Human influences and biotechnology

Eutrophication — follow every link

This is the sequence the exam asks for, and the mark scheme checks each step:

1. fertiliser (or sewage) is washed off the land into a river or lake — leaching;
2. the nitrates and phosphates make algae grow rapidly — an algal bloom;
3. the algae at the surface block the light from plants below, so those plants die;
4. decomposing bacteria feed on the dead plants and algae, and their numbers increase greatly;
5. the bacteria respire aerobically, using up the dissolved oxygen in the water;
6. fish and other aquatic animals die from lack of oxygen.

The step candidates most often leave out is step 5 — and it is the one that actually kills the fish. Blocking the light kills the plants; it is the bacteria using the oxygen that kills the animals.

Deforestation

• less photosynthesis, so less $\ce{CO2}$ is removed from the air;
• habitat loss, leading to extinction and reduced biodiversity;
• soil erosion — roots no longer hold the soil, so rain washes it away;
• increased flooding, because the trees no longer take up and hold water.

The enhanced greenhouse effect

Carbon dioxide and methane absorb heat radiated from the Earth's surface and re-radiate it back, warming the atmosphere. Human activity raises both: burning fossil fuels and deforestation raise $\ce{CO2}$; cattle and rice paddies raise methane.

Consequences include melting ice, rising sea levels, and changing climate patterns.

Conservation

Reasons to maintain biodiversity include: species may be sources of medicines or of genes for crop breeding; ecosystems provide services such as pollination; and there is an ethical case for not causing extinctions.

Methods include national parks, captive breeding programmes, seed banks, and controlling fishing by quotas and net mesh size.

Biotechnology: why microorganisms are used

• they reproduce very rapidly;
• they need simple, cheap nutrients — often industrial waste;
• they can be grown at any time of year, in any country;
• their genes can be modified relatively easily.

Yeast is used in bread-making (for the $\ce{CO2}$) and brewing (for the ethanol).

Biological washing powders contain enzymes: proteases to remove blood and food stains, lipases to remove grease. Because the enzymes work at low temperatures, less energy is needed to heat the water.

Genetic modification

The example to know is human insulin:

1. the human insulin gene is cut out of a chromosome using restriction enzymes;
2. a bacterial plasmid is cut with the same enzyme, so the ends match;
3. the gene is joined into the plasmid using ligase;
4. the plasmid is put into a bacterium, which is then grown in a fermenter;
5. the bacteria make human insulin, which is extracted and purified.

The advantage: the insulin is identical to human insulin, produced in large amounts, and free of the ethical and allergy problems of insulin extracted from animals.