Biology Unit 3 - AQA

Breif notes on Biology Unit 3 Additional Science AQA

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  • Created by: Sophie
  • Created on: 16-05-10 11:00

Exchange of Materials - Human

  • The lungs and the small intestine have very large surface areas for the exchange of substances.
  • The lungs have millions of air sacs called alveoli.
  • Carbon Dioxide and Oxygen are exchanged by the lungs.
  • The blood absorbs the products of digestion from the small intestine.
  • Thousands of villi increase the surface area of the small intestine so that absorption takes place.
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Exchange of Materials - Plants

  • Plants exchange carbon dioxide and oxygen through the surface of the leaves.
  • Plants take water and minerals up through the roots.
  • Root hairs greatly increase the surface area of roots.
  • Water is lost by plants through transpiration.
  • Temperature, humidity and wind speed all affect the rate of transpiration.
  • Transpiration: loss of water vapour from the surface of leaves.
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Transporting substances around the body

  • Humans have a double circulatory system - one is to the lungs, the other is to the body.
  • Red blood cells transport oxygen in the blood - oxygen attaches to haemoglobin to form oxy-haemoglobin.
  • Blood plasma transports - carbon dioxide to the lungs, the soluble parts of digestion to all living cells in the body, urea (made by the liver) to the kidneys where it is excreted.
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  • During exercise the heart and breathing rate are both increased and some blood vessels dilate.
  • When you exercise your muscles need more energy so they can contract.
  • Therefore you need to - increase the rate at which oxygen and glucose reach the cells and remove carbon dioxide quicker.
  • The energy needed by muscles to contract is usually provided through aerobic respiration - respiration with oxygen.
  • If insufficient oxygen is transported to the muscles they may respire anaerobically - respiration without oxygen.
  • Anaerobic respiration is inefficient - the muscles will become fatigued and lactic acid will be produced as a waste product.
  • You may also use up glycogen - a storage compound of glucose present in muscles.
  • Oxygen Debt - taking in oxygen after exercise to get rid of the lactic acid.
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  • They filter the blood - excreting substances that you do not want and keep those that you need.
  • The kidneys remove certain substances from the body - urea and excess water.
  • After filtering the blood, all of the sugar, many of the dissolved ions and water are reabsorbed. Sugar and dissolved ions may be reabsorbed against the concentration gradient, this requires energy and is thus active transport.
  • All of the urea and some ions dissolve in the remaining water and are excreted in the urine.
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Kidney Failure

  • If the kidneys fail, then dialysis or kidney transplants can keep the patient alive.
  • Dialysis - restores the concentration of substances in the blood back to normal, must have regular visits.
  • Transplant - donor must be found, must be a good 'tissue match', have to take anti-suppressant drugs to prevent rejection, no regular visits.
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Growing microbes

  • Are grown on agar in petri dishes.
  • Agar contains carbohydrate as an energy source and some minerals, proteins and vitamins as supplementary nutrients.
  • Agar is a 'culture medium' and contains carbohydrate and a variety of other growth substances.
  • Sterilise the inoculating loop, which is used to transfer microorganisms to the agar, by heating it to red hot in the flame of a Bunsen. Leave to cool.
  • Dip the sterilised loop in the bacteria you want to grow. Make zig-zag streaks across the surface of the agar.
  • Tilt the lid of the petri dish to keep out unwanted microbes and close the lid as quickly as possible to avoid contamination.
  • Secure the lid with short pieces of tape to prevent microorganisms from the air contaminating the culture, or microbes from the culture escaping.
  • DO NOT seal all the way around the edge.
  • In schools/colleges the cultures should be incubated at 25'C. Any higher and harmful pathogens could be produced.
  • In the industry, higher temperatures are used to promote faster growth.
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Food Production - Yeast and Bacteria

  • Yeast is used to make bread and alcohol - beer and wine.
  • When oxygen is present it respires aerobically and reproduces quickly.
  • When oxygen is not present it respires anaerobically and produces alcohol (ethanol) and carbon dioxide. This is known as fermentation.
  • Beer - when brewed the starch in the barley grains is used as the carbohydrate energy source for the yeast. Starch is broken down into sugars in the barley grains by enzymes during the germinating process. When the sugars have been fermented and the process completed, hops are added to give the beer flavour.
  • Wine - when wine is made, the grapes contain 'natural' sugars, which the yeast use as the energy source.
  • Bacteria is used to make yoghurt and cheese.
  • 3 stages to making yoghurt:
  • 1) Bacteria is added to warmed milk,
  • 2) The milk (lactose) is fermented by the bacteria, producing lactic acid.
  • 3) The lactic acid causes the milk to solidify (clot) and yoghurt is formed.
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Large-Scale Microbe Production / Antibiotic Produc

  • The fungus Fusarium is used to make mycoprotein.
  • Mycoprotein is a protein-rich food suitable for vegetarians.
  • Fusarium is gown aerobically on starch and the mycoprotein harvested.
  • Penicillin is made from the mould Penicillium in a fermenter.
  • The medium (solution inside the vessel) contains sugar for energy and other nutrients including nitrogen.
  • Penicillium only starts to produce the antibiotic when most of the nutrients are used up.
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  • Is mainly methane.
  • Can be made from the fermentation of 'natural' materials.
  • Can be made by plants and waste material (containing carbohydrate) being broken down by microorganisms.
  • Biogas generators are used to generate gas on a large or small scale.
  • Large scale - waste from sugar factories/sewage
  • Small scale - homes/farms
  • Ethanol-based fuels can be made from the fermentation of glucose from a variety of plant material.
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Steph Underwood


excellent notes... love the colour, nice and concise although a couple of small details were missed but nothing major... Thankk Youu!! :D



these notes helped so much! last minute revision as exam is on monday!! thank you very much!



bum crack

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