1. 23.4 Leaves

2. Blade Thin, flattened section of a plant leaf that collects sunlight

3. Petiole Thin stalk by which a leaf blade is attached to a stem

4. Mesophyll Specialized ground tissue that makes up the bulk of most leaves; performs most of a plant’s photosynthesis

5. Palisade Mesophyll Layer of tall, column-shaped mesophyll cells just under the upper epidermis of a leaf.

6. Spongy Mesophyll Loose tissue beneath the palisade layer of a leaf

7. Stoma Opening in the underside of a leaf that allows carbon dioxide and oxygen to diffuse into and out of the leaf

8. Guard Cell Specialized cell in the epidermis of plants that controls the opening and closing of stomata by responding to changes in water pressure

9. Transpiration Loss of water from a plant through its leaves

10. Key Concept The structure of a leaf is optimized for absorbing light and carrying out photosynthesis.

11. Key Concept Plants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water.