SITE OF PHOTOSYNTHESIS

Site of photosynthesis

·         All green parts of the plant are involved in photosynthesis. Leaves are the most important organ of photosynthesis. In xerophytes like opuntia, the stem is green and perform photosynthesis. Over half a million chloroplast are present in 1 sq.mm of a leaf. It measures about 4-6 µ.

·         Photosynthesis occur 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 the absorption of light and gaseous diffusion, it also provide 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 space between irregularly shaped spongy mesophyll cells within leaf permit free diffusion of gases. Turgor changes into guard cells permit gaseous exchange within the atmosphere. Cuticle on the single layered transparent upper and lower epidermis protects the leaf from desiccation and infection.

·         Though all green parts of the plant are capable of performing photosynthesis, the leaves are the most suitable organ of the process.  The cells of the leaves contain special organelle called as chloroplasts, which are the main site of photosynthesis. These are the plastids which contain light absorbing green pigments chlorophyll.

CHLOROPLAST:

·         Chloroplast is the site of photosynthesis. A typical chloroplast of higher plants is discoid shaped. It is a double membrane bound organelle containing chlorophyll,  carotenoid, xanthophyll, cytochrome, DNA, RNA, Mn   etc.

·         These biconvex organelle, containing mark flattened, fluid filled membrane sacs called thylakoids and gel like stroma and enclosed by the two membrane of the chloroplast envelope. Stacks of circular thylakoids called grana linked together by inter-granal lamellae are formed at interval throughout the chloroplast.

·         Chloroplast is an organelle i.e. thought to have been acquired by plants through the process of endosymbiosis because much like mitochondria. This organelle has its own DNA, genes and can make its proteins. Essentially, the chloroplast is an independent fully functional organelle. Although all the green parts of a plant can carry out photosynthesis, it mainly occur in the leaves due to the high abundance of chloroplast.

·         The chloroplast contains three main pigments that absorb light energy like chlorophyll a, chlorophyll b and carotenoids. Chlorophyll pigment most abundantly found in thylakoids of chloroplast.

·         The primary function of leaves is to absorb the sunlight that powers photosynthesis. As a consequences, leaves tend to be broad and flat in order to maximize the surface area exposed to sunlight. In leaves, there are several layers of mesophyll cells.

·         The passage of gases into and out of the leaf is controlled by the pores called stomata, located mostly on the underside of the leaf. This is facilitated through guard cells around the stomata.

·         During the day ,sunlight is full and leaf cause the guard cell to engorge with water.  This forces them to bow apart, opening the stomata and permitting gas to flow through them. Conversely, when sunlight is reduced the stomata gets closed because water flows out of the guard cells returning them to their unbowed shape.

·         All green parts of a plant i.e. green stems and unripened fruits have chloroplast, but the leaves are the major site of photosynthesis in most plants.

·         There are about half a million chloroplasts in 1 sq mm of leaf surface area. Light energy is absorbed by chlorophyll pigment that convert derives the synthesis of food molecule in the chloroplast.

·         Chloroplasts are found mainly in the cells of mesophyll. In the tissue of the leaf CO2 enters and O2 exits out, by the way of microscopic pores called stomata.

·         Water is absorbed by the roots and is delivered  to the veins in leaves. Leaves also use veins to export sugar to roots and other non-photosynthetic parts of the plant.

We have identified that chloroplasts are the site of photosynthesis in plants to convert the light energy into chemical energy by the process of photosynthesis.

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