CBSE Questions for Class 11 Medical Biology Plant Growth And Development Quiz 9 - MCQExams.com

• Differentiation is the ability of the cells to be specialized and perform specific functions. 
• The zygote is formed by the fusion of male and female gametes. The zygote undergoes division and forms a group of undifferentiated and unspecialized cells.
• These cells further divide and differentiate to form specialized organs. 
  
  

• Differentiation occurs in both external and internal features. The formation of two polar axis, i.e., differentiation of roots and shoots is the best example of external differentiation. 
• This differentiation occurs very early during embryonic development. The other example is the differentiation of the vegetative and reproductive phases.

• Cytokinins are plant growth hormones. They are amino derivatives. These hormones promote cell division in plants.
• They also slow down the process of senescence. When the leaves are treated with cytokinins, these allow the mesophyll cells to produce more nutrients.
• Hence, perishable vegetables are sprayed with a solution of cytokinin to keep them fresh for a longer time and increase their shelf life. They also prevent chlorophyll degradation.

$$\textbf{Correct option: }$$ B

$$\textbf{ Solution: }$$ 

$$\textbf{ Option (A): }$$

$$\bullet$$NAA stands for Naphthaleneacetic acid that is a synthetic plant hormone in the auxin family. 

$$\bullet$$it is used in vegetative propagation of plants from stem and leaf cuttings. 

$$\bullet$$It also plays a functional role in plant tissue culture.

$$\textbf{ Option (B): }$$

$$\bullet$$ Zeatin is a type of cytokinin which is the plant hormone that promotes the growth of the plant.

$$\bullet$$ Cytokinins promote the ageing of leaves and also help in breaking the dormancy of seeds and buds.

$$\textbf{ Option (C): }$$

$$\bullet$$ The compound 2,4-dichlorophenoxyacetic acid  is a synthetic auxin. 

$$\bullet$$ It is a kind of herbicide that is used to kill any dicot plant tissue.

$$\textbf{ Option (D): }$$

$$\bullet$$ 6-Benzyladenine, also called 6-benzylaminopurine, is a synthetic cytokinin. 

$$\bullet$$ This hormone stimulates the cell division in plants. 

Hence, the correct option is (B) 

• Redifferentiation is the process in which the dedifferentiated cells lose their ability to divide.
• A differentiated cell can regain its capacity for cell division under certain conditions. This phenomenon is called dedifferentiation.
• Vernalization is the artificial exposure of plants (or seeds) to low temperatures in order to stimulate flowering or to enhance seed production.
  

• ABA is an abscisic acid or stress hormone that induces dormancy in buds, promotes abscission of flowers and fruits, decreases transpiration losses, stops protein and RNA synthesis in leaves, promoted rooting in stem cutting promotes development, and maturation of seed, and inhibit seed germination, etc. 

• Naturally occurring plant hormones can be grouped into five classes of compounds: auxins, gibberellins, cytokinins, abscisic acid, and ethylene.
  
• GA$$_2$$ is a type of gibberellins while IAA (Indole acetic acid) is the type of auxin.
  
• 2,4-D is a widely used herbicide that controls broadleaf weeds.

• Abscisic acid (ABA) promotes seed and bud dormancy by inhibiting growth. It is one of the most important plant's growth regulators. ABA also plays an important role in the closure of stomata in plants under water stress and its presence inhibits opening.
• Seed dormancy is defined as a state in which seeds are prevented from germinating even under environmental conditions normally favorable for germination.
• Bud dormancy is a process in which plant meristems become mostly inactive to withstand a harsh environment.
  

In maize seed, which is moncot and endospermic seed. The embryo consists of an upper shield shaped scutellum which is actually a reduced cotyledon.  It secretes certain hormones (ABA and gibberellin) into the endosperm which synthesize enzyme responsible for the breakdown of reserve food materials into soluble forms.

A. Auxin- Responsible for shoot elongation.

B. Cytokinin- promotes cell division.

C. Gibberellin- Stimulate cell elongation,

D. Ethylene- Stimulate and regulate rioening of fruit.

So, the correct answer is 'Giberrellin'.