Free Growth and Development MCQs with Answers

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

• A. Annual Plants
• B. Floral Parts
• C. Vessel and Tracheid Elements
• D. Leaf Abscission

Explanation: (c) : Senescence is the process of ageing which is caused by cellular breakdown, increased metabolic failure, increased entropy etc. It occurs in the period between reproductive maturity and death. Cell division followed by cell enlargement and differentiation, precede the actual separation. Senescence of cell in distal region lead to lignification of cell wall. Tylose formation in tracheary element and callose deposition in sieve elements which occur in advance of abscission (i.e. senescence) finally, lead to actual separation. Thus, vessels and tracheid (trachery elements) differentiation indicates senescence.

72. The wavelength of light absorbed by Pr form of phytochrome is :

• A. 660 nm
• B. 720 nm
• C. 620 nm
• D. 640 nm

Explanation: Phytochrome is the photoreceptor pigment that controls flowering. It has two forms as Pr and Pfr. Pr is bluish phytochrome and it absorbs light at 660 to 680 nm of wavelength. P fr is (far red) yellowish green and absorbs light at 730 nm of wavelength.

73. An enzyme that can stimulate germination of barley seeds is :

• A. Invertase
• B. Amylase
• C. Lipase
• D. Protease

Explanation: (b) : The process by which the dormant embryo of seed resumes active growth and forms a seedling is known as germination. The initial step in germination process is the uptake of water and rehydration of the seed tissues by the process of imbibition. The first visible sign of germination is the emergence of the radicle from the seed. But this event is preceded by a series of biochemical reactions. Imbibition of water causes the embryo within seed to producea and bamylases. These enzymes hydrolyze the starch stored in endosperm into glucose which is necessary for use both as a respiratory substrate and as a source of carbon skeletons of the molecules needed for growth.

74. Farmers in a particular region were concerned that premature yellowing of leaves of a pulse crop might cause a decrease in the yield. Which treatment could be most beneficial to obtain maximum seed yield?

• A. Application of iron and magnesium to promote synthesis of chlorophyll
• B. Frequent irrigation of the crop
• C. Treatment of the plants with cytokinins along with a small dose of nitrogenous fertilizer
• D. Removal of all yellow leaves and spraying the remaining green leaves with 2, 4, 5 trichlorophenoxy acetic acid

Explanation: (c) : Nitrogen is the fourth most abundant element. Chief source of nitrogen for plants is nitrates of Ca and K. It is important for plants as it is a component of nucleic acids, proteins chlorophyll and cytochromes. Deficiency of nitrogen causes poor root development, lower respiration rate, chlorosis of older leaves etc. Cytokinins are also very important for plant development. They are associated with the control of apical dominance, fruit development, root growth, cambial activity. So a nitrogenous fertilizer like NPK and cytokinins are most beneficial to the plant.

75. Treatment of seeds at low temperature under moist conditions to break its dormancy is called :

• A. Stratification
• B. Scarification
• C. Vernalization
• D. Chelation

Explanation: (c) : Vernalization is the method of promoting flowering by exposing young plants to cold treatment e.g., winter verieties of wheat, barley, oats and rye are given artificial cold treatment and planted in spring in areas of very harsh winters such as Soviet Union to promote flowering in them. In most cereals optimum temperature for vernalization is 4ºC. Receptive organ to chilling is the apical meristem. Chelation is the process by which certain micronutrients are treated to keep them readily available to a plant once they are introduced into the soil. Stratification is a process by which seeds are pretreated to simulated winter conditions so that germination may occur. The degradation of the seed coat is called scarification. This process permits water to pass through the sead coat so that embryo can begin metabolism.

76. The ability of the Venus Fly-trap to capture insects is due to :

• A. Specialized "musclelike" cells
• B. Chemical stimulation by the prey
• C. A passive process requiring no special ability on the part of the plant
• D. Rapid turgor pressure changes.

Explanation: (d) : Thigmonastic movements are exhibited by some insectivorous plants such as Dionaea, venus fly trap, Drosera etc. These plants have tentacles, which are sensitive to the stimulus of touch. In the case of the venus flytrap turgor pressure changes occur in which hydrogen ions are rapidly pumped into the walls of cells on the outside of each leaf in response to the action potentials from the trigger hairs. The protons apparently loosen the cell walls so rapidly that the tissue actually becomes flaccid so that cells quickly absorb water, causing the outside of each leaf to expand and the trap to snap shut.

77. Cell elongation in internodal regions of the green plants takes place due to :

• A. Indole acetic acid
• B. Cytokinins
• C. Gibberellins
• D. Ethylene

Explanation: (c) : Gibberellins play a role in the elongation of internodes in 'rosette' plants. Before reproductive stage there is too much elongation of internodes but there is less leaf formation. An elongated internode without leaves in called a "bolt" like structure and the process is called "bolting" flowering takes place after bolting. Gibberellins induce cell division and cell elongation, when bolting takes place.

78. One set of the plant was grown at 12 hours day and 12 hours night period cycles, and it flowered while in the other set night phase was interrupted by flash of light, and it did not produce flower. Under which one of the following categories will you place this plant?

• A. Long Day
• B. Darkness Neutral
• C. Day Neutral
• D. Short Day

Explanation: (d) : Plants require a day length or light period for flowering, this light period is called as photoperiod. It was first studied by Garner and Allard (1920). Short day plants (SDP's) flower in photoperiods less than critical day length, e.g., Nicotiana tabacum, Glycine max (Soybean), Xanthium strumarium. Further, these plants require long uninterrupted dark period and hence are called long night plants. Long day plants (LDP's) flower in photoperiod more than critical day length, e.g., Hyocyamus niger (Henbane), radish, Beta, spinach, Plantago, etc. Day neutral plants flower in any photoperiod, e.g., tomato, maize, cucumber, etc.

79. Coconut milk factor is :

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

Explanation: (d) : Many experiments were done to sustain the proliferation of normal stem tissues in culture. The growth of culture was most dramatic when the liquid endosperm of coconut, also known as coconut milk, was added to the culture medium. This finding indicated that coconut milk contains a substance or substances that stimulate mature cells to enter and remain in the cell division cycle. Eventually coconut milk was shown to contain the cytokinin zeatin, but this finding was not obtained until several years after the discovery of the cytokinins. The first cytokinin to be discovered was the synthetic analog kinetin.

80. Nicotiana sylvestris flowers only during long days, and N.tabacum flowers only during short days. If raised in the laboratory under different photoperiods, they can be induced to flower at the same time and can be cross fertilized to produce self fertile offspring. What is the best reason for considering N.sylvestris and N.tabacum to be separate species ?

• A. They cannot interbreed in nature
• B. They are reproductively distinct
• C. They are physiologically distinct
• D. They are morphologically distinct

Explanation: (a) : According to biological species concept a species is a natural inbreeding or panmictic species or group of natural populations which have essentially similar morphological traits, they are genetically distinct and reproductively isolated from others. Since under laboratory conditions N. tabacum and N. sylvestris can produce selffertile offspring so they are not reproductively isolated. They are considered as separate species because since their flowering periods are different so cross pollination is not possible between them naturally. This makes them different species.