IGCSE Biology 0610
6.2 Leaf structure
Most leaves have a large surface area and are thin
Large surface area → To absorb light rays
Thin → So that gases can diffuse in and out easily
Adaptations of Plant Structures for Photosynthesis
| Chloroplasts | Many of them found in palisade mesophyll to absorb light for the reactions in photosynthesis. |
| Cuticle | Waterproof layer that reduces water evaporation. |
| Guard cells | Control opening and closing of stomata. In the day, water enters guard cells through osmosis, guard cells bend and stomata open. At night, water passes out of guard cells by osmosis and stomata close. |
| Stomata (Singular: stoma) | Small pores in epidermis that allow gases to diffuse in and out. Carbon dioxide diffuses in, water vapour and oxygen diffuses out. |
| Upper epidermis | Single layer of cells with no chloroplasts. Light goes straight through. |
| Lower epidermis | No thick cuticle, has lots of stomata |
| Palisade mesophyll | Contain many chloroplasts. Packed tightly near upper surface to maximise light absorption. |
| Spongy mesophyll | Rounded cells with many air spaces in between them for easy diffusion of carbon dioxide to mesophyll cells. Air diffusion is fast. |
| Vascular bundles | Contain xylem and phloem to transport substances. The thick cell walls of the tissue in vascular bundle also help support stems and leaves. In vascular bundles, xylem are inside and phloem are outside. |
| Xylem | Bring water and ions to mesophyll cells. |
| Phloem | Transport sucrose produced in photosynthesis to other parts of plant. |