Skip to main content
Biology LibreTexts

4.1.8: Chapter Summary

  • Page ID
    39304
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    Photosynthesis and aerobic cellular respiration are two key metabolic pathways conducted by plants. The process of photosynthesis transformed life on Earth. By harnessing energy from the sun, photosynthesis evolved to allow living things access to enormous amounts of energy. Because of photosynthesis, living things gained access to sufficient energy that allowed them to build new structures and achieve the biodiversity evident today.

    Only certain organisms, called photoautotrophs, can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that absorbs certain portions of the visible spectrum and can capture energy from sunlight. Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules and release oxygen as a waste product into the atmosphere. Eukaryotic autotrophs, such as plants and algae, have organelles called chloroplasts in which photosynthesis takes place, and starch accumulates. In prokaryotes, such as cyanobacteria, the process is less localized and occurs within folded membranes, extensions of the plasma membrane, and in the cytoplasm.

    The pigments of the first part of photosynthesis, the light-dependent reactions, absorb energy from sunlight. A photon strikes the antenna pigments of photosystem II to initiate photosynthesis. The energy travels to the reaction center that contains chlorophyll a to the electron transport chain, which pumps protons into the thylakoid interior. This action builds up a high concentration of ions. The protons flow through ATP synthase via chemiosmosis to form molecules of ATP, which are used for the formation of sugar molecules in the second stage of photosynthesis. Photosystem I absorbs a second photon, which results in the formation of an NADPH molecule, another energy and reducing power carrier for the light-independent reactions.

    Using the electron carriers formed in the first steps of photosynthesis, the light-independent reactions, or the Calvin cycle, take in CO2 from the environment. An enzyme, RuBisCO, catalyzes a reaction with CO2 and another molecule, RuBP. After three cycles, a three-carbon molecule of G3P leaves the cycle to become part of a carbohydrate molecule. The remaining G3P molecules stay in the cycle to be regenerated into RuBP, which is then ready to react with more CO2.

    Photorespiration is the process by which RuBisCO binds to O2 instead of CO2 and breaks down rather than builds sugars. C3, C4, and CAM plants have different strategies for reducing photorespiration.

    Just like animals, plants must also break down sugars to produce usable energy in the form of ATP through the process of aerobic cellular respiration. The process begins with glycolysis in the cytoplasm, continues with pyruvate oxidation and the citric acid cycle in the mitochondrial matrix, and concludes with oxidative phosphorylation in the cristae of the mitochondria. Overall, it consumes glucose and gaseous oxygen and releases carbon dioxide and water.

    After completing this chapter, you should be able to...
    • Describe the different types of energy.
    • Describe the structure and function of ATP.
    • Explain the relevance of photosynthesis to other living things.
    • Identify the substrates and products of photosynthesis.
    • Describe the main structures involved in photosynthesis.
    • Relate the light-dependent and light-independent reactions.
    • Summarize the experimental results that revealed details about the process of photosynthesis.
    • Relate wavelength, energy, and the type of electromagnetic radiation (and the color of visible light).
    • Explain how plants absorb energy from sunlight.
    • Detail the steps of the light-dependent interactions.
    • Detail the three steps of the light-independent reactions.
    • Define carbon fixation.
    • Define photorespiration.
    • Explain how C3, C4, and CAM plants reduce photorespiration.
    • Outline the C4 pathway and compare its use by C4 plants and CAM plants.
    • Identify the reactants and products of aerobic cellular respiration.
    • Explain each step of aerobic cellular respiration and where in the cell it occurs.

    Attribution

    Curated and authored by Melissa Ha using 8 Photosynthesis from Biology 2e by OpenStax (licensed CC-BY). Access for free at openstax.org.


    This page titled 4.1.8: Chapter Summary is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha, Maria Morrow, & Kammy Algiers (ASCCC Open Educational Resources Initiative) .