Factors Affecting Photosynthesis & Photosynthesis Vs. Cellular Respiration

1. Factors Affecting Photosynthesis &Photosynthesis Vs. Cellular Respiration Section 3.5 & 3.6

2. Factors affecting Photosynthesis • The rate of photosynthesis can be determined by measuring either: • CO2 uptake • O2 production

3. Factors affecting Photosynthesis • HOWEVER, CO2 and O2 participate in 2 other metabolic processes within plant cells • Cellular respiration (happens in all plant cells) • Photorespiration (happens primarily in C3 plants) • Both of these pathways consume O2 and release CO2

4. Factors affecting Photosynthesis • Therefore it is necessary to measure net gas exchange between a plant and its environment, using the following equation: Net CO2 uptake = CO2 uptake – CO2 prod’n – CO2 prod’n (rate of (Photosyn’s) (Cell. Respn) (Photorespn) photosynthesis)

5. Light Intensity • Light – saturation point • Rubisco enzymes are saturated  photosynthesis cannot go any faster • Light compensation point • CO2 in = CO2 out • Net CO2 = ZERO! • Dark Respiration Rate: cellular respiration produces CO2, thus net CO2 uptake is negative.

6. Carbon Dioxide Availability • High CO2 concentration: • Increased photosynthesis, because higher CO2 levels allow Rubisco enzymes to “take on” more CO2, even if O2 is present • Plateau still reached when Rubisco enzymes are saturated

7. Temperature • From 10 – 30 ˚C, photosynthesis is directly proportional to temperature • ↑ temp causes ↑collisions /molecular activity) • Above 30 ˚C, photosyn’s rate ↓ • Temp ↑ causes denaturation • Max rates between 20-30 ˚C • Remember: all enzymes have diff optimal temp for max activity / productivity

8. Oxygen Concentration • High levels of O2 have an inhibitory effect on photosynthesis, because of competition between O2 and CO2 active sites on Rubisco enzymes Rubisco + CO2 carbon fixation via photosynthesis Rubisco + O2  photorespiration

9. Photosynthetic efficiency • Equals the net amount of CO2 uptake per unit of light energy absorbed • Also called the quantum yield • Is determined by calculating the slope of the light-response curve

10. Photosynthetic efficiency • Note that initial slope of the curve is greater at the lower temperature • For most C3 plants, as temp increases, the rate of photorespiration increases more rapidly than the rate of photosynthesis

11. Photosynthetic efficiency • Therefore, in most C3 plants, the net CO2 uptake per unit of light absorbed (i.e. Photosynthetic efficiency) decreases as the temp. Increases • (line A on the graph)

12. Photosynthesis VersusCellular Respiration Section 3.6  Last one!!!!!!1!11!1!

13. “Worksheet Time!” Says Happy Dragon!