4.4 Bioenergetics

4.4.1 Photosynthesis

4.4.1.1 Photosynthetic reaction

Word Equation

• Light energy is used by plants cells to convert carbon dioxide and water into glucose and oxygen
• Carbon dioxide + water glucose + oxygen

Chemical

• CO2 represents carbon dioxide
• H2O represents water
• C6H12O6 represents glucose
• O2 represents oxygen

Energy Transfer in Photosynthesis

• Photosynthesis takes place in chloroplasts, using chlorophyll
• Photosynthesis is an endothermic reaction

4.4.1.2 Rate of photosynthesis

Single Factors

• A limiting factor is a condition, that when in shortage, slows down the rate of a reaction
• Light intensity, carbon dioxide concentration and temperature are limiting factors for the rate of photosynthesis

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Single Factor – Carbon Dioxide

• The higher the CO2 concentration, the higher the rateuntil a certain point
• At high CO2 concentration, rate levels off, as the enzymes required are saturated

Single Factor – Light Intensity

• The higher the light intensity, the higher the rate, as more light can be trapped by the chloroplasts
• At high light intensity, rate levels off, as the maximum amount of light has already been trapped

Single Factor – Temperature

Rate of Photosynthesis

Factors Affecting Photosynthesis Rate

• The higher the temperature, the higher the rate until a certain point, as the enzymes gain more kinetic energy
• The rate is highest at the optimum temperature
• At high temperatures, the rate falls as enzymes denature

Single Factor – Chlorophyll

• Chlorophyll can act as a limiting factor for photosynthesis
• As the amount of chlorophyll increases, more light can be trapped by the chloroplasts
• However, once there is a certain amount of chlorophyll, it will no longer be a limiting factor

Multiple Factors – Light Intensity and Temperature

• As you increase light intensity, rate increases until we reach a plateau
• As you increase temperature, the rate increases
• The light intensity affects the plateau at a higher level, so it is a limiting factor for longer

CO2 is constant so light intensity and temperature is shown

Multiple Factors – Light Intensity and CO2 Concentration

• As light intensity increases, rate increases until we reach a plateau
• As you increase CO2, the rate increases
• The light intensity affects the plateau at a higher level, so it is a limiting factor for longer

Temperature is constant so light intensity and CO2 is shown

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Canadian Pondweed Experiment

Setting up a Canadian Pondweed Experiment

1. Add a light source at a specific distance
2. Place the plant in a boiling tube underwater
3. Connect a gas syringe and capillary tube
4. Use a ruler to measure movement of the air bubble
5. Change the variables

The rate of oxygen production is proportional to the rate of photosynthesis

Investigating the Effect of Light Intensity

• Place a lamp at differing distances from the plant and observe the oxygen production through the movement of the bubble
• Control the other variables, and repeat three times at each distance for reliability
  • Obtain a mean value for drawing graphs

Investigating the Effect of Temperature

• Place the boiling tube in different temperature water baths and observe the oxygen production through the movement of the bubble
• Control the other variables, and repeat three times at each distance for reliability
  • Obtain a mean value for drawing graphs

Investigating the Effect of CO2 Concentration

• Dissolve different amount of sodium hydrogencarbonate in different boiling tubes to see the effect of CO2 concentration
• Control the other variables, and repeat three times at each distance for reliability
  • Obtain a mean value for drawing graphs

Key Rules of Plotting Graphs

• Label the axes
• Put in the units
• Take up at least half of the space on the axes with the graph

Inverse Square Law

• Inverse proportion means that when one variable goes up, the other goes down
• Light intensity is inversely proportional to the square of the distance
• Light intensity ⍺ 1/distance2

Greenhouse Conditions

• Greenhouses can optimise farming conditions
• Greenhouses control temperature via:
• Glass exterior to trap the sun’s heat
  • Blinds used if it is too hot
  • Heaters for artificial heat in colder months

• Greenhouses can burn paraffin heaters to give off carbon dioxide
• Light can be artificially provided to provide the energy
• Conditions must be carefully monitored to provide the greatest amount of produce for the money put in

4.4.1.3 Uses of glucose from photosynthesis

Respiration

• Glucose is a reactant in the reaction for respiration, which produces energy
• In plants, glucose made in photosynthesis can be used for respiration

Starch

• Glucose is not a good storage molecule as it is soluble. It can draw in water through osmosis, causing the plant to swell up
• Glucose is stored as starch. Starch is stored in the leaves, stem and roots of the plant

Fat and Oil

• Glucose can be used to make lipids
• Plants can convert the glucose into lipids for storage in seeds

Cellulose

• Glucose can be used to make cellulose
• It is made to build the cell walls, to provide strength

Amino Acids

• Glucose can be used to make amino acids
• Amino acids are the building blocks of cells, as they are made together to make proteins

Summary: Uses of Glucose

1. Used in respiration
2. Stored as starch
3. Stored as fat / oil
4. Used to make cellulose
5. Used to build amino acids

Nitrates

• Carbon, oxygen, hydrogen and nitrates are needed to make proteins
• It needs to take up nitrates from the soil
• Fertilisers can be added to soil to provide a source of nitrates
• This increases the rate of protein synthesis in the plant