ZIMSEC O Level Combined 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.
To access more topics go to the Combined Science Notes page.