Question

The large empty colourless cells seen on the upper epidermis in grasses which facilitate the curling of leaves to minimise water loss are ________

• A. Guard cells
• B. Bulliform cells
• C. Subsidiary cells
• D. Mesophyll cells

Hint:

"Bull" means bubble. Bulliform cells act like water-filled bubbles. When they pop/deflate (lose water), the leaf curls up to save itself.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept: Monocot leaves (like grasses) have evolved specialized anatomical adaptations in their epidermis to cope with severe water stress.
Step 2: Key Formula or Approach: Match the morphological description and physiological function provided in the question to the correct specialized cell type.
Step 3: Detailed Explanation: In grasses, certain adaxial (upper) epidermal cells along the veins modify themselves into large, empty, bubble-like, and colorless cells.
These specialized cells are known as bulliform cells (or motor cells).
When they are turgid (filled with water), they keep the leaf surface exposed to light.
However, when they become flaccid due to water stress, they collapse, which mechanically forces the leaf to curl inwards. This curling reduces the effective surface area exposed to the sun and significantly minimizes water loss via transpiration.
Guard cells regulate stomatal opening, subsidiary cells support guard cells, and mesophyll cells conduct photosynthesis.
Step 4: Final Answer: The correct option is (2).