Antimicrobial and therapeutic substances from plantsSpec 4.11
In short
Many plants make chemicals that protect them against microorganisms and herbivores, and some of these have antimicrobial or other therapeutic effects in humans. Examples include allicin from garlic, salicin from willow bark, and digitalis from foxglove. Plants are therefore a source of potential new medicines, which is one reason to conserve biodiversity.
Plants cannot move away from pests and pathogens, so many make chemicals that kill or deter microorganisms, fungi and herbivores. Some of these chemicals have been used in traditional medicine, and some have been developed into modern drugs.
| Plant | Substance | Use |
|---|---|---|
| Garlic | Allicin | Antimicrobial properties (antibacterial and antifungal) |
| Willow bark | Salicin, from which aspirin was developed | Pain relief and reducing fever and inflammation |
| Foxglove (Digitalis purpurea) | Digitalis (digoxin) | Treating some heart conditions |
| Cinchona bark | Quinine | Treating malaria |
| Sweet wormwood (Artemisia annua) | Artemisinin | Treating malaria |
| Madagascan periwinkle | Vincristine | Treating some cancers |
Using plant substances
- Extracts may contain many compounds, so the active compound must be identified and tested.
- The dose in a plant varies with species, age, growing conditions and part of the plant, so a purified, standardised dose is safer.
- Many plants have not been tested, so loss of plant species may lose possible medicines.
- Plant substances can be toxic, as with digitalis, and must be tested before use.
Name at least one plant, the substance and its use. "Antimicrobial" means kills or inhibits the growth of microorganisms such as bacteria.
Written and checked against the Edexcel International AS Level Biology (XBI11) specification · Updated October 2026