Photosynthesis — Practice Quiz

A Biology cheat sheet for Photosynthesis — every key formula with its symbols defined — plus a medium-level practice quiz to test recall.

Formulas & key concepts

Process by which autotrophs convert light energy into chemical energy (sugars). Equation: $$6CO_2 + 6H_2O \xrightarrow{Light} C_6H_{12}O_6 + 6O_2$$

Photosynthesis Overview

Organelle where photosynthesis occurs. <b>Thylakoids</b>: Saclike membranes (site of light-dependent reactions), arranged in stacks called <b>Grana</b>. <b>Stroma</b>: Fluid outside thylakoids (site of Calvin cycle). <b>Chlorophyll</b>: Pigment in thylakoid membranes.

Chloroplast Structure

Sunlight is a mixture of wavelengths. <b>Chlorophyll a & b</b> absorb blue-violet and red light best (reflect green). <b>Carotenoids</b> are accessory pigments (orange/red).

Light Energy & Pigments

Occur in thylakoid membranes. Require light and water. Produce ATP, NADPH, and Oxygen (byproduct). Steps: Photosystem II (splits water) -> ETC (pumps H+) -> Photosystem I (makes NADPH) -> ATP Synthase (makes ATP).

Light-Dependent Reactions

Clusters of chlorophyll and proteins. <b>PS II</b>: Absorbs light, splits water, releases O2. <b>PS I</b>: Re-energizes electrons to form NADPH.

Photosystems

Occurs in stroma. Uses ATP and NADPH from light reactions + CO2 to make sugars. Stages: 1. <b>Carbon Fixation</b> (Rubisco enzyme), 2. <b>Reduction</b> (forms G3P), 3. <b>Regeneration</b> of RuBP.

Calvin Cycle (Light-Independent)

<b>Temperature</b>: Enzymes work best at 0°C-35°C. <b>Light Intensity</b>: Rate increases with light up to a max point. <b>Water</b>: Shortage can stop photosynthesis.

Factors Affecting Photosynthesis

Adaptations for hot/dry climates. <b>C4 Plants</b> (Corn): Specialized chemical pathway to capture low CO2. <b>CAM Plants</b> (Cacti): Open stomata only at night to trap CO2.

Alternative Pathways (C4 & CAM)

Practice quiz

  1. Which of the following correctly represents the overall chemical equation for photosynthesis?

    • $6CO_2 + 6H_2O \xrightarrow{Light} C_6H_{12}O_6 + 6O_2$
    • $C_6H_{12}O_6 + 6O_2 \xrightarrow{} 6CO_2 + 6H_2O + Energy$
    • $6O_2 + C_6H_{12}O_6 \xrightarrow{Light} 6CO_2 + 6H_2O$
    • $6H_2O + C_6H_{12}O_6 \xrightarrow{} 6CO_2 + 6O_2 + Energy$

    Answer: $6CO_2 + 6H_2O \xrightarrow{Light} C_6H_{12}O_6 + 6O_2$

  2. In a chloroplast, where do the light-dependent reactions and the Calvin cycle primarily occur, respectively?

    • Thylakoid membranes; Stroma
    • Stroma; Thylakoid membranes
    • Grana; Cytoplasm
    • Cytoplasm; Grana

    Answer: Thylakoid membranes; Stroma

  3. Chlorophyll a and b pigments are most effective at absorbing which colors of light, while reflecting green light?

    • Blue-violet and red
    • Green and yellow
    • Orange and red
    • Ultraviolet and infrared

    Answer: Blue-violet and red

  4. What are the primary products of the light-dependent reactions of photosynthesis that are then used in the Calvin cycle?

    • $ATP$ and $NADPH$
    • Glucose and Oxygen
    • Carbon Dioxide and Water
    • $ADP$ and $NADP+$

    Answer: $ATP$ and $NADPH$

  5. Which photosystem is responsible for splitting water molecules to release oxygen and electrons during the light-dependent reactions?

    • Photosystem II
    • Photosystem I
    • $ATP$ Synthase
    • Rubisco

    Answer: Photosystem II

  6. The enzyme responsible for carbon fixation, combining $CO_2$ with an existing five-carbon molecule during the Calvin cycle, is known as:

    • Rubisco
    • $ATP$ Synthase
    • $NADP+$ Reductase
    • Amylase

    Answer: Rubisco

  7. A severe shortage of which factor would most directly lead to a complete halt in the process of photosynthesis?

    • Water
    • Optimal temperature ($25^\circ C$)
    • High light intensity
    • Presence of carotenoids

    Answer: Water

  8. CAM plants, such as cacti, have adapted to hot, dry climates by opening their stomata only at night. What is the primary advantage of this adaptation?

    • To trap $CO_2$ while minimizing water loss
    • To absorb more sunlight during cooler hours
    • To release excess oxygen accumulated during the day
    • To prevent herbivores from consuming them

    Answer: To trap $CO_2$ while minimizing water loss

  9. How does the Calvin cycle directly depend on the light-dependent reactions?

    • It uses the $ATP$ and $NADPH$ produced by the light-dependent reactions.
    • It provides $CO_2$ to the light-dependent reactions.
    • It regenerates chlorophyll for the light-dependent reactions.
    • It releases oxygen that is essential for the light-dependent reactions.

    Answer: It uses the $ATP$ and $NADPH$ produced by the light-dependent reactions.

  10. If a plant is exposed to light, water, and carbon dioxide, what are the main organic products it will synthesize for energy storage and growth?

    • Sugars (e.g., glucose) and oxygen
    • $ATP$ and $NADPH$
    • Water and carbon dioxide
    • Chlorophyll and carotenoids

    Answer: Sugars (e.g., glucose) and oxygen

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