Food Production
Use of Biological Resources · 3 question types
Plants need mineral ions from the soil to build the molecules that glucose alone cannot supply. Intensive farming removes these ions with every harvest, so they are replaced using fertiliser. Most commercial fertilisers are described as NPK because they supply the three ions crops need in the largest amounts:
| Element | Ion supplied | What the plant uses it for | Effect of shortage |
|---|---|---|---|
| N — nitrogen | Nitrate (NO₃⁻) | Making amino acids and therefore proteins (for growth and enzymes) | Stunted growth; older leaves turn yellow |
| P — phosphorus | Phosphate (PO₄³⁻) | Making DNA and cell membranes; needed for healthy root growth | Poor root growth |
| K — potassium | Potassium (K⁺) | Helps enzymes of photosynthesis and respiration work; controls stomata | Yellow leaf edges; weak growth |
Adding fertiliser replaces the lost ions, so plants can make more protein and chlorophyll, grow larger and faster, and produce a higher yield. Magnesium is often added too, because it is needed to make chlorophyll.
The link to the wider environment matters here: if fertiliser is washed off the land into rivers and lakes, it can cause eutrophication, covered in topic 16. Growers therefore try to apply only what the crop needs.