Bulliform or motor cells occur in the upper epidermis of monocot leaves.

Explanation:

Bulliform cells are specialized cells found in the upper epidermis of monocot leaves. These cells are responsible for the rolling and unrolling movements of the leaves in response to changes in environmental conditions.

Function of bulliform cells:

1. Leaf rolling: Bulliform cells play a crucial role in leaf rolling. When the environment becomes dry or during periods of water scarcity, these cells lose turgor and shrink, causing the leaf to roll inward. This rolling reduces the exposure of the leaf surface to the external environment, thus reducing water loss through transpiration.

2. Leaf unrolling: When the water availability improves or during periods of high humidity, the bulliform cells regain turgor and expand, causing the leaf to unroll. This unrolling increases the leaf surface area, allowing for better absorption of sunlight and improved gas exchange.

3. Protection against excessive sunlight: By rolling the leaf, bulliform cells also protect the underlying tissues from excessive sunlight. This helps in preventing damage to the photosynthetic machinery and maintains optimal leaf temperature.

4. Regulation of transpiration: The rolling and unrolling movements of monocot leaves controlled by bulliform cells also help in regulating transpiration. When the leaf is rolled, the stomata are enclosed within the rolled portion, reducing water loss. Conversely, when the leaf is unrolled, the stomata are exposed, facilitating gas exchange and transpiration.

Location of bulliform cells:

Bulliform cells are predominantly found in the upper epidermis of monocot leaves. This is because the upper epidermis is more exposed to environmental factors like sunlight and air currents. The presence of bulliform cells in the upper epidermis allows for rapid response to changes in environmental conditions and efficient regulation of leaf movements.

In contrast, dicot leaves typically do not possess bulliform cells in their upper epidermis. Instead, dicot leaves often have other adaptations, such as stomatal closure or leaf curling, to regulate transpiration and protect against water loss.