B1.3 - Respiration

• Respiration

  • The process of transferring energy from the breakdown of glucose (a sugar)
  • Respiration goes on in every cell in all living organisms, all the time.
  • Respiration is a universal chemical process
• ATP

  • The energy transferred by respiration can't be used directly in cells - so it's used to make a substance called ATP.
  • ATP stores the energy needed for many cell processes.
• Respiration

  • It's controlled by enzymes
  • The rate of respiration is affected by both temperature and pH
  • It's an exothermic reaction that transfers energy to the environment (by heat)
• Substrates for respiration

  • Glucose
  • Other carbohydrates
  • Proteins
  • Lipids
• Biological molecules

  Carbohydrates, proteins, and lipids are all organic because they contain carbon
• Aerobic respiration


  • What happens when there's plenty of oxygen available
  • Aerobic respiration produces lots of ATP - 32 molecules per molecule of glucose.
  • It's the type of respiration that you're using most of the time.
  • Glucose + oxygen --> carbon dioxide + water
• Effect of exercise

  • When you exercise, more energy is needed by your muscles to allow them to contract more. This means your rate of respiration increases, so you need to get more oxygen into your cells.
  • Your breathing rate increases to get more oxygen into the blood, and to get this oxygenated blood around the body faster your heart rate increases too.
• Investigating the effect of exercise on heart rate

  1. Measure heart rate at rest

  2. Do 3 minutes of gentle exercise, then measure heart rate immediately after

  3. Take regular measurements of heart rate until it has returned to resting rate

  4. Repeat with increasing exercise intensity

  5. Produce a bar chart to show how heart rate and recovery time are affected by exercise intensity
• Anaerobic respiration

  • Respiration without oxygen
  • Anaerobic respiration transfers much less energy per glucose molecule than aerobic respiration - just 2 molecules of ATP are produced
• Anaerobic respiration in animals

  • When you do really vigorous exercise your body can't supply enough oxygen to your muscles for aerobic respiration - even though your heart rate and breathing rate increase as much as they can. Your muscles have to start respiring anaerobically as well.
  • In anaerobic respiration, the glucose is only partially broken down, and lactic acid is also produced. All animals that respire anaerobically produce lactic acid by the same process.
  • Glucose --> lactic acid
• Lactic acid in animals

  • The lactic acid builds up in the muscles, which gets painful and makes your muscles fatigued.
  • The advantage is that you can keep on using your muscles.
  • After resorting to anaerobic respiration, when you stop exercising you'll have an oxygen debt meaning you need extra oxygen to break down all the lactic acid that's built up and to allow aerobic respiration to begin again.
  • So you need to keep breathing hard for a while.
• Anaerobic respiration in plants and fungi

  • Under certain conditions plants may also have to resort to anaerobic respiration, e.g. in waterlogged soil (where there is little or no oxygen) plant root cells respire anaerobically.
  • Some fungi (such as yeast) can respire anaerobically too.
  • Anaerobic respiration in plants and fungi produces ethanol and carbon dioxide instead of lactic acid. This is the word equation: Glucose --> ethanol + carbon dioxide
• Fermentation

  Anaerobic respiration in yeast
• Experiment to show CO2 production by respiration

  1. Use hydrogen-carbonate indicator solution

  2. Place germinating beans and boiled (dead) beans in separate test tubes

  3. Seal the test tubes and observe the colour change from red to yellow of the indicator
• Experiment to measure energy transferred by heat during respiration

  1. Prepare two sets of beans, one germinating and one boiled

  2. Place each set in a vacuum flask with a thermometer

  3. Record the temperature of each flask daily for a week
• Carbohydrates

  • Molecules containing carbon, hydrogen and oxygen
  • The smallest units, monomers, are simple sugars like glucose or fructose.
  • These can be joined together in long chains, polymers, to make large, complex carbohydrates, e.g. starch and glycogen.
  • The polymer molecules can be broken down back into sugars again when the chemical bonds between the monomers are broken.
  • In the body, carbohydrates are broken down (digested) by enzymes in the mouth and small intestine
• Proteins

  • Proteins are polymers that are made up of long chains of monomers called amino acids.
  • Amino acids all contain carbon, nitrogen, hydrogen and oxygen atoms.
  • In the body, proteins are broken down by enzymes in the stomach and small intestine.
• Lipids

  • Lipids (fats and oils) are made from glycerol and three fatty acids.
  • Unlike carbohydrates and proteins they are NOT polymers because they don't form a long chain of repeating units.
  • Lipids contain carbon, hydrogen and oxygen atoms.
  • In the body, lipids are broken down by enzymes in the small intestine.
• Test for reducing sugars using Benedict's solution


  • Reducing sugars include simple sugars made from just one unit, e.g. glucose, and a few made from two units joined together, e.g. maltose. Here's how you can test for them:
  • 1) Add Benedict's reagent (which is blue) to a sample and heat it in a water bath that's been set at 75 °C. If the test's positive it will form a coloured precipitate (solid particles suspended in the solution).2)The higher the concentration of reducing sugar, the further the colour change goes you can use this to compare the amount of reducing sugar in different solutions.
• Test for non-reducing sugar:


  • If there aren't any reducing sugars in your sample, you can test for non-reducing sugars, e.g. sucrose.

  1) Using a new sample of the test solution, add dilute hydrochloric acid and heat in a water bath that's been that's been set at 75 °C.

  2) Add sodium hydrogen-carbonate (to neutralise it) then carry out the Benedict's test.

  3) A coloured precipitate means there are non-reducing sugars present.

  If the solution stays blue, the test solution didn't contain any sugar at all.
• Test for starch using iodine


  Add iodine solution, blue-black colour indicates presence of starch
• Emulsion test for lipids


  • To find out if there are any lipids in a sample:

  1) Shake the test substance with ethanol for about a minute until it dissolves, then pour the solution into water.

  2) If there are any lipids present, they'll show up as a milky emulsion.

  3) The more lipid there is, the more noticeable the milky colour will be.

  An emulsion is when one liquid doesn't dissolve in another - it just forms little droplets.
• Biuret test for proteins


  • First, add a few drops of sodium hydroxide solution to make the solution alkaline.
  • Then add some copper(II) sulfate solution (which is bright blue).
  • If there's no protein, the solution will stay blue.
  • If protein is present, the solution will turn purple
• Benedict test:

  A) blue

  B) red

  
• Lipids:

  A) glycerol

  B) fatty acids

  C) lipid

  
• Protein:

  A) amino acids

  
• Carbohydrates:

  A) maltose

  B) simple sugars

  C) glucose

  D) starch