Lecture 19: Photosynthesis

Question 1

• Define Photosynthesis

Answer 1

The biochemical process of building Carbohydrates from

Sunlight, Carbon Dioxide, and Water

Question 2

• Describe the structure of chloroplasts and their role in Photosynthesis

Answer 2

- Enclosed by a double membrane (outer and inner membrane).
• Thylakoid membrane: highly
folded membrane inside the outer
and inner membranes
• Thylakoid membranes form Grana:
flattened sacs that are grouped into
stacks
• Within the each grana is the lumen;
the area outside is the stroma

Question 3

• Know the Photosynthesis reaction, including the components of the reaction
that are reduced/oxidized

Answer 3

6 CO2 + 12 H2O + Light energy = C6H12O6 + 6 O2 + 6 H2O
also
6CO2+6H2O=C6H12O6+6O2

• CO2 (e acceptor) is reduced to glucose (e donor)
• H2O (e donor) oxidized to Oxygen (e acceptor)

Question 4

• Describe the experiment that showed how O2 is being generated during
Photosynthesis

Answer 4

1. Place Chlorella (green algae) into 2 flasks.
2. Wait 2 hours to allow photosynthesis to occur.
3. Measure ratio of 18O2/16O2 in air above flasks.

Question 5

• Know the main type of electron carrier in Photosynthesis

Answer 5

NADP+, gets reduced to NADPH

Question 6

• Know the relationship between the light reactions and the Calvin Cycle

Answer 6

ATP and NADPH produced in light reactions are used in the Calvin cycle.

Question 7

• Know and describe the three phases of the Calvin Cycle, including the
intermediates that we cover in class

Answer 7

Stage 1: Carboxylation:
- addition of CO2 to a 5C sugar, RuBP by the enzyme rubisco to produce a 6C intermdiate that is split into 2 molecules of 3-phosphoglycerate,

Stage 2: Reduction:
- 3-phosphoglycerate receives a sugar from ATP to produce 1,3bisphosphoglycerate. This then loses a phosphate group and is reduced to G3P. G3P leaves as a sugar to form glucose.

Stage 3: Regeneration:
RuBP is regenerated. 5 molecules of G3P rearranged into 3 molecules of RuBP.

Question 8

• Describe the role of starch in plant cells

Answer 8

• Starch provides photosynthetic cells with a source of carbohydrates that
can be used in the absence of sunlight