Chapter 8 Reading Guide and Study Guide

Chapter 8 Reading Guide and Study Guide

Terms You Should Know

  • Photosynthesis

  • Reduction

  • Oxidation

  • NADPH

  • Calvin Cycle

  • Thylakoid Membrane

  • Grana

  • Lumen

  • Stroma

  • Carboxylation

  • Regeneration

  • RuBP (Ribulose bisphosphate)

  • Rubisco (Ribulose bisphosphate carboxylase/oxygenase)

  • 3-phosphoglycerate (3-PGA)

  • Triose Phosphates

  • Visible Light

  • Photosystem

  • Accessory Pigment

  • Reaction Center

  • Cyclic Electron Transport

  • Noncyclic Electron Transport

Questions You Should Be Able to Answer

  1. Define photosynthesis.

    • Photosynthesis is a biochemical process that allows plants, algae, and some bacteria to convert light energy into chemical energy stored in glucose. This process involves a series of redox (reduction-oxidation) reactions:

      • Oxidized: Water (H₂O) is oxidized to oxygen (O₂) during photosynthesis.

      • Reduced: Carbon dioxide (CO₂) is reduced to glucose (C₆H₁₂O₆).

  2. Where, in the cell, does photosynthesis take place?

    • Photosynthesis occurs primarily in the chloroplasts of plant cells. Within the chloroplasts, the process occurs in two main stages: the light-dependent reactions occur in the thylakoid membranes, while the light-independent reactions (Calvin cycle) take place in the stroma.

  3. Where does the O₂ released by the plants come from?

    • The O₂ released during photosynthesis comes from the splitting of water molecules (H₂O) in a process known as photolysis, which occurs during the light-dependent reactions.

  4. What are the two pathways involved in photosynthesis? What is the relationship between them?

    • The two main pathways are:

      • Light-dependent reactions: These reactions convert light energy into chemical energy in the form of ATP and NADPH.

      • Calvin Cycle (light-independent reactions): This cycle uses ATP and NADPH produced in the light-dependent reactions to convert CO₂ into glucose.

      • The relationship is that the products of the light-dependent reactions provide the energy and reducing power necessary for the Calvin cycle to occur.

  5. What is the Calvin cycle (light-independent reactions)? What is its function?

    • The Calvin cycle is a series of biochemical reactions that occur in the stroma of chloroplasts, which convert CO₂ into glucose using ATP and NADPH produced in the light-dependent reactions.

    • The function of the Calvin cycle is to synthesize glucose that will ultimately be used as a source of energy and carbon for the plant.

    • Three Steps of the Calvin Cycle:

      • Carboxylation: Enzyme RuBisCO incorporates CO₂ into RuBP, forming 3-PGA.

      • Reduction: 3-PGA is phosphorylated by ATP and reduced by NADPH to form triose phosphates (G3P).

      • Regeneration: Some triose phosphates are used to regenerate RuBP, enabling the cycle to continue.

    • First Step: In the first step of the Calvin cycle, CO₂ is fixed by RuBP to form 3-PGA.

    • Enzyme: The enzyme responsible for this step is Rubisco.

    • End Products: The end product of the cycle is glucose (G3P), while RuBP is regenerated for the next cycle.

    • The Calvin cycle utilizes NADPH and ATP from the light-dependent reactions.

    • CO₂ in the Calvin Cycle: CO₂ is reduced during the Calvin cycle as it combines with RuBP and gets converted into glucose.

  6. What is light?

    • Light is a form of electromagnetic radiation that is visible to the human eye. It consists of photons and travels in waves. In the context of photosynthesis, light provides the energy required to drive the chemical reactions that convert CO₂ and water into glucose.

    • Types of Molecules That Convert Light Energy Into Chemical Energy: Photosynthetic pigments such as chlorophyll a, chlorophyll b, and accessory pigments (like carotenoids) are responsible for capturing light energy.

  7. What happens to chlorophyll when it absorbs light?

    • When chlorophyll absorbs light, it becomes excited; electrons within the chlorophyll molecule are elevated to a higher energy state, initiating the process of converting solar energy into chemical energy.

    • Difference Between Absorption Spectrum and Action Spectrum:

      • Absorption Spectrum: A graphical representation showing the wavelengths of light absorbed by chlorophyll and other pigments.

      • Action Spectrum: A graph that shows the effectiveness of different wavelengths of light in driving the process of photosynthesis.

  8. What are the main pigments of photosynthesis? Why do plants have accessory pigments?

    • The main pigments involved in photosynthesis are:

      • Chlorophyll a: The primary pigment directly involved in the light reactions.

      • Chlorophyll b: An accessory pigment that helps capture light energy.

      • Carotenoids: Accessory pigments that protect chlorophyll from damage and expand the range of light wavelengths absorbed.

    • Reason for Accessory Pigments: Accessory pigments allow plants to absorb additional light wavelengths beyond those absorbed by chlorophyll a and b, thus increasing the efficiency of photosynthesis and protecting the plant from overexposure to high-intensity light.

  9. What is an antenna system?

    • An antenna system comprises a collection of pigments (including chlorophylls and carotenoids) that capture light energy and funnel it to the reaction center in photosystems.

    • Electron Transfer through Antenna System: When light energy is absorbed by the pigments in the antenna system, it excites electrons which are then transferred from one pigment molecule to another until they reach the reaction center, where the energy is used to initiate the conversion of light into chemical energy.

  10. Explain noncyclic electron transport.

    • Noncyclic Electron Transport: This is a process during the light-dependent reactions of photosynthesis involving the transfer of electrons through two photosystems (Photosystem II and Photosystem I).

      • Photosystems Involved: Two photosystems, PSII and PSI, work in succession.

      • Role of Water: Water molecules are split (photolysis) to provide electrons lost by chlorophyll in PSII.

      • Source of O₂: The O₂ produced comes from the splitting of water

      • Synthesis of NADPH and ATP: NADPH is produced at PSI, while ATP is synthesized through photophosphorylation facilitated by a proton gradient created during the electron transport chain.