5.3.2 Photosystem 1

Question 1

light-harvestin antennae or photosystems

Answer 1

• within a chloroplast are found within the thylakoid membrane and consist of proteins, chlorophyll a, and other pigments and molecules. The reaction center of a photosystem consists of a chlorophyll a molecule situated next to the primary electron acceptor, which is able to accept an excited electron.
  • There are two photosystems, photosystem 1 and photosystem 2. Each photosystem is a light-harvesting unit and both photosystems work together to produce ATP and NADPH.

Question 2

Photosystem 1

Answer 2

• also known as P700 because its reaction center is best at absorbing 700 nanometers (nm).
• An electron from chlorophyll a in the reaction center is
  excited by a photon of light. It is then passed to the primary electron acceptor. The primary electron acceptor passes the electron to a protein within the thylakoid membrane called ferredoxin (Fd). From ferredoxin the electron gets passed to NADP+, which in turn gets reduced to NADPH.
• If there is a buildup of NADPH, cyclic electron flow takes place. The excited electron gets passed from chlorophyll a in photosystem 1 to the primary electron acceptor to ferredoxin, but instead of getting passed to NADP+, the electron gets passed down an electron transport chain. As the electron is passed through a series of membrane proteins, it loses energy. The membrane proteins use the energy lost by the electron to pump protons into the lumen of the thylakoid. Eventually the electron is returned to chlorophyll
  a in photosystem 1.
• The protons within the thylakoid membrane are allowed to pass through ATP synthase where ADP is phosphorylated to make ATP. The production of ATP from cyclic electron flow is called photophosphorylation.

Question 3

When an electron from Photosystem I is excited and transferred to a primary electron acceptor, the chlorophyll a in the reaction center will be __________.

Answer 3

• oxidized

Question 4

__________ is the source of energy for life on Earth.

Answer 4

• the sun

Question 5

The purpose of cyclic electron flow is

Answer 5

• to increase the ATP/ NADPH ratio

Question 6

Which statement is true regarding cyclic electron flow in photosynthesis?

Answer 6

• ATP is produced without increasing the amount of NADPH

Question 7

A photon with a wavelength of __________ is optimal to move an electron from ground state to an excited state in Photosystem I.

Answer 7

• 700 nm

Question 8

Which of the following is the major difference between cyclic and noncyclic photophosphorylation?

Answer 8

• Photosystem II is not involved in cyclic photophosphorylation