Test Prep for AP® Courses

Q34 — Shared component in photosynthesis and respiration pathways

C) The cytochrome complex — both chloroplasts and mitochondria use cytochrome complexes in their electron transport chains; photosystems and thylakoids are only in chloroplasts.

Q35 — Evidence for common ancestry from photosynthesis and respiration

B) All organisms perform cellular respiration using oxygen and glucose, which are produced by photosynthesis — the widespread use of O₂ and glucose in respiration suggests a shared evolutionary history tied to the rise of photosynthesis.

Q36 — Correct labeling of chloroplast structures

B) A. outer membrane, B. stroma, C. granum, D. thylakoid, E. inner membrane — the outermost layer is the outer membrane, the fluid around stacks is stroma, stacks are grana, individual discs are thylakoids, and the membrane beneath the outer is the inner membrane.

Q37 — Structural/mechanistic similarity in photosynthesis and respiration

C) Both processes are contained in organelles with double membranes, and both use a version of the cytochrome complex — chloroplasts and mitochondria are double-membraned and both employ cytochromes in their ETCs.

Q38 — Why light-dependent reactions occur in thylakoids

B) The cytochrome complex requires a membrane for chemiosmosis to occur — the thylakoid membrane allows a proton gradient to be established for ATP synthesis as electrons move through the cytochrome complex.

Q39 — How the Calvin cycle harnesses, stores, and uses energy

B) The Calvin cycle harnesses energy in the form of 6 ATP and 6 NADPH that are used to produce glyceraldehyde 3-phosphate (GA3P) molecules, which store captured energy, and the cycle uses this energy to regenerate RuBP — GA3P is the main product, and ATP/NADPH drive both reduction and regeneration.

Q40 — Cause of running out of NADP

D) Not enough CO₂ — if CO₂ is low, the Calvin cycle slows and stops oxidizing NADPH back to NADP⁺, so NADP⁺ (the oxidized form) runs out because it is all reduced to NADPH.

Q41 — Effect of CO₂ loss at higher temperatures

D) Loss of gases, mainly CO₂, will affect photosynthesis because the Calvin cycle will slow down and possibly stop due to inadequate carbon to fix — CO₂ is the substrate for carbon fixation, so its loss directly limits the cycle.

Q42 — Role of cytochrome complex components in ETC

B) Plastoquinone and plastocyanine perform redox reactions that allow the electron to move down the electron transport chain into Photosystem I — they shuttle electrons between PSII, the cytochrome complex, and PSI.

Q43 — How chloroplast membranes support function

B) The inner membrane contains only the chemicals needed for the Calvin cycle; the thylakoid membrane contains components of the light-dependent reactions, photosystems I and II, and NADP⁺ reductase — this best matches the idea that light reactions occur in the thylakoid and carbon-fixation chemistry is in the stroma region bounded by the inner membrane.

Q44 — Pigment least affected if absorption restricted to green

A) Carotenoids — carotenoids absorb in blue and blue-green regions and reflect yellow/orange; among the listed pigments they are least directly tied to non-green wavelengths in the classic chlorophyll a/b sense and can still function somewhat under green-heavy light.

Q45 — Passage of energy from light to primary electron acceptor

B) Chlorophyll a molecules in the photosystems are excited and pass the energy to the primary electron acceptor, where the energy is used to excite electrons from the splitting of water — antenna pigments pass energy to chlorophyll a in the reaction center, which donates an excited electron to the primary electron acceptor, with electrons ultimately coming from water.