UV-B: a brief summary - with links to other webpages
Ultraviolet-B (UV-B) is a type of ultraviolet (UV) radiation (http://en.wikipedia.org/wiki/Ultraviolet). UV radiation is emitted by the sun. It is quite high in energy and can therefore be damaging. The most hazardous UV radiation does not reach the earth’s surface because it is blocked by the stratospheric ozone layer, a layer of gas in the earth’s atmosphere (http://www.ozonelayer.noaa.gov/science/basics.htm). So without the ozone layer life would not survive on earth.
Although most of the UV-B that reaches the earth is stopped by the stratospheric ozone layer, some passes through. UV-B radiation is only a very small fraction of sunlight at the earth's surface.
Since UV-B is the most energetic part of sunlight that reaches the earth’s surface it has the potential to cause damage to all forms of life. UV-B can directly damage molecules such as DNA found in the cells of living organisms and it can impair normal cellular processes.
UV radiation has several effects on human health (http://www.who.int/uv/faq/uvhealtfac/en/). Exposure to UV-B in sunlight may cause sunburn and is known to promote some forms of skin cancer and eye cataracts. However, UV-B also has beneficial effects, including the promotion of vitamin D production in the skin.
UV-B can affect all organisms, including animals, microorganisms and plants (http://earthobservatory.nasa.gov/Features/UVB/uvb_radiation2.php). Plants need sunlight to make sugars through photosynthesis and are therefore constantly exposed to UV-B. To permit their survival in sunlight, plants have very effective systems for UV-protection and the repair of UV-damage, including the production of ‘sunscreen’ chemicals that absorb UV-B in tissues exposed to sunlight.
UV-C radiation is more hazardous than UV-B but is totally blocked by the ozone layer. UV-C radiation is used in hospitals and the food industry to kill bacteria that may cause infections.
UV-A is less energetic than UV-B and passes through the ozone layer. Although it does not cause sunburn, UV-A is implicated in skin aging and some types of skin cancer (http://www.who.int/uv/faq/uvhealtfac/en/).
Primary school project
Title: You are my sunshine – how does UV light affect us?
Funded by a Royal Society Partnership Grant (http://royalsociety.org/education/partnership/)
This project was undertaken with two classes of Primary7 children in St John the Baptist Primary School, Uddingston, South Lanarkshire. The original aims were:
(i) To stimulate an interest in science and a basic understanding of scientific methodology.
(ii) To increase understanding about ultraviolet (UV) light, how it is measured, its effects on organisms and how we can protect against UV injury.
UV is relevant to children because it can affect their health and that of their families. At the start of the project the children were given information about sunlight and they used prisms to see the different colours of light. In addition, the children were told about the different types of ultraviolet light and their properties. They used meters to measure the amounts of UV-B and UV-A light in fluorescent sources in comparison to sunlight and they learnt how filters block particular qualities of light. They monitored the amounts of UV-A, UV-B and total light in natural sunlight over 3 weeks. They found how sunlight changed in relation to the time of day and with respect to cloud cover and they displayed their measurements graphically.
The children investigated the effectiveness of different types of suncreams and sunglasses in screening UV-B and UV-A. They did this by placing the sunglasses or suncream, smeared on cellulose acetate sheets, between a UV source and meter. The children calculated the percentage decrease in transmission and produced bar-charts to compare creams with different protection ‘factors’, water resistance, etc. They learnt the importance of using moisturizing cream with no sun protection factor as a control in their experiments.
The children examined the effects of UV light on organisms. They inoculated microorganisms from various sources onto nutrient agar in Petri dishes and found that overnight exposure to UV-C or UV-B essentially prevented growth compared to untreated controls. They counted colonies and calculated percentage survival for the different treatments. In addition, the children grew plants from seed and exposed the plants to the same UV-B source as they used for their microorganisms. They found that the plants were much more resistant to UV-B light and learnt that plants make their own type of sunscreen in their leaves to protect themselves.
Finally, the classes visited Glasgow University, where they had a tour of research facilities, saw practical demonstrations, carried out an experiment to separate leaf pigments and used microscopes.
The children produced displays, PowerPoint presentations and other illustrations of their project work for a showcase event that was attended by parents and guests. This event showed just how much they had learnt and was very impressive!
Further information can be found on the school website http://www.st-johnthebaptist-pri.s-lanark.sch.uk/