CBSE Questions for Class 11 Medical Biology Plant Growth And Development Quiz 14 - MCQExams.com

• Ethylene is a gaseous hormone. It aids in the ripening of climacteric fruits and the dehiscence of dry fruits. 
• Climacteric fruits are fleshy fruits that show a sudden sharp rise of respiration rate at the time of ripening (respiratory climacteric). 
• They are usually transported in the green or unripe stage. Ethylene is used to induce artificial ripening of these fruits e.g., Apple, Mango, Banana, etc.
• So, the correct answer is option B.

Ethylene inhibits longitudinal growth but stimulates transverse or horizontal growth and swelling of axis. It decreases the sensitivity to gravity. Roots become Apo-geotropic while stems turn positively geotropic. Leaves and flowers undergo drooping. The phenomenon is called epinasty. Seedlings develop tight epicotyl hook. It hastens the senescence of leaves and flowers.Abscission of various parts (leaves, flowers, fruits) is stimulated by ethylene which induces the formation of hydrolases. It breaks the dormancy of buds, seeds and storage organs. Rhizomes, corms, tubers, seeds (e.g., Peanut) and other storage organs can be made to sprout early by exposing them to ethylene. Initiates germination in peanut seeds. 

So, the correct answer is 'Ethylene'

• Gibberellins or gibberellic acids are plant hormones which help in stem elongation, breaking dormancy, germination, flowering, development of flower and senescence leaf and fruit.
• These are the longest-known classes of plant hormone.
• About 126 GAs have been identified from plants, fungi, and bacteria.
  
• The gibberellins are named based on GAn in order of discovery. 
• The first gibberellic acid to be structurally characterized was GA$$_3$$ and the first one to be discovered was GA$$_1$$.
  
• So, the correct answer is 'GA1'.

$$\textbf{Correct option:B}$$ 

$$\textbf{Solution:}$$

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

$$\bullet$$Indole 3 acetic acid is the natural auxin which is weakly acidic in nature and promotes apical dominance,root formation , callus formation in tissue culture,xylem differentiation, producing female flowers,induces synthesis of ethylene , enhances metabolism etc.

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

$$\bullet$$ Gibberellin stimulates the production of messenger RNAs which helps with seed germination and hydrolytic enzymes like amylases ,lipases etc which solubilise the reserved food of the seed so that it is transferred to the growing embryonal axis. This helps in seed germination.

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

$$\bullet$$ Cytokinin is essential for tissue culture, promotes morphogenesis, keeps the fruit fresh when spread with cytokinin,helps develop resistance to pathogens ,delays senescence to keep plant parts intact etc 

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

$$\bullet$$ Ethylene is a basic  gaseous phytohormone which helps in the ripening of fruits such as banana,mango,apple , tomato, feminizing effect on flowers,storage organs are stimulated to sprout such as rhizomes,corms,tubers,seeds etc.

$$\textbf{Hence, the correct option is (B)}$$

• IAA (Indole acetic acid), IBA ( Indole butyric acid) and NAA (naphthalene acetic acid) these 3 are the type of auxin hormones which is a growth hormone that is using produced at the apical tips of the growing plants.
• They have been widely used in agriculture and horticulture field which is used to promote growth in plants that are grown by cutting methods and also to prevent early ripening of the fruit and dropping of the leaves which retains the nutrients for more time in the plants and allows the fruit to grow bigger in size.
• This is also used in producing parthenocarpic fruits ie the fruits that are formed without fertilization. eg parthenocarpic tomatoes.

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

$$\textbf{ Solution: }$$

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

$$\bullet$$ Abscisic acid (ABA) mainly acts as a plant inhibitor hormone.  It promotes the dormancy of seeds and buds. 

$$\bullet$$ This plant hormone is also responsible for the witting and falling of leaves.

Ethylene is not responsible for the inhibition of plant root growth. 

$$\textbf{ Option (b,c,d): }$$

$$\bullet$$Ethylene promotes senescence and abscission of plant organs, especially of leaves and flowers.

$$\bullet$$This phytohormone is highly effective in fruit ripening.

$$\bullet$$ It enhances the respiration rate during the ripening of the fruits. 

$$\bullet$$Ethylene promotes elongation of the stem in paddy.

$$\bullet$$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.

Hence, the correct option is (a).