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13.1.313 · Photosynthesis

Thylakoids and the Stroma — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 8 parts Lesson 4 of 13 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

13.1.3 Thylakoids and the Stroma — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe how thylakoids and the stroma are adapted to the light-dependent and light-independent stages.Structure — flattened, fluid-filled sacs in the stroma that stack in places to for…

  • Light-dependent stage
  • Membrane contents
  • Large surface area
  • Many pigments
  • Arrangement
  • Photosystem

Part 1 of 6Thylakoids

1Structure
  • Structure flattened, fluid-filled sacs in the stroma that stack in places to form grana.
2Light-dependent stage
  • Light-dependent stage occurs in the thylakoid membranes and the thylakoid spaces inside the sacs.
3Membrane contents
  • Membrane contents pigments, enzymes and electron carriers needed for the light-dependent reactions.

Part 2 of 6Adaptations of the grana

Large surface area
  • Large surface area the grana membranes allow many light-dependent reactions to occur.
Many pigments
  • Many pigments the membrane system holds a large number of pigment molecules.
Arrangement
  • Arrangement pigments are arranged so that as much light as necessary is captured.

Part 3 of 6Photosystems

Photosystems
Photosystem
  • Photosystem a light-harvesting cluster of pigment molecules in the thylakoid membrane.
Funnel arrangement
  • Funnel arrangement pigments are arranged in funnel-like structures in the membrane.
Energy transfer
  • Energy transfer each pigment passes energy to the next until it reaches the primary pigment reaction centre.

Part 4 of 6The stroma

The stroma
Structure
  • Structure the fluid filling the chloroplast and surrounding the thylakoids.
Contents
  • CO2, sugars, enzymes and other dissolved molecules.
Function
  • Function site of the light-independent stage of photosynthesis.

Part 5 of 6Which reactions happen where

RegionReactionsWhy
Thylakoid membranesLight-dependentPigments, electron carriers and light are present
StromaLight-independentCalvin cycle enzymes and CO2 are present

Part 6 of 6More from the specification

More from the specification
Reduced
  • Having gained electrons
Chlorophyll
  • A green pigment in chloroplasts that transfers energy from light into chemical energy.
Photolysis
  • Splitting of water by light at PSII.
Cyclic photophosphorylation
  • ATP formation using only PSI with electrons returning to it.
Non-cyclic photophosphorylation
  • ATP formation using PSII and PSI with electrons ending in NADP.
Triose phosphate
  • Three-carbon sugar phosphate made from GP.
Chemiosmosis
  • Chemiosmosis protons flow back across the thylakoid membrane through ATP synthase by facilitated diffusion, which drives photophosphorylation.

Key terms

TermMeaning
ThylakoidFlattened membrane sac containing photosynthetic pigments.
GranumStack of thylakoids.
PhotosystemLight-harvesting cluster of pigments in the thylakoid membrane.
Reaction centrePrimary pigment that receives energy from the photosystem.
StromaFluid in the chloroplast where the light-independent stage occurs.
Thylakoid spaceFluid-filled space inside a thylakoid.

Avoid these mistakes

1
Mixing up the two stages — light-dependent reactions are in the thylakoids and light-independent reactions are in the stroma.
2
Saying the stroma contains the pigments — the pigments are in the thylakoid membranes.
3
Saying grana are single sacs — they are stacks of thylakoids.
4
Forgetting the primary pigment reaction centre — the photosystem funnels energy to it.

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