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 light reactions make them, and they are split in the thylakoids to release oxygen
   • The Calvin cycle makes them, and they go back to the light reactions to be refilled
   • The Calvin cycle makes them, and they leave the chloroplast with the G3P as waste
   • The light reactions make them, and they go to the stroma to be refilled
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 thylakoid membranes
   • Cellular respiration, in the thylakoid membranes
   • The light reactions, in the stroma
   • 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
   • Fixation, in the thylakoid membranes
   • Fixation, in the stroma
   • Reduction, in the stroma

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 rises in the dark, since the Calvin cycle is the dark reaction
   • 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 keeps going unchanged, since the light reactions build the sugar

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?

   • More sugar is made, since light alone can build the sugar
   • No oxygen is released, since water is the source of the oxygen
   • No oxygen is released, but sugar still forms, since the Calvin cycle needs no help from the light reactions
   • Oxygen is still released, since it comes from the carbon dioxide
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 rises, since the closed stomata keep more carbon dioxide inside
   • It falls, since less water reaches the stroma to be split
   • It stays the same, since the light reactions make the sugar
   • It falls, since less carbon dioxide reaches the Calvin cycle
9. 7.

   Noah reads a graph from a water plant under a lamp. Which statement fits the line?

   • More light gives more oxygen, since more water is split by the light reactions
   • More light gives more oxygen, since the Calvin cycle makes more oxygen
   • Oxygen falls, since a plant under more light uses up more oxygen
   • Oxygen stays flat, since the stage that makes it needs no light

10. Use the table

    G3P made at three carbon dioxide levels (model data). Lab card, read about only. Three tanks of water plants get the same light and water.

    carbon dioxide in the air	G3P made (units per hour)
    none	0
    half of normal	6
    normal	12

11. 8.

    Pia's class reads a card about three tanks of water plants lit equally. What does it show about carbon dioxide?

    • G3P stays the same at each level, since the light reactions make the G3P
    • Less carbon dioxide gives less G3P, since the Calvin cycle fixes it into G3P
    • Less carbon dioxide gives more G3P, since the plant makes up for it with water
    • Less carbon dioxide gives less G3P, since carbon dioxide is split to release oxygen

12. 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.

13. 9.

    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?

    • 3 turns, since 3 carbon atoms must be fixed
    • 1 turn, since 1 carbon dioxide makes 1 G3P
    • 6 turns, since glucose needs two G3P
    • 2 turns, since each turn makes 2 G3P
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 oxygen atoms of carbon dioxide
    • 16 oxygen molecules, two for each split water
    • 8 oxygen molecules, one for each split water
    • 4 oxygen molecules, made from the 8 oxygen atoms of split water