Photosynthesis and chemosynthesis are similar in that they both provide for the process by which plants produce food and fuel for growth. However, they differ in terms of how they provide for this process. Photosynthesis accomplishes this process through sunlight, while chemosynthesis accomplishes it through chemical energy.
The process of converting inorganic compounds into fuel for food or energy is the basis of all plant life and, consequently, animal life. Depending on the environment in which the plant or bacteria inhabits, the plant or bacteria will either depend on photosynthesis or chemosynthesis.
Photosynthesis utilizes sunlight in order to process carbon dioxide and water into oxygen and sugar. Plants and bacteria depending on photosynthesis can be found on land, in shallow bodies of water and even just below layers of ice.
At deeper levels beneath the surface of water, such as the bottom of the ocean, plant life and bacteria cannot rely on photosynthesis from the sun, as the sun's rays do not reach the darker, lower levels of the ocean and larger bodies of water. Inorganic chemical reactions release energy. Plant life and bacteria can utilize the process of chemosynthesis to process that released energy into sugar. Reducing sulfide or oxidizing methane can also be evidence of the chemosynthesis process. Aside from the ocean floor and deep bodies of water, chemosynthesis can also be seen with bacteria in hot springs, which are found on land.