GCSE Biology Edexcel B1 Topic 3

I made these revision notes myself. I got an A* in Biology GCSE and 72 UMS in the B1 exam for your note.

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B1 Topic 3 Problems of, and solutions to a changing environment
A drug is a chemical substance that changes the way in which the body works, including our behaviour. Some
drugs particularly affect the central nervous system and change our psychological behaviour.
There are different types of drugs:
o Narcotic: is a drug that makes us feel sleepy.
o Painkillers: blocks electrical impulses concerning pain from going up to the brain so we feel less pain.
o Hallucinogens: Drugs like LSD can distort our senses of colour, time and space.
o Stimulants: Speeds up reaction time as it increases the speed of neurotransmission (as more
neurotransmitter is released).
o Depressants: Slow down reaction times as it decreases the speed of neurotransmission (blocks the
neurotransmitter receptors)
Drugs that are used to make people feel a certain way are recreational drugs (e.g. alcohol) and there are
drugs used to heal people in medicine.
Some drugs are legal, some are only legal at certain ages and some are illegal because they are too addictive
and dangerous.
Some people can get addicted to drugs ­ they feel a physical need for it.
Damage caused by smoking
Nicotine: a drug present in cigarettes which is the addictive part of tobacco smoke. This makes it difficult to
give up smoking.
Tar is a sticky substance that contains chemical substances called carcinogens. These can cause cancers, which
develop mostly in the lungs, mouth and throat.
It coats the lungs and as it thickens it reduces the surface area of alveoli. This means less O2 can diffuse into
the blood.
Carbon monoxide
CO is a poisonous gas as it binds with the haemoglobin in the blood. This bond is 400 times stronger than the
bond in oxyhaemoglobin, therefore it is impossible to remove. This therefore reduces the amount of O2 that
can be transported in the blood.
A lack of oxygen to active muscles can cause pain, such as in the legs when walking.
CO also makes blood vessels narrower. Therefore, body cells by those blood vessels get even less oxygen
and die. Dead tissues must be removed as they can be easily infected.
Paralysed cilia
Tobacco smoke can paralyse the cilia on ciliated cells in the trachea. This means they cannot do their job of
wafting pathogens up the windpipe and therefore smokers more often get chest infections.
This is the build up of tar in the alveoli when it gets to the point that the layer is so thick the person cannot
breathe properly and needs to get treatment.
Effects of alcohol

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Short term effects
Alcohol slows down reactions because it is a depressant.
Being drunk can lead to blurred vision (making it more difficult to do simple tasks) and can lower inhibitions ­
people may do things they normally wouldn't.
The more alcohol in the body the slower the nervous system becomes. Very large amounts can cause
unconsciousness and possible death by choking on vomit. It can also slow the nervous system down so much
that breathing stops.…read more

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Animal vectors: These are animals that spread disease. Examples are the mosquito which carries the
protozoan that causes malaria. It bites other organisms to spread it. House flies can carry the
bacterium that causes dysentery. It spreads the disease by carrying the bacterium onto food.
Physical and Chemical barriers
These are both harnessed by the body to stop pathogens getting in.
Physical barriers
Skin: Outer layer skin cells contain keratin which makes the skin very effective at protecting against
microorganisms.…read more

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Antibacterials: Antibacterial antibiotics are used to treat bacterial infections. They work by killing
bacteria or stopping them from growing. However, bacteria can evolve resistance to the antibiotic,
meaning it doesn't work anymore.
o Antifungals: Antifungal antibiotics such as nystatin are used to treat fungal infections. They work by
killing the fungi or stopping them from growing.
Bacteria can become resistant to antibiotics
There is always variation within a species so naturally there will be bacteria resistant to antibiotics.…read more

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Biomass is how much the creatures at each level of a food chain would weigh if you put them together. This
biomass is a store of energy ­ so a pyramid of biomass shows how much energy there is at each stage in the
food chain.
In this pyramid of biomass, the elder tree is at the
bottom. There may be very few of them but if you weighed
them all together it ends up being the largest trophic level.…read more

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An indicator species is an organism whose presence, absences or abundance reflects a specific
environmental condition.
Indicator species can signal a change in the biological condition of a particular ecosystem and thus may be
used to diagnose the health of an ecosystem.
For example, plants or lichens sensitive to heavy metals or acids in precipitation may be indicators of air
Indicator species can also reflect a unique set of environmental qualities or characteristics found in a specific
place such as a unique microclimate.…read more

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Nutrients are constantly recycled
Living things are made of elements they take from the world around them. Plants not only take carbon from
the environment but also take oxygen, hydrogen and nitrogen from the soil or air. These elements are
formed into complex compounds that make up living organisms.
The elements are returned to the environment as waste products produced by the organisms, or when the
organisms die.…read more

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Decomposer bacteria turn the proteins and urea in dead plants and animals and waste into ammonia. This
ammonia can be converted into nitrites and then nitrates by nitrifying bacteria. As nitrates can be absorbed
by plants, the nitrogen in these organisms is recycled.
Some nitrogen-fixing bacteria live in the soil. Others live in nodules on the roots of legume plants.…read more

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Human activity and the Environment
Rapidly growing population
The population of the world is growing exponentially which means it is growing very quickly.
This is mostly due to modern medicine, making people live longer and more babies to survive at birth. It is
also due to modern farming methods, which can produce more food than they could before to feed a lot of
people.…read more


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