Photosynthesis rate is measured by a photosynthometer, calculates oxygen volume released from aquatic plant a minute; useful as oxygen released is waste and not very water-soluble (can be seen as bubbles)
Unsuitable for terrestrial plants; to measure their photosynthesis rate CO_2 uptake must be measured (using radioactive tracer) or mass increase over time
Calculating Rate
Rate of photosynthesis = volume of gas collected per minute
Volume of gas collected = length of bubble x πr^2 (r is internal radius of capillary bore, so πr^2 is its cross sectional area)
Rate calculated as: Bubble length x πr^2 / Time taken to collect gas bubble (min), units: mm^3min^-1
Limitations: Not all produced oxygen is collected, some is; used in plant respiration, dissolves into test tube water, remains in leaf air spaces, escapes collection in flared capillary tube part
Limitations: Some gas collected is nitrogen, it is present in leaf air spaces and diffuses out into water with oxygen, water contains air with dissolved nitrogen; it is less soluble in warm water
Limitations: Some gas collected is CO_2, plant respiration product, and NaHCO_3 is added to water to release CO_2 (not all released is used in photosynthesis and some CO_2 dissolves; it is less soluble in warm water)
