Biology

Plant Growth and Hormones

727 Questions

Plant growth and hormones is a vital topic in biology that covers the physiological effects of different plant regulators like auxins, gibberellins, and cytokinins. These concepts are frequently tested in various general science sections of competitive exams. Practicing these questions helps clarify complex mechanisms like vernalisation, senescence, and tropism for test takers.

Abscisic acid effectsCytokinin functionsAuxins and tropismPlant tissue cultureSenescence in plantsNatural plant hormones

Plant Growth and Hormones Questions

Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

Select the pair that consists of plant growth promoters only.

  1. Auxins and cytokinins

  2. Gibberellins and ABA

  3. Ethylene and ABA

  4. All of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Auxins and cytokinins are plant growth promoters, the roles played by auxin and cytokinin are as follows.

Auxins: Cell enlargement and longitudinal growth of root and shoot.
             Reactivation of cambium in the growth season, that is, responsible for secondary growth, promotes apical dominance and parthenocarpy, inhibits abcission.
Cytokinins: induces morphogenesis that is differentiation of cells into tissues and organs.delays senescence, breaks dormancy and promotes seed germination, enhances expression of a sexual characteristic- femaleness in some plants.
Auxin/cytokinin ratio influences root and shoot formation and growth
So, the correct answer is 'Auxins and cytokinins'

Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

Which among the following is not a function of cytokinins?

  1. Essential for Cytokinesis during cell division

  2. Delays the senescence of leaves

  3. Helps in fruit ripening

  4. Helps to overcome apical dominance
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Fruit ripening or climacteric fruit ripening is induced by ethylene in most of the fruits, and therefore is not a function of cytokinins.

So, the correct answer is 'Helps in fruit ripening'

Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

Natural cytokinins are synthesized in regions where rapid cell division occurs. Such regions are

  1. Root apices

  2. Developing shoot buds

  3. Young fruits

  4. All of these.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
About 18 types of cytokinins have been discovered till now. Some of them are constituents of t RNAs. Roots are considered as the major source of cytokinin synthesis; from roots, the cytokinins pass upwardly through the xylem. Cytokinin synthesis also occurs in the areas where cell division takes place e.g., growing embryos and developing seeds, endosperm of seeds, young fruits, developing shoot buds, etc.
So the correct option is 'All of these'.
Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

A plant hormone used for Inducing morphogenesis in plant tissue culture is ______________.

  1. abscisic acid

  2. gibberellin

  3. cytokinin

  4. ethylene.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Cytokinins play a vital role in morphogenesis in plants. It opposes initiation of roots in stem cuttings treated with auxin and results in the formation of callus at the cut end. It is now well known that kinetin-auxin interaction controls the momhogenetic differentiation of shoot and root meristems.

Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

In addition to auxins, ................ must be supplied to the culture medium to obtain a good callus in plant tissue culture.

  1. ABA

  2. Cytokinins

  3. Gibberellins

  4. Ethylene
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Callus is an unorganized, undifferentiated mass of diving cells formed during tissue culture which requires both auxins and cytokinins for its growth and differentiation. In callus, shoot regeneration is promoted by a cytokinin, such as BAP (Benzylaminopurine) and root regeneration is promoted by an auxin, such as NAA (Naphthalene acetic acid). Thus, shoot and root regenerations in callus are controlled by auxin-cytokinin balance. Usually, an excess of auxins promote root regeneration and that of cytokinins promote shoot regeneration.
So the correct answer is 'cytokinins'.
Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

Cytokinins help to produce all except

  1. New leaves

  2. Chloroplast in leaves

  3. Lateral shoot growth and adventitious shoot formation

  4. Rooting on cut stem
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Rooting of cut stem is induced by spraying synthetic auxins like NaphthaleneAceticAcid and not cytokinins, in plants that are vegetatively propagated by stem cuttings.

So, the correct answer is 'Rooting on cut stem'

Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

Pruning of plants promotes branching, because the axillary buds get sensitized to

  1. Ethylene

  2. Gibberellin

  3. Cytokinin

  4. IAA
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Cytokinin are a class of plant growth substance that promote cell division or cytokinesis in plant roots and shoots. They are involved primarily in cell growth and differentiation but also affects apical dominance, axillary bud growth and leaf sensecence. Pruning of plants promote branching because the axillary buds get sensitized to cytokinin.

Therefore, the correct answer is option C.

Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

Coconut water is rich in 

  1. Auxins

  2. Gibberellin

  3. Abscisic acid

  4. Cytokinin
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Cytokinins stimulate cell division, even in non-meristematic cells, in presence of auxin. They are most abundant in the growing tissues which are active site of cell division, for example: root, embryos, fruits etc. Coconut water is the liquid endosperm, the actively dividing tissue which serves as nutrition source for developing coconut embryo. Coconut water is used as growth promoter of developing embryos in tissue culture studies. It stimulates the growth of cultures of embryo due to presence of cytokinins. This makes option D correct. Abscisic acid (ABA) is a growth retardation hormone which inhibits seed germination and seedling growth. This makes option C incorrect as endosperm does not have growth retardation hormone. Option A is incorrect as auxin is the hormone of cell division and cell expansion, i.e., overall growth, while endosperm carries the hormone for cell division to increase the cell number only. Option B is incorrect as gibberellins are the hormone of stem elongation in genetic dwarf plants only.

Thus, the correct answer is option D.

Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

Cell division is initiated by

  1. Cytokinin

  2. Auxin

  3. Gibberellin

  4. ABA
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The cytokinin hormones promote cell division and tissue growth, and depend upon the presence of auxins to determine the extent of their activity. When the ratio of cytokinins to auxins is relatively high, stem and leaf growth is stimulated. 

So the correct option is 'Cytokinin'.

Multiple choice biology chemical coordination in plants cytokinins plant hormones plants and animal hormones

Natural hormone isolated from coconut milk and corn kernels is

  1. Florigen
  2. ${GA} _{3}$

  3. Auxins

  4. Zeatin
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Zeatin is a type of cytokinin, a plant hormone. It stimulates cell division. It is present in coconut milk. It was first isolated from Zea maize (corn kernels). It stimulates growth in plants. 

Thus, the correct answer is option D.