SME
Grade 5 Science · Life Science
Plants use sunlight to make food
Use this for “The plant gained 80 g, but the soil lost only 2 g. Where did the rest come from?”
Diagram
The plant gain is 78 more than the soil lost.
This is an example. Type your own values to start a new problem.
Plant at the start
example
Plant at the end
example
Plant gain
worked out (not typed)
Soil at the start
example
Soil at the end
example
Soil lost
worked out (not typed)
Gain not from the soil
calculated
Formulas
85 − 5 = 80
Plant at the end − plant at the start = plant gain
1,000 − 998 = 2
Soil at the start − soil at the end = soil lost
80 − 2 = 78
Plant gain − soil lost = gain not from the soil
Assumptions
•
Weigh the plant and the dried soil at the start and again weeks later.
•
The plant gains far more than the soil loses. Most of its new mass came from water and air.
•
Sunlight gives the energy to turn air and water into the plant’s food.
Step-by-step
WE KNOW
Plant at the start: 5 g
Plant at the end: 85 g
Soil at the start: 1,000 g
Soil at the end: 998 g
FIND
plant gain, soil lost, gain not from the soil
Step 1 · Find plant gain
85 − 5 = ?
Plant at the end − plant at the start = plant gain
The plant at the end minus the plant at the start: what it gained.
Plant gain = 80 g
Step 2 · Find soil lost
1,000 − 998 = ?
Soil at the start − soil at the end = soil lost
The dry soil at the start minus the dry soil at the end: what the soil lost.
Soil lost = 2 g
Step 3 · Find gain not from the soil
80 − 2 = ?
Plant gain − soil lost = gain not from the soil
Even if all the lost soil went into the plant, the rest came from somewhere else.
Gain not from the soil = 78 g
Check
Put the numbers back in. Both sides should match.
85 − 5 = 80 ✓
1,000 − 998 = 2 ✓
80 − 2 = 78 ✓
Topic check
See what you know: 5 questions on this topic
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