Edexcel Categories Archives: B1

Human activity and the Environment

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.
  • As a result: more humans = greater impact
  • Potential problems:
    • Raw materials, including non-renewable energy resources are rapidly being used up.
    • More and more waste is being produced.
    • More and more pollutants are being produced, including phosphates (from detergents), nitrates (from fertilisers) and sulphur dioxide (from coal-burning power stations).


  • Materials that aren’t recycled are thrown away as waste. This means that:
    • There is more waste therefore more land required for landfill sites. Waste is toxic so more polluted land.
    • More materials need to be extracted/manufactured therefore more energy and resources needed.
  • Recycling processes usually uses less energy and create less pollution than making from scratch.
  • Things that can be recycled:
    • Metals: Metals should be recycled as there is a limited amount of ore – recycling means less has to be extracted. Mining and extracting takes lots of energy, most of which comes from fossil fuels. Recycling therefore means fewer resources are used up, less fossil fuels, less CO2
    • Paper: Recycling paper means fewer trees are cut down, thus preventing deforestation. Recycling paper uses 28%-70% less energy than manufacturing new paper.
    • Plastics: Plastics come from crude oil so recycling plastics conserves oil resources. Plastics decompose very slowly so will stay in landfill sites for years unless recycled.

Problems with recycling

  • Recycling still uses energy.
  • Time consuming and difficult to sort out, such as plastics have to be separated from each other.
  • Equipment needed for recycling can be expensive.
  • Quality of materials isn’t always good e.g. recycled paper.
  • Some materials can only be recycled a limited number of times (but metals can be recycled indefinitely).
  • England and Wales produce over 100 million tonnes of domestic, commercial and industrial waste a year. We do recycle more each year but a lot more can be done like other European countries. New laws are being introduced in the UK and the European Union (EU) to increase recycling, e.g. by 2015, EU law requires that cars will have to be made of 95% recyclable materials.
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The Nitrogen Cycle

The Nitrogen Cycle

  • The Nitrogen Cycle: A sequence of processes by which nitrogen moves from the atmosphere through living and dead organisms, into the soil and back to the atmosphere.
  • There are four main types of bacteria involved in the Nitrogen Cycle:
    • Decomposer bacteria – decomposes proteins and urea and turns them into ammonia.
    • Nitrifying bacteria – converts ammonia to nitrites then nitrates.
    • Nitrogen-fixing bacteria – turns atmospheric nitrogen into nitrogen compounds.
    • Denitrifying bacteria – turns nitrogen compounds back into nitrogen gas. No help to living organisms.
  • Nitrogen gas takes up 78% of the air and is very unreactive. As a result, it cannot be used by organisms directly. Nitrogen is necessary for making proteins for growth, so it is essential they get it.
  • Nitrogen in the air is turned into nitrogen compounds by nitrogen-fixing bacteria which is called nitrogen fixation. Nitrogen fixation also occurs with lightning as there is so much energy in a bolt of lightning that it’s enough to make nitrogen react with oxygen to give nitrates.
  • Nitrogen compounds, such as nitrates, can be absorbed by plants through the soil and use them to make amino acids (then to proteins). As animals can only get nitrogen compounds from eating plants, nitrogen compounds are passed along the food chain.
  • 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. This is why legume plants are so good at putting nitrogen back into the soil, and for this reason they are often planted in a field before the main crop is planted in the same field so the main crop has a lot of nitrogen.
  • If soils are lacking in oxygen, such as when they are waterlogged, then some denitrifying bacteria will convert the nitrates back into nitrites and others convert nitrites back to nitrogen gas.

  • Eutrophication
    • Fertilisers are used a lot in modern farming as they help crops grow very well; meaning higher food yields so more people can be fed. Fertilisers include nitrates, and they replace the nitrates taken out of the soil when the crops grown.
    • Eutrophication usually occurs when too much fertiliser has been added to the soil and especially if it rains afterwards. Water can wash the nitrates away as nitrates are very soluble, and they can end up in water systems.

    The process:

    1. Leaching of the soil/fertilisers/sewage effluent into water system e.g. pond, stream, lake, sea
    2. Increase nitrogen in water system.
    3. Algal bloom –quick growth of algae.
    4. Algal blooms cover the surface of the water which blocks out sunlight.
    5. Plants die out as they compete for the light and cannot photosynthesise.
    6. Increase dead matter causes an increase in bacteria and microbes. These respire aerobically which uses up the oxygen and thus reduces the oxygen concentration in the water.
    7. Other organisms cannot respire due to the oxygen reduction and therefore they die as well.
    8. Mass reduction in biodiversity.

    “mega-growth mega-death mega-decay”


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The Carbon Cycle

The Carbon Cycle
• The Carbon Cycle: A sequence of processes by which carbon moves from the atmosphere, through living and dead organisms, into sediments and into the atmosphere again.
• The only way carbon dioxide is removed from the atmosphere is by photosynthesis – and there are numerous ways it returns to the atmosphere.
• Eating passes the carbon compounds in the plant along to animals in a food chain or web.
• Both plant and animal respiration put carbon dioxide back into the atmosphere.
• Plants eventually die and decay and decomposer microorganisms such as bacteria and fungi feed on them. When they respire they release carbon dioxide back into the air.
• Fossil fuels (made of decayed plant and animal matter), when burned, release carbon dioxide into the air.

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. Dead organisms decay because they’re broken down by decomposers, and the elements are put back into the soil.
• All the important elements are recycled – they return to the soil or air, ready to be used by new plants and put back into the food chain.

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Indicator species

Indicator species

  • 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 pollution.
  • Indicator species can also reflect a unique set of environmental qualities or characteristics found in a specific place such as a unique microclimate.

Water pollution

  • If raw sewage or other pollutants containing nitrates are released into a river, the bacterial population in the water increases and uses up the oxygen.
  • Some invertebrate animals like stonefly larvae and freshwater shrimps are good indicator for water pollution because they’re very sensitive to the concentration of dissolved oxygen in the water. If you find stonefly larvae in a river, it indicates that the water is clean.
  • Other invertebrate species have adapted to live in polluted conditions, so if they are seen they are sign of a problem e.g. blood worms and sludgeworms indicate a very high level of water pollution.

Air pollution

  • Air pollution can be monitored by looking at particular types of lichen that are very sensitive to the concentration of sulphur dioxide in the atmosphere (therefore can give an idea about the level of pollution from car exhausts, power stations, etc.)
  • The number and type of lichen at a particular location will indicate how clean the air is (if the air is clean there is a lot of lichen).
  • Blackspot fungus works similarly. It is found on rose leaves and is also sensitive to the level of sulphur dioxide in the air; therefore its presence will indicate clean air.

Non-living indicators

  • Dissolved oxygen meters and chemical tests are used to measure the concentration of dissolved oxygen in water, to show how the level of water pollution is changing.
  • Electronic meters and various laboratory tests are also used to measure the concentration of sulphur dioxide in air, to show how air pollution is changing.
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Food webs

Food webs

  • Interdependence: When organisms in an area depend on each other for food.
  • All organisms require food to survive. Some organisms are producers and make their own food, such as green plants, and the rest get their food from other organisms. They are either primary consumers (by eating plants) or secondary consumers (by eating primary consumers).
  • Food chains show what eats what. Organisms that feed on the same level in a food chain are in the same trophic level.
  • Food chains from a habitat can be joined together into a food web which shows the feeding relationship between the different organisms. You can see from this food web that organisms in an area depend on each other for food; they are interdependent.
  • As the numbers of one organism change, other organisms are affected so the relationships among the organisms are always changing. We call this a dynamic relationship; dynamic means changing.

Energy transfers in food chains

  • The Sun is the source of energy for nearly all life on Earth.
  • Plants convert a small percentage of light that falls on them into glucose. A rabbit, for example, may eat the plant and use up some of the energy it gets from the plant. The rest of it is stored in its body. Then a fox may eat the rabbit and therefore get some of energy stored in rabbit’s body. This is a simple food chain.
  • Energy is used up at each stage to stay alive in numerous ways. For example, respiration uses up energy, heat energy is lost to surroundings and energy is lost through excrement.
  • Heat energy lost is especially true for homeotherms whose bodies must be kept at a constant temperature which is normally higher than their surroundings.
  • The energy isn’t really ‘lost’ – it just means the next animal in the food chain can’t use it.
  • This explains why it is very rare to get food chains with more than five trophic levels. So much energy is lost at each stage that there simply isn’t enough energy to support more organisms after four or five stages.


Pyramids of biomass

  • 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.
  • Each time you go up one trophic level the mass of organisms goes down. This is because most of the biomass/energy is lost and so does not become part of the biomass in the next level up.

Parasitism and Mutualism

  • Parasitism: This is when organisms live on a host organism but the host organism is harmed and the organism on the host benefits. Win-lose situation.
  • Mutualism: This is when both organisms benefit and rely on each other for survival. Win-win situation.


  • Fleas: Fleas are insects that live in the fur and bedding of animals, including humans. They feed by sucking the blood of their hosts and can reproduce quickly. Their hosts gain nothing from having fleas.
  • Head lice: these are insects that live on human scalps, sucking blood for food.
  • Tapeworms: Tapeworms attach themselves to the intestinal wall of their hosts. They absorb lots of nutrients from the host, causing them to suffer from malnutrition.
  • Mistletoe: Mistletoe is a parasitic plant that grows on trees and shrubs. It absorbs water and nutrients from its host, which can reduce the host’s growth.


  • Oxpeckers: Oxpeckers are birds that live on the backs of buffalo. They eat the pests of the buffalo such as ticks, flies and maggots which benefits the oxpeckers as they get a source of food and the buffalo is free of pests. Not only this, but they also alert the animal to any predators that are near, by hissing. Oxpeckers are an example of a cleaner species.
  • Cleaner fish: Another example of cleaner species is cleaner fish, such as cleaner wrasses. They eat dead skin and parasites off larger fish, such as groupers. In return they get a source of food and avoid being eaten by the big fish.
  • Nitrogen-fixing bacteria in legumes: Most plants have to rely on nitrogen-fixing bacteria in the soil to get the nitrates they need. But leguminous plants (beans, peas, clover etc.) carry the bacteria in nodules in their roots. The bacteria receive a constant supply of sugar from the plant and the plant gets essential nitrates from the bacteria.
  • Chemosynthetic bacteria in deep-sea vents: Some chemosynthetic bacteria live inside giant tube worms or in the gills of molluscs in deep sea vents. The tube worms supply the bacteria with chemicals from the seawater which the bacteria turn into food for themselves and the host worms.
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Physical and Chemical barriers

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. If damaged, blood clots can seal cuts quickly to keep pathogens out.
  • Respiratory system: The whole respiratory tract is lined with mucus and cilia which are hairs that can catch dust and bacteria before they reach the lungs. The cilia push gunk-filled mucus away from the lungs.

Chemical barriers

  • Oil: Hairs on the skin contain a gland that produces oil called sebum. This kills microorganisms and keeps skin supple and waterproof.
  • Eyes: Eyes produce tears which contain a chemical called lysozyme which kills bacteria on the surface of the eye. Blinking spreads this enzyme over the eyes surface.
  • Stomach: The stomach contains hydrochloric acid that kills any swallowed bacteria in food or mucus.

White blood cells

  • There are two ways white blood cells get rid of pathogens: engulfing and digesting them or killing them with antibodies. Phagocytes engulf the white blood cells and B-Lymphocytes produce antibodies.
  • B-lymphocytes produce molecules called antibodies which remember the shape of the antigen on the pathogen. If a new antigen is found different antibodies are tried until one is found that matches the antigen.
  • The antibody locks onto the antigen and the white blood cell destroys the pathogen. Specific immune response.

Defence against invasion: Tea tree

  • A tea tree is an example of a plant that can produce chemicals to defend themselves. Its leaves produce oil that kills bacteria.
  • Indigenous people of Australia have used these leaves in their medicines for centuries. The purified oil these days is used in many different kinds of antibacterial products such as facial cleansers.


  • These are chemicals that destroy bacteria or stop them growing.
  • They can also be used to prevent pathogens entering an open wound, and around areas with a lot of pathogens (toilet, kitchen)
  • Many household products contain antiseptics such as bathroom cleaners.
  • Hospitals and surgeries use antiseptics to prevent spread of infection such as MRSA.


  • These are drugs used inside the body, usually taken as a pill or injected.
  • They are used to treat patients who already infected with bacteria and fungi.
  • However, they do not destroy viruses.
  • There are two types of antibiotics:
    • 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.
    • 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.
  • When the medicine is first taken the susceptible bacteria are killed first. However, the resistant bacteria will be left behind, especially if the person taking the medicine does not finish their course.
  • The resistant bacteria will survive and reproduce and thus making more resistant bacteria to cause illness. This is an example of natural selection.
  • An example of a resistant strain is MRSA (methicillin-resistant Staphylococcus aureus) which causes serious wound infections.
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Infectious diseases

Infectious diseases

  • Pathogens are microorganisms that cause disease. They include bacteria, protozoa, fungi and all viruses.
  • Pathogens are spread in different ways:
    • Water: Water may contain bacteria such as those that cause cholera.
    • Food: Food may contain food –poisoning bacteria such as Salmonella which is found in food that is kept too long or not cooked properly.
    • Airborne: Airborne pathogens are carried in the air in droplets and other people can breathe them in.
    • Contact: Pathogens can be picked up from touching contaminated surfaces including the skin e.g. Athlete’s foot fungus is transferred from moist surfaces.
    • Body fluids: Pathogens can be spread through body fluids such as blood and semen during sex.
    • 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.
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Ethics and organ transplants

Ethics and organ transplants

  • If an organ is severely damage it can be replaced by a donated natural organ. Many people die every year waiting for transplants so the doctors need to decide carefully who to operate on.
  • There is a shortage of organ donors in the UK. Some people say it should be made easier for doctors to use the organs of people who have died as now family’s consent is required before they can use the organs for transplant.
  • Doctors use scientific criteria to consider the likelihood of success of a transplant:
    • have similar tissues (same sort of antigens so the organ would not be attacked)
    • Are similar ages (child’s organ less likely to be successful in an adult’s organ)
    • Geographically close – quicker the organ is transplanted the more likely the operation will be successful.
    • If the patient is very ill, they won’t be considered over a person who is healthier as they would be more likely to survive the operation.
  • People may also have to be considered if they will change their lifestyle:
    • Alcoholics have to prove they can stay off alcohol for more than six months outside hospital.
    • Obese people will have to lose weight.
  • Some people believe those who have harmed their own organs through smoking, drinking etc. don’t deserve an organ transplant as much as those people whose organs have been damaged through illness. However, transplant guidelines are not based on who would “deserve” a transplant but who is most likely to benefit.
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Effects of alcohol

Effects of alcohol

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.

Long-term effects of alcohol

  • Alcohol is normally broken down in the liver into harmless by-products. However, drinking too often causes the death of liver cells.
  • This forms scar tissue that can block blood flow through the liver which is cirrhosis. If the liver can’t do its job of cleaning the blood, dangerous substances start to build up and damage the rest of the body.
  • Too much drinking can lead to brain damage.
  • Alcohol can be addictive – those addicted to alcohol are called alcoholics.
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  • 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:
    • Narcotic: is a drug that makes us feel sleepy.
    • Painkillers: blocks electrical impulses concerning pain from going up to the brain so we feel less pain.
    • Hallucinogens: Drugs like LSD can distort our senses of colour, time and space.
    • Stimulants: Speeds up reaction time as it increases the speed of neurotransmission (as more neurotransmitter is released).
    • 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.
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