SME
Grade 9 Science · Problem type
Pyramid of biomass
Use this for “Phytoplankton hold 6 g/m² and zooplankton 18 g/m². How many grams of zooplankton are there for each gram of phytoplankton?”
Diagram
Pyramid of biomass, bottom up: phytoplankton 6 g/m², zooplankton 18 g/m².
This is an example. Type your own values to start a new problem.
k
=
Z
g/m²
÷
P
g/m²
Formulas
k
=
Z
P
3
=
18
6
Assumptions
•
Biomass is the dry mass of living things in one square meter at one time.
•
On land each level usually holds about a tenth of the biomass below it.
•
Phytoplankton divide so fast they are eaten almost as they grow, so zooplankton can outweigh them at one moment; energy over a year still shrinks upward.
Step-by-step
WE KNOW
P = 6 g/m², Z = 18 g/m²
FIND
grams of zooplankton per gram of phytoplankton (k)
Step 1 · Find grams of zooplankton per gram of phytoplankton (k)
Use k = Z ÷ P
Compare the two levels: grams of zooplankton for each gram of phytoplankton. More than 1 is upside down.
k
=
18
6
k
=
3
Check
Put the numbers back in. Both sides should match.
3
=
18
6
✓
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