Biology · Cell: The Unit of Life · NEET
They are three parts, one inside the other. A thylakoid is a single flat membrane sac. A granum (plural: grana) is a stack of many thylakoids, arranged like a pile of coins. The stroma is the thick fluid that fills the whole chloroplast and surrounds all the grana. So order from small to big: thylakoid -> granum (stack of thylakoids) -> stroma (fluid holding the stacks). NCERT says the thylakoids sit inside the stroma.
It is just singular and plural. One stack of thylakoids is called a granum. Many stacks together are called grana. NEET Match-the-column questions use both words, so do not get confused. Granum = one stack. Grana = many stacks.
Both, in a way. Thylakoids are stacked to FORM the grana. And the grana themselves float in the stroma. So a thylakoid is part of a granum, and that granum sits in the stroma. NCERT: 'A number of organised flattened membranous sacs called the thylakoids are present in the stroma... arranged in stacks like piles of coins called grana.'
The stroma (the fluid inside the inner membrane) contains: enzymes for making carbohydrates and proteins, small double-stranded circular DNA, and 70S ribosomes. This is why the chloroplast is called semi-autonomous. NEET 2024 asked this directly: chloroplast DNA is circular and double-stranded, and it lives in the stroma.
Stroma lamellae are flat membrane tubules that connect the thylakoids of DIFFERENT grana. Think of them as bridges joining one coin-stack to another coin-stack, running through the stroma. The thylakoids inside a single stack are the 'grana thylakoids'; the connecting ones are the 'stroma (intergranal) thylakoids'.
Chlorophyll pigments are present in the THYLAKOIDS, not in the stroma. That is why the grana (stacks of thylakoids) trap light and carry out the light reactions. The stroma has no chlorophyll; it does the dark reactions (making sugar) using enzymes.
No. The space enclosed by the thylakoid membrane is called the lumen. It is separate from the stroma. So there are two different fluid spaces: the lumen (inside each thylakoid sac) and the stroma (outside the thylakoids, inside the inner chloroplast membrane).
Match List-I with List-II: (a) Cristae (b) Thylakoid (c) Centromere (d) Cisternae | (i) Primary constriction in chromosome (ii) Disc-shaped sacs in Golgi apparatus (iii) Infoldings in mitochondria (iv) Flattened membranous sacs in stroma of plastids
The DNA present in chloroplast is
Statement I: Mitochondria and chloroplasts are both double membrane bound organelles. Statement II: Inner membrane of Mitochondria is relatively less permeable, as compared to chloroplast.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Double membrane bound, like the mitochondrion. Of the two membranes, the inner chloroplast membrane is relatively less permeable. The space inside the inner membrane is the stroma.
The grana (stacks of thylakoids) are the site of the light reactions. The stroma is the site of the dark reactions (carbon fixation, sugar making).
Because its stroma contains its own double-stranded circular DNA and 70S ribosomes, so it can make some of its own proteins and divide by fission. But it still depends on the nucleus for other proteins.
The lumen is the space enclosed by the thylakoid membrane. It is a separate compartment from the stroma. Protons build up in the lumen during the light reaction.
NCERT: chloroplasts are 5-10 micrometre long and 2-4 micrometre wide, usually lens-shaped or oval. Numbers range from 1 per cell in the alga Chlamydomonas to 20-40 per cell in leaf mesophyll.
