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 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.
Photosynthesis is a process of formation of glucose from simple inorganic substances like CO2 and H2O. There are two types of photosynthetic reaction found in nature; Dark Reaction and Light reaction.
Many external and internal factors affect the rate of photosynthesis. Some external factors are light, CO2, temperature, water, leaf anatomy and oxygen while internal factors are chlorophyll content and protoplasmic factor. Importance of factors can be demonstrated with the help of experiments.
Pigments are molecule that absorb certain wave length of light and reflect all others,. There are two types of pigments; main pigments and accessory pigments.
Chemiosmotic hypothesis was proposed by Peter Mitchell in 1961 to describe ATP synthesis by way of a proton electro-chemical coupling.
Photorespiration is a biochemical process in plants especially under conditions of water stress and oxygen. RuBisCo is the most abundant enzyme which fixes CO2 during the Calvin cycle.
Melvin Calvin proposed the C3 pathway and showed that the pathway operated in a cyclic manner; RuBP was regenerated. C4 pathway was worked out by Hatch and Slack where Kranz anatomy is found.
In plants photosynthesis results in the production of ATP and NADPH by two step process is called non- cyclic photophosphorylation.The photophosphorylation occuring in a cyclic electgron transport called cyclic photophosphorylation.
The entire process of photosynthesis takes place in chloroplast.Photosynthesis comprises of two phases; Photochemical phase or light reaction or light dependent process and second phase is the biosynthetic phase or dark reaction of photosynthesis.