🔹 Definition & Importance
Chloroplasts are specialized
organelles in plant cells responsible for photosynthesis (conversion of
light energy into chemical energy).
Present in green structures of
plants (leaves, stems, unripe fruits).
Average density: ~ 0.5 million
chloroplasts per mm² of leaf surface.
🔹 Types of Plastids
Chloroplasts → Green,
photosynthesis.
Chromoplasts → Yellow to
red pigments (give color).
Leucoplasts → Colorless,
for storage.
🔹 Structure of
Chloroplast
Shape: Ellipsoid.
Envelop: Two membranes
(outer + inner).
Outer → More permeable.
Inner → Less permeable.
Intermembrane space →
Between outer and inner membranes.
Stroma → Semi-fluid inside
inner membrane; contains enzymes and fills most of the volume.
Thylakoids → Disk-shaped
compartments.
Grana → Stacks of
thylakoids (1 chloroplast may have 100+ grana).
Lamellae → Connect grana
(non-green compartments).
DNA → Own DNA (can
reproduce independently, like mitochondria).
🔹 Pigments
Chlorophyll a and Chlorophyll
b → Absorb light energy needed for photosynthesis.
🔹 Function / Working
Light absorbed by chlorophyll
molecules in thylakoid membranes.
Absorbed energy excites electrons
→ ATP formation.
In stroma, ATP + CO₂ used
to synthesize glucose (organic compounds).
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