Duckweed is a small floating freshwater plant that grows by producing new leaves. Many mineral ions are required for healthy plant growth.
State one named mineral ion required by plants, and describe how it helps them to grow.
Zinc ions can inhibit the growth of duckweed. To investigate this, a student set up two flasks:
The student counted the number of living leaves every two days. The table below shows her results:
| Day | Flask A (with zinc ions) | Flask B (without zinc ions) |
|---|---|---|
| 0 | 10 | 10 |
| 2 | 10 | 12 |
| 4 | 11 | 18 |
| 6 | 9 | 26 |
| 8 | 4 | 36 |
| 10 | 0 | 48 |
Calculate the percentage increase in the number of living leaves in Flask B from Day 0 to Day 10. Show your working.
State three environmental or experimental variables, other than the volume and concentration of the nutrient solution, that must be controlled to ensure the results are valid.
