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 Problem:
Grasses (isobilateral monocot leaves) possess specialized epidermal structures to adapt to water stress environments.
Step 2: Approach and Formula:
Identify the specific motor cells in the epidermis that control the physical folding/rolling mechanism of grass leaves based on turgor pressure.
Step 3: Detailed Explanation:
- In the leaves of grasses, certain adaxial (upper) epidermal cells along the veins modify themselves into large, empty, colourless cells.
- These specialized structures are called Bulliform cells (or motor cells).
- When these cells are completely turgid (full of water), the leaf surface is fully exposed to light.
- When the plant faces severe water stress, these cells become rapidly flaccid due to water loss. This physical deflation causes the leaf margins to curl inwards (roll up), drastically reducing the exposed surface area and thereby minimizing further water loss via transpiration.
- Guard cells and subsidiary cells manage stomatal pores, while mesophyll cells are photosynthetic.
Step 4: Final Answer:
These are Bulliform cells.