#4

CYK Lesson 38

#4 Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues.

The main part of the leaf is the leaf blade or lamina. It ha a big surface area that absorbs sunlight, but it is very thin. Within the lamina is four tissues that make up the leaf. The palisade mesophyll consists of many chloroplasts. This is the main photosynthetic tissue and it is near the surface where light intensity is highest. This helps the process of photosynthesis because photosynthesis requires large amounts of sunlight. The upper epidermis is a layer of cells covered by a thick waxy cuticle. This part of the leaf prevents water loss from the upper surface. The xylem brings water to replace losses due to respiration. The phloem transports products from photosynthesis out of the leaf. Guard cells open and close the stoma and they control the amount of transpration. The stoma is a pore that allows carbon dioxide for photosynthesis to diffuse in and out to diffuse out. The spoongy mesophyll provides the main gas exchange surface.