Hawaii Grade 7 Science

Correct a model that makes food matter disappear

Revise an original model of food use in an animal, distinguish rearranged matter from energy transfer, and check a Hawaiʻi middle-school reference.

The Hawaiʻi science standards directory identifies NGSS as the science standards and links the standards publisher. Use the Publisher NGSS document for the selected performance expectations and their examples and boundaries. NGSS middle-school expectations use a Grades 6–8 band. The activity here is a suggested study focus; consult the school’s plan for its local grade placement.

Does using food energy mean food matter becomes nothing?

A student draws a model for an active animal: “food goes into cells → food disappears → energy makes movement.” Revise it to show that chemical processes rearrange matter into new molecules while transferring energy. Use a simple aerobic-respiration example without writing a reaction equation. The task concerns the model’s explanation, not a measurement of any particular animal’s energy use.

Explain the evidence or model

In a simplified aerobic model, cells use molecules from food with oxygen and form different molecules, including carbon dioxide and water. Matter has been rearranged rather than erased. Energy transferred through these processes can support cell activities involved in movement, and some is transferred to the surroundings as heat. The revised model therefore needs a matter pathway with new molecules and a separate explanation of energy transfer. An arrow labeled “food disappears” hides both processes instead of explaining them.

What to check in the explanation

Matter should not be labeled as if it simply turns into movement or energy. Also, an animal at rest still has cell activities that require energy, so movement is not the only use. This example selects one simplified process; it does not describe every chemical pathway in living things. The middle-school assessment boundary excludes detailed reaction mechanisms for photosynthesis and respiration. Keep the model qualitative and distinguish it from a full biochemical account.

Plan the next activity

1. Find where the original drawing loses track of matter.
2. Add new molecules to the matter pathway and explain the rearrangement.
3. Describe energy transfer separately, including cell activity and heat.

Compare the revised model with a statement that food can also supply material used in growth. Explain how those two ideas can coexist rather than give food only one role. Ask a partner to identify which arrows show matter and which statements describe energy. Use the discussion to improve the model’s labels. This NGSS expectation belongs to the Grades 6–8 band; the school’s current sequence determines where the activity fits.