What happens to the CO2 once it is absorbed by the organisms in the ocean's surface? Where does it go? The answer is quite complicated: this little molecule is involved in many biological, chemical, and physical reactions, in what we call the ocean carbon cycle. In this article, we will focus on a portion of that cycle connected by animals. During photosynthesis, the phytoplankton transforms CO2 into organic molecules. Organic molecules are substances made of carbon atoms joined together in rings or chains, and other elements, such as hydrogen, oxygen, and nitrogen. For example, amino acids are organic molecules. These molecules are either used by phytoplankton to grow or are eventually released into seawater as waste products. Larger marine organisms eat phytoplankton, and the larger animals are, in turn, eaten by even bigger animals. This way, the organic carbon molecules produced by phytoplankton provide food and energy to all other organisms that make up marine food webs.

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