Bio energetics

• What happens in photosynthesis?

  • Light energy is absorbed
  • By chlorophyll in chloroplasts
  • Converts carbon dioxide and water to glucose (sugar) and oxygen (by - product)
• What type of reaction is photosynthesis?

  Endothermic - energy transferred from environment to chloroplast by light.
• Uses of glucose from photosynthesis

  • Produce Starch, for storage: Insoluble
  • Produce Cellulose - strengthens the walls
  • Produce Amino acids - protein synthesis
  • Used for Respiration - to release energy
  • Produce Fats/oils - for energy storage
• Explain why a leaf left in a cupboard for 2 days did contain glucose, but did not contain starch (3 marks)

  • Starch has been converted to glucose
  • Glucose can be used for respiration - to release energy.
  • As no light to make glucose by photosynthesis
• Light Intensity - Rate of photosynthesis

  1. As light intensity increases, photosynthesis increase
  2. Above certain light intensity, rate stops increasing
  3. As light provides energy needed for photosynthesis
• Temperature - Rate of photosynthesis

  • As temperature increases, rate increases
  • As enzymes controlling photosynthesis gain kinetic energy
  • Above opt temperatures, rate decreases
  • As enzymes denature
• How can farmers use their knowledge of limiting factors to increase their profits?

  • Removing limiting factors - gain maximum rate of photosynthesis, which increases plant yield
  • Profit from extra yield must be greater than the cost of providing conditions
• Why place pondweed in a solution of sodium

  hydrogen carbonate? (1)

  ● To provide carbon dioxide

  ● So that carbon dioxide is not a limiting factor
• How could you test bubbles to show they

  contained oxygen? (1)

  ● Add a burning splint - it will burn more brightly
• Why is counting bubbles not an accurate way of

  measuring volume of oxygen produced? (1)

  ● Bubbles are different sizes

  ● Bubbles can be easy to miss (move too fast)
• How could the method be improved to measure

  the rate of photosynthesis more accurately? (2)

  ● Measure volume of O2 released in a gas syringe

  ● Increase length of time
• What is the advantage of using an LED light

  source? (2)

  ● Does not emit a lot of infrared / thermal radiation

  ● So temperature is controlled

  ● Temperature affects rate of photosynthesis as

  photosynthesis is controlled by enzymes
• How could you modify the experiment to

  investigate the effect of CO2 / temperature /

  wavelength of light on the rate of

  photosynthesis? (4)

  ● Carbon dioxide - use different concentrations of

  sodium hydrogencarbonate solution

  ● Temperature - different temperature water baths

  ● Wavelength - different coloured filters over bulb

  ● Control distance from light source

  ● Control type / length of pondweed
• What is cellular respiration?

  ● A series of chemical reactions that release / transfer energy from glucose

  ● Occurs continuously in all living cells

  ● Exothermic reaction
• Describe how energy released in respiration is used

  ● Chemical reactions to build larger molecules (eg. metabolism)

  ● Keeping warm (birds and mammals only)

  ● Movement eg. muscle contraction in animals
• Explain how the body reacts to increased energy demand during exercise

  ● Increased heart rate → increased blood flow to muscles / lungs

  ● Increased breathing rate and volume → more air / oxygen enters lungs

  ● To supply more more blood containing more oxygen (and glucose) to muscles

  ● For more aerobic respiration to release energy / to reduce anaerobic respiration & lactic acid build up
• What happens when muscles are supplied with insufficient oxygen?

  ● Anaerobic respiration → oxidation of glucose is incomplete

  ● Causing a buildup of lactic acid which causes:

  ○ Oxygen debt

  ○ Muscles become fatigued and stop contracting efficiently (if activity long / vigorous)
• What is the role of the liver in recovering from vigorous exercise?

  1. Blood flowing through muscles transports lactic acid to the liver

  2. Where it is converted back to glucose
• Examples of metabolic reactions.

  1. Glucose molecules converted
  2. 1 glycerol + 3 fatty acid molecules = a Lipid molecule
  3. Glucose and nitrate ions = amino acids = used to synthesis proteins
  4. Respiration
  5. Break down of excess proteins to form urea for excretion
• Organisms A and B both keep a constant

  body temperature. The surface area to

  volume ratio is higher in organism A.

  Explain why organism A’s metabolic rate

  is greater. (4)

  ● Larger surface area to volume ratio so lose heat more

  quickly

  ● So need to generate more heat (to keep warm)

  ● So requires greater rate of respiration

  ● Respiration is a (large) part of metabolism
• Plants convert glucose into starch, and

  animals convert glucose into glycogen.

  Explain why this is necessary. (2)

  ● Both storage molecules

  ● Converted back to glucose when energy needed