Doc Brown's Edexcel GCSE Science-Biology Revision Notes
EDEXCEL GCSE Science BIOLOGY UNIT
B1 Influences on life
UNIT B1 Topic 3 Problems of, and solutions to a changing environment
3.1 Be able to define a drug as a chemical substance, such as a narcotic or
hallucinogen, that affects the central nervous system, causing changes in
psychological behaviour and possible addiction, despite their usefulness.
- Drugs are dangerous if misused, which is why
some drugs cannot be bought of the counter of a shop (e.g. local chemist)
without a medical prescription from you doctor, but other drugs, like the
painkiller paracetamol, can readily bought without prescription from your
- It can sometimes be difficult to state
whether the addiction is a physical or mental dependence.
- If some drugs are over used, you may become
addicted to them, which means you have a physical craving for more of it,
without which you can suffer withdrawal symptoms - extreme craving is
symptomatic in itself of addition, and sometimes the body reacts physically
in a negative way e.g. becoming very irritable, shaky hands.
- Tolerance is another problem that arises
when the body becomes used to a drug and progressively needs larger
quantities of the drug to give the same effect. The increasingly higher dose
rate can lead directly to addiction and examples range from legal drugs like
alcohol and nicotine in tobacco and illegal use of cocaine and heroin.
- Addiction can be cured by slowly decreasing
the amounts of the drug administered, but most drug addicts required lots of
support from e.g. the NHS in the UK, help groups and rehabilitation centres
(politely referred to in pop songs as 'rehab').
3.2 Be able to describe the general effects
- a) Painkillers that block pain nerve impulses, including morphine
- yes it is a narcotic, but widely prescribed safely and legally!
- If the nerve impulses to the brain are
blocked, we do not experience a pain sensation and morphine molecules are
very effective at doing this.
- Morphine type drugs are amongst the
strongest painkillers we use.
- Different painkillers are more effective in
particular situations and there maybe safer alternatives that are not as
dangerous or addictive e.g.
- paracetamol, an analgesic, is a good
relatively safe painkiller for headaches.
- Ibuprofen is a good anti-inflammatory drug
for muscle pain and rheumatoid arthritis.
- b) Hallucinogens
that distort sense perception, including LSD.
- When taken, hallucinogens create
hallucinations in your mind so you experience distorted sounds and images
because the normal processing of nerve impulse is interfered with.
- c) Stimulants that increase the
speed of reactions and neurotransmission at the synapse, including caffeine.
- Stimulants increase the activity of the
brain by increasing the amount of neurotransmitters at certain neurone
synapses in the central nervous system i.e. they speed up your brain
- Stimulants increase your speed of reaction
i.e. decrease your response time to a given physical or mental stimulus.
- Many people take coffee to make them more
alert and 'fully awake' in the morning because coffee is a rich source of
the stimulant caffeine.
Depressants that slow down the activity of the brain (opposite of
stimulants), including alcohol.
- Depressants slow down your responses and
increasing your reaction times to a physical or mental situation i.e. they
slow down your brain functions.
- 'Drink driving' is considered a dangerous
activity and a serious criminal offence because a drunk (or not so drunk)
driver is a danger to others and the driver himself/herself on the road.
- There is a legal limit of alcohol in your
blood which you must be below to 'legally drive' a car, and its pretty low!
- 3.3 Revise any experiments-investigations
you did on reaction times e.g. the falling ruler experiment.
- 3.4 Be able to explain the effects of some chemicals in
cigarette smoke, including:
- a) Nicotine as an addictive drug which
smokers can become dependant on and the more you smoke, the more you may
become dependent on it - like it or not, smoking can become a drug
- b) Tar as a
carcinogen - several molecules (known collectively as carcinogens) in tobacco
tar can cause mutations in the cells of the throat and lungs.
- Such mutations can eventually lead to throat
cancer, and, in particular, lung cancer - whose incidence correlates very
highly with smokers.
- c) Carbon monoxide reducing the oxygen-carrying ability of the blood
- carbon monoxide combines more strongly with haemoglobin than does oxygen
and is slower to be exhaled in the gaseous exchange in the lungs.
- Consequently, smokers will have less oxygen
in their circulatory system.
- The effect can be damaging in pregnant
women, where the foetus in the womb may receive less oxygen through the
placenta causing babies to be underweight at birth.
- 3.5 Be able to evaluate data relating to the correlation between smoking and its
negative effects on health.
- 3.6 Be able to evaluate evidence of some harmful effects of alcohol abuse:
- a) in the
short term -
- blurred vision - at high intoxication
levels you don't see things clearly as normal and your sense of balance is
affected - difficulty walking, impaired memory, slurred speech, in fact most
mental and physical activity is interfered with.
- lowering of inhibitions - antisocial
behaviour, from amusing to offensive actions you wouldn't normally do!
- slowing of reactions - alcohol is a
depressant and slows down brain activity - particularly dangerous for 'drink
- b) in
the long term -
- liver cirrhosis - many people do not
appreciate the poisonous nature of alcohol which can be toxic with a large
intake of high % alcoholic drinks. In small quantities, the liver can
metabolise the alcohol into harmless by-products. However, high 'doses' of
alcohol can cause the death of liver cells and scarring the liver tissue,
eventually restricting the blood flow to the liver. This inhibits the liver
from doing its normal cleaning-filtering job of processing waste products
from the body like urea. A build up of waste products like urea may harm the
rest of your body.
- brain damage - alcohol abuse is
associated with widespread and significant brain lesions - permanent brain
damage with potentially fatal consequences.
- 3.7 Be able to discuss the ethics of organ transplants
when the organ is so damaged that a transplant is required to prolong life, including:
- a) liver transplants
for alcoholics -
- Bearing in mind the acute shortage of organ
donors (living or dead), should alcoholics with serious cirrhosis of the
liver be given priority over someone who develops liver disease through no
fault of their own?
- A liver transplant patient should be
expected to stop drinking before and after the liver transplant operation,
otherwise why waste a valuable organ to be damaged by a transplant patient
who will not stop drinking?
- b) heart transplants for the clinically obese
- Obese people have a greater chance of dying
during and after heart surgery and doctors can insist that the heart patient
loses weight before major surgery is considered.
- c) the supply of
- Organs can be donated in advance by your own
consent at your own death eg kidney donor card, though your family must be
- Organs can come from people killed in
accidents or even from somebody declared brain dead, BUT without prior
consent of the deceased, organ transplant consent must come from relatives.
- Organs can be donated by living people e.g.
we have two kidneys and we can donate one and live (with dietary care) very
well on one kidney.
- Unfortunately there is a great shortage of
organ donors in the UK and so the medical profession is encouraging people
to become organ donors in the event of their death.
- The ethical issues are complex and whatever
you think about whether a patient deserves an organ transplant, the medical
profession basically decides on the basis of which patients are most likely
to benefit from a transplant operation - sounds simpler than it sounds, it
might not be just a medical opinion (the main factor), the likely patient's
attitude post-operation might be taken into account too? (not sure on the
last point? but alcoholics may be short on sympathy from the public? but the
public doesn't decide!)
- 3.8 Know that infectious diseases are caused by pathogens.
3.9 Be able to
how pathogens are spread, including:
- a) in water, including cholera bacterium
- You can be infected with a pathogen by
coming into contact with contaminated water - which is why swimming bath
waters are treated to kill bacteria with chlorine or ozone. In poor third
world countries the bacterial infection cholera, which causes diarrhoea and
dehydration, is readily spread in water contaminated with the faeces of
cholera sufferers. It is potentially very serious, particularly for the very
young and the very old and undernourished adults and children in poor third
world countries with poor sanitation.
by food, including Salmonella bacterium infection
- If you eat food contaminated with pathogens
the resulting food poisoning effects can be very unpleasant and potentially
very serious, particularly for the very young and the very old and the poor
of the third world. If food is kept too long at the wrong temperature, left
out in the open, or food like meat undercooked, you may be poisoned by the
- c) airborne (eg coughing, sneezing), including
influenza virus (causes flue)
- If you are suffering from a cough, chest
infection or flue etc. and you don't take precautions with a large
handkerchief or tissue, when you cough or sneeze you blast out into the air
a fine mist of water droplets containing millions of bacteria or viruses.
People around you breathe in you exhaled pathogens and potentially become
infected. Lots of people in a crowded room are great breeding places for
- d) by contact, including athlete’s foot fungus
- You can be infected with a pathogen just by
touching a contaminated surface with e.g. your hand or foot. A common
example is the spread of athlete's foot, a fungal infection easily spread in
swimming bath surfaces, shower floors, towels i.e. anything an athlete's
foot carrier has been in contact with.
- e) by body fluids,
including HIV infection
- The HIV virus causes AIDS, a disease that
stops our immune system from functioning properly - you become more
susceptible to infectious diseases than a normal healthy person and the
condition is often fatal in the end, despite the best efforts of anti-viral
drugs. These kinds of pathogens can only be passed on by direct contact with
body fluids from another person e.g. from a HIV carrier's sperm during
sexual intercourse, or some body penetrating situation e.g. using the same
drug needle as a HIV carrier.
- f) by animal vectors (animals that spread
- (i) housefly: dysentery bacterium
- The common housefly is a carrier of a nasty
protozoan bacterium. This pathogen causes dysentery, a disease that
expresses itself with severe diarrhoea and dehydration. Again this can have
serious consequences for the very young, the very old and the poor of
the third world.
Anopheles mosquito: malarial protozoan
- The mosquito is a carrier of protozoan
pathogen that causes the disease called malaria, a disease that causes
potentially fatal kidney and brain damage. This serious infectious disease
is passed onto another animal which is bitten by a mosquito - a mosquito
bite is a bit more serious than a bee or wasp sting!
- 3.10 Be able to explain how the human body can be effective against attack from
- The body has different physical and chemical ways of protecting itself
- a) Physical barriers – skin, cilia, mucus
Physical protection from
Your skin and hairs and mucous
in the respiratory tract can stop a lot of the pathogen cells from entering
your body. The whole of the respiratory tract from the nasal passage, down
the trachea and into the lungs is covered with mucous and lined cilia (fine
hairs that can move freely at their ends). The mucous traps dust and
bacteria before they can get down into the lungs and the cilia move the
mucous along from the lungs up to the nasal passage -and then you can blow
Skin in good condition acts as a
very effective barrier against pathogens. When a cut in the skin occurs,
small sections of cells called platelets help the blood to clot quickly to
seal the wound (seal = scab when dry) and prevent microorganisms entering
the skin tissue or blood stream. The greater the concentration of platelets
in the blood the faster the clotting process ('sealing') can occur.
- b) Chemical defence – hydrochloric acid in the stomach, lysozymes in tears
Chemical protection by killing
In tears our eyes produce
chemicals called lysozymes that kill bacterial microorganisms on the surface
of the eye.
Your stomach contains quite
concentrated hydrochloric acid which kills the majority of pathogenic
bacteria - sadly not all of them at times!
- 3.11 Be able to demonstrate an understanding that plants produce chemicals that have
antibacterial effects in order to defend themselves, some of which are used by
- Plants attacked by pathogens can defend
themselves by producing chemicals, often in oil secretions, that have
- Some of these oils have medicinal properties
that humans have used in traditional medicine recipes.
- Other oils have been used as additives in
products of the cosmetics industry.
- 3.12 Be able to describe how antiseptics can be used to prevent the spread of
- Antiseptic chemicals are designed to prevent
infection rather than treat and cure an existing infection - prevention is
always better than a cure!
- Antiseptics are chemicals that are applied
to the outside of your body to kill pathogens like bacteria or prevent their
- Antiseptics help to prevent infection of
cleaned skin wounds and the surface of the skin e.g. a larger area where a
surgical operation might be done and they are also applied to surfaces where
hygiene is important e.g. in the bathroom.
- Antiseptics range from those used in the
home e.g. for cuts and bruises, toilet cleaners, treating food preparation
surfaces, and in GP surgeries, and in hospitals to prevent infection during
operations and on hospital wards to prevent the spread of dangerous
pathogens like MRSA - you should always clean your hands with the antiseptic
facilities provided when visiting friends or relatives in hospital.
- 3.13 Be able to explain the use of antibiotics to control infection, including:
- Antibiotics are taken internally e.g.
intravenous syringe injection, or orally taken tablet or liquid suspension.
- In other words they are treating you from
the inside and treat an existing pathogen infection you have (bacterial or
- Compare these two point with the external
use of antiseptics in preventing infection.
- a) antibacterials to treat bacterial infections
- Probably the most well known antibacterial
is the antibiotic penicillin which is effective against many bacterial
infections BUT NOT viruses like the common cold or flue.
- An antibiotic can kill bacteria or prevent
them growing and reproducing.
- b) antifungals to treat fungal
- Antifungal chemicals kill or prevent the
growth of fungi microorganisms e.g creams for the treatment of the fungal
infection athlete's foot.
- 3.14 HT only: Be able to evaluate evidence that resistant strains of bacteria, including
MRSA, can arise from the misuse of antibiotics.
Antibiotics, including penicillin, are medicines that
help to cure bacterial disease by killing infectious
bacteria inside the body.
What is an antibiotic?
Antibiotics cannot be used
to kill viral pathogens, which live and reproduce inside
penicillin kill or prevent the growth of harmful pathogens, they kill the
bacteria but not your own body cells.
Different antibiotics attack
different bacteria, so it is important that specific bacteria should be
treated by specific antibiotics.
The use of antibiotics
has greatly reduced deaths from infectious bacterial
However, overuse and inappropriate use of antibiotics
has increased the rate of development of antibiotic
resistant strains of bacteria.
You need to be aware that it is difficult to develop
drugs that kill viruses without also damaging the body’s
Many strains of bacteria, including MRSA, have
developed resistance to antibiotics due to mutations, which cause stronger more
resilient strains of bacteria to survive as a result of
To prevent further resistance
arising it is important to avoid over-use of antibiotics.
Knowledge of the development of resistance in bacteria
is limited to the fact that pathogens mutate, producing
Mutations of pathogens produce new strains.
Antibiotics and vaccinations may no longer be effective
against a new resistant strain of the pathogen.
strain will then spread rapidly because people are not
immune to it and there is no effective treatment.
Can bacteria become resistant
Unfortunately the answer is yes!
Bacteria will sometimes quite naturally mutate into forms that are resistant
to current antibiotics, so if your infected with a new strain of bacteria,
your resistance is not as effective.
If an infection is
treated with an antibiotic, any resistant bacteria will survive and
this means resistant bacteria
can survive and reproduce to infect other people, while the non-resistant
strains will tend to be reduced.
This is an example of natural
selection at the individual cell level and drug companies are constantly
trying to develop new antibiotics to combat the new evolving strains of
harmful bacteria - but new harmful 'superbugs' are becoming more common the
more we use antibiotics and new epidemics can break out!
staphylococcus aureus, can't be treated with many current antibiotics and
causes serious wound infections that can be fatal to young babies or elderly
people in particular.
Misuse by over-prescribing antibiotics is
believed to be causing the rise of mutant resistant strains of bacteria, so
doctors are being advised to avoid over-prescribing antibiotics to reduce
the mutation rate and not treating mild infections with antibiotics.
It isn't just bacteria that can
mutate, viruses can also evolve via new mutations. Viruses are
notable for the rapidity with which they can mutate which makes it difficult
to develop new vaccines. The reason being that changes in the virus (or
bacteria) DNA leads to different gene expression in the form of different
antigens, so different antibodies are needed. The flue virus is a never
ending problem and in the past pandemics (epidemics across many countries at
the same time) have killed millions of people, mercifully this rarely
happens these days thanks to antibiotics.
Individual resistant pathogens survive and
reproduce, so the population of the resistant
Now, antibiotics are not used to treat
non-serious infections, such as mild throat
infections, so that the rate of development of
resistant strains is slowed down.
- 3.15 Revise any investigation into the effects of
antiseptics or antibiotics on microbial cultures.
- 3.16 Know that
interdependence is the dynamic relationship between all living things.
It is important to understand
that all living things are interdependent on each other, especially through
the pathways of food chains, which are effectively energy chains too.
Apart from the obvious need for
food and energy to survive and reproduce, there are many other factors too
for particular organisms e.g. most flowering plants rely on insect
Be able to demonstrate an understanding of how some energy is transferred to less useful
forms at each trophic level and this limits the length of a food chain.
- 3.18 Be able to show an understanding that the shape
of a pyramid of biomass is determined by energy transferred at each trophic
- 3.19 Be able to explain how the survival of some organisms may depend on the presence
of another species:
- a) parasitism - where one organism,
to survive, feeds off another that acts as the host - parasites 'take with
no give', live in or on the host which they may harm in the process!, including:
- (i) fleas - insects that live in the fur of
live animals and in the bedding of us humans. They feed by sucking the blood
of their host provides all their feeding needs and helps them to reproduce
rather too efficiently for our liking!
- (ii) head lice - insects that live on the
upper skin layer of the human scalp. Like fleas, they suck human blood for
all their feeding needs and make your head feel itchy!
- (iii) tapeworms - a parasite that can live
in a person's intestines (bowel) and they tend to be flat, segmented and
ribbon-like. Humans can catch them by touching contaminated faeces (stools)
and then placing their hands near their mouth, swallowing food or water
containing traces of contaminated faeces or eating raw contaminated pork,
beef or fish. Tapeworms are common in many animals and feed by attaching
themselves to the walls of an animal's intestine and absorb food through
their outer body covering. In extreme cases you can suffer from malnutrition
- all take and no give!
- (iv) mistletoe - is a parasitic plant that
attaches itself to trees and shrubs and grows by penetrating between the
branches and absorbs nutrients and water from the host plant. Like the
tapeworm producing malnutrition in animals, mistletoe can affect and reduce
the host plant's growth.
- b) mutualism - where two organisms
mutually benefit from a relationship - 'give and take' in a good
evolutionary Darwinian deal! - known as a mutualistic relationship!, including:
- (i) oxpeckers that clean other species -
these are birds that live on the backs of grazing animals (e.g. large
mammals like buffalo, oxen, rhinos etc.) and eat large quantities of ticks,
flies and maggots to feed themselves. In doing so they remove unwanted
parasites from the animal, hence they are classed as a 'cleaner species'.
cleaner fish - these small fish feed off dead skin and parasites on the skin of
larger fishes. In doing so they feed well, remove unwanted parasites from
the big host fish and don't get eaten by the host fish!
- HT only (iii) nitrogen-fixing bacteria in legumes
- most plants cannot absorb and chemically process the nitrogen in air to
help synthesise amino acids to convert into proteins. However, leguminous
plants (e.g. beans, clover, peas etc.), have in their root nodules, bacteria
with the right enzymes to convert the nitrogen in air into nitrates, which
the plant needs and can use to make proteins. In return the bacteria get a
regular supply of water and sugar for energy, to everyone's mutual
- HT only (iv) chemosynthetic bacteria
in tube worms in deep-sea vents - these extremophiles mutually depend on each
other to survive. The bacteria get their necessary 'life chemicals' from the
tube worms and in reproducing themselves they become food for the tube worms
which act as the host.
- 3.20 Be able to analyse, interpret and evaluate data on global population change.
Know and understand that rapid growth in the human
population and an increase in the standard of living means that increasingly
more waste is produced and has an increasing impact on our environment, and
on a global scale!
The world population graph above
shows the dramatic exponential growth of the global population of 'planet
Earth' over the past 2000 years.
In 2013 it is estimated that the
world population is now 7 billion! and rising fast!
Over the past few hundred years,
with increasingly more modern medicine reducing disease and more efficient agriculture (eg
artificial fertilisers increasing food production with modern farming
methods) have enabled more people
to survive and themselves reproduce!
Therefore there is a greater
demand for the Earth's resources from extracting oil for petrol and
plastics to mining/quarrying mineral/metal ores to extract metals such
as iron or copper and these resources are finite - they will run out
eventually - not sustainable for ever!
The bigger the world's
population, the bigger the environmental impact and the more waste we
create and have to deal with by 'safely dumping' in landfill sites
(which may include toxic materials), recycling selected waste materials
or burning to make useful heat etc.
Recycling reduces polluting
waste, and uses less energy than if you were e.g. producing a metal from
its naturally occurring ore.
Be able to explain how the increase in human population contributes to an increase in the
production of pollutants, including ....
- ... an increasing world population needs an
increasing amount of food and an increasing amount of energy to meet peoples
expectations and demands. This puts pressure on agriculture to produce more
food, often by using artificial fertilisers (non-organic fertiliser) and
burning more coal, gas and oil in power stations to make electrical energy
for industrial and domestic consumption.
- Phosphates - pollution from overuse of
- Nitrates - pollution from overuse of
- both phosphate and nitrate pollution
contribute to the problem of eutrophication (see below).
- Sulfur dioxide - from burning fossil fuels,
causes air pollution (affects plants, lichen) and acid rain (corrodes
stonework and metal structures).
Be able to explain how eutrophication occurs and the problems associated with
eutrophication in an aquatic environment.
- 3.23 Revise any investigation you did on the effect of
pollutants on plant germination and plant growth.
- 3.24 Be able to demonstrate an
understanding of how scientists can use the presence or absence of indicator
species as evidence to assess the level of pollution - living indicators:
- Certain organisms are very sensitive to
changes in their environment, particularly with respect to the presence of
- Some organisms can only live in unpolluted
water, air or land, but other organisms might actually thrive under polluted
- Therefore, by monitoring the populations of
both types of these organisms you can get some idea of whether the
environment is polluted or not.
- a) polluted water indicator
– bloodworm, sludgeworm
- b) clean water indicator – stonefly, freshwater shrimps
- c) air quality indicator – lichen species, blackspot fungus on roses
- Notes for section 3.24 on Indicator
You should know and understand that living organisms can be used
as indicators of environmental changes such as pollution.
Despite the presence of
pollutants, some species of plants/animals can live in polluted air or
water, but other organisms need clean air or clean water to survive and
The absence or presence of these
indicator species e.g. from monitored population counts, can say much
about whether a particular atmospheric or aquatic environment is relatively
polluted or unpolluted.
These indicator species can be
quite sensitive to their environment and we can put their sensitivity to
their surroundings to good use in environmental monitoring and hopefully
control things to improve matters.
These pollution indicators
may live ...
... on surface exposed to
air e.g. lichen on rocks/stone walls, blackspot fungus on roses,
... live in water e.g.
mayfly larvae, stonefly larvae, freshwater shrimps, bloodworms,
Lichens can be used as air pollution
indicators, particularly of the concentration of sulfur dioxide in the
The cleaner the air in
the environment, the more varied species, and the greater numbers of
an individual species of lichen colonies are seen on rocks and stone
walls. You would observe the 'cleaner air' effect if you surveyed
walls all the way from a polluted town or city centre to some rural
location away from roads well beyond the town or city boundary, and no
doubt note the greater the numbers and variety of lichen growing on the
walls the further you where from the town/city centre.
Therefore, lichen species
can be used as quite a sensitive air pollution indicator i.e. low
populations of a limited number of lichen species indicates polluted
air, usually from sulphur dioxide (SO2).
Particular lichens are
sensitive to poisonous sulfur dioxide (even in very low
concentrations of SO2) from fossil fuel burning -
road vehicle exhausts, power station chimneys etc.
Blackspot fungus readily
grows on roses in relatively clean unpolluted air, but does not grow as
readily in polluted air - the fungus is killed by the polluting sulfur
dioxide. One advantage an urban gardener has over a country gardener!
Invertebrate animals can be used as
water pollution indicators
and are used as indicators of the concentration of dissolved oxygen in
Lakes that are stagnant
from overgrowth of algae (eutrophication) become devoid of oxygen at
lower levels because the decay bacteria use up the oxygen. This
decreases invertebrate populations and animals that feed on them,
like fish, also decline - so whole food-chains and complex
ecosystems are disrupted.
If rivers become
polluted from raw sewage spills or silage spills, the concentration of
pathogens rise (extra food for them e.g. nitrate nutrients) and these microorganisms use up the
oxygen, so all species needing oxygen decline - which is nearly
Certain bacteria will
thrive in these conditions and consume oxygen in the process.
Some species actually
thrive in low oxygen polluted water e.g. a high population of blood
worms and sludge worms indicates very polluted water.
animals like the mayfly larvae and stonefly nymphs are particularly
sensitive to pollution, so their population size is a very good
indicator of the purity of the water. The less pollution in the lake
or river water, the less the growth of algae/bacteria etc. and the more
oxygen dissolve in the water (less used up), therefore the more mayflies
and stoneflies hatched out for the trout! and more trout for the
fisherman! BUT only in clean unpolluted water!
Environmental changes can be
measured using non-living indicators (usually sensors) to monitor factors such as oxygen levels
in water, temperature and
You should understand the use of
equipment to measure oxygen levels, temperature and rainfall, all of which
are important indicators of environment change on land or in water and
the bigger picture of global climate change.
Special meter probes can
be dipped into water to measure oxygen levels, a bit like pH meter
probes that measure pH (which is also an important indicator of
relative acidity-alkalinity). A decline in aquatic oxygen levels as
measured by an oxygen probe gives an
immediate warning of pollution.
Temperature can be
measured directly and very accurately with a mercury thermometer
(being replaces on health and safety grounds),
or, electronically using a thermocouple system. Average temperatures
for the year, or seasonal averages, are important indicators of
climate change. Both air and sea temperatures are monitored.
instruments can automatically and continuously monitor air pollution
levels of carbon monoxide, sulphur dioxide and ozone levels in the
The data can be
continuously fed, stored and analysed in computer systems for
detailed analysis of air pollution patterns on a long-term basis, so
a decline or an improvement in environmental conditions can be seen
and its progress monitored.
You can do the same with
pH, oxygen level and temperature probes continually monitoring water
systems like rivers.
- 3.25 Be able to demonstrate an understanding of how recycling can reduce the demand for
resources and the problem of waste disposal, including ....
- Paper from wood - recycling paper reduces
the number of trees to be cut down (e.g. deforestation) and both transport
and energy costs are reduced. Recycled paper has become quite acceptable for
many paper based products.
- Plastics from limited oil reserves - oil is
becoming increasingly expensive and the reserves will not last forever, so
recycling plastics makes the oil go a bit further and reduces waste that is
often not biodegradable or take a very long time to degrade and decompose.
- Metals from limited mineral ore deposits -
high grade ores are being used up and less economic lower grade ores are
increasingly exploited using even more energy, often from burning fossil
- We are using up lots of non-renewable
resources e.g. like fossil fuels and metal ores.
- However, in the case of metal ores, we can
recycle metals to reduce costs, including energy bills, and make the
original ore source go further.
- BUT note that recycling isn't without its
costs and inconveniences. Recycling involves collection of waste, sorting
into different material categories, purifying each material and then dealing
with the residual waste.
- Sorting can take time and some materials are
difficult to separate efficiently e.g. plastics, whereas iron objects can be
readily separated with a magnet.
- Sorting equipment can be expensive and some
sorting is done by hand.
- Recycled material is often not as good as
the original material and cannot be recycled forever. Its easy to recycle
metals like iron, steel, aluminium and copper many times, though each time
useful metal is lost, but plastics and paper can only be recycled a few
- 3.25 and 3.26 Nature's great natural
- All living things are made of elements like
carbon, nitrogen, hydrogen and oxygen which are all obtained from the
environment they live in e.g. from the air, soil or water.
- By one means or other these elements are
returned to the environment as e.g. carbon dioxide in air, water or nitrogen
in air or nitrogen compounds in soil.
- If this did not happen, new life could not
be formed from the living feeding on pre-existing food (alive or dead).
- Food chains and decomposers play important
roles in this recycling as exemplified by the carbon cycle and nitrogen
cycle, both of which are illustrated and described below.
- The function of bacteria, decomposers, food
chains etc. is all explained.
- 3.26 Be able to show an understanding of how carbon is recycled
(CARBON CYCLE diagram above):
- a) during
photosynthesis plants remove carbon dioxide from the atmosphere
carbon dioxide + water == light
energy/chlorophyll ==> glucose + oxygen
is the process by which plants make food, for themselves, and for most
animal life, including us too!
Note that the only way carbon
dioxide is removed from the air is photosynthesis in green land based plants
or marine organisms like phytoplankton (this point ignores long term
formation of carbonate rocks like limestone).
- b) carbon compounds pass along a food chain
- All food chains involve the passing of
carbon compounds e.g. sugars, carbohydrates, fats and proteins up to the
next trophic level i.e. the consecutive eating along a food chain (and waste
produced on the way).
- e.g. grass ==> cow ==> human
- c) during plant or animal aerobic respiration organisms release carbon dioxide into the
- sugars e.g. glucose + oxygen ==> carbon dioxide + water (+
- this is the main aerobic energy releasing
process in most living organisms.
- d) decomposers release carbon dioxide into the atmosphere
- slow aerobic respiration
- Microorganisms like bacteria and fungi in
the soil feed off decaying plant material and animal droppings or remains.
- Most dead plant matter consists of cellulose
which most animals can't digest, but bacteria and fungi, do have the enzymes
to break it down and without their help there would be no carbon cycle.
- Most of these bacteria and fungi respire
aerobically so they need a good supply of oxygen to produce the carbon
dioxide essential to keeping the carbon cycle going.
- e) combustion of fossil fuels releases carbon dioxide into the
millions of years from the remains of tropical plant material, mainly
consists of carbon, Burning coal produces a lot of pollution as
the greenhouse gas carbon dioxide.
Natural gas (mainly
methane) and petrol molecules like octane (and lots of other
molecules) from oil and gas reserves.
- 3.27 HT only: Be able to show an understanding of how nitrogen is recycled
(NITROGEN CYCLE diagram above):
- a) Nitrogen gas
in the air (78%, ~4/5th) cannot be used directly by
most plants and all animals.
- No animals and only a few specialised plants
can directly use the very unreactive nitrogen from air, but all
plants nitrogen in some form to synthesise amino acids and proteins for
growth and maintenance and for DNA in cell reproduction.
- However, nitrogen can be changed into
nitrogen compounds like nitrates which the plants can use.
- Animals rely on plants or other animals in
the food chain for their source of nitrogen compounds e.g. protein in grass,
crops or other animals.
- b) Nitrogen-fixing
bacteria living in root nodules of plants or in the soil can fix nitrogen gas.
- Leguminous plants like peas, lentils, clover
and beans can absorb nitrogen from the air via their root nodules (swellings
on the root surface) which contain enzymes capable of converting ('fixing')
atmospheric nitrogen into soluble nitrate - a nutrient essential for amino
acids, proteins and therefore plant growth.
- Legumes and their root nodule bacteria are
an example of mutualism (see section 3.19 b) because the plant root supplies
the bacteria with carbohydrate food and minerals and the bacteria supplies
the plant in the form of the nitrate ion.
- The process of converting nitrogen in air
into nitrogen compounds is sometimes called 'nitrogen fixation'.
- c) The action of
lightning can convert nitrogen gas into nitrates.
- The very high electrical energy discharges
from lightning activates nitrogen and oxygen molecules to react and form
nitrogen oxides. These dissolve in rain to form nitrates which end up in the
soil when rainwater trickles into the soil.
- d) Decomposers break down dead
animals and plants
- Decomposers, e.g. various organisms like
bacteria, fungi or worms can break down dead animals or plants. They break
down proteins to amino acids.
- e) Soil bacteria convert proteins and urea into ammonia
or ammonium ions.
- Decomposer bacteria in the soil can change
proteins from dead plants/animals and urea in animal urine/droppings into
ammonia/ammonium ion compounds.
- d) plus e) is sometimes called putrefaction
by putrefying bacteria.
Nitrifying bacteria convert this ammonia to nitrates - the process of
- Nitrifying bacteria oxidise ammonia/ammonium
ions from the decayed material to form nitrates, the nitrate ion can be
absorbed by plants through their root systems.
- g) Plants absorb nitrates
from the soil.
- Plants absorb nitrates (soluble in water) in
the moisture that the roots absorb from the surrounding soil.
- Plants can use the nitrate ion in forming
amino acids from which the plant can make its proteins.
- h) Nitrates are needed by plants to make proteins for growth.
- Nitrates are an essential nutrient for
plants to synthesis amino acids and hence proteins.
Nitrogen compounds pass along a food chain or web of food chains.
- All food chains involve the passing of
carbon compounds e.g. sugars, carbohydrates, fats and proteins up to
the next trophic level i.e. the consecutive eating along a food chain (and
waste produced on the way).
- e.g. grass ==> cow ==> human
- Plants make their own protein from nitrates,
but animals must obtain it from plants or other animals. In fact the protein
is broken down in digestion to amino acids and each animal makes its own
proteins from these amino acid residues.
- j) Denitrifying bacteria
convert nitrates to nitrogen gas.
- Particular bacterial organisms can remove
the oxygen from nitrate compounds to form the element nitrogen gas.
- These denitrifying bacteria live in
anaerobic conditions like waterlogged soils and use the nitrate ion to
- This is the opposite function of the
nitrogen-fixing bacteria (b).
Edexcel GCSE Biology
When revising, these pages
provide you with a summary of what you need to know and be able to do.
BUT remember, your primary
source of revision are your class notes, investigations and Edexcel GCSE
Edexcel GCSE Science BIOLOGY
When revising, these pages
provide you with a summary of what you need to know and be able to do.
BUT remember, your primary
source of revision are your class notes, investigations and Edexcel GCSE
science textbooks as well as examination practice with past papers.
EDEXCEL GCSE Science
BIOLOGY 1 UNIT 1
Classification, variation and inheritance INDEX
ALL Edexcel GCSE Science Units:
Edexcel GCSE Science Biology Unit B1 Influences on life
Edexcel GCSE Science Biology Unit B2 The components of life
* Edexcel GCSE Science Unit B3 Using biology
Edexcel GCSE Science Unit C1 Chemistry in our world
* Edexcel GCSE Science Unit C2 Discovering Chemistry
Edexcel GCSE Science Unit C3 Chemistry in action *
GCSE Science Unit P1 Universal Physics
GCSE Science Unit P2 Physics for your future * Edexcel GCSE
Science Unit P3 Applications of Physics
GCSE Science-Biology courses
AQA GCSE Science A BIOLOGY *
EDEXCEL GCSE Science BIOLOGY
OCR GCSE 21st Century
Science A BIOLOGY * OCR GCSE Gateway
Science A BIOLOGY
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