Plants as sustainable resources (4.13, 4.14, 4.15)
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William Withering carried out an early clinical trial for the drug digitalin, extracted from foxgloves, in the 18th century.
Withering studied a patient with dropsy (oedema) who improved after taking a herbal remedy of “Digitalis soup” – a tea containing multiple plants, including foxgloves.
Withering used a trial-and-error approach by observing patient symptoms. Withering treated oedema by slowly increasing the dose of foxglove until the patient showed signs of improvement.
Drug testing now follows a more controlled process. The drug must be proven to be safe, effective, and capable of generating profit.
Chemicals used for drug testing are identified and produced in labs synthetically. These chemicals can either be identified by investigating natural remedies or by computer modelling of chemical structures.
Pre-clinical testing is carried out to assess the safety of a potential drug.
Potential drugs are tested on cells and tissue cultures in the lab. They are then also tested on animals, which are authorised by the UK MHRA (the Medicines and Healthcare products Regulatory Agency).
Many potential drugs are tested at this stage, with few successfully approved for clinical testing on humans.
Phase I clinical trials involve testing the drug on volunteers at different doses. These volunteers are usually healthy, but sometimes people with health conditions are involved in these tests.
Phase I trials investigate how the drug is absorbed, circulated, metabolised and excreted by the body. The effects of the drug are monitored, with results sent to the UK MHRA.
Phase II clinical trials involve testing the drug in volunteers with the target condition. This stage usually involves trialling the drug on around 200 people.
Phase II clinical trials investigate the drug’s effectiveness at treating the health condition.
Phase III clinical trials involve testing the drug on a larger group of volunteer patients with the health condition. This stage usually involves around 2 000 people.
Phase III clinical trials investigate the effectiveness of the drug compared to either a placebo or an existing treatment for a health condition. The side effects of the drug are also investigated at this stage.
Phase III clinical trials usually involve double-blind randomised control trials. This means the patients are randomly assigned to one of two groups. One group receives the drug being tested, the other group receives either the placebo or the existing treatment (if available).
Neither the patients nor the doctors are aware of who is receiving the drug or the placebo.
After a drug has completed clinical trials, the drug can be licensed and used to treat more people. Data on the effectiveness and safety will continue to be monitored.
Bacteria divide by the process of binary fission and can divide up to every 20 minutes.
This exponential growth only occurs when conditions are optimal for the bacteria. These conditions include sufficient oxygen, nutrients, correct and optimum temperature.
If bacteria are grown in a closed (batch) culture, there are four distinct phases.
In the lag phase, microorganisms are adapting to the new environment. There is little replication, but microorganisms are synthesising enzymes.
In the log (exponential) phase, replication is near or at the theoretical maximum, when the growth rate is highest.
In the stationary phase, the number of cells remains constant, as the nutrients decrease and waste products start to build up. The rate at which cells are produced equals the rate at which cells die.
In the death phase, the number of cells decreases, and waste products build up to toxic levels. Many waste products are acidic, causing the to change, inhibiting enzymes.
Culturing microorganisms requires aseptic techniques. This prevents contamination and ensures only the desired microorganism is cultured.
Aseptic conditions require a sterilised growth medium, usually sterilised broth or sterilised agar.
The desired bacteria are added to the sterile growth medium; this process is called inoculation.
Broth can be inoculated by adding a bacterial sample to sterile broth with an inoculating loop or micropipette.
- The inoculating loop is sterilised using a Bunsen burner.
- The loop tip is submerged, and the bacterial sample is added to the broth.
- The mouths of the bottles are also sterilised after opening and before sealing to ensure no unwanted bacteria enter the broths.
- The inoculated broth is then partially sealed, either using cotton wool or by loosely placing a lid on the bottle.
Agar can be inoculated using many different methods.
In a simple benchtop method:
- The bacterial sample is added to a sterile agar plate using an inoculating loop.
- The lid of the agar plate is opened as little as possible to prevent airborne microorganisms from accessing the agar.
- The inoculating loop is sterilised using a Bunsen burner, added to the bacterial sample, and then gently zig-zagged across the surface of the sterile agar.
- The agar plate is then partially sealed using tape.
Traditional plastics are made from petrochemicals derived from crude oil, making them unsustainable:
- Non-renewable resource. Crude oil is finite and takes millions of years to form.
- Non-biodegradable. Most microorganisms lack the enzymes required to break down strong synthetic polymer bonds.
- Environmental pollution. Plastic waste accumulates in landfills and aquatic ecosystems, where it can fragment into toxic microplastics.
- Carbon emissions. Extracting crude oil, manufacturing plastics, and incinerating plastic waste releases carbon dioxide (), contributing to climate change.
Plant fibres are elongated structural cells obtained from the stems, leaves, or seeds of plants. They are primarily made of cellulose embedded in a matrix of hemicellulose and pectin.
Many mature plant fibres are lignified (strengthened with lignin), increasing their strength and rigidity.
Most plant fibres used commercially come from sclerenchyma fibres, although xylem tissue also contains lignified cells that provide mechanical support.
Plant fibres have high tensile strength, are flexible, renewable, and biodegradable, making them useful as sustainable materials.
Plant fibres (e.g., cotton, hemp, flax) are increasingly used to replace synthetic fibres in textiles, ropes, and packaging.
Advantages of plant fibre usage:
- Strength and flexibility.
- Biodegradable.
- Lower dependence on fossil fuels.
- Lower carbon footprint as the carbon released during decomposition / burning is absorbed via photosynthesis.
Disadvantages of plant fibre usage:
- Land and water are required for plant growth.
- Fertilisers and pesticides may damage ecosystems.
- Transport and processing still produce carbon dioxide.
Starch from crops such as maize or potatoes can be processed and made into biodegradable plastics.
Advantages of biodegradable plastics from starch:
- Reduces reliance on crude oil.
- Can decompose more rapidly than conventional plastics.
- Unlike crude oil plastics that persist for centuries, starch-based packaging is degraded rapidly by microbes into water and
- Reduces persistent plastic pollution.
Disadvantages of biodegradable plastics from starch:
- Uses agricultural land.
- May compete with food production.
- Some bioplastics require industrial composting to degrade efficiently.