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Doc Brown's Edexcel GCSE Science-Biology Revision Notes

EDEXCEL GCSE Science BIOLOGY UNIT B1 Influences on life

BIOLOGY 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 GP.
    • 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 of:
    • 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 functions.
      • 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.
    • d) 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 inhaled 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 addiction.
    • 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 drivers'
    • 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 e.g.
      • Organs can be donated in advance by your own consent at your own death eg kidney donor card, though your family must be consulted too.
      • 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.
    • An infectious disease is one that spreads from one person to another.
    • Microorganisms that cause infectious disease are called pathogens.

    • Bacteria and viruses may reproduce rapidly inside the body and may produce poisons (toxins) that make us feel ill.

      • Bacteria and certain protozoa are very small cells which can rapidly reproduce by cell division in your body making you feel ill by damaging your body's cells and producing toxins (poisons produced as a by-product of the bacteria's cell chemistry).

      • Viruses are NOT cells and much smaller than bacteria and damage the cells in which they reproduce.

        • Viruses replicate by invading a cell and using the cell's genetic machinery to reproduce themselves ie copies of the original virus.

        • The virus 'invaded' cell then bursts releasing lots of new viruses.

        • Fungi are also pathogens and includes microorganisms like yeasts and moulds (so don't eat mouldy food!).

      • (Knowledge of the structure of bacteria and viruses is not required here.)

      • Fungi are also pathogens and includes microorganisms like yeasts and moulds.

  • 3.9 Be able to describe 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.
    • b) 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 bacterium salmonella.
    • 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 pathogens!
    • d) by contact, including athlete’s foot fungus infection
      • 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 diseases), including:
      • (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.
      • (ii) 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 pathogens, including:
    • The body has different physical and chemical ways of protecting itself against pathogens.
    • a) Physical barriers – skin, cilia, mucus
      • Physical protection from pathogens

      • 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 your nose!

      • 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 pathogens

      • 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 humans.
    • Plants attacked by pathogens can defend themselves by producing chemicals, often in oil secretions, that have antibacterial properties.
    • 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 infection.
    • 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 growth.
    • 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 fungal microorganism)
        • 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 infections
      • 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 cells.

        • Antibiotics do not destroy viruses, typified by the cold and flue viruses we all suffer from. Viruses make your own body cells reproduce the invasive virus and unfortunately anti-viral drugs may attack good cells too!

      • Antibiotics like 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 diseases.

      • 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 tissues.

    • 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 natural selection.

      • 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 resistant strains.

    • Mutations of pathogens produce new strains.

      • Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen.

      • The new strain will then spread rapidly because people are not immune to it and there is no effective treatment.

      • Can bacteria become resistant to antibiotics?

        • 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!

        • MRSA, methicillin-resistant 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 strain increases.

        • 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 pollination,

  • 3.17 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.
    • Radiation from the Sun is the initial source of energy for most communities of living organisms - just a bit of revision of what the main 'producer' is all about.

      • Green plants and algae absorb a small amount of the light that reaches them.

      • The transfer from light energy to chemical energy occurs during photosynthesis.

        • Photosynthesis uses sunlight energy to convert water and carbon dioxide into sugars like glucose, the 'waste product' being oxygen - though plants need oxygen for their respiration at night!

        • the simple equation to illustrate photosynthesis is

        • water + carbon dioxide (+ sunlight) == chlorophyll ==> glucose + oxygen

      • This energy is stored in the substances that make up the cells of the plants.

        • Green plants and algae are the initial producers of food, after that its all consumers, including us!

        • Most food chains, and therefore most life-forms, are therefore dependent on the initial input of sunlight energy.

        • The energy from photosynthesis produces sugars and other carbohydrates, which in turn a source of energy to make fats and amino acids and proteins.

        • The carbohydrates and fats in the cells of plants and algae form part of the cell structure.

        • Plants are consumed by animals which in turn use the energy in respiration to build their fat and protein structures etc.

  • 3.18 Be able to show an understanding that the shape of a pyramid of biomass is determined by energy transferred at each trophic level.
    • Know and understand that the mass of living material (the biomass) at each stage in a food chain is less than it was at the previous stage.

      • Appreciate that the biomass at each stage can be drawn to scale and shown as a pyramid of biomass.

      • Food chain and biomass pyramid introduction

        • Up the food chain: producer ==> primary consumer ==> secondary consumer ==> tertiary consumer etc.

          • The producer is usually a photosynthesising plant or algae.

        • In a biomass pyramid, each horizontal bar (drawn to scale) is proportional to the mass of the living material at that producing level and feeding levels (trophic levels).

        • How to construct a biomass pyramid: To draw to scale, you can keep the vertical height the same for each level and make the horizontal length of the bar proportional to the biomass of that level in the pyramid.

          • Obviously, the bigger the bar, the greater the biomass at the producer/feeding-trophic level.

        • Up the food chain and 'up the pyramid' the biomass gets less because of loss of organic material, waste energy and even the energy from respiration, required to sustain life, eventually becomes waste energy too eg heat energy to the surroundings. More in section (c).

        • -

      • Food chain and biomass pyramid example 1

        • Butterflies/caterpillars feed off cabbage ==> butterflies eaten by blue/great tit birds ==> bird of prey eg kestrel, catches smaller birds eg blue/great tits

        • It takes plenty of vegetables to feed the local population of cabbage white butterflies.

        • -

      • Food chain and biomass pyramid example 2

        • Pondweed eat by tadpoles ==> eaten by water beetle ==> perch fish eat water beetle ==> otter eats perch

        • It takes al lot of pondweed to feed a batch of tadpoles.

        • -

      • Know and understand that the amounts of material and energy contained in the biomass of organisms is reduced at each successive stage in a food chain because:

      • (i) some materials and energy are always lost in the organisms’ waste materials by eg excretion (urine, droppings), fallen leaves from trees etc.

      • (ii) respiration supplies all the energy needs for living processes, including movement and much of this energy is eventually transferred to the surroundings, particularly with warm blooded mammals where much energy is spent in maintaining their raised body temperature.

        • the overall simplistic equation for respiration is the opposite of photosynthesis

        • glucose + oxygen ==> water + carbon dioxide (+ energy)

        • This energy is needed for all life processes, energy to do things like movement of any organism, heat to keep mammals warm,

        • The fact of the matter is, that up a food chain/biomass pyramid, only a small percentage of the mass is passed on eg

          • plants producers (100%) ==> primary consumers (caterpillars, 40%) ==> secondary consumers (small birds 5%) ==> bird of prey (owl, 0.5%)

          • This means in this particular food chain, that of all the mass /energy you start with, only 0.5% (1/200th) eventually ends up as the owl.

          • In the food chain: plants ==> rabbits ==> foxes, all these fields of plants of large areas of grass support a relatively smaller population of rabbits, which in turn support a very small number of foxes - you only get a relatively small numbers of a top predator!

          • This is the reason why you rarely get food chains of more than five stages (feeding/trophic levels) because there is so little mass/energy left in the end.

          • Once the energy is lost, it can't be used by the animal in the next stage of the food chain i.e. the next trophic level.

  • 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'.
      • (ii) 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 satisfaction!
      • 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.

  • 3.21 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 artificial fertilisers
    • Nitrates - pollution from overuse of artificial fertilisers
      • 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).
  • 3.22 Be able to explain how eutrophication occurs and the problems associated with eutrophication in an aquatic environment.
    • Eutrophication is a rather deadly situation for aquatic ecosystems in lakes and rivers.

      • Fertilisers have improved agricultural crop yields enormously over the past hundred years, but overuse of nitrogen based artificial fertilisers (e.g. NPK varieties) has caused some major pollution problems. Rainwater will dissolve some of the fertilisers salts (e.g. nitrates and phosphates) and the resulting run-off will concentrate in streams, rivers and lakes. This increases the nutrient concentrations well above the normal background levels associated with a stable ecosystem. The richer source of nutrients, like nitrates, causes a rapid growth in algae, but, so much algae forms, that plants beneath the surface are starved of light and begin to die. The dead plant material is fed on by microorganisms and in doing so, use up the oxygen in the water. The lack of oxygen then begins to kill fish and other animals, which effectively suffocate due to the lack of oxygen for respiration. Sections of streams, rivers and lakes can be devoid of most organisms except the algae!

  • 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 pollution.
    • Some organisms can only live in unpolluted water, air or land, but other organisms might actually thrive under polluted conditions.
    • 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 Species
    • 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 prosper.

      • 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, sludgeworms

    • Lichens can be used as air pollution indicators, particularly of the concentration of sulfur dioxide in the atmosphere.

      • 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 water.

      • 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 everything!

        • 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.

      • Particular invertebrate 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 rainfall.

      • 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.

        • Specialised electronic instruments can automatically and continuously monitor air pollution levels of carbon monoxide, sulphur dioxide and ozone levels in the atmosphere.

          • 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 fuels.
      • 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 times.
  • 3.25 and 3.26 Nature's great natural recycling systems!
    • 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

      • This 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 atmosphere
      • sugars e.g. glucose + oxygen ==> carbon dioxide + water (+ energy)
      • 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 atmosphere
      • Coal, formed 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.

        • The main reaction on burning is ...

        • carbon + oxygen ==> carbon dioxide

        • C(s) + O2(g) ==> CO2(g)

      • Natural gas (mainly methane) and petrol molecules like octane (and lots of other molecules) from oil and gas reserves.

        • methane + oxygen ===> water + carbon dioxide

        • octane + oxygen ===> water + carbon dioxide

  • 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.
    • f) Nitrifying bacteria convert this ammonia to nitrates - the process of nitrification
      • 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.
    • i) 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 respire.
      • This is the opposite function of the nitrogen-fixing bacteria (b).

 

 

 

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