Tracer Experiments Reveal Photosynthesis Atoms

Use the tracer sheet to connect chemistry to living things, then use the nitrogen cycle as a labeling review. Ask students to say where an atom is after each step.

Follow oxygen-18 through the 1941 algae experiments to find where photosynthesis oxygen comes from. The directions on the page read: Read the text and study the setups and equations. Then answer the questions on page 2. An answer key is included.

Yes, both. We made it for 8th grade ecosystems, and it works the same at home or at school. At home, a student can work through it alone and then go over it with you, which shows quickly what is solid and what needs another look. In class it works as independent practice, homework or a warm-up, and you can print one copy or a full set.

It comes from water. In 1941, Samuel Ruben, Martin Kamen and coworkers gave algae water or carbon dioxide marked with oxygen-18 and tested the oxygen gas. The tracer sheet has students compare the two setups.

Nitrogen-fixing bacteria and lightning turn nitrogen gas into forms that plants can take up through their roots. Animals get nitrogen by eating plants, and decomposers return it to the soil. Label the Nitrogen Cycle in a Prairie maps these steps.

A tracer is a form of an atom that acts the same in reactions but can be told apart, such as oxygen-18, which is slightly heavier than oxygen-16. A machine that sorts atoms by mass shows where it ends up. That lets scientists follow atoms through a reaction.