A level-readyAll subjects · Biology · WBI12 (Unit 2)
Plant fibres, sustainability and mineral ions
Plants give us renewable materials and need certain mineral ions to grow. Both link plant structure to how we use plants.
Sustainable materials
Plant fibres (such as cotton, hemp and flax) and starch can replace some materials made from oil:
- Fibres make ropes, textiles and composites; starch can be made into bioplastics for packaging.
- They are renewable (regrown each season), usually biodegradable, and the plants absorb CO2 as they grow.
- But growing them uses land, water, fertilisers and pesticides, which has environmental costs.
Water and mineral ions
Plants absorb water and mineral ions through their roots.
| Need | Why | If deficient |
|---|---|---|
| Water | Photosynthesis, transport, turgor, solvent for reactions | Wilting |
| Nitrate ions | Making amino acids (proteins), nucleic acids and chlorophyll | Stunted growth, yellowing of older leaves |
| Calcium ions | Making calcium pectate for the middle lamella | Poor growth, dying growing tips |
| Magnesium ions | Part of the chlorophyll molecule | Yellowing between the veins of leaves (chlorosis) |
Investigating deficiencies
A recommended practical: grow seedlings in culture solutions, each lacking one ion, with a complete solution as the control. Keep light, temperature, volume and species the same. Compare growth (height, mass, leaf number) and leaf colour over several weeks.
Worked example
Seedlings grown without magnesium have yellow leaves and grow poorly. Explain.
- Magnesium is part of the chlorophyll molecule.
- Without it, less chlorophyll is made, so leaves are yellow.
- Less light is absorbed, so less photosynthesis and less growth.
Answer: No magnesium means less chlorophyll, so less photosynthesis and growth.
Check yourself
- Why do plants need magnesium ions?
- To make chlorophyll
- To make calcium pectate
- To make cellulose
- To make starch
Show answer
To make chlorophyll. Magnesium is at the centre of the chlorophyll molecule.
- Why do plants need calcium ions?
- To make chlorophyll
- To make amino acids
- To make calcium pectate for the middle lamella
- To make DNA
Show answer
To make calcium pectate for the middle lamella. Calcium pectate cements cells together.
- Nitrate ions are used to make
- amino acids and proteins
- starch
- cellulose
- glucose
Show answer
amino acids and proteins. Nitrogen is in amino acids, nucleic acids and chlorophyll.
- In a mineral deficiency experiment, what is the control?
- Seedlings in distilled water only
- Seedlings in the dark
- Seedlings with no roots
- Seedlings in a complete culture solution containing all ions
Show answer
Seedlings in a complete culture solution containing all ions. The complete solution shows normal growth for comparison.
- Why are starch-based plastics considered more sustainable than oil-based plastics?
- They last forever in landfill
- They come from a renewable source and are usually biodegradable
- They need no land to produce
- They are made from fossil fuels
Show answer
They come from a renewable source and are usually biodegradable. Crops regrow, and the plastics can break down.
- Which is a drawback of growing crops for plant-based materials?
- They release more CO2 than oil
- They cannot be regrown
- They contain no cellulose
- They use land, water and fertilisers
Show answer
They use land, water and fertilisers. Land use and inputs have environmental costs.
Sources
Last updated 7 November 2026. Spotted a mistake? Tell us.