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

4. 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.

5. 3.

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

   • Electron transport chain, on the inner membrane
   • Pyruvate oxidation, in the mitochondrial matrix
   • Glycolysis, in the mitochondrial matrix
   • Pyruvate oxidation, in the cytoplasm
6. 4.

   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
   • Glycolysis, about 90 percent of the ATP
   • Chemiosmosis, about 90 percent of the ATP
   • Chemiosmosis, a net gain of just 2 ATP

7. 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.

8. 5.

   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

9. 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

10. 6.

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

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

11. Glycolysis table (real data, from OpenStax Biology 2e)

    measure	per glucose
    ATP spent	2
    ATP made	4
    net ATP	2
    NADH made	2
    pyruvate made	2

12. 7.

    Milo reads the glycolysis table. Which statement does the table support?

    • Glycolysis makes 4 ATP and spends 2, so the net is 2
    • Glycolysis nets 4 ATP, since the 2 ATP spent are not counted
    • Glycolysis makes about 90 percent of the ATP, since it comes first
    • Glycolysis nets 6 ATP, since 2 spent plus 4 made is 6
13. 8.

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

14. Use this

    Flow diagram (model, not to scale), drawn inside a mitochondrion. Inputs in boxes on the left: 2 pyruvate (3 carbons each). Outputs in boxes on the right: CO2, amounts not shown. Stages shown in order: pyruvate oxidation, then the citric acid cycle. The 6 carbons of one glucose all end as CO2.

15. 9.

    Pia follows the 6 carbons of one glucose, and all 6 end up in CO2. Which statement about how the CO2 forms is right?

    • 6 CO2 form: 2 as pyruvate is oxidized and 4 in the citric acid cycle
    • 6 CO2 form: 3 in each of the 2 pyruvate steps and 0 in the citric acid cycle
    • 6 CO2 form at the last stage, when the oxygen picks up carbon from glucose
    • 6 CO2 form: 2 in glycolysis in the cytoplasm and 4 in the electron transport chain

16. 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

17. 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
    • The number of hydrogen ions pumped and how electrons enter the mitochondrion
    • The number of breaths the person takes in a minute
    • How much extra energy the cell creates beyond what glucose holds