Free Growth and Development MCQs with Answers

91. The response of different organisms to the environmental rhythms of light and darkness is called :

• A. Vernalization
• B. Photoperiodism
• C. Phototaxis
• D. Phototropism.

Explanation: b) : Photoperiodism is the response of plants to relative length of light and darkness. Phototaxis is plant movement where the stimulus is light. Phototropism is tropism in which stimulus is light. Vernalization is application of cold treatment to plants to effect flowering.

92. Which combination of gases is suitable for fruit ripening?

• A. 80% CH4 and 20% CO2
• B. 80% CO2 and 20% O2
• C. 80% C2 H4 and 20% CO2
• D. 80% CO2 and 20% CH2

Explanation: c) : In most of the plants, there is a sharp rise in respiration rate near the end of the development of fruit, which sets in progress those changes, which are involved in ripening of fruit. The ripening on demand can be induced in these fruits by exposing them to normal air containing about 1 ppm of ethylene. Suitable combination of gases in atmosphere for fruit ripening is 80% ethylene (C 2 H 4 ) and 20% CO 2 .

93. Phytochrome becomes active in :

• A. Red Light
• B. Green Light
• C. Blue Light
• D. None of these.

Explanation: Important plant responses regulated by the phytochrome system include photoperiodic induction of flowering, chloroplast development, leaf senescence and leaf abscission. Phytochrome occurs in two forms: Pr (red light) and Pfr (far red light) and both are interconvertable. It is considered that during day time Pfr form accumulates in plants which is inhibitory to flowering in SDP. During night Pr form accumulates in plants which is stimulatory to flowering.

94. Which one among the following chemicals is used for causing defoliation of forest trees?

• A. Malic Hydrazide
• B. 2,4D
• C. Both A and B
• D. None of these

Explanation: (b) : 2,4D is a famous herbicide or weedicide which especially kills broad leaved weeds. It kills weeds perhaps by over stimulated root growth. Other auxins like 2, 4, 5 T have also been used as defoliants during early sixties.

95. A pigment which absorbs red and farred light is :

• A. Cytochrome
• B. Xanthophyll
• C. Phytochrome
• D. Carotene

Explanation: Phytochrome is a bright blue or bluish green pigment which was first of all isolated from plasma membrane of alga Mougeotias. It is a photoreceptive pigment. Phytochrome has a light absorbing or light detecting portion (the chromophore) attached to small protein of about 1,24,000 daltons. Phytochrome occurs in 2 forms, i.e., P R and P FR (i.e., red light and far red light absorbing forms) and these 2 forms are interconvertible. It is involved in the perception of photoperiodic stimuli controlling flowering and other morpho genetic phenomenon in plants.

96. What will be the effect on phytochrome in a plant subjected to continuous red light?

• A. Phytochrome synthesis will increase
• B. Level of phytochrome will decrease
• C. Phytochrome will be destroyed
• D. First (b) then (a)

Explanation: d) : When continous red light is given the level of P R decreases as most of it is converted to P FR form. When the concentration ofP R reaches below a critical value, it starts synthesis of more phytochromes in the P R form so that there is an equilibrium betweem synthesis and destruction of P R form.

97. If a tree flowers thrice in a year (Oct., Jan. and July) in Northern India, it is said to be :

• A. Photo and Thermoinsensitive
• B. Photo and Thermosensitive
• C. Photosensitive but Thermoinsensitive
• D. Thermosensitive but Photoinsensitive.

Explanation: a) : Flower formation is a transitional phase in the life eycle of plant. During flowering, vegetative shoot apex is converted into reproductive shoot apex. The physiological mechanism for flowering is controlled by 2 factors : photoperiod or light period, i.e., photoperiodism and low temperature, i.e., vernalization.

98. The twining of tendrils around a support is a good example of :

• A. Phototropism
• B. Chemotropism
• C. Nastic Movements .
• D. Thigmotropism

Explanation: (d) : Thigmotropism involves nastic movements resulting from touch. It occurs in tendrils which coil around support and help the plant in climbing. Phototropism is a paratonic movement in response to unidirectional light stimulus. Chemotropism is a directional paratonic movement that occurs in response to a chemical stimulus.

99. The closure of lid of pitcher in pitcher plant, is due to :

• A. Paratonic Movement
• B. Autonomous Movement
• C. Turgor Movement
• D. Tropic Movement

Explanation: (a) : Plants have the capacity of changing their position, in response to external or internal stimuli which are known as plant movements. The movements which occur due to internal stimuli are called autonomic movements and those that occur due to external stimuli are called paratonic movements. Nepenthes (pitcher plant) is an insectivorous plant. In this the leaf lamina is modified to form a pitcher and leaf apex forms a coloured lid. When the insect enter the pitcher it is an external stimuli, so the closure of the lid is paratonic movement.

100. The movement of auxin is largely :

• A. Centripetal
• B. Basipetal
• C. Acropetal
• D. Both (a) and (c).

Explanation: b) : Auxin is a growth promoting phytohormone. It moves mainly from the apical to the basal end (basipetally). This type of unidirectional transport is termed polar transport. Auxin is the only plant growth hormone known to be transported polarly. Recently it has been recognized that a significant amount of auxin transport also occur acropetally (from basal end to the apical end) in the root.