Photosynthesis and Cellular Respiration Quiz

Grade 9 · Science · Quiz

Challenge yourself with this 8-question quiz on energy transformation, metabolic pathways, and the complementary nature of photosynthesis and respiration.

Questions

1. What are the raw materials (reactants) of photosynthesis?

   1. Glucose and oxygen
   2. Carbon dioxide, water, and light energy
   3. ATP, NADPH, and carbon dioxide
   4. Oxygen and water
   Show answer

   Answer: Carbon dioxide, water, and light energy

   Photosynthesis requires carbon dioxide (CO₂) from the air, water (H₂O) absorbed through roots, and light energy — all converted into glucose and oxygen.

2. In which part of the mitochondrion does the Krebs cycle take place?

   1. Outer membrane
   2. Intermembrane space
   3. Inner membrane
   4. Matrix
   Show answer

   Answer: Matrix

   The Krebs cycle (citric acid cycle) takes place in the mitochondrial matrix, the innermost fluid-filled compartment of the mitochondrion.

3. Which stage of cellular respiration produces the most ATP?

   1. Glycolysis
   2. Krebs cycle
   3. Electron transport chain
   4. Fermentation
   Show answer

   Answer: Electron transport chain

   The electron transport chain produces approximately 34 of the ~36-38 total ATP generated per glucose molecule, far more than glycolysis (2 net) or the Krebs cycle (2 ATP directly).

4. What happens to oxygen in the light-dependent reactions of photosynthesis?

   1. It is consumed to produce water
   2. It is released as a byproduct when water is split
   3. It combines with carbon dioxide to form glucose
   4. It is used to power the Calvin cycle
   Show answer

   Answer: It is released as a byproduct when water is split

   In the light-dependent reactions, water molecules are split by photolysis. The electrons go to replace those lost from excited chlorophyll, and oxygen is released as a byproduct.

5. A student keeps a plant in complete darkness for 48 hours. Which of the following would most likely still continue?

   1. Light-dependent reactions
   2. Calvin cycle (using stored ATP)
   3. Cellular respiration
   4. Oxygen production
   Show answer

   Answer: Cellular respiration

   Cellular respiration does not require light — it breaks down glucose that was already stored. The plant would continue respiring even in complete darkness.

6. Which electron carrier is produced during the Krebs cycle and delivers electrons to the electron transport chain?

   1. ATP
   2. ADP
   3. NADH
   4. Glucose
   Show answer

   Answer: NADH

   NADH (and FADH₂) are high-energy electron carriers produced in the Krebs cycle. They donate their electrons to protein complexes in the electron transport chain to drive ATP production.

7. During lactic acid fermentation in human muscle cells, glucose is partially broken down and NAD⁺ is regenerated so glycolysis can continue.

   Show answer

   Answer: True

   Lactic acid fermentation converts pyruvate to lactate, regenerating NAD⁺ from NADH. This allows glycolysis to keep running even without oxygen, providing 2 ATP per glucose.

8. The organelle where cellular respiration mainly occurs (Krebs cycle and ETC) is the ___.

   Show answer

   Answer: mitochondria

   The mitochondria (singular: mitochondrion) is the site of the Krebs cycle (matrix) and electron transport chain (inner membrane), making it the primary site of aerobic ATP production.

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