coriander
(b) Buttercup
(c) Maize
(d) Cotton

Ans: (c)
Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity e.g. heterophylly in cotton, coriander and larkspur. In such plants, leaves of juvenile plant are different in a shape from those in mature plants.
Maize does not show plasticity.

Q2: The gaseous plant growth regulator is used in plants to:      (NEET 2022 Phase 1)
(a) promote root growth and root hair formation to increase the absorption surface
(b) help overcome apical dominance
(c) kill dicotyledonous weeds in the fields
(d) speed up the malting process

Ans: (a)
Ethylene is a gaseous plant hormone. It induces development of adventitious roots on various types of cutting. It promotes the development of lateral roots and growth of root hairs. Cytokinin helps to overcome the apical dominance.
Auxin is used to kill dicot weeds. Gibberellin speeds up the malting process.

Q3: Production of Cucumber has increased manifold in recent years. Application of which of the following phytohormones has resulted in this increased yield as the hormone is known to produce female flowers in the plants:    (NEET 2022 Phase 1)
(a) ABA
(b) Gibberellin
(c) Ethylene
(d) Cytokinin
Ans: (c)
Ethylene increases the number of female flowers and fruits in certain plants such as cucumber. Gibberellins are used to increase the size of fruits in some plants.

Q4: The ability of plants to follow different pathways in response to environment leading to formation of different kinds of structures is called     (NEET 2022 Phase 2)
(a) Differentiation
(b) Redifferentiation
(c) Development
(d) Plasticity
Ans: (d)

• The ability of plant to follow different pathways and produce different structures in response to environment is called plasticity.
• During differentiation, cells lose their ability to divide and form permanent cell.
• The process where the differentiated cells again lose the ability to divide and form permanent cells is called redifferentiation.

Q5: Which of the following growth regulators is an adenine derivative?    (NEET 2022 Phase 2)
(a) Abscisic acid
(b) Auxin
(c) Cytokinin
(d) Ethylene
Ans: (c)

• Cytokinins are derived from adenine.
• Auxins are derivatives of indole compounds.
• Abscisic acid is derived from carotenoids.
• Ethylene is derived from methionine.

2021

Q1: The plant hormone used to destroy weeds in a field is:     (NEET 2021)
(a) 2, 4-D
(b) IBA
(c) IAA
(d) NAA
Ans: (a)

• Some synthetic auxins are used as weedicides. 2, 4-D is widely used to remove broad leaved weeds or dicotyledonous weeds in cereal crops or monocotyledonous plants.
• Auxins like IAA and IBA are used to induce parthenocarpy. IAA also stimulate nodule formation.
• Auxin like NAA is used to increase dwarf shoots.

Q2: Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called:     (NEET 2021)
(a) Plasticity
(b) Maturity
(c) Elasticity
(d) Flexibility
Ans: (a)
Plant plasticity refers to the ability to modify itself by forming different kind of structures to adapt and cope with changes in its environment. It can be intrinsic plasticity or extrinsic plasticity. In both the cases plants shows heterophylly along with other morphological features, e.g. in the leaves Larkspur and buttercup.

Examples:

• Cotton, coriander and larkspur show heterophylly in which the leaves of a juvenile plant are different in shape from those in mature plants.
• Buttercup produces leaves of different shapes in air and water, which is also an example of heterophylly.

Q3: The site of perception of light in plants during photoperiodism is:     (NEET 2021)
(a) Axillary bud
(b) Leaf
(c) Shoot apex
(d) Stem
Ans: (b)

• The site of perception of light in plants during photoperiodism is leaf.
•  The site of perception of low temperature stimulus during vernalisation is shoot apex and embryo.
• Axillary bud are not sites of perception of photoperiod.

2020

Q1: Name the plant growth regulators which upon spraying on sugarcane crop, increases the length of stem, thus increasing the yield of sugarcane crop.     (NEET 2020)
(a) Ethylene 
(b) Abscisic acid 
(c) Cytokinin
(d) Gibberellin 
Ans: (d)
Spraying sugarcane crop with gibberellins increases the length of the stem, thus increasing the yield by as much as 20 tonnes per acre.

Q2: Which of the following is not an inhibitory substance governing seed dormancy?    (NEET 2020)
(a) Para-ascorbic acid
(b) Abscisic acid
(c) Gibberellic acid
(d) Phenolic acid
Ans: (c)
Gibberellic acid breaks seed dormancy. It activate synthesis of alpha-amylase which breakdown starch into simple sugar.

2019

Q1: What is the site of perception of photoperiod necessary for induction of flowering in plants?     (NEET 2019)
(a) Leaves
(b) Lateral buds
(c) Pulvinus
(d) Shoot apex

Ans: (a)
The site of perception of light / dark duration are leaves. It is hypothesized that there is a hormonal substance migrates from leaves to shoot apices for inducing flowering when plants are exposed to the necessary inductive photoperiod.

2017

Q1: Fruit and leaf drop at early stages can be prevented by the application of     (NEET 2017)
(a) Ethylene
(b) Auxins
(c) Gibberellic-acid
(d) Cytokinins

Ans: (b)
In low concentrations, auxins such as 2, 4- D(2,4- Dichlorophenoxy acetic acid) is useful in preventing pre-harvest fruit drop and leaf drop.

2016

Q1: You are given a tissue with its potential for differentiation in an artificial culture. Which of the following pairs of hormones would you add to the medium to secure shoots as well as roots?     (NEET 2016 Phase 2)
(a) IAA and gibberellin
(b) Auxin and cytokinin
(c) Auxin and abscisic acid
(d) Gibberellin and abscisic acid
Ans: (b)
Cytokinin and auxin are two plant hormones that are supplied to the tissue culture medium in definite proportions. They bring about cell division and differentiation of callus. A low auxin to cytokinin ratio promotes shoot formation whereas a high auxin to cytokinin ratio promotes rooting of callus.

Q2: Phytochrome is a     (NEET 2016 Phase 2)
(a) Flavoprotein
(b) Glycoprotein
(c) Lipoprotein
(d) Chromoprotein
Ans: (d)

Phytochrome is a chromoprotein, plant pigment that can detect the presence or absence of light and is involved in regulating many processes that are linked to day length (photoperiod), such as seed germination and initiation of flowering. It consists of a light detecting portion, called a chromophore, linked to a small protein and exists in two inter-convertible forms with different physical properties.

Q3: The Avena curvature is used for bioassay of     (NEET 2016 Phase 1)
(a) IAA
(b) ethylene
(c) ABA
(d) GA₃
Ans: (a)
Auxin has been clearly demonstrated in the leaf sheath or coleoptile of oat plant (Avena sativa). This plant coleoptile has been used for the test of hormone Auxin (IAA) participating in the growth of the plant.

2015

Q1: Typical growth curve in plants is:     (AIPMT 2015 Cancelled Paper)
(a) Linear
(b) Stair-steps shaped
(c) Parabolic
(d) Sigmoid
Ans: (d) 
Geometric growth cannot be sustained for long in natural condition. Limited nutrient availability slows down the growth. It leads to a stationary phase or even a decline. Plotting the growth against time, gives a typical sigmoid or S-curve. Sigmoid curve of growth is typical of most organisms in their natural environment including plants.
An idealised sigmoid growth curve is drawn below:

Q2: What causes a green plant exposed to the light on only one side, to bend toward the source of light as it grows? 
(a) Green plants seek light because they are phototropic
(b) Light stimulates plant cells on the lighted side to grow faster
(c) Auxin accumulates on the shaded side, stimulating greater cell elongation there.
(d) Green plants need light to perform photosynthesis    (AIPMT 2015 Cancelled Paper)
Ans: (c) 
Auxin stimulates cell elongation. It accumulates on shaded side which results in more elongation of cells towards shaded side of the plant. This causes bending of the plant towards source of light.

Q3: Auxin can be bioassayed by:    (NEET 2015 / AIPMT 2015)
(a) Hydroponics
(b) Potometer
(c) Lettuce hypocotyl elongation
(d) Avena coleoptile curvature
Ans: (d)}
Avena coleoptile curvature is used for the bioassay of auxin.

2014

Q1: Dr. F. Went noted that if coleoptile tips were removed and placed on agar for one hour, the agar would produce a bending when placed on one side of freshly-cut coleoptile stumps. Of what significance is this experiment?     (NEET 2014 / AIPMT 2014)
(a) It made possible the isolation and exact identification of auxin.
(b) It is the basis for quantitative determination of small amounts of growth-promoting substances.
(c) It supports the hypothesis that IAA is auxin.
(d) It demonstrated polar movement of auxins.
Ans: (b)
Charles Darwin and his son Francis Darwin observed that the coleoptiles of Oat (Avena sativa) and canary grass (Phalaris canariensis) responded to unilateral illumination by growing towards the light source (phototropic curvature or phototropism). After a series of experiments, it was concluded that the tip of the coleoptile was the site of production of a substance, that caused the bending of coleoptile.

Q2: A few normal seedlings of tomato were kept in a dark room. After a few days they were found to have become white-coloured like albinos. Which of the following terms will you use to describe them?       (NEET 2014 / AIPMT 2014)
(a) Mutated
(b) Embolized
(c) Etiolated
(d) Defoliated
Ans: (c)
Etiolation is the abnormal form of growth observed when plants grow in darkness or severely reduced light. Such plant characteristically have branched leaves and shoots, excessively long shoots and reduced leaves and root systems.

Q3: Which one of the following growth regulators is known as 'stress hormone'?       (NEET 2014 / AIPMT 2014)
(a) Abscissic acid
(b) Ethylene
(c) GA₃ 
(d) Indole acetic acid
Ans: (a) 
Abscisic Acid (ABA) is called stress hormone which works in adverse environmental condition when there is low water content in atmosphere or in drought conditions. ABA causes the stomatal closure of leaves due to which the water loss by the plant is minimized.