Question

electrons enter the complex at the bottom middle at a site where the electron carrier from the etc binds. once the electrons reach an excited state, they are passed up and out of the complex to another electron carrier, which binds to the complex at the top middle. in most cases, the electron carrier passes these excited electrons to an enzyme that reduces nadp+ to nadph. nadph is a molecule that is essential for reducing the carbon atoms in co2 and producing sugars.
examine the model of psi in detail. indicate which of the following statements are accurate. select all that apply.
□ psi, like psii, obtains electrons by oxidizing, or \splitting\ water.
□ chlorophyll molecules are embedded throughout the machine.
□ psi is embedded in a membrane and has many alpha - helices, as is typical of integral membrane proteins.
□ the most prominent beta - pleated sheets in the machine appear to be in the center bottom and top, which is where electrons come into the machine, get excited to a high - energy state, and then get transferred out to another electron carrier.
in some cases, the electron carrier that is reduced by the excited electrons emerging from psi doesnt pass its excited electrons to the enzyme that reduces nadp+. instead, the electron carrier takes the excited electrons to the etc, where they lead to proton pumping and production of atp by atp synthase. in this way, psi can contribute to the production of both nadph and atp.
when electrons from psi feed the etc, they come back to psi at the end of the etc. predict what name life scientists use to describe this process.
○ a short circuit, because electrons cant complete their normal path, causing the photosynthesis circuit to shut down.
○ cyclic electron flow, because electrons flow in a loop into and out of psi.
○ chemical energy co - creation, because additional atp is being produced.
did you fully understand the concept covered in this section?

Explanation:

• Statement 1: PSI does not obtain electrons by oxidizing water. That is the role of PSII. So this statement is incorrect.
• Statement 2: Chlorophyll molecules are indeed embedded throughout the photosystem (PS) complex. This is a correct statement.
• Statement 3: PSI is an integral membrane protein. Integral membrane proteins often have alpha - helices that span the membrane. This is a correct statement.
• Statement 4: In PSI, the prominent beta - pleated sheets are in the center bottom and top where electrons enter, get excited, and are transferred. This is a correct statement.
• For the second part: In cyclic electron flow, electrons from PSI flow through the electron transport chain (ETC) and then return to PSI. This is in contrast to non - cyclic flow where electrons go to NADP⁺.

Answer:

• For the first part: Chlorophyll molecules are embedded throughout the machine. PSI is embedded in a membrane and has many alpha - helices, as is typical of integral membrane proteins. The most prominent beta - pleated sheets in the machine appear to be in the center bottom and top, which is where electrons come into the machine, get excited to a high - energy state, and then get transferred out to another electron carrier.
• For the second part: Cyclic electron flow, because electrons flow in a loop into and out of PSI.