The use of oxygen-18 (heavy oxygen) has aided biologists in determining that o2 released in photosynthesis comes from the chemical breakdown of water. which organisms did the biologists most likely use in their investigation? a algae b paramecium c arthropods d fungi

The correct option is A. Algae

Explanation:

Algae is the best possible answer because the process of photosynthesis can be carried out only by plants, algae and cyanobacteria.  Hence, option A is correct. These organisms are called autotrophs as they are capable of making their own food.

Other organisms like paramecium, arthropods and fungi are not capable of photosynthesis. These organisms like arthropods are called heterotrophs. They do not make their own food and feed on other organisms for food.