SME
Grade 9 Science · Problem type
Transpiration rate
Use this for “A leafy shoot in a potometer takes up 4.8 mL of water in 6 hours. What is its rate?”
Diagram
t = 6 h on the top line sits over 4.8 mL on the bottom line: each 1 above is 0.8 below.
This is an example. Type your own values to start a new problem.
W (mL)
=
R (mL/h)
×
t (h)
Formulas
W
=
R
×
t
4.8 = 0.8 × 6
Assumptions
•
A potometer measures the water a cut shoot takes up; nearly all of it leaves the leaves as vapor.
•
The rate is steady over the time measured: the light, heat, wind and humidity stay the same.
•
More light, heat or wind, or drier air, raises the rate; closing the stomata lowers it.
Step-by-step
WE KNOW
W = 4.8 mL, t = 6 h
FIND
water taken up each hour (R)
Step 1 · Find water taken up each hour (R)
Use W = R × t
Share the water over the hours measured.
R
=
W
t
R
=
4.8
6
R
=
0.8
mL/h
Check
Put the numbers back in. Both sides should match.
4.8 = 0.8 × 6 ✓
Topic check
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