Cellular Respiration and Photosynthesis Flashcards

Which of the following correctly compares the primary products of the light-dependent reactions of photosynthesis and the Krebs cycle in cellular respiration?

Answer: Light-dependent reactions produce ATP and NADPH, while the Krebs cycle produces ATP, NADH, and FADH2.

The light-dependent reactions of photosynthesis capture light energy to produce the energy-carrying molecules ATP and NADPH. [4, 11] The Krebs cycle, a key stage of cellular respiration, breaks down acetyl-CoA to produce ATP, as well as the electron carriers NADH and FADH2, which will be used in the electron transport chain. [22, 23]

A scientist designs an experiment to measure the rate of photosynthesis in a green alga. She places the alga in a sealed container with a buffered solution and a light source. Which of the following environmental changes would most likely lead to an increase in the rate of O2 production?

Answer: Increasing the intensity of the white light.

The rate of photosynthesis is limited by factors such as light intensity, CO2 concentration, and temperature. Increasing the intensity of white light provides more energy for the light-dependent reactions, thus increasing the rate of water splitting and O2 production, up to a certain saturation point. [12] Decreasing CO2 would limit the Calvin cycle, and green light is largely reflected by chlorophyll, making it ineffective for photosynthesis.

Which statement best describes the relationship between photosynthesis and cellular respiration?

Answer: Photosynthesis stores energy in organic molecules, while cellular respiration releases it.

Photosynthesis is an anabolic process that uses light energy to build energy-rich glucose molecules from CO2 and H2O. [5, 17] Cellular respiration is a catabolic process that breaks down glucose to release stored chemical energy in the form of ATP. [16, 20] The products of one process are essentially the reactants of the other, creating a cycle of energy conversion and matter. [17]

In the overall equation for cellular respiration, C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP, the oxygen (O2) molecules are primarily used during which stage?

Answer: The Electron Transport Chain

Oxygen acts as the final electron acceptor in the electron transport chain. It combines with electrons and hydrogen ions to form water. This process is crucial for the continuous flow of electrons and the efficient production of ATP through oxidative phosphorylation. [22, 23] Glycolysis is anaerobic, and while the Krebs cycle requires aerobic conditions to proceed, it does not directly consume oxygen. [26]

An organism that produces its own food using light energy is known as a photoautotroph. This organism serves as a primary producer in an ecosystem. Which of the following is a heterotroph?

Answer: A mushroom absorbing nutrients from decaying leaves.

Heterotrophs cannot produce their own food and must obtain energy by consuming other organisms. [8, 15] A mushroom is a fungus that acts as a decomposer, absorbing nutrients from dead organic matter, which classifies it as a heterotroph. [19] Cyanobacteria and trees are photoautotrophs, while chemosynthetic bacteria are autotrophs that use chemical energy instead of light.

The Calvin cycle (light-independent reactions) of photosynthesis is responsible for which of the following processes?

Answer: Fixing carbon dioxide into organic molecules.

The Calvin cycle, which occurs in the stroma of the chloroplast, uses the ATP and NADPH produced during the light-dependent reactions to convert inorganic carbon dioxide into organic sugar molecules, a process known as carbon fixation. [9, 11] The other options are all key events of the light-dependent reactions that take place in the thylakoid membranes.