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 its own, since the Calvin cycle needs no help from the light reactions
   • 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 leftover ATP and NADPH, then stops when they are used up
3. 2.

   Bo's class reads a card about a water plant lit two ways. Which explanation fits the card?

   • The Calvin cycle absorbs green light poorly, so it makes less G3P directly from the light
   • Chlorophyll absorbs little green light, so few ATP and NADPH reach the Calvin cycle
   • The light reactions build G3P from light, and green light is a poor source
   • The Calvin cycle makes the oxygen, and green light slows its work

4. 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.

5. 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?

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

6. 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.

7. 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

8. 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.

9. 5.

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

10. 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.

11. 6.

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

    • 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
    • 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

12. 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.

13. 7.

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

    • 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
    • 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

14. 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

15. 8.

    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 extra carbon atoms come from the oxygen released earlier
    • The cycle makes new carbon atoms when it spends ATP and NADPH
    • 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
16. 9.

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

17. Use this

    Flow diagram (model, not to scale), drawn inside a chloroplast of a cactus. Night: stomata open; carbon dioxide is taken in and stored. Day: stomata closed; light energy goes in at the thylakoid membranes; stored carbon dioxide goes to the stroma; G3P comes out.

18. 10.

    A cactus opens its stomata at night and takes in carbon dioxide. Zee says the Calvin cycle must run alone in the dark. What does the cactus show?

    • The Calvin cycle makes G3P at night, since it needs no light-made ATP or NADPH
    • The light reactions run at night in cacti, using stored sunlight to make ATP
    • The cactus stores oxygen at night, and the Calvin cycle uses it by day
    • Carbon dioxide is stored at night, then used by day, when the light reactions supply ATP and NADPH