Photosynthesis

Photosynthesis occurs only in the green parts of the plant. For efficient photosynthesis the leaf should be thin and have a large surface area. This helps in absorption of light and gaseous diffusion, and a means of preventing excessive water loss through stomata and epidermis. Large number of chloroplasts in palisade mesophyll cells provide the main photosynthetic tissue. The spaces between the irregularly shaped spongy mesophyll cells within leaf permit free diffusion of gases. Turgor changes into guard cells permit gaseous exchange with the atmosphere. Cuticle on the single layered transparent upper and lower epidermis protects the leaf from desiccation and infection.

These biconvex organelles, containing many flattened, fluid filled membranous sacs called thylakoids and a gel like stroma are enclosed by the two membranes of the chloroplast envelope. Stacks of circular thylakoids called grana linked together by intergranal lamellae, are formed at intervals throughout the chloroplast.