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This chapter is mostly description, which makes it tempting to read once and assume you know it. But NEET questions rarely ask "what is a mitochondrion?". They ask which two organelles share a feature, which one lacks a membrane, or what a number in a diagram means. This post sets out cell theory, then compares the organelles side by side, works a counting question that catches many students and ends with a revision routine.
What does the NEET syllabus ask from this chapter?
Unit 3 of the NEET (UG) 2026 syllabus lists cell theory and the cell as the basic unit of life; prokaryotic and eukaryotic cells; plant and animal cells; the cell envelope, membrane and wall; the endomembrane system (ER, Golgi bodies, lysosomes, vacuoles); mitochondria, ribosomes, plastids and microbodies; the cytoskeleton, cilia, flagella and centrioles; and the nucleus. All of it is in NCERT Class 11 Chapter 8, Cell: The Unit of Life.
What is cell theory, and who added what?
NCERT's account has three names and three dates:
Matthias Schleiden (1838), a botanist, observed that plants are made of different kinds of cells that form tissues.
Theodor Schwann (1839), a zoologist, reported the thin outer layer of animal cells now called the plasma membrane, concluded that the cell wall is unique to plant cells, and proposed that animals and plants are made of cells and their products.
Rudolf Virchow (1855) explained that new cells form from pre-existing cells (Omnis cellula-e cellula).
The modern statement has two parts: all living organisms are made of cells and products of cells, and all cells arise from pre-existing cells.
How do prokaryotic and eukaryotic cells differ?
Nucleus: prokaryotes have no membrane-bound nucleus; their genetic material is naked. Many bacteria also carry small circular DNA called plasmids, which can confer traits such as antibiotic resistance.
Organelles: prokaryotes have no membrane-bound organelles; ribosomes are the only organelle they share with eukaryotes. They have a mesosome, an infolding of the cell membrane.
Ribosomes: 70S in prokaryotes, 80S in the eukaryotic cytoplasm.
Cell wall: all prokaryotes have one except mycoplasma.
How do the organelles compare?
Sort every organelle by three questions: how many membranes, does it have its own DNA, and what are its ribosomes?
Double membrane: mitochondria, chloroplasts and the nuclear envelope. Mitochondria and chloroplasts each have their own circular DNA and 70S ribosomes, and mitochondria divide by fission.
Single membrane: endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles and microbodies. The vacuole's membrane has its own name, the tonoplast.
No membrane: ribosomes, centrosome and centrioles, the cytoskeleton and the nucleolus.
A few functions that questions pair with structures:
RER carries ribosomes and is common in cells making and secreting protein. SER is the main site of lipid synthesis; in animal cells, steroid hormones are made there.
Golgi apparatus packages materials. Vesicles from the ER fuse with its convex cis (forming) face and leave from the concave trans (maturing) face. It is a major site of glycoprotein and glycolipid formation.
Lysosomes are formed by Golgi packaging and hold hydrolytic enzymes that are optimally active at acidic pH.
Mitochondria are the sites of aerobic respiration. NCERT gives a diameter of 0.2 to 1.0 µm (average 0.5 µm) and a length of 1.0 to 4.1 µm. The inner membrane folds into cristae, which increase surface area.
Chloroplasts are 5 to 10 µm long. Chlamydomonas has one per cell; a mesophyll cell has 20 to 40.
The endomembrane system is ER, Golgi, lysosomes and vacuoles. NCERT leaves out mitochondria, chloroplasts and peroxisomes because their functions are not coordinated with the others, and that exclusion is a frequent question.
The people behind these structures are also examinable. Camillo Golgi first described the Golgi bodies (1898), and George Palade first saw ribosomes under the electron microscope (1953). Palade shared the 1974 Nobel Prize in Physiology or Medicine with Albert Claude and Christian de Duve for discoveries concerning "the structural and functional organization of the cell".
Worked example: counting microtubules and ribosome units
Question. How many microtubules appear in a cross-section of a cilium's axoneme, and in one centriole? And why is a ribosome made of 60S and 40S subunits called 80S, not 100S?
The axoneme has nine peripheral doublets and a central pair, the 9+2 array. That is 9 × 2 + 2 = 20 microtubules.
A centriole has nine peripheral triplets in a cartwheel arrangement and no central pair: 9 × 3 = 27 microtubules.
S stands for Svedberg unit, a sedimentation coefficient. NCERT calls it an indirect measure of density and size. Sedimentation coefficients do not add, so 60S + 40S gives an 80S ribosome, and 50S + 30S gives 70S.
Common mistakes and how to avoid them
Calling ribosomes membrane-bound. They have no membrane, and neither do centrioles.
Putting mitochondria in the endomembrane system. They are excluded, along with chloroplasts and peroxisomes.
Mixing up cis and trans faces. Cis is the forming, receiving face; trans is the maturing, shipping face.
Forgetting the exception. Mycoplasma is the prokaryote without a cell wall.
A revision routine for this chapter
Make one comparison sheet with every organelle against the three questions above.
Draw a plant cell and an animal cell from memory, labelled, then check against NCERT's figure. In seven experiments, Wammes, Meade and Fernandes (2016) found that people recalled words they had drawn better than words they had written out. Our guide to learning NCERT biology diagrams shows how to practise labelling.
After a few days, answer ten comparison questions without your sheet. Mark which comparisons you missed.
Move on to the cell cycle, mitosis and meiosis, which builds on the nucleus and centrioles.
When a structure is hard to picture from a flat diagram, such as how cristae fold, the Fermi Concept Library has every concept in biology with its own lesson, so you can see it explained before you return to the book.
Today, fill in the three-question comparison sheet for ten organelles without opening NCERT, then check every row.
