Photosynthesis: the balanced equation and where the energy goes

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Use this

   Flow diagram (model, not to scale), drawn inside the chloroplast. Inputs in boxes on the left: 6CO₂; 6H₂O. Outputs in boxes on the right: C₆H₁₂O₆; 6O₂. A wavy arrow points into the reaction: light energy.

2. 1.

   Luz counts oxygen atoms in 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. How many are on each side of the arrow?

   • 12 on the left, 18 on the right: 6 are made in the reaction
   • 18 on the left, 12 on the right: 6 are used up in the reaction
   • 18 on the left, 18 on the right
   • 12 on the left, 12 on the right
3. 2.

   Noah counts atoms in the photosynthesis equation and leaves light energy out of the count. Why is that right?

   • Light energy is not matter, so it has no atoms to count
   • Light energy is a product, so it is counted on the right
   • Light energy turns into the atoms of glucose, so it is counted there
   • Light energy changes from leaf to leaf, so no count exists
4. 3.

   Pia follows the carbon atoms in glucose through photosynthesis. Which input supplies them?

   • Carbon dioxide taken in through the stomata
   • Oxygen gas taken in from the air
   • Light energy absorbed by chlorophyll
   • Soil taken in through the roots

5. Use this

   Flow diagram (model, not to scale), drawn inside the leaf. Inputs in boxes on the left: carbon dioxide, which enters through open stomata; water. Outputs in boxes on the right: glucose; oxygen gas. A wavy arrow points into the reaction: light energy. The stomata are closed.

6. 4.

   On a hot, dry afternoon, the guard cells of Tala's sunflower close its stomata. What happens to photosynthesis, and why?

   • It slows, since less water can enter the leaf
   • It slows, since less carbon dioxide can enter the leaf
   • It stays the same, since light energy still arrives
   • It speeds up, since the leaf turns trapped CO₂ into O₂

7. Use this

   Flow diagram (model, not to scale), drawn inside the chloroplast. Inputs in boxes on the left: 6CO₂; 6H₂O. Outputs in boxes on the right: C₆H₁₂O₆; 6O₂. A wavy arrow points into the reaction: light energy.

8. 5.

   Zee sorts photosynthesis as endergonic or exergonic, using the flow diagram. Which choice is right?

   • Endergonic: energy goes in, and the products hold more free energy
   • Endergonic: energy goes in, and the products hold less free energy
   • Exergonic: the oxygen gas leaving the leaf carries energy out
   • Exergonic: energy is released as the glucose is built

9. Two glucose equations (real data, from OpenStax Biology 2e)

   change	equation
   glucose synthesis (photosynthesis)	6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂
   glucose breakdown	C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

10. 6.

    Ari compares the two equations in the table. Which statement is right?

    • Energy comes out for both, since both change glucose
    • Energy goes in for breakdown and out for synthesis
    • Energy goes in for synthesis and out for breakdown
    • Synthesis makes atoms that breakdown later destroys

11. Use this

    Flow diagram (model, not to scale), drawn inside the chloroplast. Inputs in boxes on the left: 6CO₂; 6H₂O. Outputs in boxes on the right: C₆H₁₂O₆; 6O₂. A wavy arrow points into the reaction: light energy.

12. 7.

    Bo reads that sunlight energy ends up as chemical energy in glucose. Where is that chemical energy stored?

    • In light that stays trapped inside the molecule
    • In heat that the leaf holds as warmth
    • In the covalent bonds between the atoms of glucose
    • In the O₂ molecules that leave the leaf
13. 8.

    Esme scales the equation up. A leaf takes in 12 CO₂ molecules, with enough water and light. How many glucose molecules can form?

    • 12 glucose molecules, since each CO₂ makes one
    • 2 glucose molecules, since each needs 6 CO₂
    • 72 glucose molecules, since 6 × 12 = 72
    • 6 glucose molecules, since the equation has a 6
14. 9.

    Flow diagram (model, not to scale), drawn inside the chloroplast. O₂, number not shown. One glucose goes with 6 O₂. Jun scales the equation up. Three glucose molecules form from the equation in the figure. How many O₂ molecules are released?

    • 18 O₂ molecules, since 3 × 6 = 18
    • 6 O₂ molecules, the number in one equation
    • 3 O₂ molecules, one for each glucose
    • 36 O₂ molecules, since 6 × 6 = 36

15. Use this

    Flow diagram (model, not to scale), drawn inside the leaf cell. Inputs in boxes on the left: carbon dioxide; water. Outputs in boxes on the right: 4C₆H₁₂O₆; oxygen gas. A wavy arrow points into the reaction: light energy. Each CO₂ molecule holds 1 carbon atom.

16. 10.

    Kira counts carbon in 4 glucose molecules, C₆H₁₂O₆. How many carbon atoms is that, and where do they come from?

    • 24 atoms, from 24 CO₂ molecules
    • 24 atoms, from 4 CO₂ molecules
    • 24 atoms, from 24 H₂O molecules
    • 24 atoms, from soil taken in by the roots