3.4 - Mineral Requirements

Nitrate ions for amino acids and proteins

• Plants make glucose by photosynthesis, but they also need certain mineral ions, which they take up from the soil.
• One of the most important is the nitrate ion.

Why plants need nitrate ions

• Nitrate ions contain nitrogen.
• The plant uses this nitrogen to make amino acids, which are then joined together to build proteins.
• Proteins are needed for cell growth, so a steady supply of nitrate ions is essential for the plant to grow and develop properly.

How nitrate ions are absorbed

• Nitrate ions are dissolved in the water in the soil.
• The plant absorbs them through its root hair cells.
• The concentration of nitrate ions is usually higher inside the root than in the soil around it.
• Because of this, the root hair cells take them up by active transport, against the concentration gradient.

Magnesium ions for chlorophyll

• Plants take up magnesium ions from the soil.
• They're needed in much smaller amounts than nitrate, but are just as essential.
• Magnesium ions are used to make chlorophyll - the green pigment found in chloroplasts that absorbs light energy for photosynthesis.
• Without enough magnesium, a plant can't make the chlorophyll it needs to photosynthesise properly.

Mineral deficiency symptoms

• Plants absorb mineral ions from the soil through their roots.
• If a plant cannot get enough of a particular mineral ion, it shows deficiency symptoms - visible signs that something is missing - and its growth suffers.

Symptoms of each mineral shortage

• Nitrate ions - Needed to make protein. A shortage means poor, stunted growth and yellowing of older leaves.
• Magnesium ions - Needed to make chlorophyll. A shortage causes leaves to turn yellow.
• Potassium ions - A shortage causes yellowing of the leaves and poor flower and fruit growth.
• Phosphate ions - A shortage causes poor root growth.