Free Growth and Development MCQs with Answers

101. If the growing plant is decapitated, then :

• A. Its growth stops
• B. Leaves become yellow and fall down
• C. Axillary buds are inactivated
• D. Axillary buds are activated

Explanation: d) : Decapitating a growing plant means removing shoot apex of the plant. Auxin, a growth promoting phytohormone present in apex inhibits the growth of axillary buds so that only the apex continues to grow. When the apex containing auxin is removed or decapitation is done, then axillary buds show their growth, this is because the apical dominance is removed. This practice of removal of apical dominance is applied in tea gardens, hedges, rose gardens etc.

102. Removal of apical bud results in :

• A. Formation of new apical bud
• B. Elongation of main stem
• C. Death of plant
• D. Formation of lateral branching

Explanation: d) : Decapitating a growing plant means removing shoot apex of the plant. Auxin, a growth promoting phytohormone present in apex inhibits the growth of axillary buds so that only the apex continues to grow. When the apex containing auxin is removed or decapitation is done, then axillary buds show their growth, this is because the apical dominance is removed. This practice of removal of apical dominance is applied in tea gardens, hedges, rose gardens etc.

103. The regulator which retards ageing/senescence of plant parts is :

• A. Cytokinin
• B. Auxin
• C. Gibberellin
• D. Abscisic acid.

Explanation: a) : Richmond and Lang, 1967 observed that degradation of protein and chlorophyll was delayed in the detached leaves, if there was cytokinin in the medium. The senescence in the detached leaves was controlled by cytokinin first by keeping the stomata open thus allowing more CO 2 to enter. This suppresses the action of ethylene which promotes senescence.

104. The hormone produced during adverse environmental conditions is :

• A. Benzyl Aminopurine
• B. Bichlorophenoxy Acetic Acid
• C. Ethylene
• D. Abscisic Acid.

Explanation: d) : Abscisic acid is a hormone which is produced during adverse environmental condition. It also causes the closure of stomata under conditions of water stress as also under high concentration of CO 2 in the guard cells. ABA plays an important role in plants during water stress and drought conditions. The concentration of ABA increases in the leaves of plants facing such stresses, hence it is called as a stress hormone.

105. Klinostat is employed in the study of :

• A. Osmosis
• B. Growth Movements
• C. Photosynthesis
• D. Respiration

Explanation: b) : Klinostat is used to study growth movements. Klinostat comprises a disc with pot which are rotated by an axial rod with the help of a motor. Auxin get uniformly distributed on all sides and, hence the stem grows horizontally forward.

106. Which is produced during water stress that brings stomatal closure?

• A. Ethylene
• B. Abscisic acid
• C. Ferulic acid
• D. Coumarin

Explanation: b) :Abscisic acid is produced during water stress that brings stomatal closure. Abscisic acid is a stress hormone and it is produced during water scarcity, when the transpiration rate exceeds absorption, the plant faces water stress condition. As a result, incipient wilting occurs. Under water stress condition ABA increases which induces stomatal closure.

107. Flowering dependent on cold treatment is :

• A. Cryotherapy
• B. Cryogenics
• C. Cryoscopy
• D. Vernalization

Explanation: d) : In several plants, particularly bienniales and perennials, light does not seem to be the only factor controlling the process of flowering. Temperature, particularly the low temperature treatment induce flowering. Vernalization means ability of low temperature to convert winter cereal into spring cereal as a result of satisfaction of their low temperature requirement.

108. Apical dominance is caused by :

• A. Abscisic acid in lateral bud
• B. Cytokinin in leaf tip
• C. Gibberellin in lateral buds
• D. Auxin in shoot tip

Explanation: d) : According to Thimann and coworkers, auxin is responsible for the dominance of apical bud. The apical dominance is due to interaction between auxin and cytokinin. If the auxin concentration is higher than cytokinin, the apical bud will dominate the growth.

109. In short day plants, flowering is induced by :

• A. Photoperiod less than 12 hours
• B. Photoperiod below a critical length and uninterrupted long night
• C. Long night
• D. Short photoperiod and interrupted long night

Explanation: b) : No flowering takes place if the dark period is less than the critical day length. The flowering is inhibited if weak intensity of light is given during the dark period. If the dark period is interrupted mid way by even a single flash of light, no flowering takes place. If this flash is given in the beginning or near the end of the dark phase, they produce flowers.

110. Cytokinins :

• A. Promote abscission
• B. Influence water movement
• C. Help retain chlorophyll
• D. Inhibit protoplasmic streaming.

Explanation: Richmond and Lang, 1967 observed that degradation of protein and chlorophyll was delayed in the detached leaves, if there was cytokinin in the medium. The senescence in the detached leaves was controlled by cytokinin first by keeping the stomata open thus allowing more CO 2 to enter. This suppresses the action of ethylene which promotes senescence.