Question

Grass leaves curl inwards during very dry weather. Select the most appropriate reason from the following.

• A. Closure of stomata
• B. Flaccidity of bulliform cells
• C. Shrinkage of air spaces in spongy mesophyll
• D. Tyloses in vessels

Answer 1

The correct option is B

Flaccidity of bulliform cells

The correct option is B.

Explanation of Correct option:

1. Bulliform, also known as motor cells, are present in isobilateral leaves.
2. They are larger than epidermal cells and are hygroscopic, containing large vacuoles which can store a large amount of water.
3. They play an important role in leaves folding and unfolding.
4. When they have enough amount of water, they store the water in vacuoles and become turgid.
5. In dry weather or stress condition and the water is lower, vacuoles releases the water, and bulliform cells become flaccid,
6. The flaccid condition causes folding of leaves which prevents further loss of water.

Explanation of Incorrect option:
Option A:

1. Stomata is defined as a tiny opening present on the epidermis.
2. Most of the stomata are present on the lower epidermis.
3. They play an important role in gaseous exchange and photosynthesis.
4. They consist of a minute pore stoma that is surrounded by guard cells.
5. Stomata open and close due to the turgidity of guard cells caused by the osmotic flow of water.
6. When the guard cell loses water, they become a flaccid, causing water loss but only due to natural conditions.

Option C:

1. Spongy mesophyll is composed of loose-packed irregular shapes that are surrounded by air spaces.
2. Their main function is to store sugar and helps in the exchange of gases.
3. They create air spaces inside leaves to allow the movement of gases inside and out.
4. So they do not perform any role in the curling of leaves.

Option D:

1. Tyloses are swellings that look like a ballon caused due to bulging of the cell wall of adjacent wood parenchyma or medullary ray cell through pit opening into cavity.
2. They are found in many plants formed due to a wound and thus by pruning,
3. They are produced to block the cut vessels, which blocks the further advancement of pathogens.

Final answer: Flaccidity of bulliform cells causes grass leaves to curl inwards during very dry weather.