Photosynthesis

Question 1

What is photosynthesis?

Answer 1

Photosynthesis is the process by which cells synthesize organic compounds (e.g. glucose) from inorganic molecules (CO2 and H2O) in the prsence of sunlight

Question 2

What is the equation for photosynthesis?

Answer 2

6CO2 + 12H2O => C6H12O6 + 6O2 + 6H2O

Question 3

What are the stages of photosynthesis?

Answer 3

1. Light dependent reactions
   - Light is absorbed by chlorophyll and results in production of ATP
   - Photolysis: splitting of water after it absorbs light
2. Light independent reactions
   - ATP and hydrogen are transferred to chloroplast
   - hydrogen combines with CO2 to form organic compounds
   - ATP provides the energy for the process

Question 4

What is the electronic magnetic spectrum?

Answer 4

The range of all possible wavelengths of electromagnetic radiation

Question 5

What is the spectrum used in photosynthesis?

Answer 5

Wavelengths in the range of 400 nm to 700 nm.

- chlorophyll absorbs red and blue light most effectively

Question 6

What is absorption spectrum?

Answer 6

The absorption spectrum indicates the percentage of light absorbed at each wavelength by pigments in the organism

Question 7

What is the action spectrum?

Answer 7

The action spectrum indicates the overall rate of photosynthesis at each wavelength of light

Question 8

What are the trends in absorption and action spectrum?

Answer 8

1. Both display peaks at the blue region (450 nm) and red region (670 nm)
2. Both display a trough in the green/yellow region (550) of the visible spectra

Question 9

What is the significance of photosynthesis on the atmosphere?

Answer 9

Photosynthesis is the only significant source of oxygen gas that exists.

1. Led to the production of iron oxides formed at the bottom of the ocean - i.e. banded iron formations (helps in steel production)
2. 20% of atmosphere consists of oxygen
3. Rising O2 levels was a critical determinant to the evolution of aerobically respiring organisms

Question 10

What are the 3 limiting factors of photosynthesis?

Answer 10

1. Temperature
2. Light Intensity
3. CO2 Concentration

Question 11

How does temperature affect photosynthesis?

Answer 11

1. At low temperature, enzymes that catalyze photosynthesis work slowly
2. Higher the temperature, more the frequency of collisions, high the rate of enzyme activity, higher the rate of photosynthesis
3. At temperatures above 30 degrees, the enzyme used to fix CO2 (rubsico) is decreasingly effective, and after a certain point enzymes begin to denature

Question 12

How does light intensity affect photosynthesis?

Answer 12

1. At low light intensities, the rate of photolysis and ATP production by chlorophyll will be low, resulting in a low rate of photosynthesis
2. At high light intensities, the rate of photolysis will be high while all chlorophyll will be saturated, which is why rate of photosynthesis will plateau

Question 13

How does CO2 concentration affect photosynthesis?

Answer 13

1. As CO2 concentration increases, reaction rate will increase, as more organic molecules are being produced
   - At lower levels of CO2, ATP and electrons are not used as rapidly as they are produced
2. At a certain concentration of CO2, the rate of photosynthesis will plateau as all enzymes will be saturated

Question 14

How to measure CO2 uptake?

Answer 14

1. Boil water to remove dissolved CO2
2. Enclose leaf tissue in a space with water
3. Increased uptake of CO2 by the plant will lower the concentration of CO2 in the solution and increase the alkalinity

Question 15

How to measure O2 production?

Answer 15

1. Place plant in a water tank

2. Bubbles formed are oxygen

Question 16

What is an alternative to measuring CO2 or O2?

Answer 16

1. Measuring biomass; this requires plant tissue to be completely dehydrated prior to weighing
2. Starch iodine test on leaf