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 Gases
1. Carbon Dioxide
2. 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 source
2. 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 change
2. Extreme weather conditions in some areas
3. 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.
2.
3.
Are the changes reported significantly large?
Are they properly matched in terms of the times over which they are
reported?
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)