For a deeper dive into this material, go to Topic 3.5, Part 5: The Calvin Cycle
1. Watch this Video
2. Study this Summary
Overview of the Calvin Cycle
- The Calvin cycle uses the products of the light reactions (ATP and NADPH) and carbon dioxide to synthesize sugars.
- The process occurs in three phases:
- Carbon Fixation: CO2 is incorporated into the biosphere by combining with RuBP.
- Energy Investment and Harvest: ATP and NADPH are used to create high-energy G3P molecules.
- Regeneration: RuBP is regenerated to continue the cycle.
Phase 1: Carbon Fixation
- CO2 combines with RuBP (a 5-carbon compound) to form an unstable 6-carbon product.
- The enzyme rubisco catalyzes this reaction.
- The 6-carbon product immediately splits into two 3-carbon molecules.
- Total carbon count:
- 3 RuBP molecules (15 carbons) + 3 CO2 molecules (3 carbons) = 18 carbons.
- Result: 6 molecules of a 3-carbon compound (18 carbons total).
Phase 2: Energy Investment and Harvest
- Each 3-carbon molecule undergoes phosphorylation (enzymes take a phosphate group from ATP and add it to the 3-carbon intermediate compound).
- NADPH donates electrons, which reduces one of these 3-carbon intermediates to G3P (glyceraldehyde-3-phosphate), a high-energy molecule.
- Total carbon count:
- 6 G3P molecules are produced, each with 3 carbons (18 carbons total).
- One G3P molecule is removed from the cycle to be used for biosynthesis.
- This leaves 5 G3Ps, with a total of 15 carbons.
Phase 3: Regeneration
- The 5 remaining G3P molecules (15 carbons) are rearranged into 3 molecules of RuBP (5 carbons each).
- This process requires phosphates from ATP (energy investment from the light reactions).
- Total carbon count remains constant at 15 carbons throughout this phase.
Key Points About the Calvin Cycle
The Calvin cycle
- Is a cyclical process that starts and ends with 5-carbon RuBP (ribulose bisphosphate).
- Its harvestable product is G3P: A high-energy molecule that forms the basis for sugars and other biomolecules.
- It relies on ATP and NADPH generated during the light reactions.
- It brings inorganic carbon (from carbon dioxide) into the biosphere, a process known as carbon fixation.
3. Master these Flashcards
[qdeck]
[h] The Calvin Cycle
[i]
[q json=”true” yy=”4″ unit=”3.Cellular_Energetics” dataset_id=”AP_Bio_Flashcards_2022|1c502ffe82910″ question_number=”118″ topic=”3.5.Photosynthesis”] Where does the Calvin cycle occur, what does it produce, and how?
[a] The Calvin Cycle occurs in the stroma (the fluid in between the thylakoids and the chloroplasts’ inner membrane). Using the products of the light reactions (ATP and NADPH) and carbon dioxide, the cycle creates the reduced 3-carbon compound G3P, which is converted by other enzymes into carbohydrates (or anything else a plant cell needs).
[q json=”true” yy=”4″ unit=”3.Cellular_Energetics” dataset_id=”AP_Bio_Flashcards_2022|1c45b5c900910″ question_number=”119″ topic=”3.5.Photosynthesis”] List the three phases of the Calvin cycle.
[a]
- Carbon fixation phase
- Energy investment and harvest
- Regeneration of RuBP
[q json=”true” yy=”4″ unit=”3.Cellular_Energetics” topic=”3.5.Photosynthesis” dataset_id=”AP_Bio_Flashcards_2022|1148f750b64a19″ question_number=”120″] Describe what happens during the carbon fixation phase of the Calvin cycle.
[a] During the carbon fixation phase, carbon dioxide is combined with a five-carbon molecule called RuBP. This reaction is catalyzed by the enzyme RuBisCo. The six-carbon product of this reaction immediately dissociates into two 3 carbon molecules.
[q json=”true” yy=”4″ unit=”3.Cellular_Energetics” topic=”3.5.Photosynthesis” dataset_id=”AP_Bio_Flashcards_2022|11483610db5e19″ question_number=”121″] Describe what happens during the energy investment and harvest phase of the Calvin cycle.
[a] During investment and harvest (II), the three-carbon products (b) of carbon fixation are reduced and phosphorylated into six molecules of glyceraldehyde-3-phosphate (d: AKA G3P or PGAL). The energy comes from the ATP and NADPH from the light reactions. One of these G3Ps is then harvested (removed from the cycle).
[q json=”true” yy=”4″ unit=”3.Cellular_Energetics” topic=”3.5.Photosynthesis” dataset_id=”AP_Bio_Flashcards_2022|114735f3bf6619″ question_number=”122″] Describe what happens during the last phase of the Calvin cycle.
[a] The last phase is the regeneration of RuBP. During this phase, the remaining five G3Ps are rearranged into three 5-carbon RuBPs, the compound that acts as one of the substrates during the carbon fixation phase (the other substrate being carbon dioxide).
[/qdeck]
4. Tackle these Quizzes
4.1. Photosynthesis and the Calvin Cycle
[qwiz]
[h]Photosynthesis and Calvin Cycle Overview
[i]
[q dataset_id=”SMV_PSN_Part 5 (Calvin Cycle) Introduction|171ddd77ccc756″ question_number=”1″]We’ve seen so far that photosynthesis involves two phases. The one indicated by “II” is called the [hangman] cycle.
[c]Q2Fsdmlu
Cg==[Qq]
[q dataset_id=”SMV_PSN_Part 5 (Calvin Cycle) Introduction|171d9e9a8bbb56″ question_number=”2″]The Calvin cycle takes the outputs of the light reactions, and along with carbon dioxide, uses them as inputs. Which number indicates carbon dioxide?
[textentry single_char=”true”]
[c]Ng ==[Qq]
[f]WWVzLiDigJw24oCdIGlzIGNhcmJvbiBkaW94aWRl[Qq]
[c]Kg==[Qq]
[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIEZpbmQgYW4gYXJyb3cgdGhhdCYjODIxNztzIGdvaW5nIGludG8gdGhlIENhbHZpbiBjeWNsZSwgYnV0IHdoaWNoIGlzIG5vdCBvbmUgb2YgdGhlIG91dHB1dHMgb2YgdGhlIGxpZ2h0IHJlYWN0aW9ucy4=
Cg==[Qq]
[q dataset_id=”SMV_PSN_Part 5 (Calvin Cycle) Introduction|171d6211569356″ question_number=”3″]Carbon dioxide, at “6,” can be considered the external input of the Calvin cycle. An internal input includes the reduced mobile electron carrier [hangman], which is shown at “5.”
[c]TkFEUEg=
Cg==[Qq]
[q dataset_id=”SMV_PSN_Part 5 (Calvin Cycle) Introduction|171d2588216b56″ question_number=”4″]One of the internal inputs of the Calvin cycle is the reduced mobile electron carrier NADPH, shown at “5” below. The other input is [hangman], indicated by “4.”
[c]QVRQ
Cg==[Qq]
[q dataset_id=”SMV_PSN_Part 5 (Calvin Cycle) Introduction|171ce8feec4356″ question_number=”5″]While the light reactions occur in the thylakoid sacs, the Calvin cycle occurs in the [hangman].
[c]c3Ryb21h
Cg==[Qq]
[q dataset_id=”SMV_PSN_Part 5 (Calvin Cycle) Introduction|171ca7cd9f5356″ question_number=”6″]Which letter or number shows the structures that carry out the light reactions?
[textentry single_char=”true”]
[c]YQ ==[Qq]
[f]WWVzLiBUaGUgbGV0dGVyIOKAnGHigJ0gaW5kaWNhdGVzIHRoZSB0aHlsYWtvaWRz[Qq]
[c]SQ ==[Qq]
[f]WWVzLiAmIzgyMjA7SSYjODIyMTsgc2hvd3MgYSBzdGFjayBvZiB0aHlsYWtvaWRzIChhbmQgaW5kaWNhdGVzIHRoZSBsaWdodCByZWFjdGlvbnMpLg==[Qq]
[c]Kg==[Qq]
[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFRoZSBsaWdodCByZWFjdGlvbnMgb2NjdXIgaW4gdGhlIHRoeWxha29pZCBzYWNzLCB3aGljaCBhcmUgdGlueSBvdmFsIHN0cnVjdHVyZXMgd2l0aGluIHRoZSBjaGxvcm9wbGFzdCwgb3JnYW5pemVkIGludG8gc3RhY2tzLg==
Cg==[Qq]
[q dataset_id=”SMV_PSN_Part 5 (Calvin Cycle) Introduction|171c68f05e4756″ question_number=”7″]Which letter or number shows the area in the chloroplast where the Calvin cycle takes place? (Note: don’t enter a roman numeral)
[textentry single_char=”true”]
[c]Yg ==[Qq]
[f]WWVzLiBMZXR0ZXIg4oCcYuKAnSBpbmRpY2F0ZXMgdGhlIHN0cm9tYSwgd2hpY2ggaXMgd2hlcmUgdGhlIENhbHZpbiBjeWNsZSB0YWtlcyBwbGFjZS4=[Qq]
[c]Kg==[Qq]
[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFRoZSBDYWx2aW4gY3ljbGUgb2NjdXJzIGluIHRoZSBlcXVpdmFsZW50IG9mIHRoZSBjeXRvcGxhc20gb2YgdGhlIGNobG9yb3BsYXN0JiM4MjExO3RoZSBmbHVpZCB0aGF0IGlzIGJldHdlZW4gdGhlIHRoeWxha29pZHMgYW5kIHRoZSBjaGxvcm9wbGFzdCYjODIxNztzIGlubmVyIG1lbWJyYW5lLg==
Cg==[Qq]
[q dataset_id=”SMV_PSN_Part 5 (Calvin Cycle) Introduction|171c256b057356″ question_number=”8″]To the extent that any biological process can be said to have a purpose, then the purpose of photosynthesis, from a plant’s perspective, is to create
[textentry single_char=”true”]
[c]Nw ==[Qq]
[f]WWVzLiBMZXR0ZXIg4oCcN+KAnSBpbmRpY2F0ZXMgY2FyYm9oeWRyYXRlLiBTeW50aGVzaXppbmcgY2FyYm9oeWRyYXRlcyBpcywgZnJvbSBhIHBsYW50JiM4MjE3O3MgcGVyc3BlY3RpdmUsIHRoZSBwdXJwb3NlIG9mIHBob3Rvc3ludGhlc2lzLg==[Qq]
[c]Kg==[Qq]
[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFRoZSBwdXJwb3NlIG9mIHBob3Rvc3ludGhlc2lzLCBmcm9tIGEgcGxhbnQmIzgyMTc7cyBwZXJzcGVjdGl2ZSwgaXMgdG8gY3JlYXRlIHN1Z2FycyB0aGF0IGNhbiBiZSB1c2VkIGZvciBncm93dGggYW5kIGVuZXJneS4gV2hpY2ggcGFydCBvZiB0aGUgZGlhZ3JhbSBjb3VsZCByZXByZXNlbnQgYSBzdWdhcj8=[Qq]
[x][restart]
[/qwiz]
4.2. The Calvin Cycle (the details)
[qwiz random = “true” width:700px]
[h]Calvin Cycle: Checking Understanding
[i]
[q labels = “top” dataset_id=”SMV_PSN_Calvin Cycle Quiz|171a2e80fd1356″ question_number=”1″]
[l]Carbon Dioxide
[fx] No, that’s not correct. Please try again.
[f*] Excellent!
[l]Carbon Fixation Phase
[fx] No. Please try again.
[f*] Excellent!
[l]Energy Investment Phase
[fx] No. Please try again.
[f*] Excellent!
[l]G3P
[fx] No. Please try again.
[f*] Great!
[l]Phosphorylation
[fx] No. Please try again.
[f*] Great!
[l]Reduction
[fx] No, that’s not correct. Please try again.
[f*] Correct!
[l]RuBP
[fx] No, that’s not correct. Please try again.
[f*] Good!
[l]RuBP Regeneration Phase
[fx] No. Please try again.
[f*] Great!
[q dataset_id=”SMV_PSN_Calvin Cycle Quiz|1719f69fdfb356″ question_number=”2″]After carbon dioxide is combined with RuBP, the six carbon product immediately dissociates into which of the molecules shown below?
[textentry single_char=”true”]
[c]Yg ==[Qq]
[f]WWVzLiBMZXR0ZXIg4oCcYuKAnSBpbmRpY2F0ZXMgdGhlIHRocmVlLWNhcmJvbiBtb2xlY3VsZSB0aGF0IGFwcGVhcnMgaW4gdGhlIENhbHZpbiBjeWNsZSBpbW1lZGlhdGVseSBmb2xsb3dpbmcgY2FyYm9uIGZpeGF0aW9uLg==[Qq]
[c]Kg==[Qq]
[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFVzZSB0aGUgbGVnZW5kICh1cHBlciByaWdodCkgdG8gZmlndXJlIG91dCB3aGljaCBtb2xlY3VsZSBpcyBjYXJib24gZGlveGlkZS4gUmlnaHQgbmVhcmJ5LCB5b3UmIzgyMTc7bGwgZmluZCB5b3VyIGFuc3dlci4=
Cg==[Qq]
[q dataset_id=”SMV_PSN_Calvin Cycle Quiz|1719bebec25356″ question_number=”3″]Which letter in the diagram below indicates RuBP, the starting and ending compound in the Calvin cycle?
[textentry single_char=”true”]
[c]Zg ==[Qq]
[f]WWVzLiBMZXR0ZXIg4oCcZuKAnSBpbmRpY2F0ZXMgUnVCUCwgdGhlIENhbHZpbiBjeWNsZSYjODIxNztzIHN0YXJ0aW5nIGFuZCBlbmRpbmcgY29tcG91bmQ=[Qq]
[c]Kg==[Qq]
[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFVzZSB0aGUgbGVnZW5kICh1cHBlciByaWdodCkgdG8gZmlndXJlIG91dCB3aGljaCBtb2xlY3VsZSBpcyBjYXJib24gZGlveGlkZS4gUnVCUCBpcyB0aGUgbW9sZWN1bGUgdGhhdCBnZXRzIGNvbWJpbmVkIHdpdGggY2FyYm9uIGRpb3hpZGUgYXMgdGhlIENhbHZpbiBjeWNsZSBiZWdpbnMu
Cg==[Qq]
[q dataset_id=”SMV_PSN_Calvin Cycle Quiz|17197d8d756356″ question_number=”4″]Which letter in the diagram below shows a molecule that results from the chemical reduction that occurs within the Calvin cycle?
[textentry single_char=”true”]
[c]ZA ==[Qq]
[f]WWVzLiBMZXR0ZXIg4oCcZOKAnSBpbmRpY2F0ZXMgRzNQLCB3aGljaCByZXN1bHRzIHdoZW4gY29tcG91bmQgJiM4MjIwO2MmIzgyMjE7IGdldHMgcmVkdWNlZCwgcmVjZWl2aW5nIGVsZWN0cm9ucyBhbmQgaHlkcm9nZW4gZnJvbSBOQURQSC4=[Qq]
[c]Kg==[Qq]
[f]Tm8uIEhlcmUmIzgyMTc7cyBhIGhpbnQuIFRoZSBiaW9sb2dpY2FsIHJlZHVjdGlvbnMgaW4gdGhlIENhbHZpbiBjeWNsZSBpbnZvbHZlIGVsZWN0cm9ucyBhbmQgaHlkcm9nZW5zIHRoYXQgYXJlIGNvbnRyaWJ1dGVkIGJ5IE5BRFBILiBGaW5kIE5BRFBILCBhbmQgeW91JiM4MjE3O2xsIGhhdmUgeW91ciBhbnN3ZXIu
Cg==[Qq]
[q dataset_id=”SMV_PSN_Calvin Cycle Quiz|171945ac580356″ question_number=”5″]Which of the phases of the Calvin cycle involves carbon fixation?
[c]SSDCoC DCoCA=[Qq][c]SUkgwqAgwqAg[Qq][c]SUlJ
Cg==[Qq][f]WWVzLiBQaGFzZSBJIG9mIHRoaXMgQ2FsdmluIGN5Y2xlIGRpYWdyYW0gaW52b2x2ZXMgY2FyYm9uIGZpeGF0aW9uLg==[Qq]
[f]Tm8uIFRoaXMgaXMgdGhlIGVuZXJneSBpbnZlc3RtZW50IHBoYXNlLiBUaGVyZSBhcmUgcmVkdWN0aW9ucyBhbmQgcGhvc3Bob3J5bGF0aW9ucywgYnV0IG5vIGNhcmJvbiBmaXhhdGlvbi4gTG9vayBmb3IgYSBwaGFzZSB3aGVyZSBjYXJib24gaXMgY29taW5nIGludG8gdGhlIGN5Y2xlLg==[Qq]
[f]Tm8uIFRoaXMgaXMgdGhlIFJ1QlAgcmVnZW5lcmF0aW9uIHBoYXNlLiBMb29rIGZvciBhIHBoYXNlIHdoZXJlIGNhcmJvbiBpcyBjb21pbmcgaW50byB0aGUgY3ljbGUu
Cg==[Qq]
[q dataset_id=”SMV_PSN_Calvin Cycle Quiz|17190b772ebf56″ question_number=”6″]Which of the phases of the Calvin cycle shown below involves energy investment?
[c]SSDCoCDCoCA=[Qq][c]SUkgwq AgwqAg[Qq][c]SUlJ
Cg==[Qq][f]Tm8uIFBoYXNlIEkgb2YgdGhpcyBDYWx2aW4gY3ljbGUgZGlhZ3JhbSBpbnZvbHZlcyBjYXJib24gZml4YXRpb24uIExvb2sgZm9yIHRoZSBwaGFzZSB3aGVyZSBlbmVyZ3kgdHJhbnNmZXIgbW9sZWN1bGVzIChzdWNoIGFzIEFUUCBhbmQgTkFEUEgpIGFyZSBjb252ZXJ0ZWQgaW50byBsb3dlci1lbmVyZ3kgZm9ybXMu[Qq]
[f]WWVzLiBUaGlzIGlzIHRoZSBlbmVyZ3kgaW52ZXN0bWVudCBwaGFzZS4gVGhlcmUgYXJlIHJlZHVjdGlvbnMgYW5kIHBob3NwaG9yeWxhdGlvbnMsIGJvdGggb2Ygd2hpY2ggYWRkIGVuZXJneSB0byB0aGUgbW9sZWN1bGVzIGluIHRoZSBDYWx2aW4gY3ljbGUu[Qq]
[f]Tm8uIFRoaXMgaXMgdGhlIFJ1QlAgcmVnZW5lcmF0aW9uIHBoYXNlLiBMb29rIGZvciB0aGUgcGhhc2Ugd2hlcmUgZW5lcmd5IHRyYW5zZmVyIG1vbGVjdWxlcyAoc3VjaCBhcyBBVFAgYW5kIE5BRFBIKSBhcmUgY29udmVydGVkIGludG8gbG93ZXItZW5lcmd5IGZvcm1zLg==
Cg==[Qq]
[q dataset_id=”SMV_PSN_Calvin Cycle Quiz|1718d396115f56″ question_number=”7″]Which of the phases of the Calvin cycle shown below involves regeneration of RuBP?
[c]SSDCoCDCoCA=[Qq][c]SUkgwqAgwqAg[Qq][c]SU lJ
Cg==[Qq][f]Tm8uIFBoYXNlIEkgb2YgdGhpcyBDYWx2aW4gY3ljbGUgZGlhZ3JhbSBpbnZvbHZlcyBjYXJib24gZml4YXRpb24uIExvb2sgZm9yIGEgcGhhc2Ugd2hlcmUgdGhlIHN0YXJ0aW5nIGNvbXBvdW5kICh0aGUgNSBjYXJib24gbW9sZWN1bGUgUnVCUCkgaXMgYmVpbmcgcmVnZW5lcmF0ZWQu[Qq]
[f]Tm8uIFRoaXMgaXMgdGhlIGVuZXJneSBpbnZlc3RtZW50IHBoYXNlLiBMb29rIGZvciBhIHBoYXNlIHdoZXJlIHRoZSBzdGFydGluZyBjb21wb3VuZCAodGhlIDUgY2FyYm9uIG1vbGVjdWxlIFJ1QlApIGlzIGJlaW5nIHJlZ2VuZXJhdGVkLg==[Qq]
[f]WWVzLiBUaGlzIGlzIHRoZSBSdUJQIHJlZ2VuZXJhdGlvbiBwaGFzZS4=[Qq]
[q]In the diagram below, compound “a” is [hangman] [hangman].
[c]Y2FyYm9u[Qq]
[c]ZGlveGlkZQ==[Qq]
[q]In the diagram below, the acronym for compound “f” is [hangman], and the acronym for compound “d” is [hangman].
[c]UnVCUA==[Qq]
[c]RzNQ[Qq]
[q]In the diagram below, Phase I is [hangman] [hangman], and phase II is [hangman] [hangman].
[c]Y2FyYm9u[Qq]
[c]Zml4YXRpb24=[Qq]
[c]ZW5lcmd5[Qq]
[c]aW52ZXN0bWVudA==[Qq]
[x][restart]
[/qwiz]
What’s Next?
This tutorial completes AP Bio Unit 3 (Cellular Energetics).
- To review the entire unit, please go to our Unit 3 Review Page: Objectives, Flashcards, and Quizzes
- To choose another tutorial in our AP Bio Video Pathway, go to the AP Bio Video Pathway Main Menu