Correct Option
The correct option is (c) 1 and 3 only.
Explanation
Guard cells are specialized plant cells located in the epidermis of leaves, stems, and other organs. They surround the stomatal pores and are primarily responsible for regulating gas exchange and transpiration.
Statement-wise Analysis
- Statement 1 is Correct: Guard cells are typically kidney-shaped (or bean-shaped) in dicotyledonous plants. They are arranged in pairs and enclose the stomatal pore. While they are dumbbell-shaped in monocots (like grasses), the general description of guard cells as kidney-shaped enclosing the stomata is factually accepted in this context.
- Statement 2 is Incorrect: Guard cells play a critical role in the opening and closing of stomata. The mechanism depends on the turgor pressure within these cells. When water flows into the guard cells, they become turgid and the stomatal pore opens. Conversely, when they lose water and become flaccid, the pore closes.
- Statement 3 is Correct: The epidermal tissue system forms the outer protective covering of the plant body. It comprises epidermal cells, stomata, and epidermal appendages (trichomes and hairs). Guard cells are modified epidermal cells and are an integral part of this tissue system.
Key Takeaway: Guard cells are specialized epidermal cells that regulate the opening and closing of stomata through changes in turgor pressure, facilitating gas exchange and transpiration.