Biology-Bioenergetics

• Plants make use of the Sun's energy to make food (glucose)
• Photosynthesis


  The process where plants manufacture glucose from carbon dioxide and water using energy transferred from the environment to the chloroplasts by light
• Endothermic reaction


  Photosynthesis needs an input of energy from the environment
• Photosynthesis


  Carbon dioxide + water -> glucose + oxygen
• You need to be able to recognise the chemical symbols for the molecules involved in photosynthesis
• The rate of photosynthesis will increase when a plant is given higher concentrations of carbon dioxide up to a certain point
• Photosynthesis

  1. Water using energy transferred from the environment to the chloroplasts by light

  2. Carbon dioxide + water -> Glucose + oxygen
• The word equation which represents photosynthesis is: carbon dioxide + water -> glucose + oxygen
• Molecules involved in photosynthesis

  • Carbon dioxide
  • Water
  • Oxygen
  • Glucose
• You need to be able to recognise the chemical symbols for these molecules
• The balanced symbol equation which represents photosynthesis is: 6CO2 + 6H2O -> C6H12O6 + 6O2
• Carbon dioxide

  • One of the reactants needed for plants to make glucose. The rate of photosynthesis will increase when a plant is given higher concentrations of carbon dioxide up to a point
• As temperature increases

  Chemical reactions including photosynthesis speed up
• Enzyme controlled reaction

  If the temperature increases too much, the enzymes become denatured and the rate of reaction will decrease and stop
• As light intensity increases

  The rate of photosynthesis increases up to a point
• Investigating the effect of light intensity on photosynthesis in pondweed

  1. Fill a boiling tube with 0.2% sodium hydrogen carbonate solution

  2. Place a 10 cm piece of pondweed in the boiling tube

  3. Set up an LED lamp at a distance of 10 cm to the boiling tube and leave to settle for 5 minutes

  4. Start the stopwatch and count the number of bubbles released in one minute

  5. Repeat twice and calculate the mean number of bubbles

  6. Repeat steps 1-6, altering distance of the lamp so it is 30 cm, 40 cm and 50cm away from the boiling tube
• Why is an LED lamp used?

  LED lamps produce less heat and this reduces the effect of temperature on the experiment
• Light Intensity


  1/distance^2
• If sunlight shines onto water and carbon dioxide, a reaction will not occur. The energy must be transferred from the environment, to the chlorophyll, by light
• Chlorophyll is essential to the process of photosynthesis
• If there is a reduction in the amount of chlorophyll available to the plant then the amount of glucose made by photosynthesis will reduce. The plant will not grow as well
• Variegated leaves are white and green. The white areas do not have any chlorophyll
• If light intensity is increased

  The reaction rate also increases
• Farmers apply their understanding of limiting factors

  • They can control conditions inside greenhouses more easily than in the fields
  • Heating can be used to provide optimum temperatures for maximum plant growth
  • Artificial lighting enhances the natural sunlight especially overnight and on cloudy days
  • Extra carbon dioxide gas can be pumped into the air inside the greenhouses
• In commercial greenhouses the environmental factors are often controlled by computerised systems to minimise cost
• Uses of glucose made from photosynthesis

  • Energy release through respiration
  • Amino acid synthesis for protein
  • Cellulose production for cell walls
  • Starch storage
  • Fat/oil production
• Respiration is also sometimes called cellular respiration. This is because the reactions of respiration occur inside cells
• Every living cell needs energy and this energy is released from food (glucose) by a series of chemical reactions called respiration
• An organism will receive all the energy it needs for living processes as a result of the energy transferred from respiration
• The reactions of respiration occur 24 hours a day, continuously, in all living cells
• Respiration is an exothermic reaction which means energy is transferred to the environment. Some of the energy is used inside cells and the rest will be transferred out of the cell
• Why do living organisms need energy?

  • For movement
  • To keep warm
  • For chemical reactions
• Aerobic respiration

  Respiration that occurs with oxygen
• Anaerobic respiration in animal cells

  1. Glucose is not completely broken down to carbon dioxide and water, so less energy is transferred

  2. An end product called lactic acid is formed

  3. Lactic acid builds up in the muscle cells
• Anaerobic respiration

  Respiration that occurs without oxygen
• Anaerobic respiration in plant and yeast cells

  End products are ethanol and carbon dioxide
• Respiration summary

  • Aerobic respiration
  • Anaerobic respiration in animal cells
  • Anaerobic respiration in plant and yeast cells
• Aerobic respiration

  • Oxygen required
  • End products are carbon dioxide and water
  • Oxidation of glucose is complete
  • Efficiency of energy transfer is high
• Anaerobic respiration in animal cells

  • Oxygen not required
  • End product is lactic acid
  • Oxidation of glucose is incomplete
  • Efficiency of energy transfer is low
• Anaerobic respiration in plant and yeast cells

  • Oxygen not required
  • End products are ethanol and carbon dioxide
  • Oxidation of glucose is incomplete
  • Efficiency of energy transfer is low