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 life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Choose the correct answer from the alternatives given.
Which of the following statements about plant hormones is not true?

  1. Each naturally occurring hormone has a specific chemical structure

  2. Hormones are among the principal internal regulators of plant growth

  3. Responses to plant hormones may be observed in nearly any part of a plant

  4. All known growth regulators of plant activities are chemicals produced naturally in plants
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Cytokinins have specific effects on cytokinesis and were discovered as kinetin (a modified form of adenine, a purine) from the autoclaved herring sperm DNA. Kinetin does not occur naturally in plants.

So, the correct option is 'All known growth regulators of plant activities are chemicals produced naturally in plants'.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Choose the correct answer from the alternatives given.
Plant hormones

  1. interact with one another

  2. are influenced by environmental cues

  3. are active in plant embryos within seeds

  4. all of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Plant hormones can work in combination and are dependent on the environmental cues or signals to act. They are also active in plant embryos within the seed such as Gibberellic acid.

So, the correct option is 'all of the above'.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Choose the correct answer from the alternatives given.
The plant hormone that causes cell elongation is:

  1. citric acid

  2. indole 3-acetic acid

  3. ethylene

  4. abscisic acid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Plant cells elongate irreversibly only when load-bearing bonds in the walls are cleaved. Auxin causes the elongation of stem and coleoptile cells by promoting wall loosening via cleavage of these bonds. This process may be coupled with the intercalation of new cell wall polymers.

So, the correct option is 'indole 3-acetic acid'.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Find the odd man out:

  1. Auxin

  2. Abscisic acid

  3. Thyroxine

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

  • Auxin is a plant hormone that is produced in the tip of the stem that works in elongation.
  •  Auxin helps the plant to move to the darker side, the cell grows larger than corresponding cells present on the lighter side of the plant.
So, the correct option is 'Auxin'.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

A high concentration of synthetic auxin is generally used for

  1. Weed control

  2. Preventing the growth of the lateral buds

  3. Enhancing root initiation

  4. Controlling of cell enlargement
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In the course of research on auxin biology, many compounds with noticeable auxin activity were synthesized. Many of them had been found to have the economical potential for man-controlled growth and development of plants in agronomy. Auxins are toxic to plants in large concentrations. They are most toxic to dicots and less so to monocots. Because of this property, synthetic auxin herbicides, including 2,4-D and 2,4,5-T, have been developed and used for weed control. However, synthetic auxins, especially 1-naphthaleneacetic acid (NAA) and indole-3-butyric acid (IBA), are also commonly applied to stimulate root growth when taking cuttings of plants or for different agricultural purposes such as the prevention of fruit drop in orchards. Used in high doses, auxin stimulates the production of ethylene. Excess ethylene (also native plant hormone) can inhibit elongation growth, cause leaves to fall (abscission), and even kill the plant. 

Therefore, the correct answer is option A.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

During adverse environmental conditions, plants develop a stress hormone, which is

  1. Abscisic acid

  2. Ethylene

  3. Benzyl amino purine

  4. Dichlorophenoxy acetic acid
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Abscisic acid or ABA plays a regulatory role in many physiological processes in plants. Different stress conditions such as water, cold, light, and temperature result in increased amounts of ABA. The action of ABA involves modification of gene expression and analysis of responsive promoters revealed several potential cis- and trans- acting regulatory elements. Stress may induce common responses such as enhancement of plant hormones. For instance, wounding can induce the production of increased ethylene, auxin, and abscisic acid (ABA). Since, many kinds of stresses including water, salt, and cold temperatures, induce ABA synthesis, ABA may be considered a plant stress hormone. It regulates several important aspects of plant growth and development. Recent studies have demonstrated a pivotal role for ABA in modulation at the gene level of adaptative responses for plants in adverse environmental conditions.
Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Which among the following hormones is toxic to plants in large concentrations, regulates protein synthesis and causes bud formation and root initiation?

  1. Ethylene

  2. Auxin

  3. Cytokinin

  4. Gibberellins
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

  • Auxins are a group of hormones that positively influence cell enlargement, bud formation, and root initiation. 
  • In conjunction with cytokinins, they control the growth of stems, roots, and fruits, and convert stems into flowers. Auxins were the first class of growth regulators discovered. 
  • They affect cell elongation by altering cell wall plasticity. Auxins act to inhibit the growth of buds lower down the stems, and also to promote lateral and adventitious root development and growth. 
  • Leaf abscission is initiated by the growing point of a plant ceasing to produce auxins. Auxins in seeds regulate specific protein synthesis, as they develop within the flower after pollination, causing the flower to develop a fruit to contain the developing seeds. 
  • Auxins are toxic to plants in large concentrations, they are most toxic to dicots and less so to monocots. 

Therefore, the correct answer is option B.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Which hormone works during seed dormancy?

  1. Auxin

  2. Gibberellins

  3. Abscisic acid

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

  • Abscisic acid is one of the most important plant growth regulators. This class of PGR is composed of one chemical compound normally produced in the leaves of plants, originating from chloroplasts, especially when plants are under stress. In general, it acts as an inhibitory chemical compound that affects bud growth, and seed and bud dormancy. 
  • It mediates changes within the apical meristem, causing bud dormancy and the alteration of the last set of leaves into protective bud covers. 

Therefore, the correct answer is option C.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

If a person tests plant hormones for increasing the crop yield, he sprays a large plot with a selected hormone to determine its effect in hybrid vigor. Which of the following he should avoid?

  1. $2, 4-$D

  2. IAA

  3. Gibberellin

  4. Cytokinin

  5. Abscisic acid
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There are five major types of plant hormones. Abscisic Acid also called ABA is one of the most important plant's growth regulators and under water stress, this hormone plays a role in closing the stomata. Auxins are hormones that  positively influence cell enlargement, bud formation and root initiation. Cytokinins tend to positively influence cell enlargement, bud formation and root initiation. Others are ethylene regulates the fruit ripening and Gibberellins stimulates the flower production, cell elongation. Whereas 2, 4-D is not a plant hormone but a chemical weedicide. 

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Match the columns and choose the correct combination.

    I           II
(a) Cytokinin (p) Stress hormone
(b) Auxins (q) Ripening of fruits
(c) Abscisic acid (r) Apical dominance
(d) Ethylene (s) Bolting
(t) Richmond-Lang Effect

  1. a - t, b - r, c - p, d - q

  2. a - t, b - r, c - p, d - s

  3. a - r, b - s, c - q, d - p

  4. a - q, b - s, c - t, d - r
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Cytokinin is a plant hormone that produces the Richmond Lang effect. It inhibits ageing process of the plant. Auxin is a plant hormone that induces apical dominance. It promotes the growth of stem tip and inhibits the growth of lateral buds. Abscisic acid is a plant hormone. It is also called as stress hormone as under stress environmental condition, its concentration increases. It induces seed dormancy. Ethylene is a plant hormone. It is also called as ripening hormone as it induces ripening of fruits. 

Thus, the correct answer is option A.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Hormones used to speed up malting in Barley, promote flowering in Pineapple and delaying leaf senescence are respectively

  1. Auxin, Gibberellin and Cytokinin

  2. Gibberellin, Cytokinin, Auxin

  3. Gibberellin, Auxin, Cytokinin

  4. Cytokinin, Auxin, Gibberellin

  5. Auxin, Cytokinin, Gibberellin
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Gibberellic acid is a plant hormone. It stimulates stem elongation, germination, flowering. It also causes fruit elongation and delays senescence. Hence in brewery industry, it is used to speed up malting process. Auxin is a plant hormone which is used to induce flowering in pineapple as it induces synthesis of ethylene. Cytokinin is a plant hormone that stimulates cell division. It delays the senescence in leaves. 

Thus, the correct answer is option C.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Identify the incorrect matched pair.

  1. Auxin - Phototropism

  2. Gibberellin - Foolish seeding disease of rice

  3. Ethylene - Induces fruit ripening

  4. Cytokinin's - Promotes apical dominance
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Cytokinins promote lateral bud growth and counteract apical dominance. Therefore, stating that cytokinins promote apical dominance makes the pair incorrectly matched.

Multiple choice biology life processes: control and coordination control and coordination in plants growth in plants chemical coordination in plants animal senses sense organs in animals sense organs in humans

Match the following columns.

Column I(Bioassays of phytohormones) Colum  II(Characteristics of phytohormones)
a. Avena curvature test (i) Delay leaf senescence
b. Chlorophyll preservation test (ii) Promote female flowers in cucumber
c. Triple response test (iii) Initiate rooting in stem cutting
d. Cotton test (iv) Antagonist to GAs

  1. a(iii), b(i), c(iv), d(ii)

  2. a(iii), b(ii), c(i), d(iv)

  3. a(iii), b(i), c(ii), d(iv)

  4. a(iii), b(iv), c(ii), d(i)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Avena curvature test (Auxin/rooting), Chlorophyll preservation (Cytokinin/senescence), Triple response (Ethylene/female flowers), Cotton test (Auxin/antagonist).