Photosynthesis

Question 1

What is photosynthesis?

Answer 1

The process of converting light into chemical bond energy

Sunlight energy, CO2 and H2O go into the plant, carbohydrates are formed, O2 is released

O2 is the key to unlocking the newly stored energy

Question 2

Thermodynamics: Gibbs free energy

Answer 2

deltaG = “Gibbs free energy” = a measure of chemical energy for reactions

deltaG(W) = change in free energy at 1atm, 25C pH7

production of glucose:

6CO2 + 6H2O –> C6H12O6 + 6O2
deltaG = +ve = reaction requires energy

C6H12O6 + 6O2 –> 6CO2 + 6H2O
delataG = -ve = reaction releases energy

Question 3

Oxidation vs Reduction

Answer 3

Oxidation: during the light phase of photosynthesis, atoms lose electrons

Reduction (synthesis): during the dark phase (no light required), can happen in both daylight and darkness, atoms receive electrons

***refer to L12 slide 14 for example of cancelling electrons and slide 16 for a graph of oxidation vs synthesis

Question 4

How does fall effect photosynthetic pathways?

Answer 4

ratio of photosystem II to photosystem I decreases (less photosystem II)

photosystem II responsible for chlorophyll (green)

photosystem I responsible for carotene (yellow) and anthocyanins (red)

that’s why leaves change colours :0

Question 5

What are some important measures in photosynthesis?

Answer 5

Gross primary productivity (GPP): total amount of CO2 that is fixed by the plant through the process of photosynthesis

Plant Respiration (Ra): the total amount of CO2 that is lost through metabolic activity (aka autotrophic respiration)

Net Primary Productivity (NPP):
NPP = GPP - Ra
measure of plant growth(gC/m^2/year)

Question 6

What are some climate change impacts on photosynthesis?

Answer 6

Climate change generally increases photosynthesis:
- more Co2
- warmer temps

Photoperiod (daylight hours):
affects relative participation of photosystems I and II

Temperature:
- warmer temp (or related cold temp) in fall
- delayed fall foliage colours

Question 7

What are some measures of photosynthesis?

Answer 7

Photosynthetic Rate: measure of the changes on input and output in photosynthesis
- uptake of CO2 by plants
- release of O2
- plant dry biomass content
- chlorophyll fluorescence (plant stress level)

Photosynthesis Remote Sensing: monitoring the earth surface by measuring the reflectance and emitted radiation at a distance

Question 8

What are some important non-photosynthesis photosystems?

Answer 8

UV disinfection of drinking water:
- UV light oxidizes DNA, prevents replication of microorganisms