Biology

Plant Growth and Hormones

695 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

Abscisic acid regulates

  1. Shoot elongation

  2. Cell elongation and cell wall formation

  3. Cell division

  4. Leaf fall and dormancy
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Abscisic acid regulates leaf fall and dormancy.

Other functions of abscisic acid includes:
  1. It induces bud dormancy in a number of plants. In perennial plants, ABA causes the active axillary buds to become dormant.
  2. It maintains dormancy in many seeds.
  3. It inhibits mitosis in vascular cambium.
  4. It accelerates senescence in leaves.
  5. It functions as a stress hormone by inducing a temporary closure of stomata, to tide over adverse environmental conditions.
  6. It promotes abscission of leaves, flowers and fruits in most of the plants.
  7. It inhibits seed germination.
  8. It delays cell division and cell elongation.
  9. It promotes rooting of stem cuttings in some plants like ivy and bean.
  10. It inhibits flowering except in some short day plants where it promotes flowering.

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

Plant hormone is also known as___________________

  1. Planktohormone

  2. Phytohormone

  3. Photohormone

  4. All of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

  • Plant hormones are also known as phytohormones, they are chemicals that regulate plant growth. 
  • Plant hormones are signal molecules produced within the plant and occur in extremely low concentrations. 
  • Hormones regulate cellular processes in targeted cells locally and, moved to other locations, in another functional part of the plant. 
Hormones also determine the formation of flowers, stems, leaves, the shedding of leaves, and the development and ripening of fruit. The term 'Phytohormone' was coined by Thimann in 1948. 

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

Hormone which initiates mobilization of storage materials is_________________ 

  1. Gibberellins

  2. Abscisic acid

  3. Cytokinin

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

  • Gibberellins are phytohormones that initiate mobilization of storage materials in seeds during germination. 
  • They also cause elongation of stems, stimulate bolting in biennials stimulate pollen tube growth. 
  • Gibberellins include a large range of chemicals that are produced naturally within plants and by fungi. 
  • Gibberellins are important in seed germination, affecting enzyme production that mobilizes food production used for the growth of new cells. 

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

Plants do not have glands, then how do they secrete hormones?

  1. Each cell is capable of producing hormones

  2. One cell produces hormone and then is transferred to others

  3. Hormones are produced by soil and taken up by the roots

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  • In animals, there are various glands that produce different hormones but such glands are absent in the plants. Instead, each cell is capable of producing hormones. 
  • Plant hormones shape the plant, affecting seed growth, time of flowering, the sex of flowers, senescence of leaves, and fruits. 
  • They affect which tissues grow upward and which grow downward, leaf formation and stem growth, fruit development and ripening, plant longevity and even plant death. 
  • Hormones are vital to plant growth and lacking them, plants would be mostly a mass of undifferentiated cells. So, they are also known as growth factors or growth hormones.

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

Which hormones coordinate the root growth process?

  1. Cytokinins

  2. Auxins

  3. Ethylene

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

  • A class of plant hormones called auxins coordinates the root growth process.
  •  Auxins play a key role in bending the plant roots towards the water because they cause one side of the root to grow faster than the other and thus the bending of the root. 

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

Auxins play a key role in tropism

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  • Auxins- play a key role in tropism (controlling the direction of plant growth). 
Geotropism- Under the influence of gravity, auxins accumulate in the lower side of a horizontal stem, causing cells to enlarge faster, turning the stem upright. 
  • Phototropism- The auxin concentration on the shaded side stimulates cell elongation, turning the stem to the sun. 


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

The role of gibberellin is

  1. Inhibits lateral buds

  2. Stimulates fruit ripening

  3. Maintains seed dormancy

  4. Stimualtes rapid stem elongation

  5. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The gibberellins are plant growth hormones which enhance the longitudinal growth of stem when applied to the intact plant. Gibberellins produce extraordinary elongation of stems and leaf sheaths in intact plants. The elongation of the stem is caused due to cell division and cell elongation induced by gibberellic acid. Thus option D is the correct answer.

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 of the following regulates phototropism?

  1. Ethylene gas

  2. Abscisic acid

  3. Auxin

  4. Gibberellins

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

The directional growth of organisms in response to light is called phototropism. In plants, aerial shoots usually grow towards the light. The phototropic response is controlled by 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

Which of the following is a gaseous hormone?

  1. Kinetin

  2. Zeatin

  3. Auxin

  4. Ethylene
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • Ethylene is a gaseous hormone, which stimulates transverse or isodiametric growth but retards the longitudinal one. 
  • It is a gas that forms through the break down of methionine, which is in all cells. 
  • It has very limited solubility in water and does not accumulate within the cell but diffuses out of the cell and escapes out of the plant.
  • Thus, the correct option is D.
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

Closure of stomata is caused by 

  1. Auxin

  2. Gibberellin

  3. Cytokinin

  4. Abscisic Acid
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • Abscisic acid is a carotenoid-derived plant hormone known to regulate critical functions in growth, development and responses to environmental stress.
  • It plays a key role in the regulation of stomatal closure by regulating ion channel activities and water exchanges across the plasma membrane of guard cells.
  • It increases the influx of calcium ions and efflux of potassium ions, which results in the closure of stomata.
  • So, the correct option is D.
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

Of the following which plant hormone inhibits growth?

  1. Cytokynins

  2. Gibberelins

  3. Auxins

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

Abscisic acid is the plant growth hormone which is responsible for inhibiting growth. The hormone causes inhibition in the growth of the roots and shoots. The hormone also causes abscission which is the falling of the leaves, fruits and flowers. The hormone suppresses all the processes in the plants during unfavourable conditions. 

Thus, the correct answer is option D. 

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

Auxin does not increase

  1. The plasticity of cell walls

  2. The rate of photosynthesis

  3. The uptake of water by cells

  4. Rate of respiration
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Auxin is a plant hormone that plays important role in plant growth. It stimulates stem elongation by increasing permeability of cells which in turn increases uptake of water by cells. It also enhances plasticity of cell walls which results in cell enlargement. It also increases the respiration rate.

Thus, 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

Leaf fall can be prevented with the help of 

  1. Abscisic acid

  2. Auxins

  3. Florigen

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

Leaf abscission is a detachment or fall of older leaves.It occurs at the base of the petiole. When auxin is applied to the base of petiole of young leaf, the abscission is greatly suppressed. Also, it is observed that the intact leaf does not fall off because it synthesizes auxin.

Thus, 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 is not an influence of auxins?

  1. Tropical movements

  2. Bolting

  3. Parthenocarpy

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

Auxin is a plant hormone which is involved in various physiological processes. It is present on the tip of the stem and helps in phototropic movement in response to light. It also maintains apical dominance where there is more growth on the stem tip and growth of lateral bud is inhibited. Auxin along with cytokinin and gibberellin helps in the process of parthenocarpy. It does not cause bolting. It does not influence flowering in the plant.

Thus, the correct answer is option B.