Sustainability and conservation of speciesEdexcel A-Level Biology A: Revision notes

A process is sustainable if it meets present needs without using up resources that future generations will need. Many plastics are made from crude oil, which is finite (non-renewable), and they can persist in the environment for hundreds of years. Plants are renewable: they can be regrown and they absorb carbon dioxide in photosynthesis, so a plant-based product can have a lower net release of carbon dioxide than a product from fossil fuels.

Plant fibres such as flax, hemp and jute can be used for rope, textiles, paper, packaging and composite materials in place of synthetic fibres. They are strong because of their cellulose microfibrils and lignin, they are biodegradable and they are made from a renewable resource.

Starch is a polymer of α-glucose made by plants as an energy store. Starch from crops such as maize and potato can be processed into bioplastics (for example thermoplastic starch, or polylactic acid made by fermenting the sugars from starch), which can be used for bags, packaging, cutlery and bottles to replace oil-based plastics.

Plant fibres and starch can also be combined as composites. Because the carbon in the plastic was taken from the air by the crop, the net release of carbon dioxide is lower than for fossil fuel plastics.

Advantages: renewable raw material; less use of crude oil; lower net carbon dioxide emissions; many are biodegradable, so they cause less litter.

Disadvantages: growing crops needs land, water, fertiliser and energy, and may compete with food production or lead to deforestation; some bioplastics break down only in industrial composting conditions, and if they enter plastic recycling they can contaminate it; they can be more expensive.

When evaluating, give both sides, use the data in the question and end with a justified judgement.

Zoos help to conserve endangered species (ex situ conservation, away from the natural habitat) by:

• Captive breeding programmes: animals breed in protected conditions and numbers rise. A studbook records parentage and animals or sperm are exchanged between zoos to avoid inbreeding and maintain genetic diversity.
• Reintroduction programmes: offspring are released into protected habitat to restore wild populations. They need to be prepared for life in the wild and checked for disease, and the original cause of the decline must have been dealt with.
• Scientific research: into diet, behaviour, breeding and disease, which helps with conservation in the wild.
• Education: the public learn about threatened species, supporting and funding conservation.

Limitations: small populations mean low genetic diversity and possible inbreeding; space and cost limit the number of species; captive animals may lose natural behaviours.

A seed bank stores seeds of endangered and useful plants ex situ. Seeds are collected from many individuals and populations to capture genetic diversity, dried to a low moisture content and stored at about −20 °C. Low water content and low temperature mean that metabolism is very slow, so germination and fungal growth are prevented and the seeds stay viable for decades.

Advantages: a very large number of species can be stored in a small space at low cost; they are safe from habitat loss and disease; the seeds can be germinated to reintroduce the species or for research.

Limitations: some seeds (for example many tropical species) cannot survive drying and freezing; viability must be tested, and seeds regrown periodically, which costs money and may select for different traits; the ecosystem and pollinators are not conserved; and the cause of decline is not tackled.

When asked to evaluate, set out the strengths and weaknesses and finish with a judgement supported by the evidence.

• Seed banks are cheaper and hold far more species, but cannot store every seed and do not conserve habitats.
• Zoos can protect charismatic species, educate and reintroduce, but they conserve few species at high cost and small populations lose genetic diversity.
• Both are ex situ methods. They work best as a back-up to in situ conservation, which protects species in their natural habitat.