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 chemical coordination in plants abscisic acid fruit plants: structure and function

Phytohormone commonly called as stress hormone is 

  1. Auxin

  2. Abscissic acid

  3. Gibberellin

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

Abscisic acid (ABA) was discovered for its role in regulating abscission and dormancy. But like other PGRs, it also has other wide ranging effects on plant growth and development. It acts as a general plant growth inhibitor and an inhibitor of plant metabolism. ABA inhibits seed germination. ABA stimulates the closure of stomata in the epidermis and increases  the tolerance of plants to various kinds of stresses. Therefore, it is also called as the stress hormone. ABA plays an important role in seed development, maturation and dormancy. By inducing dormancy, ABA helps seeds to withstand desiccation and other factors unfavourable for growth. In most situations, ABA acts as an antagonist to gibberellins.

Thus, the correct answer is option B.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

The plant hormone that inhibits growth is called as

  1. Cytokinins

  2. Gibberellins

  3. Auxins

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

Auxin is the plant growth hormone that promotes lengthening and coordinates with other growth hormones to regulate growth; it also causes apical dominance. Cytokinin is the plant growth hormone that promotes cell division in shoot apical meristem and differentiation in root apical meristem. It works antagonistically to auxin to balance the growth with development in the shoot and root apex. Gibberellins are responsible for stem elongation, breaking seed dormancy, mobilization of endosperm reserves as well as regulate sex determination, flower initiation and fruit set. Abscisic acid is a plant growth hormone involved in seed dormancy by suppressing seed germination and growth as well as in responses of plants to stress. This makes option D correct. 

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

The naturally occurring growth inhibitor is

  1. IAA (indoleacetic acid)

  2. ABA (abscisic acid)

  3. NAA (naphthalene acetic acid)

  4. GA (gibberellic acid)
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The naturally occurring growth inhibitor is ABA (abscisic acid).
Abscisic acid is a growth inhibitor which retards or suppresses growth and metabolism.
It induces bud dormancy in a number of plants. In perennial plants, ABA causes the active axillary buds to become dormant.
ABA maintains dormancy in many seeds.
It inhibits mitosis in vascular cambium.
It accelerates senescence in leaves
It functions as a stress hormone by inducing a temporary closure of stomata, to tide over adverse environmental conditions
It promotes abscission of leaves, flowers and fruits in most of the plants
It inhibits seed germination.
It delays cell division and cell elongation
It inhibits flowering except in some short day plants where it promotes flowering.
Thus, the correct answer is option B.
Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

Which of the following induces dormancy?

  1. Auxin

  2. Cytokinin

  3. Both (A) and (B)

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

Abscisic acid (ABA) induces dormancy. Robinson and Warming (1964), isolated a substance responsible for dormancy in Acer pseudoplatanus, and named it as dormin. This hormone was similar to abscission It is a naturally occurring hormone that is present in all vascular plants and some mosses but is not present in bacteria, algae fungi and liverworts. This hormone is responsible for dormancy.

Thus, the correct answer is option D.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

The following is a naturally occuring growth inhibitors ............

  1. IAA

  2. ABA

  3. NAA

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

IAA, NAA - are several forms of auxin hormone which promotes plant growth. At the same time, GA is gibberellic acid which initiates shoot elongation. ABA is abscissic acid which is an inhibiting hormone which causes dormancy and also inhibits the longitudinal growth of plant.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

Which of the following is true?

  1. ABA open stomata.

  2. ABA and cytiokinin does not effect on stomata.

  3. ABA open, cytokinin close stomata.

  4. ABA close and cytokinin open the stomata.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

ABA is an inhibiting hormone which helps in the closure of stomata. It thus helps in control of transpiration. Whereas cytokinin promotes the opening of stomatal pore. It also initiates mitotic cell divisions.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

Which one of the following plant hormones (phytohormone) is known as a stress hormone?

  1. Gibberellins

  2. Kinetin

  3. Auxin

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

The synthesis of ABA is stimulated by drought, water logging and other adverse environmental condition. Therefore, it is also called as stress hormone. It is also called as 'growth inhibitor hormone', because it causes inhibition of seed germination, flowering and so on.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

Abscisic acid treatment results in ..................

  1. Leaf expansion

  2. Stem elongation

  3. Stomatal closure

  4. Root elongation
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
ABA inihibits the H+/K+ exchange and promotes the leakage of maleic acid. The reduction of osmotically active solutes would render the guard cells flaccid and keep the stomatal pore closed. ABA is a growth inhibitor which retards or suppresses growth and metabolism. It induces bud dormancy in a number of plants. In perennial plants, ABA causes the active axillary buds to become dormant
So, the correct answer is 'Stomatal closure'
Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

One hormone helps in ripening of fruits while the other stimulates closure of stomata. These are respectively ..................

  1. Abscisic acid and auxin

  2. Ethylene and abscisic acid

  3. Anscisic acid and rthylene

  4. Ethylene and gibberellic acid

  5. Gibberellic acid and abscisic acid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ethylene hormone in plants helps in ripening of fruits. Abscisic acid is known for its inhibiting nature in growth. It causes bud dormancy in several plants. It also causes closure of stomata to minimize the loss of water by transpiration.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

In the extreme drought condition, which of the following plant hormone is produced, due to which stomata closes?

  1. ABA

  2. IAA

  3. Gibberellin

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

ABA is a plant hormone which is inhibiting in nature. It causes the closure of stomata, in order to reduce the rate of transpiration and the loss of water thereby. It is also well known for its dormant activity. ABA promotes early aging in the plant and also inhibits flowering, fruiting, germination, etc. 

Thus, the correct answer is option A.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

Senescence as an active developmental cellular process in the growth and functioning of a flowering plant, is indicated in 

  1. Annual plants

  2. Floral parts

  3. Vessels and tracheid differentiation

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

Senescence is a programmed developmental process. Leaf abscission is a classic example of programmed cell death and senescence in plants, allowing the plant to shed older or damaged leaves.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

Which one is not a growth promoter?

  1. ABA

  2. GA

  3. IAA

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

There are various plant hormones which act as growth regulators. Hormones like gibberellic acid (GA), Indoleacetic acid (IAA), a type of auxin, cytokinin (CK) are growth promoter. Hormones like Abscisic Acid (ABA), ethylene are growth inhibitor. These hormones accelerate abscission process.

Thus, the correct answer is option A.

Multiple choice biology chemical coordination in plants abscisic acid fruit plants: structure and function

Abscisic acid causes

  1. Stomatal closure

  2. Stem elongation

  3. Leaf expansion

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

 It inhibits root elongation, stem elongation and seed germination. It brings out the stomatal closure when soil water is insufficient to keep up with transpiration. It binds to receptor present on the guard cells and hence closes stomata.

So, the correct answer is 'Stomatal closure'