Free Growth and Development MCQs with Answers

61. Which one of the following growth regulators is known as 'stress hormone' ?

• A. Abscisic Acid
• B. Ethylene
• C. GA 3
• D. Indole Acetic Acid

Explanation: Abscisic acid prepares plants to cope with stress conditions like drought etc. by inducing stomatal closure and other reactions. Hence it is named stress hormone.

62. Through their effects on plant growth regulators, what do the temperature and light control in the plants ?

• A. Apical Dominance
• B. Flowering
• C. Closure of Stomata
• D. Fruit Elongation

Explanation: Light and temperature may affect flowering in plants in various ways. The effect of photoperiods or daily duration of light hours (and dark periods) on flowering is called photoperiodism. For example, in short-day plants flowering occurs when the day length is below critical period, e.g., dahlia, rice etc. In long day plants, flowering occurs when day length is above critical period, e.g., spinach, lettuce etc. In short long day plants, short photoperiod is required for floral initiation and long photoperiod is required for blossoming and viceversa for long short day plants.

63. Which one of the following generally acts as an antagonist to gibberellins?

• A. Zeatin
• B. Ethylene
• C. ABA
• D. IAA

Explanation: Abscisic acid or ABA is an antagonist to gibberellins. This is discussed in the table given below:

64. Vernalization stimulates flowering in :

• A. Zamikand
• B. Turmeric
• C. Carrot
• D. Ginger

Explanation: (c) : Carrot is a biennial plant that requires stimulus of low temperature for flowering. It remains vegetative during the warm season and bears flowers and fruits only during winter. It can be made to flower in one growing season by providing low temperature treatment to young plants or seedlings which is referred to as vernalization. Hence, vernalization stimulates flowering in carrot.

65. Phototropic curvature is the result of uneven distribution of :

• A. Gibberellin
• B. Phytochrome
• C. Cytokinins
• D. Auxin

Explanation: Phototropic curvature is the result of uneven distribution of auxin. Charles Darwin and his son Francis Darwin observed that the coleoptiles of canary grass responded to unilateral illmination by growing towards the light source (phototropism). After a series of experiments, it was concluded that the tip of coleoptile contain auxin that caused the bending of the entire coleoptile in relation to the direction of light.

66. Photoperiodism was first characterised in :

• A. Tobacco
• B. Potato
• C. Tomato
• D. Cotton

Explanation: (a) : Photoperiodism is the response to duration and timings of light and dark period. It was first studied by W.W. Garner and H.A. Allard (1920) in tobacco. They observed that Maryland Mammoth variety of tobacco could be made to flower in Summer by reducing the light hours with artificial darkening.

67. Coiling of garden pea tendrils around any support is an example of :

• A. Thigmotaxis
• B. Thigmonasty
• C. Thigmotropism .
• D. Thermotaxis

Explanation: (c) : The growth movement in response to touch, or contact of a foreign body, in plants is called thigmotropism or thigmotropic movement. The stems and tendrils of the climbers are positively thigmotropic in their response. The coiling of garden pea tendrils around any support is an example of thigmotropism. Thigmonastic (haptonastic) movements are induced by some external stimuli. For example, tentacles of Drosera leaf curve and the lamina lobes of Dionaea fold on coming in contact with an insect.

68. One of the commonly used plant growth hormone in tea plantations is :

• A. Ethylene
• B. Abscisic acid
• C. Zeatin
• D. Indole 3-Acetic Acid

Explanation: (d) : Indole3acetic acid (also called auxin) is a phytohormone which is generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action. It is observed that the growing apical bud inhibits the growth of the lateral (axillary) bud. (apical dominance). Since apical meristem is the site of auxin synthesis, it is the physiological effect of the auxin which results in the phenomenon of apical dominance. When shoot tips is removed it usually results in the growth of lateral buds. This phenomenon is widely applied in tea plantations and hedgemaking because as in tea plantation and industries, the apical bud is plucked for tea processing which results in more lateral buds thus enhancing plantation and further industrial purposes.

69. Which one of the following acids is a derivative of carotenoids?

• A. Indole-3 Acetic Acid
• B. Gibberellic Acid
• C. Abscisic Acid
• D. Indole Butyric Acid

Explanation: Biosynthesis of abscisic acid (ABA) in most plants occur indirectly by degradation of certain carotenoids present in chloroplasts or other plastids. The biosynthetic pathway follow mevalonic acid pathway for their synthesis. The sites of synthesis are fruits, tissues, leaves, roots and seeds.

70. Importance of day length in flowering of plants was first shown in :

• A. Cotton
• B. Petunia
• C. Lemna
• D. Tobacco

Explanation: (d) : The effect of photoperiods or daily duration of light hours (and dark periods) on the growth and development of plants, especially flowering, is called photoperiodism. Photoperiodism was first studied by Garner and Allard (1920). They observed that 'Maryland Mammoth' variety of tobacco could be made to flower in summer by reducing the light hours with artificial darkening. It could be made to remain vegetative in winter by providing extra light