The Light-Independent Reactions of Photosynthesis (College Board AP® Biology)

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Phil

Written by: Phil

Reviewed by: Lára Marie McIvor

The Calvin Cycle

  • The light-independent stage of photosynthesis, also referred to as the Calvin cycle, occurs in the stroma of the chloroplast

  • This stage produces complex organic molecules, including (but not limited to) carbohydrates, such as:

    • Starch (for storage)

    • Sucrose (for translocation around the plant)

    • Cellulose (for making cell walls)

  • The light-independent stage does not require energy from light and can therefore take place in light or darkness

  • However, as it requires inputs of ATP and NADPH from the light-dependent stage, it cannot continue indefinitely in darkness, as these inputs will run out

  • An overview of the Calvin cycle is as follows:

    • Carbon dioxide is absorbed through the stomata of leaves into the stroma.

    • Carbon dioxide is fixed - meaning it is incorporated into organic molecules

    • NADPH and ATP are involved in converting fixed carbon into three-carbon and subsequently six-carbon sugars (e.g. glucose)

Calvin Cycle Diagram

regeneration-of-rubp-in-the-calvin-cycle

The Calvin cycle

Examiner Tips and Tricks

You will not need to memorize the steps of the Calvin cycle, the structures of the intermediate molecules or the names of the enzymes, with the exception of ATP synthase in the light-dependent stage.

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Phil

Author: Phil

Expertise: Biology Content Creator

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.

Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.