06 | January | 2013

Photosynthesis involves absorbing sunlight (first step of process)
- Pigments: chemical substances used in light absorption
  - They can absorb light so they look colored in our eyes
  - White, transparent things don’t absorb visible light
  - Pigments that only absorb light and do not emit appear black to us
- How we see colors: when pigments absorb some visible light, the others are reflected. These “other” visible light waves go into our eyes and recognized by our retina as that certain color.
- ex. Something is green. That means that something absorbs all visible light except green. Therefore the green light waves are reflected and we perceive it as the color green.
Organisms that photosynthesize use many pigments but usually, they use chlorophyll.

Light energy in photosynthesis is used for the following:
- ADP is phosphorylated to form ATP
- Photolysis: H2O is split
  - H2 is used later to make carbohydrates
  - O2 diffuses out of organisms because it is a “toxic waste product”
Light intensity affects photosynthesis as the following:
- Rate of photosynthesis increases when light intensity increases from a low intensity
- Rate of photosynthesis stays the same when light intensity increases from a high intensity.
  - Another reason stops further rise in the rate of photosynthesis. This blockade must be changed in order to continue increasing the rate.
- Thus, with increasing light intensity to low to high, the rate of photosynthesis increases rapidly in the start but plateaus as the intensity increases.

CO2 concentration affects photosynthesis as the following:
- Rate of photosynthesis increases when light intensity increases from a low intensity
- Rate of photosynthesis stays the same when light intensity increases from a high intensity.
- This still affects photosynthesis even though CO2 levels have been rising over the past 100 years
Carbon Fixation: Converting CO2 into solid/liquid organic molecules
- Makes CO2 essential to photosynthesis
- Stops in darkness, slows down when light intensity decreases
  - ATP (energy supply), hydrogen (from water photolysis) will be unavailable without light

Low temperatures = photosynthesis rate is low or none
Increasing temperature = photosynthesis rate increases until maximum (see next bullet)
Optimum photosynthesis temperature = maximum photosynthesis rate is reached
Above optimum temperature = photosynthesis rate decreases until 0
Reasons
- Effect of temperature on enzymes is similar to the effects on photosynthesis
- Enzymes catalyze carbon fixation, and they have optimum temperatures
General pattern
- Most plants’ optimum temperature = 25-35˚C
- Enzymes do not denature at these low temperatures but one enzyme in photosynthesis does not work above 30˚C.

pH was measured because the CO2 lowers the pH of a medium. Thus, the increase of pH can mean uptake of CO2 by the pondweed for photosynthetic purposes, while the decrease of pH can mean emission of CO2 by the pondweed due to aerobic respiration.
Independent variable = Time intervals (hours) and temperature (˚C); Dependent variable = pH (±0.05) at 1-hour time intervals
Time = x-axis; pH (±0.05) at 1-hour time intervals = y-axis; different temperatures can be made into different series.
Generally 22.5 to 27.5˚C, but no significant difference is evident because of the uncertainty.
Different alga would have different optimum temperatures and rates of photosynthesis and cellular respiration.
Evaluation: Effect of temperatures is not very clear (not a lot of fluctuations among the pH levels with the chosen treatments). Effect of time is clear but relatively, the uncertainty is high so it can be made even clearer. Precision of pH probe is low.; Improvements: Choose temperatures of a wider range (ex. start at 15˚C and end at 45˚C) to see significant effects made by the changes in temperature. Record data for a longer time period (ex. 10 hours) to be able to see even larger and significant changes in the pH. Use equipment with higher precision.

14liedan