Explain photosynthesis as a process that rearranges matter, carbon dioxide and water into sugar and oxygen, while storing light energy as chemical energy.
Photosynthesis is how plants build their own food using light. Inside chloroplasts, plant cells combine carbon dioxide, taken in mostly through the leaves, and water, taken up through the roots, using energy captured from sunlight, to build a sugar called glucose, releasing oxygen as a byproduct. Written as a word equation: carbon dioxide plus water plus light energy yields glucose plus oxygen.
Notice what is happening to matter and to energy separately, since they follow different rules. The atoms from carbon dioxide and water are not destroyed; they are simply rearranged into new molecules, glucose and oxygen, which is why matter is conserved, just like the mixing and dissolving studied in earlier grades. Energy, meanwhile, is not created either; light energy from the sun is converted into chemical energy, stored in the bonds holding the glucose molecule together, ready to be released later when the plant, or something that eats the plant, needs it.
Mastery looks like: They can state the photosynthesis word equation and correctly explain it as matter rearranging, conserved, while energy converts from light into stored chemical energy.
Common stumbles: Thinking a plant "eats" soil or dirt for food instead of building its own sugar from carbon dioxide, water, and light; forgetting that oxygen is a released byproduct, not an input.