Light reactions and the Calvin cycle

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   Use the table

   Reactions after the lamp goes off (model data). Lab card, read about only.

   time	ATP and NADPH made	G3P made, in units per minute
   lamp on	8	8
   just after the lamp goes off	0	5
   a while after the lamp goes off	0	0

2. 1.

   Ari's class reads a card about a water plant. Which explanation fits all three rows?

   • G3P making runs on oxygen left in the stroma, until the oxygen is gone
   • G3P making runs on leftover light, which the thylakoid membranes turn into sugar
   • G3P making runs on its own, since the Calvin cycle needs no help from the light reactions
   • G3P making runs on leftover ATP and NADPH, then stops when they are used up

3. Use this

   Flow diagram (model, not to scale), drawn inside a chloroplast. Thylakoid membranes: water and a wavy arrow of light energy go in. Stroma: the carbon dioxide box is empty. Arrows run both ways between the zones: ATP and NADPH to the stroma; ADP, Pi and NADP+ back to the thylakoid membranes.

4. 2.

   Esme imagines a chloroplast with plenty of light and water but no carbon dioxide. Which prediction follows from the arrows?

   • The Calvin cycle stalls and stops returning ADP and NADP+, leaving the light reactions short of empty carriers
   • ATP and NADPH are made faster, since used carriers are thrown away and then replaced from the water supply
   • The light reactions stop at once, since the water that they split in the stroma cannot reach it
   • The light reactions are not affected, since they do not depend on anything the Calvin cycle does

5. Use this

   Flow diagram (model, not to scale), drawn inside the stroma. An arrow runs back to the thylakoid membranes; its counts are not shown.

6. 3.

   Jun reads that three turns of the Calvin cycle use 6 ATP and 6 NADPH in reduction and 3 more ATP in regeneration. How many ADP and NADP+ return to the light reactions?

   • Zero ADP and NADP+, since the carriers are used up for good
   • 6 ADP and 6 NADP+
   • 9 ADP and 6 NADP+
   • 9 ADP and 9 NADP+

7. Use this

   Flow diagram (model, not to scale), drawn inside a chloroplast. Thylakoid membranes: water and light energy go in; oxygen comes out. Stroma: carbon dioxide goes in; G3P comes out. An arrow carries ATP and NADPH from the thylakoid membranes to the stroma. An arrow carries ADP, Pi and NADP+ back.

8. 4.

   Kira compares the two stages in a chloroplast diagram. Which statement describes how they depend on each other?

   • The stages are separate, with the Calvin cycle running at night and sharing nothing with the light reactions
   • The light reactions make ATP and NADPH for the Calvin cycle, which returns ADP, Pi and NADP+ to them
   • The Calvin cycle makes oxygen for the light reactions, which return carbon dioxide to it
   • The light reactions make G3P for the Calvin cycle, which returns ATP and NADPH to them

9. Use the table

   The Calvin cycle: three turns and six turns. Card (counts from OpenStax Biology 2e; the six-turn row is left blank)

   turns	carbon dioxide fixed	ATP used	NADPH used	sugar made
   3	3	9	6	1 G3P
   6	?	?	?	1 glucose, which is 2 G3P

10. 5.

    Luz reads a card of the Calvin cycle. Six turns make one glucose, which is two G3P. What fills the blank row for six turns?

    • 6 carbon dioxide, 18 ATP and 12 NADPH
    • 6 carbon dioxide, 9 ATP and 6 NADPH
    • 3 carbon dioxide, 18 ATP and 12 NADPH
    • 6 carbon dioxide, 12 ATP and 18 NADPH

11. Use this

    Notebook entry and chloroplast diagram. The notebook says: The Calvin cycle is the dark reaction, so it makes most of its sugar at night. Diagram (model, not to scale): in the stroma, carbon dioxide and ATP and NADPH go in; G3P comes out. ATP and NADPH arrive from the thylakoid membranes.

12. 6.

    Milo's notebook says the Calvin cycle is the dark reaction, so it makes most of its sugar at night. What is the flaw?

    • It happens in the thylakoid membranes, which stop working when the sun sets
    • It spends ATP and NADPH made in the light, and those last only moments after the light is gone
    • It releases oxygen, not sugar, so the notebook has the product of the cycle wrong
    • It is the light reactions that build sugar, so the cycle has nothing to make at night

13. Use this

    Notebook entry and chloroplast diagram. The notebook says: The oxygen a leaf releases comes from carbon dioxide split in the Calvin cycle. Diagram (model, not to scale): in the thylakoid membranes, water and a wavy arrow of light energy go in; oxygen comes out. In the stroma, carbon dioxide goes in; G3P comes out.

14. 7.

    Noah's notebook says the oxygen a leaf releases comes from carbon dioxide split in the Calvin cycle. What is the flaw?

    • The oxygen does come from carbon dioxide, but the regeneration step of the cycle releases it
    • The oxygen comes from water split in the light reactions, not from carbon dioxide
    • The oxygen comes from the ATP, which loses a phosphate group as the Calvin cycle runs
    • The oxygen comes from the G3P, which light splits as it leaves the stroma

15. Use this

    Student diagram (model, not to scale), drawn inside a chloroplast. In the thylakoid membranes: light energy and water go in; G3P comes out. In the stroma: nothing is drawn.

16. 8.

    Pia's diagram shows G3P built in the thylakoid membranes from light and water. What is the flaw?

    • The light reactions belong in the stroma, so the whole diagram should be moved there
    • G3P is built in the stroma from carbon dioxide, using ATP and NADPH
    • G3P is built in the stroma from carbon dioxide, with no help from the light reactions
    • G3P is built in the thylakoid membranes, but from carbon dioxide instead of water

17. Use the table

    Card (real data, from OpenStax Biology 2e), first stage of three turns, not to scale.

    step	molecules	carbon atoms in total
    carbon dioxide going in	3	3
    five-carbon molecules going in	3	15
    three-carbon molecules formed	6	18

18. 9.

    Ren reads a card from the first stage of three turns. Only 3 carbon atoms came from carbon dioxide, yet 18 are in the new molecules. Why?

    • The cycle makes new carbon atoms when it spends ATP and NADPH
    • The extra carbon atoms come from the oxygen released earlier
    • The 3 carbon atoms join 15 already held by the five-carbon molecules, so no carbon atoms are made
    • The light reactions make the extra carbon atoms from light and water
19. 10.

    Tala counts 100 oxygen molecules released by a leaf's light reactions (model data), but only 90 reach the air. What explains the missing 10?

    • 10 oxygen molecules are used up making the ATP and NADPH
    • The Calvin cycle takes in 10 oxygen molecules to build G3P
    • Mitochondria in the leaf use about 10 percent of the oxygen themselves
    • 10 oxygen molecules stay trapped in the stroma, where the light reactions happen