Unit 4

• Section 4- Respiration and Gas Exchange
• Respiration


  The process of transferring energy from glucose, which happens constantly in every living cell
• You need energy to keep your body going. Energy comes from food, and it's released by respiration.
• Respiration is NOT "Breathing In and Out"
• Respiration


  1. Transferring energy from glucose

  2. Some of the energy is transferred by heat

  3. The energy transferred by respiration can't be used directly by cells - so it's used to make a substance called ATP

  4. When a cell needs energy, ATP molecules are broken down and energy is released

  5. There are two types of respiration, aerobic and anaerobic
• The Temperature Change Produced can be Measured
• Practical


  1. First, soak some dried beans in water for a day or two. They will start to germinate (you should see little sprouts coming out of them). Germinating beans will respire.

  2. Boil a similar-sized, second bunch of dried beans. This will kill the beans and make sure they can't respire. The dead beans will act as your control.

  3. Add each set of beans to a vacuum flask, making sure there's some air left in the flasks (so the beans can respire aerobically).

  4. Place a thermometer into each flask and seal the top with cotton wool.

  5. Record the temperature of each flask daily for a week.

  6. Repeats should be carried out, using the same mass of beans each time.
• The beans are well-insulated in the flasks, so when the germinating beans respire, the test flask's temperature will increase compared to the control flask.
• Respiration releases energy from glucose
• Aerobic Respiration


  What happens when there's plenty of oxygen available. It's the most efficient way to transfer energy from glucose and produces lots of ATP-32 molecules per molecule of glucose.
• Aerobic Respiration


  glucose + oxygen → carbon dioxide + water (+ energy)
• Anaerobic Respiration


  Respiration that doesn't use oxygen at all. It's NOT the best way to convert glucose into energy-it releases much less energy per glucose molecule than aerobic respiration (just 2 molecules of ATP are produced). In anaerobic respiration, the glucose is only partially broken down, and lactic acid is also produced.
• Anaerobic Respiration in Animals

  glucose → lactic acid (+ energy)
• Lactic acid can be removed from the muscles by the blood flowing through them
• Practical


  1. Prepare one set of germinating beans and one set of boiled beans (the control).

  2. Put the same amount of hydrogen-carbonate indicator into two test tubes.

  3. Place a platform made of gauze into each test tube and place the beans on this.

  4. Seal the test tubes with a rubber bung.

  5. Leave the apparatus for a set period of time (e.g. an hour).
• During that time the CO₂ produced by the germinating beans should have had an effect on the hydrogen-carbonate indicator-it will have turned yellow.
• The control tube will have stayed the same.
• Anaerobic Respiration in Plants

  Plants can respire without oxygen too, but they produce ethanol (alcohol) and CO₂ instead of lactic acid.
• Anaerobic Respiration in Plants

  glucose → ethanol + carbon dioxide (+ energy)
• Fungi, like yeast, also respire anaerobically like this and people use yeast to make bread rise
• Only aerobic respiration uses oxygen...but when you do hard exercise, you can't get enough oxygen to your muscles, so you use anaerobic respiration too.
• You can also do this experiment with small organisms like woodlice or maggots (the control for these would be glass beads though). Make sure you treat any animals ethically
• Section 4-Respiration and Gas Exchange
• Diffusion


  The net movement of particles from an area of higher concentration to an area of lower concentration
• Gas Exchange in Flowering Plants

  1. When plants photosynthesise they use up CO₂ from the atmosphere and produce O₂ as a waste product

  2. When plants respire they use up O₂ and produce CO₂ as a waste product

  3. These waste products are lost through little holes in the undersides of leaves called stomata
• Plants Exchange Gases By Diffusion
• When a plant is photosynthesising it uses up lots of CO₂ so there's hardly any inside the leaf


  This makes more CO₂ move into the leaf by diffusion (from an area of higher concentration to an area of lower concentration)
• At the same time lots of O₂ is being made as a waste product of photosynthesis


  Some is used in respiration, and the rest diffuses out through the stomata (moving from an area of higher concentration to an area of lower concentration)
• Net Exchange of Gases Depends on Light Intensity

  1. Photosynthesis only happens during the day (ie. when there's light available)

  2. During the day (when light intensity is high) plants make more oxygen by photosynthesis than they use in respiration. So in daylight, they release Oxygen. They also use up more carbon dioxide than they produce, so they take in carbon dioxide.

  3. At night though (or when light intensity is low) plants only respire-there's not enough light for photosynthesis. This means they take in oxygen and release carbon dioxide- just like us.
• Leaves are Adapted for Efficient Gas Exchange

  • Leaves are broad, so there's a large surface area for diffusion
  • They're also thin, so gases only have to travel a short distance to reach the cells where they're needed
  • There are air spaces inside the leaf. This lets gases like carbon dioxide and oxygen move easily between cells. It also increases the surface area for gas exchange
  • The lower surface is full of little holes called stomata. They're there to let gases like CO₂ and O₂ diffuse in and out. They also allow water to escape - which is known as transpiration
• Stomata


  Little holes in the undersides of leaves that allow gases like CO₂ and O₂ to diffuse in and out
• Stomata can be Opened and Closed

  1. Stomata begin to close as it gets dark. Photosynthesis can't happen in the dark, so they don't need to be open to let CO₂ in. When the stomata are closed, water can't escape. This stops the plant drying out.

  2. Stomata also close when supplies of water from the roots start to dry up. This stops the plant from photosynthesising (bad), but if they didn't close, the plant might dry out and die (worse).

  3. The opening and closing of stomata is controlled by the cells that surround them (called guard cells). Guard cells do this by changing their shape and volume. Guard cells increase in volume to open stomata and decrease in volume to close stomata.
• Gases move in and out of plants by diffusion
• Which gases move in or out depends on the time of day. Just remember, plants photosynthesise when the Sun is shining, so in the day they'll be taking in lots of carbon dioxide and giving out oxygen.
• Interesting fact - stomata is the plural of stoma
• If you're asked to explain how leaves are adapted for gas exchange, don't just describe the features of the leaves. You also need to go on to say how these features make gas exchange efficient.
• Paper 2
• Practical Investigating Gas Exchange in Plants
• Hydrogen-carbonate Indicator Shows CO₂ Concentration.
• Practical


  1. Add the same volume of hydrogen-carbonate indicator to four boiling tubes.

  2. Put similar-sized, healthy-looking leaves into three of the tubes and seal with a rubber bung. Trap the leaf stem with the bung to stop it falling down into the solution if you need to. Keep the fourth tube empty as a control.

  3. Completely wrap one tube in aluminium foil, and a second tube in gauze.

  4. Place all the tubes in bright light. This will let plenty of light on to the uncovered leaf, and a little light onto the leaf covered in gauze. The leaf covered in foil will get no light-assuming you've wr