Chloroplasts
5.9 Understand the structure of chloroplasts in relation to their role in photosynthesis.
Thylakoid Membrane
• System of interconnected, flattened, fluid-filled sacs.
• Photosynthetic pigments (e.g. chlorophyll a, chlorophyll b, carotene) attached to proteins, electron
carriers and ATP synthase molecules are embedded within the membrane for the light-dependent
reactions.
• Large surface area to allow maximum absorption of light.
Granum
• Stack of thylakoid membranes joined to one another by stromal lamellae (plural: grana).
Lamella
• Connections between stacks of thylakoid membranes (plural: lamellae).
Outer Membrane
• Permeable to carbon dioxide and water.
• Contains complex proteins called porins – beta barrel proteins that cross the outer membrane and act
as a pore, through which molecules can diffuse.
Inner Membrane
• Contains many transport molecules.
• Membrane proteins regulate the passage of substances in and out of the chloroplast, e.g. sugars and
proteins synthesised in cytoplasm of cell to be used in chloroplast.
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, Chloroplasts
5.9 Understand the structure of chloroplasts in relation to their role in photosynthesis.
Thylakoid Space
• Fluid within the thylakoid membranes sacs
• Contains enzymes for photolysis.
Chloroplast Envelope
• Inner and outer membranes form an envelope.
• Keeps reactants for photosynthesis close to their reaction sites.
Stroma
• Colourless fluid within the inner membrane, surrounding the thylakoid membranes.
• Contains enzymes, sugars and organic acids for light-independent reactions.
• Contains chloroplast DNA and chloroplast ribosomes for protein synthesis.
Starch Grain
• Stores products of photosynthesis.
• Synthesised from glucose that is not used directly in respiration or converted into other biochemicals.
DNA Loop
• Contains genes for some proteins produced by the chloroplast.
Photosystems
• Photosystem: Cluster of photosynthetic pigments found in the thylakoid membranes.
• There are two structurally different types of photosystem: PSI and PSII.
o PSI absorbs light best at a wavelength of 700nm.
o PSII absorbs light best at a wavelength of 680nm.
• They are part of the electron transport chain in the light-dependent reactions.
• In the light-dependent reaction, the light energy absorbed by the photosystems is used for:
1. The photophosphorylation of ADP to ATP.
2. The reduction of NADP to NADPH.
3. The photolysis of H2O into H+ ions (protons), electrons and oxygen.
Chloroplasts also contain lipid droplets.
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