5.4.3 A Review of Photosynthesis

Question 1

notes

Answer 1

• Review: In the light reactions, light energy is converted into chemical energy in the form of NADPH and ATP. Light excites an electron in chlorophyll a, causing the chlorophyll to lose the electron. As excited electrons are passed down an electron transport chain, their energy is used to pump protons into the lumen of the thylakoid. Eventually an electron is passed to NADP+ to form NADPH. Water is split and also loses electrons, producing oxygen gas and H+ ions in the lumen
  of the thylakoid. These H+ ions pass through ATP synthase, which produces ATP. At photosystem 2, noncyclic electron flow occurs. At photosystem 1, cyclic electron flow will take place when NADPH builds up.
  • Review: In the Calvin cycle, carbon dioxide is fixed to ribulose bisphosphate (RuBP) to eventually form
  glyceraldehyde 3-phosphate, a major building block of glucose and many other molecules. In the process, ATP and NADPH from the light reactions are used.
  • Mitochondria and chloroplasts have several striking similarities that suggest a common ancestry.
• Mitochondria are organelles that convert the energy stored in glucose into ATP, the energy currency of the cell. A mitochondrion consists of an inner membrane enclosed by an outer membrane. Proteins such as ATP synthase, NADH reductase, and FADH2 reductase are present. Protons (H+) are pumped into the intermembrane space and allowed to diffuse back into the mitochondrial matrix through the enzyme complex ATP synthase, which produces ATP in the process.
• Chloroplasts are organelles found in plants that convert light energy into chemical energy. Chloroplasts have an outer membrane surrounding an inner membrane network called the thylakoid membrane. Proteins such as ATP synthase and NADP+ reductase are present. Protons (H+) are pumped into the lumen of the thylakoid and allowed to diffuse back into the stroma of the chloroplast through the ATP synthase complex, which produces ATP in the process.

Question 2

A proton gradient is formed in both mitochondria and chloroplasts. The chloroplasts differ from the mitochondria in that their proton gradient

Answer 2

• flows outward from a lumen rather than inward

Question 3

Electrons are excited and leave Photosystem I where they are then taken up by an electron acceptor. The electron acceptor passes them down an electron transport chain of proteins and eventually they are passed back to Photosystem I. What is the name of this pathway?

Answer 3

• cyclic electron flow

Question 4

Ribulose bisphosphate plays an important role in

Answer 4

• the light independent reactions of photosynthesis

Question 5

Aerobic respiration and the light dependent phases of photosynthesis have all of the following characteristics in common except

Answer 5

• they both consume oxygen

Question 6

The addition of carbon dioxide to a five-carbon intermediate followed by a reduction of the product of that reaction is called __________ and occurs in the __________.

Answer 6

• the light-independent reactions; the stroma of the chloroplast