Carbon, Water & Cycling Matter — Practice · Grade 7 Science

Chapter: Ecosystems, Matter & Energy

What this practice covers

By the end of Carbon, Water & Cycling Matter you should be able to:

8 questions, written answer, multiple choice and numeric, each with a worked explanation.

Vocabulary used: reservoir, transpiration, condensation, runoff, storage change.

Problem 1

Does sunlight supply the carbon atoms in sugar?
Answer and explanation

No. Carbon dioxide supplies carbon matter in the plant model; light supplies energy.

Problem 2

Does a cycle mean no reservoir can change?
Answer and explanation

No. Inputs and outputs can differ over an interval, changing a reservoir’s stored amount.

Problem 3

Does evaporation destroy water molecules in this model?
Answer and explanation

No. It changes state and location while the water remains matter in the larger system.

Problem 4

Why can a pond lose water while matter is conserved?
Answer and explanation

Water can leave its chosen boundary through evaporation, flow, or other transfers and remain elsewhere in the larger system.

Problem 5

Illustrative pond interval: rain adds 40 L; runoff adds 20 L; evaporation removes 25 L; outflow removes 15 L. Other pathways are excluded. Calculate storage change, label inputs and outputs, and explain the conservation distinction.
Answer and explanation

The modeled pond gains 20 L. Rain and runoff are inputs, while evaporation and outflow cross outward. The changing pond amount is consistent with matter conservation because the pond is only one boundary. The result assumes the stated pathways are complete for the interval and does not predict future weather or every real pond exchange.

Inputs: 40+20=60 L.

Outputs: 25+15=40 L.

Change: 60−40=+20 L.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

Why does a carbon reservoir not necessarily return all its carbon to air each day?
Answer and explanation

Pathways have different rates and storage durations. Some carbon remains in tissues, soils, sediments, or other reservoirs over longer periods.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

Which contributes carbon matter to photosynthetic sugar production?
  1. Carbon dioxide
  2. The color of sunlight
  3. Only a thermometer
  4. A graph title
Answer and explanation

Carbon dioxide

Carbon dioxide supplies carbon atoms; light provides energy.

Problem 8

A water store receives 30 L and loses 18 L in one stated interval. Find storage change.
Answer and explanation

12 L

30−18=+12 L under the stated complete budget.

Browse all courses