Lesson 3 of 12 · 7 min
Where photosynthesis takes place
NCERT §11.3
Kavya knows the underside of a rice leaf feels rougher than the top. The difference is not texture for its own sake: it is where the leaf hides its light-catching machinery.
The lesson in notes
In short
Photosynthesis occurs in the green leaves and also in other green parts; within the leaf, it happens mainly in the chloroplasts of mesophyll cells.
Mesophyll cells are packed with chloroplasts, which generally arrange themselves along the cell walls to catch an optimum amount of the light falling on them.
Inside the chloroplast, the membrane system (grana, stroma lamellae) traps light energy and makes ATP and NADPH.
In the stroma, enzymes reduce CO₂ to carbohydrates and the sugar is later converted to starch.
The membrane-bound events are directly light-driven and are called light reactions; the stroma events do not directly need light but use the ATP and NADPH made in light, and are called carbon reactions.
The older label 'dark reaction' is misleading: these reactions do not take place in darkness and are not independent of light, since they depend on the products of the light reactions.