4.1.3Use of Biological Resources
Crop Plants: Fertiliser — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 2 Revision Notes & Topical Questions
5 min read 8 parts Lesson 4 of 15
Part 1 of 6Why use fertiliser?
1Crops remove minerals
- Crops remove minerals As plants grow they take mineral ions out of the soil, and these leave the field when the crop is harvested.
2Soil becomes depleted
- Soil becomes depleted If the same field is cropped year after year, the supply of ions falls.
3Fertiliser replaces them
- Fertiliser replaces them Adding fertiliser puts the missing mineral ions back into the soil.
4Better growth
- Better growth Plants stay healthy and grow larger and faster, so the yield increases.
Part 2 of 6Types of fertiliser
Organic
- Organic Made from natural materials such as farmyard manure and compost.
- They release minerals slowly as they are broken down by decomposers.
Chemical (inorganic)
- Chemical (inorganic) Manufactured mineral salts, applied as dry granules or sprayed as a liquid.
- They contain known amounts of ions that plants can absorb quickly, but excess can wash into water and cause eutrophication.
Part 3 of 6Two key mineral ions
| Mineral ion | Use in the plant | Sign of deficiency |
|---|---|---|
| Magnesium (Mg2+) | Needed to make chlorophyll | Leaves turn yellow, especially between the veins |
| Nitrate (NO3-) | Needed to make amino acids, which are joined to form proteins | Weak, stunted growth and yellowing of the leaves |
Part 4 of 6Other mineral ions plants need
| Mineral ion | Use in the plant | Sign of deficiency |
|---|---|---|
| Phosphate | Used to make ATP, DNA and RNA | Poor root growth, stunted plants and dark green or purple-tinged leaves |
| Calcium | Used in cell walls and cell membranes | Deformed young leaves and stunted growth |
| Potassium | Helps the stomata to open | Yellowing around the leaf edges |
Part 5 of 6Applying fertiliser sensibly
1
Identify the symptoms or test the soil to find which mineral ions are short.
2
Choose a fertiliser that supplies those ions, organic or chemical, depending on cost and how fast the effect is needed.
3
Apply it at the right time, when the crop is growing and able to take up the ions, and in the right amount.
4
Avoid applying it just before heavy rain, so that less is washed into nearby rivers and lakes.
Part 6 of 6Linking function to symptom
Mineral deficiency
Less chlorophyll
- Less chlorophyll Without magnesium, less chlorophyll forms, so leaves look yellow and absorb less light for photosynthesis.
Less protein
- Less protein Without nitrate, the plant cannot make enough amino acids and proteins, so it cannot build new cells and grows poorly.
Lower yield
- Lower yield Either deficiency reduces growth and so reduces the mass of crop harvested.
Key terms
| Term | Meaning |
|---|---|
| Fertiliser | A substance added to soil to supply mineral ions that plants need. |
| Mineral ion | A dissolved charged particle, such as nitrate, absorbed by roots. |
| Chlorophyll | The green pigment that absorbs light energy for photosynthesis. |
| Amino acid | A building block of proteins, containing nitrogen. |
| Deficiency | A shortage of a nutrient that causes visible symptoms. |
Avoid these mistakes
1
Writing 'nitrite' or 'nitrogen' instead of nitrate — plants absorb nitrate ions through the roots.
2
Saying fertilisers are plant food — plants make their own food by photosynthesis; fertilisers supply minerals.
3
Mixing up the deficiency symptomsmagnesium is linked to chlorophyll and yellow leaves, nitrate to proteins and stunted growth.
4
Forgetting the cost to the environmentover-use leads to run-off and eutrophication.
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