Photosynthesis is a process by which plants and other photoautotrophic organisms can synthesize carbohydrates (glucose) and oxygen using carbon dioxide from the atmosphere through stomata, light energy from the sun, and water. Palisade cells consist of chloroplasts which are the main site of photosynthesis. There are different ways in which chloroplasts are adapted to their function. They have a large surface area which maximises the amount for light to be caught. It takes place in the middle layer, mesophyll of the leaves (like in the palisade mesophyll cells) so that most sunlight is captured. Chloroplasts are double membrane organelles, which have their own circular DNA and 70S ribosomes. They have their own ribosomes for making proteins. They have chlorophyll pigments that are arranged in photosystems embedded in the thylakoid, for maximum light absorption. Many thylakoids, when stacked together, form a granum. The granum is connected with another one using lamella. The aqueous part of the chloroplast is called stroma where all enzymes and reactants are present for the Calvin cycle, with a suitable pH. They also have small lipid droplets that can be used for the formation of phospholipid bilayer of the inner and outer membrane of the chloroplast.
The light dependent stage involves the capturing of light energy by chlorophyll pigments that are arranged in two photosystems (PSI and PSII) which are found in the thylakoid. Mainly red and blue wavelengths of the visible spectrum are absorbed, reflecting green wavelength which makes the plants look green. Many thylakoids are stacked together to form a granum which is then connected by lamellae. The light energy is used to excite the electrons in the photosystems which then pass along the electron transport chain in the thylakoid membrane. Then, this light energy is converted into chemical energy in the form of NADPH and ATP.
Then, the light independent stage happens outside the thylakoid membrane which is the stroma of the chloroplast that consists of many enzymes. The newly formed NADPH and ATP enter the stroma along with the carbon dioxide that diffuses in the plant through stomata. The carbon fixation happens in the Calvin Cycle that produces glyceraldehyde-3-phosphate (a 3-carbon sugar) which is further used to make different sugars like glucose, starch and cellulose. Hence, stroma is adapted to this function by having numerous enzymes.
