Plants and Mineral Ions

Section 1 of 7Why minerals are needed

More than carbohydrates

• More than carbohydrates Photosynthesis only supplies carbohydrates, which contain carbon, hydrogen and oxygen.
• Plants also need proteins, lipids and nucleic acids such as DNA, and some of these contain extra elements, including nitrogen.

Making their own molecules

• Making their own molecules Plants do not eat,
  • so they must build all of these molecules themselves, using elements taken up from the soil as dissolved mineral ions.

Two key ions

• Two key ions Nitrate and magnesium ions are the two you need to know.
  • Without them a plant cannot photosynthesise or grow properly.

Section 2 of 7Uptake from the soil

1Ions dissolve in soil water

• Ions dissolve in soil water Nitrates and magnesium salts are present in the soil solution.

2Root hair cells absorb

• Root hair cells absorb The root hair cells have a large surface area,
  • and they take the ions in by active transport against the concentration gradient.

3Carried upwards

• Carried upwards The ions travel in the water in the xylem to the stem and leaves.

4Used in the cells

• Used in the cells Leaf and growing cells use them to make amino acids, proteins and chlorophyll.

Section 3 of 7Mineral ions and deficiency

Mineral ion	Used to make	Symptoms of deficiency
Nitrate	Amino acids and so proteins; also DNA	Stunted growth and yellowing of older leaves
Magnesium	Chlorophyll	Yellow leaves (chlorosis), especially between the veins

Section 4 of 7Linking deficiency to function

Mineral deficiency

Lack of nitrate

• Lack of nitrate The plant cannot make enough amino acids and proteins, so cells cannot grow and divide, and growth is stunted.

Lack of magnesium

• Lack of magnesium Less chlorophyll is made, so the leaves turn yellow and absorb less light, which lowers the rate of photosynthesis.

Overall effect

• Overall effect Less glucose is produced, so there is less energy and fewer raw materials for growth, and the plant is weak and has lower yields.

Section 5 of 7Providing minerals in practice

Fertilisers

• Fertilisers Farmers add fertilisers containing nitrate to replace what crops remove from the soil.

Investigating deficiency

• Investigating deficiency Seedlings can be grown in solutions that are complete or that lack one ion, with all other conditions kept the same.
• The appearance of the leaves and the mass of the plants are then compared.

Section 6 of 7Key terms

Term	Meaning
Mineral ion	A dissolved charged particle from the soil that a plant needs in small amounts.
Nitrate	An ion containing nitrogen, used to make amino acids and proteins.
Magnesium	An element needed to make chlorophyll.
Active transport	The movement of substances against a concentration gradient using energy from respiration.
Chlorosis	Yellowing of leaves caused by a lack of chlorophyll.
Deficiency	A shortage of a nutrient that stops an organism working properly.

Section 7 of 7Exam technique

1

Saying that plants get their food from the soil. They make food by photosynthesis; the soil only provides water and mineral ions.

2

Mixing up the two ions. Magnesium is for chlorophyll, and nitrate is for amino acids and proteins.

3

Describing mineral absorption as simple diffusion. Root hair cells use active transport, which needs energy.

4

Claiming that mineral ions are a source of energy for the plant. They provide chemical elements, not energy.