Directions: In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true.
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Assertion: Primary growth of the plants contributes to the elongation of the plants along their axis.
Reason: Root apical meristem and shoot apical meristem are responsible for primary growth of the plants.
(a) Plant growth is unique because plants retain the capacity for unlimited growth throughout their life. This ability of the plants is due to the presence of meristems at certain locations in their body. The cells of such meristems have the capacity to divide and self-perpetuate. The root apical meristem and shoot apical meristem are indeterminate meristems because these meristems continue their activity throughout life of the plant. Root apical meristem and shoot apical meristem cause primary growth of plants. It also causes the elongation of the plants along their axis.
Assertion: The constantly dividing cells both at the root apex and the shoot apex, show the mersitematic phase of growth.
Reason: The cells of this region are rich in protoplasm and are without nuclei.
(c) The root apex, shoot apex and many other regions have meristematic tissue. New cells are produced by mitotic divisions of the meristematic cells. These cells have cellulosic cells walls, large nucleus and rich in protoplasm. It is called the phase of cell formation or cell division.
Assertion: Nutrients are required by plants for the synthesis of protoplasm and act as source of energy.
Reason : Water provides the medium for enzymatic activities needed for growth.
(b) Nutrients are raw materials required for synthesis of protoplasm as well as source of energy. Nutrients should be rich in nitrogenous components for increased synthesis of protoplasm and carbohydrates for energy and cell wall synthesis. All types of micronutrients and macronutrients should be available for proper growth. Water is required for cell elongation, maintenance of turgidity of growing cells and providing medium for enzyme action. Even a slight deficiency of water reduces growth. It may, however, promote differentiation. Water stress completely stops growth.
Assertion: Development is the sum of growth and differentiation.
Reason: Development in plants is under the control of extrinstic factors only.
(c) Growth, differentiation and development are closely related events in the life of a plant. Development is the sum of growth and differentiation. Development in plants is under the control of both intrinsic and extrinsic factors.
Assertion : The difference in shapes of leaves produced in air and those produced in water in buttercup represent the heterophyllous development due to environment.
Reason: The phenomenon of heterophylly is an example of plasticity.
(b) Different structures are developed during different phases of growth as well as in response to the environment. To cope up with the changes in the environment, the plant organs also change their structures and it is called plasticity. Heterophylly is the occurrence of different types of leaves on the same plant in different growth phases or under different environmental conditions. In the case of environmental plasticity as shown by aquatic buttercup Ranunculus flabellaris, the submerged leaves are highly dissected while the emerged leaves are broad and lobed.
Assertion: Auxins help to prevent fruits and leaves drop at early stages.
Reason: Auxins promote the abscission of older mature leaves and fruits.
(b) Auxin delays the abscission of young leaves and fruits. Its effect is through the nonformation of the abscission zone below a leaf or fruit. Abscission zone cuts off nutrients and water supply. However, auxin promotes the abscission of mature or older leaves and fruits.
Assertion: Decapitation is widely used in tea plantation and hedge-making.
Reason: Removal of shoot tips usually results in the growth of lateral buds.
a
Assertion: 2, 4-D is extensively used in agricultural and horticultural practices.
Reason: 2, 4-D is a herbicide.
(a) NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic acid) are synthetic auxins. All these auxins have been used extensively in agricultural and horticultural practices. They are widely used as herbicides. 2, 4-D is widely used to kill dicotyledonous weeds and it does not affect mature monocotyledonous plants. It is used to prepare weed-free lawns by gardeners.
Assertion: Gibberellins cause fruits like apple to elongate and improve their shape.
Reason: \(\mathrm{GA}_3\) is used to speed up the malting process in brewing industry.
(b) Application of gibberellins increases the number and size of several fruits, e.g., grapes, tomato. Size and shape of apple fruits is enhanced by the application of \(\mathrm{GA}_4\) and \(\mathrm{GA_7}\) mixture. Gibberellins (e.g., \(\left.\mathrm{GA}_3\right)\) increase the yield of malt from barley grains, i.e., malting.
Assertion: Kinetin is found naturally in plants.
Reason: ABA induces seed and bud dormancy.
(d) The first cytokinin was discovered from degraded autoclaved Herring sperm DNA. It is called kinetin (6-furfuryl amino-purine). Kinetin does not occur naturally. It is a synthetic hormone. ABA induces seed and bud dormancy.
Assertion: The most widely used compound as source of ethylene is ethephon.
Reason: Ethephon hastens fruit ripening in tomatoes and apples and accelerates abscission in stems and leaves.
(c) Ethylene is a simple gaseous PGR. The most widely used compound as source of ethylene is ethephon. Ethephon in an aqueous solution is readily absorbed and transported within the plant and releases ethylene slowly. Ethephon hastens fruit ripening in tomatoes and apples and accelerates abscission in flowers and fruits (thinning of cotton, cherry, walnut). It promotes female flowers in cucumbers thereby increasing the yield.
Assertion: Auxin was isolated by F.W. Went from the tips of coleoptiles of wheat seedlings.
Reason: Ethylene promotes senescence and abscission of plant organs.
(d) Auxin was isolated by F.W.Went from the tips of coleoptiles of oat seedlings. Ethylene promotes senescence and abscission of plant organs, especially of leaves and flowers.
Assertion: Abscisic acid (ABA) is also called stress hormone.
Reason : ABA increases the tolerance of plants to various kinds of stresses.
(a) Abscisic acid increases the resistance of plants to cold and other types of stresses like drought, water logging, etc. It is therefore also known as stress hormone.
Assertion: In some plants, flowering depends only on a combination of light and dark exposure.
Reason: The site of perception of light or dark duration are leaves of plants.
(d) Some plants require periodic exposure to light to induce flowering. It is now also known that not only the duration of light period but the duration of the dark period is also of equal importance. Hence, it can be said that flowering in certain plants depends not only on a combination of light and dark exposures but also on their relative durations. This response of plants to periods of day/night is termed photoperiodism. The shoot apices modify themselves into flowering apices prior to flowering, shoot apices cannot perceive photoperiods by themselves. The site of perception of light/dark duration are the leaves.
Assertion: Vernalisation is the promotion of flowering by a period of low temperature.
Reason: Vernalisation prevents precocious reproductive development late in the growing season.
(b) There are plants for which flowering is either quantitatively or qualitatively dependent on exposure to low temperatures. This treatment is termed as vernalisation. It prevents precocious reproductive development late in the growing season and enables the plant to have sufficient time to reach maturity.
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