9.5Chapter 9: Plants and Photosynthesis

The need for minerals — Alhussan Biology - Stage 9 Revision Notes & Topical Questions

5 min read 9 parts Lesson 5 of 9 2 quizzes

📚 Alhussan Biology - Stage 9 Hub / Topical Revision

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Lesson summary

9.5 The need for minerals — Nitrates and Magnesium in Plants — Alhussan International Academy — Biology (Stages 7–9) notes: Explain why plants need nitrate and magnesium ions, where they obtain them and what deficiency symptoms show.Food — plants make carbohydrates by photosynthe…

Without minerals
Active transport
Replacement
Expected results
Fertilisers
Natural sources

Part 1 of 7Plants make food but need minerals

Food

Food plants make carbohydrates by photosynthesis, and use glucose in respiration or build it into starch, cellulose and lipids.

Minerals

Minerals water-soluble substances that plant cells can absorb.

Some substances cannot be made from carbohydrates alone.

Without minerals

Without minerals a plant in light, water and air looks sickly and eventually dies.

Part 2 of 7Where plants get minerals

Soil

Soil plants absorb mineral ions dissolved in soil water through root hairs.
The minerals are carried around the plant in its transport systems with the water.

Active transport

Active transport nitrate ions are taken up by active transport, which needs energy from respiration.

Replacement

Replacement harvesting crops uses up soil minerals, so they must be replaced by fertilisers or natural recycling by decomposers.

Part 3 of 7Nitrate

Source

Source decomposers produce nitrates by breaking down waste and dead bodies of plants and animals.

Use

Use nitrates supply nitrogen to make amino acids and proteins, and also DNA and chlorophyll.
Proteins control many reactions in plant cells, including photosynthesis, and are part of the cell structure.
Plants cannot use nitrogen gas from the air directly.

Deficiency

Deficiency growth is stunted because proteins for new cells cannot be made.
Older leaves turn yellow because nitrogen is moved to the growing tips.

Part 4 of 7Magnesium

Use

Use magnesium ions (Mg²⁺) are at the centre of every chlorophyll molecule.
Plants need magnesium to make chlorophyll for new chloroplasts and to replace worn-out or damaged chlorophyll.

Deficiency

Deficiency without magnesium less chlorophyll is made, so less light is absorbed and photosynthesis falls.
Leaves turn pale or yellow (chlorosis), often between the veins and on the older leaves first.

Part 5 of 7Mineral deficiencies compared

Mineral	Used for	Deficiency
Nitrate	Amino acids, proteins, chlorophyll	Poor growth, yellow older leaves
Magnesium	Chlorophyll	Pale or yellow leaves with green veins
Phosphate	DNA, ATP, cell membranes	Poor root growth, purple leaves
Potassium	Enzymes, flowers and fruit	Yellow leaves with dead edges

Part 6 of 7Investigating mineral deficiency

Grow seedlings in culture solutions: one with all minerals (the control) and others each lacking one mineral, such as no nitrate or no magnesium.

Use the same type of plant, volume of solution, light and temperature.

Observe over two to three weeks and measure height, number of leaves and leaf colour.

Compare each plant with the control to identify the effect of each mineral.

Repeat with several plants and take means to improve reliability.

Expected results
- the complete solution grows best, the no-nitrate plant is short and pale, and the no-magnesium plant has yellow leaves.

Part 7 of 7Legumes and fertilisers

Legumes

Legumes peas, beans and clover have root nodules full of bacteria that make nitrates from nitrogen in the air.
The plants give the bacteria sugar from photosynthesis in return.
Legumes grow well in nitrate-poor soil and add nitrates to the soil, making it more fertile.
Farmers grow them in crop rotation to improve the soil for crops that need lots of nitrogen.

Fertilisers

Fertilisers they contain nitrogen, phosphorus and potassium (NPK) to replace minerals.

Natural sources

Natural sources compost and manure return minerals as they decompose.

Key terms

Term	Meaning
Mineral	A water-soluble substance that plant cells absorb from the soil.
Nitrate	A mineral ion containing nitrogen, used to make proteins.
Magnesium	A mineral ion needed to make chlorophyll.
Mineral deficiency	Poor growth caused by a lack of a mineral.
Legume	A plant such as peas, beans or clover with nitrogen-fixing root nodules.
Fertiliser	A substance added to soil to replace minerals.