Light reactions and the Calvin cycle

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Ari reads that ADP, Pi and NADP+ leave the stroma. Which stage makes them, and what happens to them next?

   • The Calvin cycle makes them, and they go back to the light reactions to be refilled
   • The light reactions make them, and they go to the stroma to be refilled
   • The light reactions make them, and they are split in the thylakoids to release oxygen
   • The Calvin cycle makes them, and they leave the chloroplast with the G3P as waste
2. 2.

   Flow diagram (model, not to scale), drawn inside a chloroplast. Which zone box M is in is not shown. Bo reads that water is split and oxygen is released. Which stage is this, and where does it happen?

   • The light reactions, in the stroma
   • The light reactions, in the thylakoid membranes
   • Cellular respiration, in the thylakoid membranes
   • The Calvin cycle, in the stroma
3. 3.

   Esme reads that the enzyme RuBisCO joins carbon dioxide to a molecule that already holds carbon. Which step is this, and where does it happen?

   • Light absorption, in the thylakoid membranes
   • Reduction, in the stroma
   • Fixation, in the stroma
   • Fixation, in the thylakoid membranes

4. Read this first

   Use the table

   A water plant when the lamp goes off (model data). Lab card, read about only. A water plant is lit by a lamp, and then the lamp goes off.

   time	oxygen released	ATP and NADPH made	G3P made, all in units per minute
   lamp on	10	10	10
   just after the lamp goes off	0	0	6
   a while after the lamp goes off	0	0	0

5. 4.

   Jun's class reads a card about a water plant. Which statement fits the card?

   • G3P making keeps going unchanged, since the light reactions build the sugar
   • Oxygen and ATP and NADPH stop first; G3P making falls to zero a little later
   • G3P making stops first, then oxygen and ATP and NADPH stop
   • G3P making rises in the dark, since the Calvin cycle is the dark reaction

6. Use this

   Flow diagram (model, not to scale). In the thylakoid membranes: a wavy arrow of light energy goes in, but the water box is empty. In the stroma: carbon dioxide goes in.

7. 5.

   Kira imagines a leaf with light and carbon dioxide but no water for the light reactions to split. Which prediction fits?

   • Oxygen is still released, since it comes from the carbon dioxide
   • No oxygen is released, but sugar still forms, since the Calvin cycle needs no help from the light reactions
   • More sugar is made, since light alone can build the sugar
   • No oxygen is released, since water is the source of the oxygen
8. 6.

   “Flow diagram (model, not to scale),” Luz reads that on a hot, dry day a leaf's guard cells close its stomata. What happens to sugar making?

   • It falls, since less water reaches the stroma to be split
   • It stays the same, since the light reactions make the sugar
   • It rises, since the closed stomata keep more carbon dioxide inside
   • It falls, since less carbon dioxide reaches the Calvin cycle

9. Use the table

   Oxygen from a water plant under four lamp colors (model data). Lab card, read about only. A water plant is lit by four lamps of equal brightness, one color at a time.

   lamp color	oxygen released (units per hour)
   blue	10
   green	1
   yellow	5
   red	9

10. 7.

    Milo's class reads a card of oxygen released by a water plant under lamps of four colors. Which color gave the least oxygen, and why?

    • Green, since green light has too little energy to split water
    • Blue, since chlorophyll cannot absorb short wavelengths
    • Red, since red light has too little energy for chlorophyll
    • Green, since chlorophyll reflects green light instead of absorbing it

11. Use this

    Flow diagram (model, not to scale), drawn inside the stroma. Each turn: 1 carbon dioxide goes in. One G3P with 3 carbon atoms leaves the cycle. The number of turns is not shown.

12. 8.

    Ren reads that each turn of the Calvin cycle fixes one carbon dioxide, and the G3P that leaves has three carbon atoms. How many turns does one leaving G3P take?

    • 2 turns, since each turn makes 2 G3P
    • 1 turn, since 1 carbon dioxide makes 1 G3P
    • 3 turns, since 3 carbon atoms must be fixed
    • 6 turns, since glucose needs two G3P
13. 9.

    Tala reads that three turns of the Calvin cycle use 6 ATP and 6 NADPH in the reduction step. How many ADP and NADP+ return to the light reactions?

    • 6 ATP and 6 NADPH
    • 6 ADP and 6 NADP+
    • Zero ADP and NADP+, since the 6 ATP and 6 NADPH are used up for good
    • 3 ADP and 3 NADP+
14. 10.

    Flow diagram (model, not to scale), drawn inside the thylakoid membranes. Zee reads that one split water releases one oxygen atom, and two atoms join to make one O2. How many O2 form from 8 split water molecules, and from which atoms?

    • 4 oxygen molecules, made from the 8 oxygen atoms of split water
    • 16 oxygen molecules, two for each split water
    • 4 oxygen molecules, made from the oxygen atoms of carbon dioxide
    • 8 oxygen molecules, one for each split water