ZIMSEC O Level Integrated Science Notes: The structure of the leaf and photosynthesis
- The leaves are the main organs of photosynthesis.
- Their structure is adopted for the process of photosynthesis.
- Veins-vein networks support the physical structure of the leaf and transport substances to (water etc) and from (soluble carbohydrates from the leaf) the cells in the leaf.
- A large surface area-Most leaves are broad and so have a large surface area allowing them to absorb more light.
- A thin shape-means there a short distance for carbon dioxide to diffuse in and oxygen to diffuse out much more easily.
- Chlorophyll-this chemical is what gives the leaves their green colour and converts light energy to chemical energy.
- Stomata- are small holes on the underside of the leaf that allow gases to diffuse in and out.
The internal structure of the leaf.
- Cuticle- The cuticle is a waxy, waterproof layer reduces the water lost by evaporation and protects against parasitic fungi.
- Upper Epidermis-A single layer of cells that are transparent and contain no chloroplast allowing light to pass straight through.
- Palisade Layer-This layer is made up of palisade cells which contain chloroplasts. This is where most of the photosynthesis takes place.
- Vein– The vein contains tubes called the xylem and phloem. The xylem brings water and salts to the leaf for photosynthesis. The phloem transports the dissolved foods away.
- Spongy Layer-This layer consists of irregularly shaped cells with large air spaces between them allowing gas exchange (diffusion) between stomata and photosynthesising cells.
- Lower Epidermis-This layer contains lots of tiny holes or pores called stomata at regular intervals. These allow gases to diffuse in and out of the leaf.
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