Cellular respiration: the equation and its three stages

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Equation card, from OpenStax Biology 2e

   C6H12O6 + 6O2 → 6CO2 + 6H2O + energy. Inputs in boxes on the left: glucose, C6H12O6; oxygen, 6O2. Outputs in boxes on the right: carbon dioxide, 6CO2; water, 6H2O. A wavy arrow points out: energy.

2. 1.

   Tala counts the oxygen atoms on each side of C6H12O6 + 6O2 → 6CO2 + 6H2O. How many are on the left side, and how many on the right side?

   • 12 on the left and 18 on the right
   • 18 on the left and 18 on the right
   • 12 on the left and 12 on the right
   • 18 on the left and 12 on the right
3. 2.

   Zee counts atoms in the respiration equation and finds both sides balanced. The right side also lists energy. What does the energy term show?

   • Energy moved out of glucose's bonds into ATP and heat
   • A product made of atoms that must also be counted
   • Energy stored in the CO2 and water, kept for later
   • New energy that the cell creates during the reaction
4. 3.

   Ari reads that a potato plant's cells break down 2 glucose in the dark. Using the equation, how many H2O form, and how many hydrogen atoms do they hold?

   • 0 H2O, since plant cells do not break glucose down
   • 12 H2O holding 12 hydrogen atoms
   • 12 H2O holding 24 hydrogen atoms
   • 6 H2O holding 12 hydrogen atoms

5. Use this

   Flow diagram (model, not to scale), drawn inside a mitochondrion. Inputs in boxes on the left: pyruvate (3 carbons). Outputs in boxes on the right: acetyl CoA (2 carbons); CO2 (1 carbon); NADH. No wavy arrow label is drawn.

6. 4.

   Bo reads a model where pyruvate loses one carbon as CO2 while NADH forms. Which stage is this, and where does it happen?

   • Pyruvate oxidation, in the mitochondrial matrix
   • Glycolysis, in the mitochondrial matrix
   • Electron transport chain, on the inner membrane
   • Pyruvate oxidation, in the cytoplasm
7. 5.

   No wavy arrow label is drawn. Esme reads that hydrogen ions flow through ATP synthase in the inner mitochondrial membrane and ATP forms. Which stage is this, and what share of the ATP does it make?

   • The citric acid cycle, about 90 percent of the ATP
   • Chemiosmosis, about 90 percent of the ATP
   • Chemiosmosis, a net gain of just 2 ATP
   • Glycolysis, about 90 percent of the ATP

8. Use this

   Flow diagram (model, not to scale), drawn inside a mitochondrion. Inputs in boxes on the left: NADH in the matrix; oxygen at the inner membrane. Outputs in boxes on the right: CO2 leaving the matrix; water forming at the inner membrane. No wavy arrow label is drawn.

9. 6.

   Jun reads a diagram with CO2 leaving the matrix and water forming at the inner membrane. Which stage uses oxygen directly?

   • The lungs, which use the oxygen as soon as it is breathed in
   • Glycolysis, which starts by splitting glucose in the cytoplasm
   • The electron transport chain, which forms water from the oxygen
   • The citric acid cycle, which turns oxygen into the CO2 it releases
10. 7.

    Read about only: the teacher handles the equipment. Kira reads a respirometer card of pea seeds. Which statement does the card support?

    • Dry seeds respire faster, since tube 2 used more oxygen
    • Germinating seeds respire more, since tube 1 used more oxygen and released more CO2
    • The germinating seeds created new energy, which is why they used oxygen
    • The seeds are plants, so the gas changes come from photosynthesis, not respiration

11. Breathing rate card (model data)

    moment	breaths per minute
    resting	14
    after 3 minutes of jogging in place	30
    after 5 minutes of rest	16

12. 8.

    Luz reads a card about a teen volunteer who jogs in place. Which explanation fits the card?

    • Cellular respiration happens in the lungs, so the lungs worked much harder
    • Muscle cells created extra energy from nothing, which made them need extra air
    • Muscle cells made less ATP, so they used less oxygen and the breathing slowed
    • Muscle cells made more ATP, so they used more oxygen and released more CO2
13. 9.

    Real-data note: chemiosmosis makes about 90 percent of the ATP. Noah reads that chemiosmosis makes about 90 percent of the ATP from glucose. A model cell makes 20 ATP from one glucose. How are the 20 shared?

    • 18 from chemiosmosis and 2 from the other stages
    • 2 from chemiosmosis and 18 from glycolysis
    • 20 from chemiosmosis and 0 from the other stages
    • 10 from chemiosmosis and 10 from the other stages

14. ATP per glucose card (real data)

    source	ATP per glucose in aerobic respiration
    Judge and Dodd 2020	about 30 to 32
    OpenStax Biology 2e	the number varies

15. 10.

    Ren reads that the ATP yield per glucose varies. What can make the number vary from cell to cell?

    • Glycolysis nets 2 ATP in some cells and 30 ATP in others
    • How much extra energy the cell creates beyond what glucose holds
    • The number of breaths the person takes in a minute
    • The number of hydrogen ions pumped and how electrons enter the mitochondrion