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 go to the stroma 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 are split in the thylakoids to release oxygen
   • The Calvin cycle makes them, and they go back to the light reactions to be refilled

2. 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

3. 2.

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

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

4. 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.

5. 3.

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

   • 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
   • More sugar is made, since light alone can build the sugar
   • Oxygen is still released, since it comes from the carbon dioxide
6. 4.

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

7. 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

8. 5.

   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 chlorophyll reflects green light instead of absorbing it
   • Red, since red light has too little energy for chlorophyll
   • Green, since green light has too little energy to split water
   • Blue, since chlorophyll cannot absorb short wavelengths
9. 6.

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

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

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. 7.

    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 less G3P, since carbon dioxide is split to release oxygen
    • Less carbon dioxide gives more G3P, since the plant makes up for it with water

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. 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?

    • 3 turns, since 3 carbon atoms must be fixed
    • 1 turn, since 1 carbon dioxide makes 1 G3P
    • 2 turns, since each turn makes 2 G3P
    • 6 turns, since glucose needs two G3P
14. 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+
15. 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?

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