CBSE Questions for Class 11 Medical Biology Plant Growth And Development Quiz 8 - MCQExams.com

A.Correct option B

B.Explanation for correct option:

Cytokinins are a group of plant growth regulators which are primarily involved in performing the function of cell division in plant roots, shoot system. This hormone helps in promoting the cell's growth, development, differentiation, affecting apical dominance and delay in leaf senescence.

• The term ‘auxin’ is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth-regulating properties.
• They are mostly produced by the growing apices of the shoot and roots, from where they migrate to the regions of their action.
• They help to initiate rooting in stem cuttings, an application widely used for plant propagation.
• Hence Most of the plant's auxin is produced in its shoot apex.
• So, the correct answer is 'Shoot apex'.

• 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. 

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

$$\textbf{ Solution: }$$

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

$$\bullet$$Ethylene is a phytohormone that regulates both growth, and senescence.

$$\bullet$$ It promotes or inhibits growth and senescence processes in the plants. 

ethylene inhibits lateral buds and causes apical dominance.

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

$$\bullet$$ GA stands for Gibberellic acid. 

$$\bullet$$ Gibberellin is one of the plant hormones which promotes the growth and differentiation of the plant. 

$$\bullet$$ It also promotes cell differentiation and cell enlargement in the presence of auxin.

$$\bullet$$ Gibberellin break seed dormancy by promoting mobilisation of reserve food material

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

$$\bullet$$Pruning is cutting off the apical portion of branches to induce growth which in turn lowers the amount of auxin synthesized as shoot apex. 

$$\bullet$$The lowered auxin synthesis allows translocation of cytokinins to lateral bud stimulating cell division and growth of lateral branches.

$$\bullet$$ Cytokinins are the plant hormone that promotes the growth of the plant.

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

$$\bullet$$ Auxins are present at the tip region of the plant stem and promote the growth of the plant. 

$$\bullet$$ The tip of the plant stem is made up of meristematic tissue which is responsible for secretion and storage of auxin hormone.

$$\bullet$$IAA stands for  Indole-3-acetic acid which belongs to auxin class.

Hence, the correct option is (c).

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

$$\textbf{ Solution: }$$ 

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

$$\bullet$$ Cortex is the tissue of unspecialized cells lying between the epidermis and the vascular conducting tissues of stems and roots.

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

$$\bullet$$ Xylem conducts water and dissolved minerals from the roots to the rest of the plant.

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

$$\bullet$$ Phloem is the conducting tissue of the plants of material such as minerals and nutrients throughout the plants.  

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

$$\bullet$$ The bending of the stem of plants towards light is promoted by auxin which is a plant growth hormone. 

$$\bullet$$ Auxin is produced by the cells present on the tip of the stems and roots. 

$$\bullet$$ Auxin controls a plant’s response towards light and gravity as a stimulus. 

$$\bullet$$ Therefore, Auxin moves away from light, and towards gravity. 

Hence, the correct option is (d)