Metabolism encompasses all chemical reactions in a cell, producing energy for vital processes and synthesizing new organic materials. It is divided into two main types: anabolism and catabolism. Anabolism consists of constructive reactions that build complex molecules from simpler ones, requiring energy (e.g., protein, nucleic acid, and polysaccharide synthesis). Conversely, catabolism involves destructive reactions that break down complex molecules into simpler ones, releasing energy (e.g., the breakdown of proteins, fatty acids, and glucose). Photosynthesis, a crucial process for plants, involves a series of reactions using light energy to convert CO2 and water into glucose and oxygen, primarily occurring in the leaves. This process provides food for plants and energy, raw materials, and oxygen for heterotrophs. Photosynthesis includes light-dependent reactions in the thylakoids, producing ATP and NADPH, and light-independent reactions in the stroma, using ATP and NADPH to synthesize glucose. Leaf structure is key to photosynthesis, with the external epidermis secreting a waxy cuticle for protection and stomata, controlled by guard cells, allowing gas exchange. Internally, the mesophyll contains palisade mesophyll cells, rich in chloroplasts for photosynthesis, and spongy mesophyll cells with air spaces for gas exchange. Chloroplasts have a structure that includes the stroma, a fluid-filled matrix for light-independent reactions, and grana, stacks of thylakoids where light-dependent reactions occur. Photosynthetic pigments, such as chlorophylls (a and b), carotenoids, and phycobilins, play vital roles in absorbing light for photosynthesis. Chlorophyll a absorbs violet-blue and reddish-orange light, chlorophyll b absorbs blue and yellow light, and carotenoids absorb blue-green light, transferring energy to chlorophyll.