UV hits the base of the food web: Phytoplankton make the food for almost all ocean life. UV slows their photosynthesis, and the loss passes up the food chain.
The points to remember
- UV (mainly UVB) reduces photosynthesis in phytoplankton.
- Phytoplankton float near the sunlit surface, so they cannot escape the UV.
- They are the base of ocean food webs: less phytoplankton means less food for krill, fish, whales and penguins.
- So UV lowers the productivity of the whole ecosystem.
- Phytoplankton also take in carbon dioxide, so less of them means less carbon taken up by the ocean.
- On land, UV damages leaves and slows plant growth, including crops.
More UV
- More UVB reaches the sea surface.
Phytoplankton
- Less photosynthesis, slower growth.
Krill
- Less food, so fewer krill.
Whales, penguins
- Less food further up the chain.
Real example: in spring 1990 scientists sailed through the Bellingshausen Sea, off Antarctica, as the ozone above thinned. Under the thin ozone, phytoplankton produced at least 6 to 12% less food than nearby.
Remember it as: Less phytoplankton, less food for everything above it.
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UV does more than burn. It carries enough energy to damage the DNA inside cells.
The points to remember
- UV has enough energy to damage DNA in living cells.
- When a damaged cell divides, the damage can be copied as a mutation.
- Mutations in skin cells can lead to skin cancer.
- Melanoma is the most dangerous skin cancer; other skin cancers are more common but less deadly.
- DNA damage harms all living things: plants, plankton, animals and people.
Real example: the World Health Organization's cancer agency found that of 331,700 people diagnosed with melanoma in 2022, about 267,000 (83%) got it because of UV.
Use the words 'mutation' and 'cell division': 'UV damages DNA, causing mutations when cells divide, which can lead to skin cancer' is the full chain. 'UV causes cancer' alone is too short.
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Skin cancer is the best known harm, but UV hurts people in several other ways, in the skin and in the eyes.
The points to remember
- Sunburn: red, painful skin, caused mainly by UVB.
- Premature ageing of the skin: UVA reaches deep into the skin, causing wrinkles and spots.
- Cataracts: the lens of the eye turns cloudy, which can cause blindness; up to 10% of cataracts may come from UV.
- Skin cancer, including melanoma, from DNA damage.
- A weaker immune system: UV on the skin can lower the body's defences.
- The one benefit: a little UVB makes vitamin D.
Skin
- Sunburn (UVB).
- Premature ageing (UVA).
- Skin cancer.
Eyes
- Cataracts: a cloudy lens.
- Sunburn of the eye surface.
Body
- Weaker immune system.
- Benefit: vitamin D.
Real example: in 1981 the Cancer Council in Victoria, Australia, launched 'Slip! Slop! Slap!': slip on a shirt, slop on sunscreen, slap on a hat. It became one of the best-known health campaigns in the world.
Keep the right effect with the right radiation: Sunburn, cataracts and skin cancer come from UV. Ground-level ozone in smog harms the lungs; do not give UV effects for it.
Papers give data on UV and its harm, then ask you to read it or to list effects. The UV index is the scale forecasts use.
The points to remember
- The UV index tells you how strong the Sun's UV is: the higher the number, the faster skin burns.
- 0-2 low, 3-5 moderate, 6-7 high, 8-10 very high, 11+ extreme.
- Protect your skin at 3 or above.
- When you use data, quote the numbers: 'at a UV index of 11, cases rose to 34'.
- A 'list' question on human health: name human effects only, not effects on plants or plankton.
Real example: Australia's free SunSmart app shows each day's UV index and the 'sun protection times', the hours when the index is 3 or above.
Read the question's target: 'List two risks to human health': skin cancer, cataracts, sunburn, premature ageing, DNA damage. Effects on phytoplankton or crops score nothing here.
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How this comes up: Paper 2, Section A: list or explain the harm UV does, usually beside a figure about the ozone layer. One effect per mark, and only the effects the question asks for.
In spring, the ozone over the Southern Ocean around Antarctica thins, and more UV reaches the sea surface. Antarctic krill feed on phytoplankton, and whales and penguins feed on krill.
Explain how an increase in UV radiation could affect this food chain.
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