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Photosystem II

In brief

Photosystem II is a membrane protein complex that starts electron transfer from water in oxygenic photosynthesis. Antenna pigments collect light energy and pass excitation to a reaction centre. Water oxidation supplies electrons and releases oxygen. Transfer onward to plastoquinone connects the complex to the rest of the pathway. [5] [6]

Evidence for this statement

Source-based explanation

Where to check this statement

biology59-photosynthesis
Electron Flow through Photosystems I and II; electron transport and ATP/NADPH paragraphs
biology59-light
How Light-Dependent Reactions Work; Figure8.17 explanatory text: PSII/PSI, ATP, NADPH and proton gradient; no figure reused
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The water-oxidising step

D1 and D2 form a pair of reaction-centre proteins. UniProt connects Arabidopsis D1 to gene psbA and locus AtCg00020. A photosystem complex and one protein are distinct scientific objects.

[1] [2]
Evidence for this statement

Source-based explanation

Where to check this statement

go-photosystem2
Captured GO ontology JSON: results[].id and definition.text
uniprot-P83755
Captured UniProt JSON: primaryAccession, organism, sequence and FUNCTION comments

In entry P83755, the function and location carry evidence code ECO:0000255 and HAMAP rule MF_01379. This is a model-based annotation, not a direct measurement of the pictured plant.

[1] [2]
Evidence for this statement

Source-based explanation

Where to check this statement

go-photosystem2
Captured GO ontology JSON: results[].id and definition.text
uniprot-P83755
Captured UniProt JSON: primaryAccession, organism, sequence and FUNCTION comments

A reaction centre and its partners

D1 and D2 are reaction-centre proteins; other components collect excitation energy, carry electrons or support water oxidation. Function depends on an organised set of molecules in a membrane. Opening D1 selects one component and its sequence, rather than the complete photosystem.

[1] [2] [5] [6]
Evidence for this statement

EcoGenesis

Where to check this statement

go-photosystem2
GO definition / UniProt FUNCTION / original figure caption, as applicable
uniprot-P83755
GO definition / UniProt FUNCTION / original figure caption, as applicable
biology59-photosynthesis
Electron Flow through Photosystems I and II; electron transport and ATP/NADPH paragraphs
biology59-light
How Light-Dependent Reactions Work; Figure8.17 explanatory text: PSII/PSI, ATP, NADPH and proton gradient; no figure reused

Reaction centre and partners

The photosystem II definition includes a reaction centre, accessory pigments and electron carriers. Following D1 selects one protein of that complex. A component description does not replace the whole complex’s composition and interactions; the source record must identify the object and organisational level being discussed.

[1] [2]
Evidence for this statement

Explanation of retained sources

Where to check this statement

go-photosystem2
Captured GO ontology JSON: results[].id and definition.text
uniprot-P83755
Captured provider JSON; named selected record and native source versions

Direction of transfer

In chloroplasts and cyanobacteria, illuminated photosystem II transfers electrons from water to plastoquinone. Water and plastoquinone occupy different sides of that transfer. This states a complex’s function; it supplies no numerical rate, product yield or result of a particular experiment.

[1]
Evidence for this statement

Explanation of retained sources

Where to check this statement

go-photosystem2
Captured GO ontology JSON: results[].id and definition.text

Checking the molecular record

The Arabidopsis UniProt D1 entry is linked to psbA and locus AtCg00020. Its retained function and location annotations carry ECO:0000255 and HAMAP rule MF_01379. Preserve these grounds with the statement: a reviewed entry does not make every annotation a direct experiment.

[2]
Evidence for this statement

Explanation of retained sources

Where to check this statement

uniprot-P83755
Captured provider JSON; named selected record and native source versions

Connected concepts

D1 protein · PsbA

P83755 is the photosystem II D1 protein record for Arabidopsis thaliana, NCBI Taxonomy 3702. The retained UniProt version identifies psbA / AtCg00020 and a sequence of 353 amino acids.

[2]
Evidence for this statement

Source-based explanation

Where to check this statement

uniprot-P83755
Captured provider JSON; named selected record and native source versions
Chloroplast

A chloroplast is a chlorophyll-containing plastid. It contains thylakoids and stroma, with some thylakoids organised into stacks called grana.

[3] [4] [2]
Evidence for this statement

Source-based explanation

Where to check this statement

go-chloroplast
Captured GO ontology JSON: results[].id and definition.text
uniprot-P83755
Captured provider JSON; named selected record and native source versions

Continue with an organism

The photographs and molecular record come from separate source materials.

Norway spruce →Arabidopsis thaliana →

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Sources and versions

Editorial draft · human review pending

  1. GO:0009523 · photosystem II

    2026-09-09T01:17:35.068503+00:00 · CC-BY-4.0

    Provenance and original
    Original SHA-256
    56537702684f4e6949eb9b16430a8830740bc9fd3369b21e7b5a9b711a341b4f
    Processing
    Unmodified provider response; article text is an attributed educational summary.
    Version details
    QuickGO response did not supply a native ontology release; retrieval time and exact response hash retained.

    View original JSON · Download original

  2. UniProt P83755 · entry 161 / sequence 2

    2026-09-09T01:17:34.554931+00:00 · CC-BY-4.0

    Provenance and original
    Source version
    entry 161; sequence 2
    Original SHA-256
    f16a5f33fbf85a12aa5c91ab31f6092f0bbe3be874040c84c4954e87b20ae3a9
    Processing
    Unmodified provider response; article text is an attributed educational summary.
    Version details
    Provider entry/sequence versions retained.

    View original JSON · Download original

  3. GO:0009507 · chloroplast

    2026-09-09T01:17:34.931415+00:00 · CC-BY-4.0

    Provenance and original
    Original SHA-256
    13082607c7dcc9e92cd281f1fc6a8fdf2878bceba74e9d7b6ad50d43b0ce33ba
    Processing
    Unmodified provider response; article text is an attributed educational summary.
    Version details
    QuickGO response did not supply a native ontology release; retrieval time and exact response hash retained.

    View original JSON · Download original

  4. Arabidopsis thaliana, first leaf of control seedling grown without added NaCl; Figure 3A

    Retrieval date unknown · CC BY 4.0

    Provenance and original
    Original SHA-256
    fe305c7d3a3327a06dda04c186989b5b8b6dec101bfe13aa851a3bc47dc07b14
    Processing
    Panel A extracted; original g/t annotations and 1 µm scale retained; encoded as WebP.
  5. Cooper (2000) · Photosynthesis

    2026-10-01 · Terms of use on source site

    Provenance and original
    Source version
    Selected web passages checked 2026-10-01; no immutable response edition asserted
    Source reading scope
    Named background passages only; not new experimental evidence.
    Location in the original source
    Electron Flow through Photosystems I and II; electron transport and ATP/NADPH paragraphs
  6. Clark, Douglas & Choi · Biology 2e · 8.2 Light-Dependent Reactions

    2026-10-01 · Terms of use on source site

    Provenance and original
    Source version
    Selected publisher HTML passages checked 2026-10-01
    Source reading scope
    Named foundational biology paragraphs only; background facts checked against classical textbooks and captured GO/UniProt records; not an experimental result.
    Location in the original source
    How Light-Dependent Reactions Work; Figure8.17 explanatory text: PSII/PSI, ATP, NADPH and proton gradient; no figure reused
Inspect structured data
Content version
5bfa388d8b0b5b907bd0ee820a122122c75d0519b12118b17ab45cbf50b4da5b
Source version
knowledge-20260909.1
Updated
2026-10-01