In an uncovered storage tank, which organism is likely to grow?

In an uncovered storage tank, algae are likely to grow because they thrive in environments where light is available. Algae require sunlight to perform photosynthesis, which allows them to convert carbon dioxide and nutrients into organic compounds, promoting growth. The open exposure to sunlight in an uncovered tank creates ideal conditions for algae proliferation, particularly in stagnant water where nutrients may be present.

The other organisms mentioned, while they can be associated with water systems, generally require different conditions for growth. For instance, bacteria can grow in such environments but do not specifically thrive solely because of light exposure. Legionella, known for its association with water systems, typically arises in warm, stagnant water but does not necessarily depend on sunlight. Protozoa can also exist in water systems but are usually considered indicators of water quality and often come from different sources. In summary, the conditions of an uncovered storage tank primarily favor the growth of algae due to their need for sunlight, making this the most appropriate answer.