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 plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Stomatal closing during full sunlight is best defined by

  1. Hormonal control
  2. $K^+$ion hypothesis
  3. $CO _2$ concentration

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

Many hormone-like abscisic acid (for closing)  cytokinin (for opening) and ethylene (for opening and closing both) are responsible for opening and closing of stomata. 

So the correct option is 'Hormonal control'.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Seed dormancy is induced by

  1. ABA

  2. GA

  3. Thiourea

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

Abscisic acid is a plant hormone. It is also called as stress hormone. During unfavourable environmental conditions like drought, it induces seed dormancy. When there is favaourable condition, seed dormancy is broken and germination takes place.

Thus, the correct answer is option A.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

One hormone helps in ripening of fruits and other brings about stomatal closure. They are respectively

  1. ABA, IAA
  2. ${C} _{2}{H} _{4}$, ABA

  3. ABA, ehtylene
  4. ${C} _{2}{H} _{4}$, GA

  5. GA, ABA
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ethylene and abscisic acid both are the plant hormones. Ethylene hormone is also called as ripening hormone as it helps in the ripening of fruits. Abscisic acid is also called as a stress hormone. It promotes stomatal closure when insufficient water is available in the soil. 

Thus, the correct answer is option B.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Abscisic acid is called stress hormone as it 

  1. Induces flowering

  2. Breaks seed dormancy

  3. Promotes leaf fall

  4. Promotes stomatal closure
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Abscisic acid is a plant hormone. It is also called as stress hormone as under stress environmental condition, it induces seed dormancy. It promotes stomatal closure under water stress condition to decrease the rate of transpiration.

Thus, the correct answer is option D.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Which of the following is a correct statement?

  1. Negative geotropism in horizontal stems is caused by accumulation of auxin on the lower side.

  2. Pineapple can be made to flower in off season by the application of ethylene.

  3. The ratio of auxin to cytokinin controls cell differentiation.

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

Berry size of many seedless table grape cultivars can be substantially increased by applying gibberellic acid.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Which of the following is wrong about ethylene?

  1. Inhibit growth of root

  2. Ripening of fruits

  3. Elongation of stem in paddy

  4. Promote senescence of leaves & flowers
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • Ethylene is a simple gaseous Plant growth hormone. It is synthesized in large amounts by tissues undergoing senescence and ripening fruits.
  • Ethylene promotes senescence and abscission of plant organs, especially of leaves and flowers.
  • Ethylene is highly effective in fruit ripening. It enhances the respiration rate during the ripening of the fruits. 
  • Ethylene promotes elongation of the stem in paddy.
  • Ethylene also promotes root growth and root hair formation, thus helping the plants to increase their absorption surface.
  • Hence Ethylene inhibits the growth of roots is a wrong statement about ethylene.
  • So, the incorrect option is 'Inhibit growth of root'.
Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Choose the wrongly matched pair from the following.

  1. Auxins - to grow

  2. Gibberellins - Gibberella fujikuroi

  3. Cytokinins - herring sperm DNA

  4. Abscissic acid - flowering hormone
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Abscisic acid is a plant hormone which causes abscision. It never promotes flowering in plants. ABA owes its name to its role in the abscission of plant leaves. In preparation for winter, ABA is produced in terminal buds. This slows plant growth and directs leaf primordia to develop scales to protect the dormant buds during the cold season. ABA also inhibits the division of cells in the vascular cambium, adjusting to cold conditions in the winter by suspending primary and secondary growth. It also promotes dormancy in buds.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Plant hormone associated with climacteric respiration is 

  1. Auxin

  2. Cytokinin

  3. Ethylene

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

Ethylene is a simple gaseous plant growth regulator (PGR). It is synthesised in large amounts by tissues undergoing senescence and ripening fruits. Influences of ethylene on plants include horizontal growth of seedlings, swelling of the axis and apical hook formation in dicot seedlings. Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. Ethylene is highly effective in fruit ripening. It enhances the respiration rate during ripening of the fruits. This rise in rate of respiration is called as respiratory climactic.

Thus, the correct answer is option C.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Which one of the following is a naturally occurring growth inhibitor?

  1. IAA

  2. ABA

  3. NAA

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

Abscisic acid is the plant growth hormone which is responsible for inhibiting growth. This is the natural growth inhibitor which is produced in the plants. 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 plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Which one of the following triggers the ripening of fruits? 

  1. Ethylene

  2. Indoleacetic acid

  3. Gibberellic acid

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

Ethylene is the gaseous hormone that stimulates growth and development of floral organs and promotes fruit ripening. It does so by causing softening of fruit due to enzymatic breakdown of cell walls, starch hydrolysis, sugar accumulation and disappearance of organic acids and phenolic compounds. Thus, option A is correct. 

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

_______ is naturally occurring growth inhibitor.

  1. Ethylene

  2. Abscissic acid

  3. Cytokinin

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

During drought and other unfavorable climatic conditions it is very important to maintain viability of the seeds. Abscissic acid is released during this condition and interacts with growth hormone in order to inhibit the growth of plant.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Which hormone is responsible for spoiling the whole barrel containing one bad apple?

  1. Ethylene gas

  2. Abscisic acid

  3. Auxin

  4. Gibberellins

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

Ethylene is gaseous hormone promotes fruit ripening and abscission. It diffuses from the rotten apple to other apples in the barrel and thereby causing spoilage of the whole barrel. ABA, auxins, gibberellins and cytokines are not gaseous hormones and therefore can not diffuse from one fruit to other. Thus, the correct answer is A.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

"One bad apple spoils the whole barrel" because of

  1. Ethylene gas

  2. Abscisic acid

  3. Auxin

  4. Gibberellins

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

Ethylene gas is the plant hormone that promotes fruit ripening and rotting. It also controls flower wilting and leaf fall by stimulating the conversion of starch and acid to sugars. Therefore, it is said that one bad apple will spoil the whole barrel because of ethylene gas.

Therefore, the correct answer is option A.

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

Presence of ethylene gas causes fruits to ripen. As fruit ripens, it produces increasing amounts of ethylene.

This is an example of

  1. Positive feedback

  2. Negative feedback

  3. Homeostasis

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

ethylene gas is an aging hormone used for fruit ripening but may also cause the plant to die. Ethylene gas is released when the plant is damaged mechanically or physically.

So the correct option is 'Positive feedback.'

Multiple choice biology plant growth other plant hormones cytokinins, ethylene and abscisic acid plant hormones

In the fall, the leaves of deciduous trees change color, fall off and die. This shedding of leaves is Mated by which of the following plant hormones? 

  1. auxin

  2. gibberellin

  3. abscisic acid

  4. cytokinin

  5. ethylene
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
A. Auxin plays role in cell elongation, apical dominance, root initiation, prevention of abscission, induction of parthenocarpy and also used as herbicide.
B. Gibberellin plays role in stem elongation, seed germination, breaking dormancy, elongation of internodes and inducing parthenocarpy.
C. Abscisic acid or ABA is known as stress hormone and induces stomatal closure, provides defence against salt and cold stress, induces dormancy, causes geotropism in roots and abscission of leaves, flowers and fruits.
D. Cytokinin plays role in promoting cell division and organ formation, delay in senescence, promoting lateral bud development in dicots, cell expansion in cotyledons leaves, promoting chloroplast development and chlorophyll synthesis.
E. Ethylene is a gaseous hormone and causes ripening of fruit.
So, the correct answer is 'Abscisic acid'.