In grasses, certain adaxial epidermal cells along the veins modify themselves into large empty, colourless cells calleda)Guard cellsb)Subsidiary cellsc)Companion cellsd)Bulliform cellsCorrect answer is option 'D'. Can you explain this answer?

Question

Accepted Answer

In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty, colourless cells. These are called bulliform cells or motor cells. Bulliform cells help in folding and unfolding of grass leaves.

When the bulliform cells in the leaves have absorbed water and are turgid, the leaf surface is exposed. When they are flaccid due to water stress, they make the leaves curl inwards (inrolling) to minimise water loss (transpiration).

Answer

Given in ncert

Answer

Adaxial Epidermal Cells in Grasses

In grasses, certain adaxial (upper) epidermal cells along the veins undergo modification to form specialized cells known as bulliform cells. These cells are large, empty, and colorless, and they play an important role in the adaptation of grasses to environmental conditions.

Function of Bulliform Cells

The main function of bulliform cells is to control leaf rolling or folding in response to changes in environmental conditions, particularly water availability. They are involved in the regulation of leaf surface area, which helps the plant to conserve water during periods of water scarcity or drought.

Mechanism of Leaf Rolling

When water availability is reduced, such as during hot and dry conditions, the bulliform cells lose turgidity and become flaccid. This causes the leaf to roll or fold, reducing the exposed surface area and minimizing water loss through transpiration. On the other hand, when water becomes available, the bulliform cells regain turgidity, allowing the leaf to unroll and maximize the surface area for photosynthesis.

Location and Distribution

Bulliform cells are typically found in the adaxial epidermis along the veins of grass leaves. They are often concentrated towards the base of the leaf blade, where the veins are more prominent. This distribution allows for efficient control of leaf rolling, as the veins provide structural support for the folding or rolling movement.

Adaptation to Water Stress

The presence of bulliform cells in grasses is an adaptation to water stress. By controlling leaf rolling, these cells help to reduce the exposure of the leaf surface to direct sunlight and wind, which can accelerate water loss. This adaptation allows grasses to survive in dry environments and endure prolonged periods of water scarcity.

Conclusion

In grasses, certain adaxial epidermal cells modify themselves into large empty, colorless bulliform cells along the veins. These cells play a crucial role in regulating leaf rolling or folding in response to changes in water availability. By controlling leaf surface area, bulliform cells help grasses conserve water and adapt to water stress, making them well-suited for survival in dry environments.

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