Which eukaryotic organelle is composed of column-shaped cells that lie just under the epidermis in plant leaves and is primarily responsible for photosynthesis?

• A. Stomata
• B. Guard cells
• C. Spongy mesophyll
• D. Palisade mesophyll

Answer: (D)

Verified step by step guidance

1. Understand the structure of a plant leaf: A plant leaf is composed of several layers, including the epidermis, mesophyll, and vascular tissues. The mesophyll layer is divided into two types: palisade mesophyll and spongy mesophyll.
2. Learn the function of the palisade mesophyll: The palisade mesophyll is composed of column-shaped cells that are tightly packed and located just beneath the upper epidermis of the leaf. These cells contain a high concentration of chloroplasts, making them the primary site for photosynthesis.
3. Differentiate between palisade mesophyll and spongy mesophyll: While the palisade mesophyll is responsible for most of the photosynthesis due to its dense chloroplasts, the spongy mesophyll is located below the palisade layer and has loosely arranged cells with air spaces to facilitate gas exchange.
4. Understand the role of stomata and guard cells: Stomata are small openings on the leaf surface that allow gas exchange, and guard cells control the opening and closing of stomata. These structures are not directly involved in photosynthesis but are essential for its regulation.
5. Conclude that the palisade mesophyll is the correct answer: Based on its location, structure, and function, the palisade mesophyll is the eukaryotic organelle responsible for photosynthesis in plant leaves.