What is a common characteristic of algae?

Algae are primarily autotrophic organisms, which means they can produce their own food through the process of photosynthesis, primarily using chlorophyll to harness sunlight. This characteristic distinguishes them from heterotrophs that must consume other organisms for energy.

Regarding the option that mentions algae can kill fish in ponds, while certain types of algae, particularly harmful algal blooms, can release toxins that are harmful to aquatic life, this is not a defining characteristic of algae as a whole. Most algae, especially those that are more common and abundant, do not exhibit this behavior.

The characteristics reflected in the other choices—heterotrophy, lack of chlorophyll, and being a type of reptile—do not align with the biological classification of algae. Algae are not reptiles, they possess chlorophyll, and they are largely autotrophic instead of heterotrophic. Therefore, the statement related to their impact on aquatic ecosystems is specific but not universally applicable to all algae.