P2 - Radiation and Life

Electromagnetic (EM) Spectrum• List the electromagnetic radiations in order of

the energy delivered by each photon

Earth is surrounded by an atmosphere which allows light radiated

from the Sun to pass through

Sun = Source

Person = Detector

UV is absorbed, reflected and

transmitted through the atmosphere

Photons• A beam of EM radiation

delivers energy in ‘packets’ called photons

• Energy deposited by a beam of EM radiation depends on both the:– Number of photons

arriving – Energy that each

photon delivers

Intensity• Intensity of EM radiation is the energy arriving at

a surface each second• Intensity decreases with distance and be able to

explain why

Ionising Radiation• Ionising radiation is able to break molecules into

bits (called ions), which can then take part in other chemical reactions

• Ionising radiation includes ultraviolet radiation, X-rays and gamma rays

Ionising Radiation Cell Damage• Ionising radiation can damage living cells. Different

amounts of ionising radiation can affect living cells. • Physical barriers protect people from ionising radiation,

for example, sun-screens and clothing can be used to absorb most of the ultraviolet radiation from the Sun.

Non-Ionising Radiation• Can cause things to heat up. The heating effect of

absorbed radiation can damage living cells • This is due to it’s intensity and duration of exposure.• Low intensity microwave radiation, for example from

mobile phone hand sets and masts, may be a health risk, but this is disputed

Microwaves• Microwaves heat materials containing particles

that the microwaves can vibrate • Metal cases and door screens of microwave

ovens protect users from the radiation

Transmitting Information• Infrared: Optical Fibres• Microwaves: Mobile Phones• Radio Waves: Television and Radio

Ozone Layer• Ozone layer protects living organisms, especially

animals, from the harmful effects ultraviolet radiation • Ozone layer absorbs UV radiation, producing reversible

chemical changes in that part of the atmosphere

Photosynthesis• Photosynthesis removes carbon dioxide from

the atmosphere and adds oxygen • Photosynthesis and Respiration are opposites

Greenhouse Effect• Earth emits EM radiation that is absorbed by

some gases in the atmosphere, so keeping the Earth warmer than it would otherwise be.

Greenhouse Gases1. Carbon Dioxide2. Water 3. Methane

Carbon Cycle• For thousands of years the amount of carbon dioxide in the Earth’s

atmosphere was fairly constant.• For thousands of years there has been no burning fossil fuels or land

use

Rising Carbon Dioxide in the Atmosphere

• During the past two hundred years, the amount of carbon dioxide in the atmosphere has been steadily rising. This is due to: 1. burning increased amounts of fossil fuels as an energy source2. burning forests to clear land

• Both of these release carbon into the atmosphere that otherwise would have been locked up for many years

Decomposers• Decomposers, such as microbes and fungi, play an

important role in the carbon cycle. They break down the remains of dead plants and animals and, in doing so, release carbon dioxide through respiration.

Global Warming• Most, but not all, scientists agree that the climate is getting

gradually warmer. • Most, but not all, scientists lay the blame for this on human

activities increasing the amount of carbon dioxide in the atmosphere.

• Global warming could cause:1. Climate change2. Extreme weather conditions in some areas3. Climate change may make it impossible to grow certain food

crops in some regions. 4. Melting polar ice, and the thermal expansion of sea water,

could cause rising sea levels and the flooding of low-lying land

Computer Climate Models• One piece of evidence which supports the view of

scientists who blame human activities for global warming has been provided by supercomputers.

• Computer climate models, based on different amounts of carbon dioxide in the atmosphere, produce the same changes as have been observed in the real world.

Factors and Outcomes• Any process can be thought of in terms of factors

that may affect an outcome.• In global warming, one factor is the amount of

carbon dioxide in the atmosphere. The outcome is the mean temperature of the atmosphere.

Correlation and Cause• To establish a correlation between a factor and an outcome,

convincing evidence is needed. This usually means that enough data must be collected, and that different samples should match.

• Compare these two graphs and consider these questions:1. Are the changes reported significantly large?2. Are they properly matched in terms of the times over which they are reported?3. Do these two graphs match well enough?

Correlation and Cause• A correlation between a factor and an outcome does not mean that

the factor causes the outcome. They could both be caused by some other factor.

• Example– Children with bigger feet (factor) are, on average, better readers (outcome).– There is another factor which, in fact, causes both of these. It is age, because

older children usually have bigger feet, and older children are usually better readers!

– To investigate the relationship between a factor and an outcome, it is important to control all other factors that may affect the outcome.

Other factors affecting global warming

• Another factor that may affect the mean temperature of the atmosphere is the amount of energy given out by the Sun. Most scientists agree that this has not changed in the past 200 years.

• There are some scientists who agree that global warming is taking place, but do not agree that carbon dioxide levels are to blame.

Scientific Explanation • Once experiments have shown that there is a definite

correlation between a factor and an outcome, it is still not enough to prove that the factor causes the outcome.

• For this to be proven, there must be some scientific explanation of how the relationship can happen.

• For carbon dioxide and global warming, the explanation is that carbon dioxide is a greenhouse gas. It absorbs infrared given off by the warm Earth, and this infrared cannot then escape into space. This keeps the Earth warmer than it would be if the carbon dioxide did not absorb so much infrared.

Benefits and Risks• It is impossible for anything to be completely safe. EG:

getting sunlight each day can be beneficial (Vitamin D) but too much could cause skin cancer.

• Offer reasons for people’s willingness (or reluctance) to accept the risk of a given activity. EG: Getting a tan.

The Precautionary Principle• The ‘precautionary principle’ tells you to avoid

any activity if serious harm could arise.• Parents may insist that their children are not allowed

out on the beach at all in the summer months.

Real v Perceived Risk• The real risk may be very different from the

perceived risk ie: the risk that you think is there.– You can’t see ultraviolet, and the word ‘radiation’ sounds

frightening to many people. This makes the risk seem worse than something you can see, and which is more familiar.

– Some parents may assume that summers are no different from when they were young, so there is no danger to their children.

ALARA Principle• The ALARA principle is to make any risk As Low

As Reasonably Achievable. This usually applies to an organisation which is responsible for its employees.– A company employing lifeguards on the beach may

insist that they wear lycra sun-suits and sun-screen cream to absorb ultraviolet when they are on duty

– The company may also arrange that lifeguards take turns at covering the hottest part of the day, when the intensity of ultraviolet is greatest

Designing a Study

• Evaluate the design for a study to test whether or not a factor increases the chance of an outcome, by commenting on:1. Sample size (the more people the better)2. How well the samples are matched (both

samples should be the same except for the variable that is being tested)