Chloroplasts

Edexcel A-level BiologyPhotosynthesisLesson 3 of 20

Chloroplasts are the organelles in which photosynthesis takes place. They are found mainly in the palisade mesophyll cells of leaves, and are usually disc-shaped, about 2 to 10 µm across.

Structures and functions:
• Envelope: a double membrane that surrounds the chloroplast and controls what enters and leaves.
• Thylakoids: flattened membrane sacs. Their membranes hold the photosynthetic pigments (in photosystems), electron carriers and ATP synthase, so they are the site of the light-dependent reactions.
• Grana (singular granum): stacks of thylakoids, which give a very large surface area for absorbing light.

More in Photosynthesis

• Autotrophs and Heterotrophs
• The Process of Photosynthesis
• Chlorophyll
• Absorption Spectrum Chlorophyll
• Chromatography
• Photosystems
• The Light-Dependent Reactions
• Cyclic Photophosphorylation

All 20 lessons in Photosynthesis · All Edexcel A-level Biology topics