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Photosynthesis and Chloroplast Function in General Biology

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  • What is photosynthesis?

    Photosynthesis is the process by which solar energy is converted into chemical energy in organic molecules, primarily glucose, providing energy and organic matter for most living organisms.

  • Define autotrophs and their types.

    Autotrophs produce their own food from inorganic substances. Types: Chemoautotrophs use inorganic compounds for energy; Photoautotrophs use light energy to convert CO2 into organic molecules.

  • What is the photosynthesis chemical equation?

    \(6\ CO_2+6\ H_2O+Light\ Energy\rightarrow C_6H_{12}O_6+6\ O_2\)

  • Explain the redox nature of photosynthesis.

    Water is oxidized to O2 (loses electrons), and CO2 is reduced to glucose (gains electrons).

  • Where does photosynthesis primarily occur in plants?

    Photosynthesis mainly occurs in leaves, specifically in the mesophyll cells containing many chloroplasts.

  • What is the role of chlorophyll in photosynthesis?

    Chlorophyll is the green pigment in chloroplasts that absorbs light energy to drive photosynthesis.

  • What are stomata and their function?

    Stomata are microscopic pores in leaves that allow gas exchange: CO2 enters and O2 exits.

  • Describe the structure of a chloroplast relevant to photosynthesis.

    Chloroplasts have outer and inner membranes, contain stacks of thylakoids (grana), and a fluid-filled stroma where the Calvin cycle occurs.

  • What are the two main stages of photosynthesis?

    1) Light Reactions in thylakoids produce ATP, NADPH, and O2.
    2) Calvin Cycle in stroma uses ATP and NADPH to form sugars from CO2.

  • What is the nature of sunlight relevant to photosynthesis?

    Sunlight is electromagnetic energy composed of photons; wavelength determines the type of radiation absorbed by pigments.

  • What are photosynthetic pigments and their roles?

    Chlorophyll a initiates light reactions; chlorophyll b and carotenoids are accessory pigments that broaden light absorption.

  • Why do leaves appear green?

    Leaves appear green because chlorophyll reflects green light and absorbs mainly blue and red wavelengths.

  • What did Engelmann’s experiment demonstrate?

    It showed photosynthesis is most efficient at blue and red wavelengths by observing bacteria clustering where oxygen was produced.

  • What happens in the light reactions of photosynthesis?

    Light excites electrons in photosystems, water is split releasing O2, and ATP and NADPH are produced via electron transport and chemiosmosis.

  • What are Photosystem II and Photosystem I roles?

    Photosystem II splits water and initiates electron transport; Photosystem I transfers electrons to NADP+ to form NADPH.

  • How is ATP synthesized during photosynthesis?

    ATP is produced by ATP synthase using a proton gradient created by electron transport across the thylakoid membrane (chemiosmosis).

  • What are the three phases of the Calvin cycle?

    1) Carbon fixation: CO2 attaches to RuBP.
    2) Reduction: ATP and NADPH convert 3-PGA to G3P.
    3) Regeneration: RuBP is regenerated using ATP.

  • What is the fate of G3P produced in the Calvin cycle?

    G3P can be used to synthesize glucose, fatty acids, amino acids, and other organic molecules.

  • What adaptations do C4 and CAM plants have?

    C4 plants fix CO2 into a 4-carbon compound spatially to reduce photorespiration.
    CAM plants fix CO2 at night temporally to conserve water in hot, dry environments.

  • Why are phytoplankton important globally?

    Phytoplankton produce 50-85% of the world’s oxygen and form the base of aquatic food webs.