Plant Growth and Development Test - 47

2,4-D stands for 2,4-Dichlorophenoxyacetic acid. It is an herbicide that kills terrestrial and aquatic weeds by changing the way its cells grow. It mimics the plant growth hormone auxin resulting in uncontrolled growth of cells eventually leading to death of unwanted plants. Thus the correct answer is option B.

• In pants, just like animals, there are many chemical substances in their bodies that act as messengers. These are called plant pheromones. These are responsible for proper growth and development and proper regulation of different functions in a plant body. One of these pheromones is gibberellin.
• Different fungi are associated with plants and are also involved in their defence mechanism against various pathogens. They are also related to the production of various plant hormones, one of them is gibberellin. So, degrading yeast also shows gibberellin present in it.
•  Apart from this, gibberellin is associated with ripening and parthenogenetic development of fruits.  So, their juices contain adequate amounts of gibberellin.
• So, option C "Gibberellin" is the correct answer. 

Cytokinins are the growth substances which act primarily on cell division and have little or no effect on extension growth. Cytokinins are derivatives of purine base, adenine, bearing furfuryl substituent. Thus option C is the correct answer. 

Ethylene is also known as ripening hormone.It is responsible for the changes in texture, softening, colour and other attributes of ripening. Thus the correct answer is option A. 

The cells derived from root apical and shoot-apical meristems and cambium differentiate and mature to perform specific functions. This act leading to maturation is termed as differentiation. During differentiation, cells undergo few to major structural changes both in their cell walls and protoplasm. The living differentiated cells, that by now have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation. For example, formation of meristems – interfascicular cambium and cork cambium from fully differentiated parenchyma cells. While doing so, such meristems / tissues are able to divide and produce cells that once again lose the capacity to divide but mature to perform specific functions, i.e., get redifferentiated. 

Phototropism is the growth of an organism in response to a light stimulus. Auxins such as Indole acetic acid (IAA) play an important role in phototropism. IAA is found on the shoot tips and is responsible for directional movement of the plant in response to sunlight. Thus the correct answer is option D.

Ethylene is a volatile compound and the only gaseous plant growth hormone which is mainly found in ripening fruits, flowers and leaves. Its unsaturated nature and small structure make it a volatile compound. It is responsible for fruit ripening and induction of leaf senescence. This makes option B correct. Auxins are growth hormones that stimulate growth by cell division and cell elongation. They are synthesized in shoot and root tip and are also used as weedicide that selectively acts against certain weeds. Auxins includes IAA, IBA and 2,4-D which are complex compounds and are not gaseous. Cytokinins stimulate cell division, even in non-meristematic cells, in presence of auxin. They are most abundant in the growing tissues which are active site of cell division, for example: root, embryos, fruits etc. They are substituted adenosine compounds and are not gaseous. Gibberellins are hormones of bolting (stem elongation) and reversal dwarfism by increasing the internodal length. They are tetra carbocyclic compounds with characteristic gibbane skeleton having four rings of carbon and hence are not gaseous hormones. Thus, the correct answer is option B.

Fruit ripening is controlled by hormone, ethylene. Ethylene is a gaseous hormone. It affects the growth, development, ripening and senescence (aging) of all plants.

Cytokinins stimulate cell division, even in non-meristematic cells, in presence of auxin. They are most abundant in the growing tissues which are active site of cell division, for example: root, embryos, fruits etc. Cytokinins delay senescence of leaves via their effect on translocation of metabolites and by reducing breakdown of proteins and chlorophyll (the Richmond-Lang effect). Option A is correct. Cytokinins treated leaves withdraw their nutrients from adjacent leaves and maintain their viability. Option C is incorrect as gibberellins (GA) cause cell elongation. Treatment with gibberellins causes bolting (stem elongation) and reverses dwarfism by increasing the intermodal length. Exogenous application of gibberellins prevents senescence in leaves and fruits. Auxin serves as inhibitor of leaf senescence by inhibiting synthesis of abscission layer at the base of petiole or pedicel which in turn causes leaf shedding. Option B is incorrect as auxin is the hormone of cell division and cell expansion both. CoA is a coenzyme which is involved in many metabolic activities like synthesis and oxidation of fatty acid. This makes option D incorrect as CoA is not a plant growth hormone