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Self Quiz

1. A cat eats a bird, which ate a caterpillar that chewed on a weed. Which organisms are autotrophs? Which ones are heterotrophs?

   The weed is an autotroph. The cat, bird, and caterpillar are all heterotrophs.

2. Plants use ___ as an energy source to drive photosynthesis

   a. sunlight

3. Most of the carbon dioxide that plants use for photosynthesis comes from ___

   b. the atmosphere

4. Which of the following statements is incorrect

   c. Chlorophyll is green because it absorbs green light

5. In plants and other photosynthetic eukaryotes, the light dependent reaction proceed in/at the___

   a. thylakoid membrane

6. When a photosystem absorbs light, ___

   b. electrons are transferred to ATP

7. In the light-dependent reactions, ___

   b. ATP forms

8. What accumulates inside the thykaloid compartment of chloroplasts during the light-dependent reactions?

   b. hydrogen ions

9. The atoms in the molecular oxygen released during photosynthesis come from ___ molecules

   c. water

10. Light-independent reactions in plants proceed in/at the ___ of cholorplasts

    c. stroma

11. The Calvin-Benson cycle starts when ____

    a. light is available

12. Which of the following substances does not participate in the Calvin-Benson cycle

    e. O_²

13. Closed stomata ___

    b. permits water loss

14. In C3 plants, ___ makes sugar production inefficient when stomata close during the day

    c. photorespiration

15. Match each with its most suitable description

    PGAL formation

    CO_²

    photolysis

    ATP forms; NADPH does not

    photorespiration

    photosynthesis

    pigment

    autotroph

Critical Thinking

2. While gazing into an aquarium, you see bubbles coming from an aquatic plant. What are the bubbles?

   The bubbles coming from the aquatic plant are most likely oxygen. During photosynthesis, plants use sunlight, water, and CO_² to produce energy, in which oxygen is released as a byproduct. If not used by the plant, and not absorbed into the water, oxygen can possibly form bubbles.

3. A C3 plant absorbs a carbon radioisotope (as part of ¹⁴CO₂). In which compound does the labeled carbon appear first? Which compound forms first if a C4 plant absorbs the same radioisotope?

   ¹⁴CO₂ would first appear in the compound 3-PGA (3-phosphoglyceric acid). A C3 plant is a plant that only uses the Calvin Benson cycle to fixate carbon into sugars. The first step of the Calvin Benson cycle is CO₂ molecules being split into 3-PGA molecules, so the labeled carbon would be able to be found in 3-PGA first since it’s the initial organic compound during the Calvin Benson cycle. While C4 plants also use PGA despite slightly differing from the Calvin Benson cycle, it is not the initial organic compound split from CO₂. Due to C4 plants usage of two carbon fixation processes, the labeled carbon would be found in oxaloacetate, the initial organic compound.

4. As you learned in this chapter, cell membranes are required for electron transfer phosphorylation. Thylakoid membranes in chloroplasts serve this purpose in photosynthetic eukaryotes. Prokaryotic cells do not have this organelle, but many are photosynthesizers. How do you think they carry out the light-dependent reactions given that they have no chloroplasts?

   If chloroplasts are not available to perform photosynthesis, then it most likely happens in another part of a prokaryotic cell. With a lack of chloroplasts it could possibly occur in the ribosome or the cell membrane. Prokaryotic cells could also still utilize some of photosynthesis properties like absorbing light.