Bioenergetics

• Where does photosynthesis occur?

  Chloroplasts - they contain pigments like chlorophyll that absorb light.
• Is Photosynthesis endothermic or exothermic?

  Endothermic - energy is transferred to the chloroplasts from the sun.
• What is the word equation for photosynthesis?

  Carbon dioxide + water -> glucose + oxygen.
• What is the symbol equation for photosynthesis?

  6CO2 + 6H2O → C6H12O6 + 6O2.
• Where in the leaf does most photosynthesis occur?

  In the palisade (1st) and spongy (2nd) mesophyll cells
• How do the reactants for photosynthesis get into the plant?

  Water - through the roots via osmosis and then up the xylem to the leaves

  CO2 - From the air through the stomata
• What happens to the waste product of photosynthesis?

  Oxygen is used for respiration by the plant or released
• What are the main five ways that plant use glucose?

  1) For respiration.

  2) Making cellulose, for strong plant cell walls.

  3) Making amino acids, combined with nitrate ions.

  4) Stored as oils or fats in seeds.

  5) Stored as starch, insoluble so better for storage
• What 3 things affect the rate of photosynthesis?

  - CO2.

  - Light.

  - Temperature.
• What does the limiting factor of photosynthesis at any given time depend on?

  The environmental conditions.
• What can be an extra limiting factor of photosynthesis?

  Chlorophyll - amount can be affected by disease or environmental stress.
• As light/CO2 levels increase, the rate of photosynthesis increases up to a point and then stops increasing - why?


  Another factor is limiting.
• In a lab, how can you investigate light intensity as a limiting factor of photosynthesis?

  Move a lamp further/closer to a plant.

  
• Why is temperature usually a limiting factor of photosynthesis?

  It is normally too low which slows enzyme activity.
• What happens to the rate of photosynthesis when the temperature gets too high?

  At around 45 degrees the enzymes needed are denatured (active site changes shape and substrate can´t attach).

  
• How can you determine limiting factors?

  Use a graph that shows more than one limiting factor.
• How can you measure the effect of light intensity on the rate of photosynthesis?

  Observe the rate at which Canadian pondweed produces oxygen.
• Required Practical: Describe how to measure the effect of light intensity on the rate of photosynthesis:

  - Leave pondweed to photosynthesize for set amount of time.

  - O2 will collect in capillary tube.

  - Use syringe to draw gas bubble in tube alongside ruler.

  - Measure the length of the gas bubble.

  - Repeat twice.

  - Calculate mean volume of O2 produced.

  - Repeat at different distances from light.

  - Calculate light intensity for each distance.

  - Plot a graph of light intensity against length of bubble per unit of time.

  
• What links light intensity and distance?

  The inverse square law.
• What is the inverse square law?

  When studying light intensity, doubling the distance between the lamp and sample (pondweed) will reduce the light intensity by a quarter.

  
• What is light intensity measured in?

  Arbitrary units.
• What is the most common way to create an ideal environment for plants to grow?

  Grow them in a greenhouse.
• How do greenhouses ensure temperature isn't limiting?

  - Trap sun's heat.

  - Heater in winter.

  - Vents in summer.
• How do greenhouses ensure light isn't limiting?

  - Artificial light often supplied.
• How do greenhouses ensure CO2 isn't limiting?

  - Use paraffin heater which produce CO2 as a byproduct.
• Aside from tackling limiting factors, how are greenhouses ideal for plant growth?

  - Easier to keep plants free from pests/diseases.

  - Can add fertilisers to soil to provide all minerals needed.
• Why can a farmer not just give a green house loads and loads of light and heat?

  It may be more than the plant needs which wastes money.
• What is respiration?


  A chemical reaction that releases energy from glucose which goes on in every cell.
• What type of process in respiration?

  Exothermic - transfers energy to the environment.
• Give 3 examples of how organisms use the energy they gain from respiration:

  - To build up larger molecules from smaller ones.

  - To contract muscles.

  - To keep a constant body temperature.
• What are the chemical reactions in a cell controlled by?

  Enzymes.
• Give 3 examples of reactions in which larger molecules are made from smaller ones:

  - Glucose molecules are joined together to make starch, glycogen and cellulose.

  
  

  - Lipid molecules are made from one glycerol and three fatty acids.

  
  

  - Glucose is combined with nitrate ions to form amino acids which combine to form proteins.
• Give 2 examples of reactions is which larger molecules are broken down into smaller ones:

  - Glucose is broken down in respiration.

  - Excess protein is broken down to produce urea.
• What is metabolism?


  Sum of all chemical reactions in the body.
• What is aerobic respiration?

  Respiration with oxygen, the most efficient way to transfer energy from glucose.
• Where do most of the reactions in aerobic respiration happen?

  Inside the mitochondria.
• What is the word equation for aerobic respiration?

  Glucose + Oxygen --> Carbon Dioxide + Water (+ energy).
• What is the symbol equation for aerobic respiration?

  C6H1206 + 6O2 --> 6CO2 + 6H2O (+ energy).
• When does anaerobic respiration occur in the body?

  When you do vigorous exercise and your body cannot supply enough oxygen to your muscles.
• What is anaerobic respiration?

  The incomplete breakdown of glucose producing lactic acid.