Mineral nutrition

Biology · Plant nutrition. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

Test this topic free All Biology topics

The idea

Photosynthesis gives a plant carbohydrates, which contain only carbon, hydrogen and oxygen. To make other substances the plant needs mineral ions, which it absorbs from the soil through its root hair cells.

Nitrate ions supply nitrogen. The plant combines nitrogen with carbohydrate to make amino acids, and joins amino acids to make proteins. Proteins are needed for growth, so a plant short of nitrate stays small.

Magnesium ions are needed to make chlorophyll. Without magnesium the leaves turn yellow, less light is absorbed, less photosynthesis takes place and growth slows.

Rules to remember

Nitrate ions → amino acids → proteins → growth.
Lack of nitrate: stunted growth, with weak stems and yellowing older leaves.
Magnesium ions → chlorophyll.
Lack of magnesium: yellow leaves (chlorosis), less photosynthesis, poor growth.
Mineral ions are usually taken up by root hair cells by active transport.
Fertilisers containing nitrates are added to soil to increase the growth and yield of crops.

Common mistake

Writing that plants take nitrogen from the air. Most plants cannot use nitrogen gas. They absorb nitrogen as nitrate ions from the soil.

Worked example

Two groups of seedlings are grown in the light. Group 1 has a complete mineral solution. Group 2 has the same solution without magnesium ions. After four weeks group 2 has pale yellow leaves and is much smaller. Explain the difference.

Magnesium ions are needed to make chlorophyll.
Group 2 cannot make enough chlorophyll, so the leaves are yellow instead of green.
Less chlorophyll absorbs less light, so less photosynthesis takes place.
Less glucose is made for energy and for new cell material, so growth is slower.

Answer: Without magnesium the plants make little chlorophyll, photosynthesise less and so grow less.

Ask about this

Type what you are stuck on. The helper finds the explanation, worked examples and the notes to read, free and instant.

Read the full notes

Nutrition in Plants

Keep going

← Leaf structure Uptake and transport of water and ions →Take a Biology test