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Chloroplast Structure: Grana, Stroma, Thylakoids and Lamellae

Biology · Photosynthesis in Higher Plants · NEET

A chloroplast has two parts that do two jobs. The membrane system (flat sacs called thylakoids, stacked into piles called grana, joined by stroma lamellae) traps light and does the light reaction. The fluid around them, called stroma, does the dark reaction (Calvin cycle). Memory hook: "Grana Grab light, Stroma Sews sugar."
Chloroplast (stroma = fluid matrix, does dark reaction)Granum(stacked thylakoids)GranumStroma lamella(PS I only)Thylakoidlumen: most H+1 sac = thylakoidGrana + lamellae = membrane system (light reaction)
Inside a chloroplast: single thylakoid sacs stack into grana, grana are joined by stroma lamellae (PS I only), all bathed in the stroma fluid where the Calvin cycle runs. The thylakoid lumen holds the most protons.

Your doubts, answered

What is the difference between grana and stroma?

They are different structures with different jobs. Grana are stacks of flat membrane sacs (thylakoids) inside the chloroplast; this is where the light reaction happens and ATP + NADPH are made. Stroma is the colourless fluid (matrix) surrounding the grana; this is where the dark reaction (Calvin cycle) fixes CO2 into sugar. Short rule: grana = light reaction, stroma = dark reaction. For NEET, do not mix up 'stroma' (the fluid) with 'stroma lamellae' (membrane tubes).

What are thylakoids and lamellae in a chloroplast?

A thylakoid is a single flat, disc-shaped membrane sac. Many thylakoids stack up like a pile of coins to form a granum (plural: grana). The flat membrane sheets that connect one granum to another are called stroma lamellae (or intergranal lamellae). So thylakoid = one sac, granum = a stack of thylakoids, lamellae = the bridges joining stacks. The space inside a thylakoid is the thylakoid lumen.

Where does the light reaction and dark reaction take place in the chloroplast?

The light reaction (photochemical phase) takes place on the thylakoid membranes of the grana, because the pigments, photosystems and ATP synthase sit there. The dark reaction (biosynthetic phase / Calvin cycle) takes place in the stroma, the fluid part, because the enzyme RuBisCO and the CO2-fixing enzymes are dissolved there. NCERT calls this 'a clear division of labour within the chloroplast.'

What is the difference between grana lamellae and stroma lamellae?

Grana lamellae are the stacked thylakoids inside the grana and carry BOTH Photosystem I (PS I) and Photosystem II (PS II), plus NADP reductase, so they can do non-cyclic photophosphorylation and make NADPH. Stroma lamellae are the unstacked membranes connecting grana; they carry ONLY PS I and lack PS II and NADP reductase, so they cannot split water or make NADPH. This exact point was tested in NEET 2019/2021.

Which part of the chloroplast has the highest number of protons (H+)?

The thylakoid lumen (the space inside the thylakoid) has the highest number of protons and the lowest pH. Reason: water is split on the inner side of the thylakoid membrane and the H+ released collects inside the lumen, and more protons are pumped in during electron transport. This proton build-up drives ATP synthase (chemiosmosis). NEET 2016 asked exactly this.

⚠️ The NEET trap
✗ Stroma has the highest number of protons because it is the largest space.
✓ The thylakoid lumen has the highest number of protons (lowest pH). Water splitting happens on the inner thylakoid surface and releases H+ into the lumen, and protons are pumped from the stroma into the lumen during electron transport.
🧠 Protons pile up INSIDE the sac (lumen), not in the surrounding fluid (stroma). Splitting of water dumps H+ into the lumen.

Real NEET questions

NEET 2016

In a chloroplast the highest number of protons are found in:

A · Stroma
B · Lumen of thylakoids ✓
C · Inter membrane space
D · Antennae complex
Solution: During the light reaction, water is split on the inner side of the thylakoid membrane, so the H+ released collects inside the thylakoid lumen. More protons are also pumped from the stroma into the lumen during electron transport. This makes the lumen the compartment with the highest proton concentration and lowest pH, which then drives ATP synthesis by chemiosmosis. So the answer is the lumen of thylakoids (B), not the stroma.
NEET 2019 / 2021

Which of the following statements is incorrect?

A · Grana lamellae have both PS I and PS II
B · Cyclic photophosphorylation involves both PS I and PS II ✓
C · Both ATP and NADPH + H+ are synthesized during non-cyclic photophosphorylation
D · Stroma lamellae have PS I only and lack NADP reductase
Solution: This question checks grana vs stroma lamellae and the two photophosphorylations. Grana lamellae carry both PS I and PS II (correct). Stroma lamellae carry only PS I and lack NADP reductase (correct). Non-cyclic photophosphorylation makes both ATP and NADPH (correct). Cyclic photophosphorylation uses ONLY PS I, so saying it involves both PS I and PS II is wrong. The incorrect statement is B.

Solved Photosynthesis in Higher Plants NEET PYQs

Try the real previous-year questions from this chapter — each with the answer and a full solution.

See all 32 Photosynthesis in Higher Plants NEET PYQs ›
Next concept: Difference Between Light Reaction and Dark Reaction of Photosynthesis →Keep learning — 2 minFeeling ready? Solve the Photosynthesis in Higher Plants NEET PYQs ›Or practice on your phone — get the free MedicNEET app ›

Frequently asked

Is stroma the same as stroma lamellae?

No. Stroma is the colourless fluid matrix that fills the chloroplast and holds the Calvin cycle enzymes. Stroma lamellae are flat membrane tubes that connect one granum to the next and carry only PS I. Same word 'stroma', totally different structures.

What is the difference between a thylakoid and a granum?

A thylakoid is one flat membrane sac. A granum is a stack of many thylakoids piled like coins. One chloroplast can have 40 to 60 grana, each with 5 to 25 thylakoids.

What does the chloroplast membrane system do versus the stroma?

NCERT states there is a 'division of labour'. The membrane system (grana + stroma lamellae) traps light energy and makes ATP and NADPH. The stroma uses that ATP and NADPH to fix CO2 into sugar and starch.

Why is the thylakoid lumen important for NEET?

Because water splitting dumps protons into the lumen, giving it the most H+ and lowest pH. This proton gradient across the thylakoid membrane powers ATP synthase. It is a repeat NEET point (2016).

Do stroma lamellae make NADPH?

No. Stroma lamellae have only PS I and lack PS II and NADP reductase, so they cannot split water or reduce NADP+. NADPH is made on the grana thylakoids during non-cyclic photophosphorylation.

Related concepts:
Where Does Photosynthesis Take Place? Chloroplast and MesophyllDifference Between Light Reaction and Dark ReactionProton Gradient: Why the Thylakoid Lumen Has the Most ProtonsPhotosystems PS I and PS II and the Light Harvesting Complex (LHC)Cyclic vs Non-Cyclic Photophosphorylation
Practise Biology for NEET:
Biology MCQs (free, chapter-wise)Photosynthesis in Higher Plants PYQs