Ultraviolet waves can cause skin to age prematurely and increase the risk…

The idea

Ultraviolet (UV) waves carry enough energy to damage skin: they break down collagen and elastin, so skin loses elasticity and ages prematurely, and they damage DNA in skin cells, increasing the risk of skin cancer. X-rays and gamma rays are even more energetic and are ionising: when they pass through living cells they can knock electrons from atoms and molecules, forming ions. This ionisation can alter DNA, causing gene mutations. Mutations may disrupt how a cell divides and grows, so the cell can divide uncontrollably and form a cancer. A concrete example is a radiographer who leaves the X-ray room during exposures and stands behind a lead screen; lead absorbs X-rays, reducing the dose received. Similarly, gamma rays from a radioactive tracer are used in small controlled doses, while workers use shielding and distance to limit exposure.

What earns the marks

• Ultraviolet waves can cause skin to age prematurely, for example by damaging collagen and elastin so the skin loses elasticity and develops wrinkles.
• Ultraviolet waves increase the risk of skin cancer because they damage DNA in skin cells.
• X-rays and gamma rays are ionising radiation: they carry enough energy to remove electrons from atoms or molecules, forming ions.
• Ionisation can cause mutation of genes because it changes the DNA base sequence in a cell.
• Mutations in genes that control cell division can lead to uncontrolled cell division and the formation of a cancer.
• The risk from X-rays and gamma rays is reduced by limiting exposure time, increasing distance and using absorbing shielding such as lead.

Common mistakes and how to put them right

• Saying UV is ionising like X-rays and gamma rays.

  Put it right: UV can damage skin and DNA, but X-rays and gamma rays are described as ionising radiation in this specification.

• Confusing mutation with immediate burning.

  Put it right: Premature ageing and cancer risk are long-term effects of UV damage, not the same as a short-term sunburn.

• Writing that X-rays and gamma rays only harm people who work with them.

  Put it right: Any exposure carries some risk, so medical doses are kept as low as reasonably practicable and shielding is used.

Exam tips

• Link each named wave to its effect: UV to premature skin ageing and skin cancer risk; X-rays and gamma rays to ionisation, gene mutation and cancer.
• Use the term ionising correctly by explaining that electrons are removed from atoms or molecules, forming ions.
• When asked about safety, give practical control measures such as lead shielding, shorter exposure time and greater distance rather than saying 'be careful'.