Bjlgl
A. Converting photosynthesis rate from volume of oxygen produced per gram leaf per minute to mol CO2 fixed per area of leaf (in m2) per second.
B. Why would one want to express photosynthesis rate as µmol CO2 m-2 s-1? What is the advantage.
Answers:
A. How to convert photosynthesis rate from volume of oxygen produced per gram leaf per minute to mol CO2 fixed per area of leaf (in m2) per second.
Photosynthesis rate can be measured either by seeing how much oxygen is produced by a leaf, or how much CO2 is fixed by that leaf (more correct would be to say "how much CO2 is assimilated by the leaf" – another name for photosynthesis is "CO2 assimilation"). In your experiment you measured the production of oxygen and calculated photosynthesis rate as the volume of oxygen that one gram of leaf produces in one minute. More usually, photosynthesis rate is expressed as how many moles (actually micromoles) of CO2 does one square meter of leaf assimilate in a second. Basing the rate on a square meter of leaf might seem strange since most leaves are small; nowhere near a square meter in area, more like a few square cm. However, the meter, not the cm, is the base unit of length in the SI system, and the second, not the minute, the base unit for time.
The reason that moles, not volume, of CO2 is the unit used when expressing photosynthesis rate is twofold. (1) the mole is the base unit for quantity, (2) living cells do not work with volumes of substances, or even masses of substances. The chemical reactions that occur in the cell are based on molecules (or Avogadro's number of molecules, which is the mol). Think of respiration:
C6H12O6+ 6O2 → 6H2O + 6 CO2
The cell uses one molecule (or one mole) of glucose and six molecules (or moles) of oxygen to produce six molecules (or moles) of water and six molecules (or moles) of carbon dioxide. It does not use one g (or litre) of glucose and six g (or litres) of oxygen to produce six g (or litres) of water and six g
B. Why would one want to express photosynthesis rate as µmol CO2 m-2 s-1? What is the advantage.
Answers:
A. How to convert photosynthesis rate from volume of oxygen produced per gram leaf per minute to mol CO2 fixed per area of leaf (in m2) per second.
Photosynthesis rate can be measured either by seeing how much oxygen is produced by a leaf, or how much CO2 is fixed by that leaf (more correct would be to say "how much CO2 is assimilated by the leaf" – another name for photosynthesis is "CO2 assimilation"). In your experiment you measured the production of oxygen and calculated photosynthesis rate as the volume of oxygen that one gram of leaf produces in one minute. More usually, photosynthesis rate is expressed as how many moles (actually micromoles) of CO2 does one square meter of leaf assimilate in a second. Basing the rate on a square meter of leaf might seem strange since most leaves are small; nowhere near a square meter in area, more like a few square cm. However, the meter, not the cm, is the base unit of length in the SI system, and the second, not the minute, the base unit for time.
The reason that moles, not volume, of CO2 is the unit used when expressing photosynthesis rate is twofold. (1) the mole is the base unit for quantity, (2) living cells do not work with volumes of substances, or even masses of substances. The chemical reactions that occur in the cell are based on molecules (or Avogadro's number of molecules, which is the mol). Think of respiration:
C6H12O6+ 6O2 → 6H2O + 6 CO2
The cell uses one molecule (or one mole) of glucose and six molecules (or moles) of oxygen to produce six molecules (or moles) of water and six molecules (or moles) of carbon dioxide. It does not use one g (or litre) of glucose and six g (or litres) of oxygen to produce six g (or litres) of water and six g