Biomass, more specifically phytobiomass, can be defined as all materials, molecules, or structures produce by photosynthesis, using carbon dioxide (CO2) and water (H2O) as substrates, processed using solar light as the energy source, producing all the diversity of molecules that compose plants, including forest trees, fruit trees, cereals, vegetables, grains, flowers, planktons, micro- and macroalgae, and all organisms that contain chlorophyll. This chapter brings basic informations to provide a brief description of the photosynthesis process, the main energy molecule that is accumulated by these organisms, the structural molecules of the lignocellulosic vegetal structure, and its composition, along with the importance of the photosynthesis process that changes light energy into chemical energy and stores it at the chemical linkage C–C in the synthetized molecules that form the chlorophyll organisms available to be used by other organisms, including human beings, at its own metabolisms, metabolic energy of vital importance to the survival of life on Earth. Besides, as phytobiomass structural molecules are basically composed of carbonaceous matter, the photosynthetic process throught phytobiomass synthesis contributes to preserving atmospheric quality in terms of its characteristic composition, which is essential for human breathing. This occurs due to the carbon from CO2 storage capacity of phytobiomass. Thus, CO2 is removed from the atmosphere and incorporated into its structure.