Photosynthesis captures sunlight and converts it into chemical energy that can support organisms and ecosystems. This lesson introduces where photosynthesis occurs, how pigments collect light, and how light-dependent reactions make energy carriers.
In phototrophic eukaryotes, photosynthesis takes place in chloroplasts. Each chloroplast has an outer and inner membrane, as well as an internal membrane system. The internal membranes form disc-shaped thylakoids; stacks of thylakoids are called grana (singular: granum). The fluid-filled space surrounding the grana is the stroma.
All flashcards
What are thylakoids, grana, and stroma?
Thylakoids are disc-shaped photosynthetic membranes inside eukaryotic chloroplasts. A stack of thylakoids is a granum; the fluid-filled space around the grana is the stroma.
What does a photosystem contain, and what does each part do?
A photosystem has a light-harvesting complex, which absorbs light and passes energy among pigments, and a reaction center, where an excited pigment gives an electron to an electron transport system.
How do photosynthetic pigments affect light capture?
Different pigments absorb different wavelengths. A mixture of pigments lets an organism capture energy from a broader range of light wavelengths.
How do oxygenic and anoxygenic photosynthesis differ?
Oxygenic photosynthesis uses water as the electron donor and releases oxygen. Anoxygenic photosynthesis uses a different reduced electron donor, such as hydrogen sulfide, and does not release oxygen.
What are the three stages of the Calvin-Benson cycle?
Fixation attaches carbon dioxide to RuBP; reduction converts 3-PGA into G3P; regeneration uses remaining G3P to restore RuBP.
Quiz questions
Where does photosynthesis take place in phototrophic eukaryotes?Answer: In chloroplasts.
What passes between pigments in a light-harvesting complex before reaching the reaction center?Answer: Energy.
In oxygenic photosynthesis, what supplies replacement electrons, and what byproduct is released?Answer: Water supplies electrons, and oxygen is released.
Which electron-flow pathway uses both PSII and PSI and supports production of ATP and NADPH?Answer: Noncyclic photophosphorylation, with electrons moving from PSII through an ETS to PSI.
When a photosynthetic cell needs more ATP relative to NADPH, which pathway can help meet that demand?Answer: Cyclic photophosphorylation, because PSI electrons return through an ETS and support ATP production.
Based on Microbiology by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.