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3.5 Photosynthesis and the Environment

3.5 Photosynthesis and the Environment. How do environmental conditions affect the rate of photosynthesis?. Rate of Photosynthesis. The Rate of Photosynthesis, is the rate in which a plant absorbs CO 2 and evolves O 2 .

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3.5 Photosynthesis and the Environment

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  1. 3.5 Photosynthesis and the Environment How do environmental conditions affect the rate of photosynthesis?

  2. Rate of Photosynthesis • The Rate of Photosynthesis, is the rate in which a plant absorbs CO2 and evolves O2. • (It is not the rate of sugar production because sugar is stored in plants and can’t be measured directly.) • Since CO2 and O2 are consumed and evolved in other metabolic processes, we must look at the NET gas exchange.

  3. Equations: Net CO2 = Photosynthetic – Photorespiratory – Respiratory uptake CO2 uptake CO2 evolution CO2 evolution Net O2 = Photosynthetic – Photorespiratory – Respiratory evolution O2 evolution O2 uptake O2 uptake

  4. Light Intensity and the Rate of Photosynthesis The Light Intensity per unit area of leaf

  5. Light Intensity • Beyond the light-compensation point, the rate of photosynthesis increases in direct proportion to irradiance. • The Light Saturation Point is the point at which the carbon fixation reactions reach a maximum rate, and can’t go any faster – even if more light is shone on the leaf.

  6. What does the graph tell us? • At some point (the light-saturation point), it does not matter how much light a plant receives, (and therefore how much ATP and NADPH it makes in the light reactions) because the Calvin Cycle is operating at full capacity and cannot convert substrate (CO2) into product (G3P – sugar) any faster. • Under normal conditions, the CO2 availability limits the rate of photosynthesis.

  7. Light Intensity • In general, ↑ of light → ↑ ATP and NADPH → ↑ rate of Carbon fixation (to a certain point) Therefore, ↑ of light = ↑ in rate of photosynthesis.

  8. II. Temperature and the Rate of Photosynthesis

  9. Temperature • Up to a certain temperature, increases in temperature lead to increases in the rate of photosynthesis. ↑ temperature = ↑ photosynthesis • But if the temperature gets too high, the enzymes denature and do not catalyze the reactions. • Therefore, photosynthesis stops. • Optimal temp for C3 plants: 15º C – 25º C.

  10. III. Oxygen andthe Rate of Photosynthesis • O2 makes up ~20% of the atmosphere. • High levels of oxygen inhibits photosynthesis • Remember: O2 and CO2 can both bind to the enzyme rubisco. • When CO2 binds  carbon is fixed to sugar • When O2 binds  photorespiration happens and photosynthesis decreases.

  11. Oxygen

  12. Photosynthetic Efficiency • Photosynthetic Efficiency is the amount of CO2 uptake per unit of light. In C3 plants: as the temperature increases, photosynthetic efficiency decreases. (The plants will close their stomata to decrease water loss, leads to build up of O2, which leads to photorespiration.)

  13. …Photosynthetic Efficiency In C4 plants: as the temperature increases, photosynthetic efficiency remains constant. (These plants are anatomically adapted to minimize photorespiration.)

  14. C4 plants are better at fixing CO2 at higher temperatures. C3 are better at fixing CO2 at lower temperatures …Photosynthetic Efficiency

  15. Some plants are better adapted for growth in direct sunlight, and others prefer shade or indirect light. Leaves of shade plants differ from those of Sun plants. (IVY is an example of a plant that prefers the shade) Sun Plants vs. Shade Plants

  16. Sun vs. Shade Plants Shade Plants: • Thinner, broader, greener (more chlorophyll) and more efficient at harvesting light at low intensities. Sun Plants: • Have a higher light compensation point.

  17. Which is a shade plant and which is a sun plant? Shade plant or Sun plant???

  18. 3.6 Comparing Photosynthesis and Cellular Respiration

  19. Photosynthesis and Cellular Respiration • Photosynthesis and Cellular Respiration are closely related to each other. • In plants (and other autotrophs) both processes may occur within the same individual cell. • Photosynthesis uses the products of cellular respiration, and cellular respiration uses the products of photosynthesis.

  20. Photosynthesis and Cellular Respiration are related in several ways: • Calvin Cycle includes reactions that are similar to those in cellular respiration (in reverse) • Proteins in the ETC of both processes are similar (or the same) • Both processes uses chemiosmosis to phosphorylate ADP to ATP.

  21. The relationship between photosynthesis and cellular respiration reveal a dependency between autotrophs and heterotrophs. • Heterotrophs produce the majority of CO2 in the environment used by autotrophs in photosynthesis. • Autotrophs produce the majority of O2 in the environment that heterotrophs and autotrophs use in cellular respiration.

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