# Cell: The Unit of Life Notes, Class 11 Biology | SwaVid Cell: The Unit of Life, NCERT Class 11 Biology: notes with key ideas, key terms, common mistakes and 3 quick checks with worked answers. Canonical: https://www.swavid.com/cbse/class-11/biology/chapter/cell-the-unit-of-life Source: https://www.swavid.com/cbse/class-11/biology/chapter/cell-the-unit-of-life # Cell: The Unit of Life ## Key terms ## Key ideas ## Common mistakes ## Quick checks ## Keep going ## Questions parents ask ## Class 11 Biology on SwaVid ### Cell theory ### Prokaryotic cells ### Cell membrane structure ### Endomembrane system ### Semiautonomous organelles ### Cytoskeleton, cilia, and flagella ### Nucleus and chromosomes ### Next chapter ### Related chapter ### All chapters SwaVid › CBSE › Class 11 › Biology › Cell: The Unit of Life Notes written by SwaVid from the NCERT textbook. Class 11 Biology, Chapter 8. Key ideas, formulas and common mistakes. CBSE prints 15 marks for Unit III, not for this chapter alone. Short answer. This chapter describes the cell as the basic structural and functional unit of all living organisms. It explains the differences between prokaryotic and eukaryotic cells, their detailed internal structures, and the functions of various cell organelles. Source: NCERT Biology (Reprint 2026-27) , Chapter 8, Cell: The Unit of Life Anton van Leeuwenhoek first observed live cells, and Robert Brown discovered the nucleus. Schleiden and Schwann formulated the initial cell theory, which was modified by Rudolf Virchow to state that all living organisms are composed of cells and products of cells, and all cells arise from pre-existing cells (Omnis cellula-e cellula). Prokaryotic cells include bacteria, blue-green algae, mycoplasmas, and PPLO. They lack a membrane-bound nucleus and organelles, possessing a specialised differentiated cell envelope, a nucleoid, plasmids, and specialised surface structures like flagella, pili, and fimbriae. The fluid mosaic model proposed by Singer and Nicolson in 1972 describes the cell membrane as a phospholipid bilayer with embedded integral and peripheral proteins. Lipids provide quasi-fluidity, allowing lateral movement of proteins within the bilayer. The endomembrane system includes the endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles because their functions are coordinated. Chloroplasts, mitochondria, and peroxisomes are not part of this system as their activities are not coordinated with these organelles. Mitochondria and chloroplasts are double-membrane-bound organelles containing their own circular DNA, RNA molecules, and 70S ribosomes. Mitochondria are the sites of aerobic respiration producing ATP, while chloroplasts carry out photosynthesis in plant cells. The cytoskeleton consists of microtubules, microfilaments, and intermediate filaments providing mechanical support and shape. Cilia and flagella have an axoneme showing a 9 + 2 array of microtubules, while the centrosome contains two centrioles displaying a 9 + 0 organization. The nucleus is enclosed by a double-layered envelope with nuclear pores and contains chromatin and nucleoli. During cell division, chromatin condenses into chromosomes, classified into metacentric, sub-metacentric, acrocentric, or telocentric based on the position of the centromere. Try each question first. Then tap it to see the answer. Organelles are grouped into the endomembrane system if their functions are coordinated. The functions of mitochondria and chloroplasts are not coordinated with the ER, Golgi apparatus, lysosomes, or vacuoles. Therefore, they function independently of the endomembrane network. Their functions are not coordinated with the other components of the endomembrane system Eukaryotic cytoplasm contains 80S ribosomes composed of 60S and 40S subunits. Mitochondria and chloroplasts possess their own specific protein synthesis machinery. The ribosomes found inside these organelles are smaller and are of the 70S type. 70S ribosomes Metacentric chromosomes have equal arms with a median centromere. Sub-metacentric chromosomes have slightly unequal arms. Acrocentric chromosomes have the centromere situated very close to one end, producing one extremely short arm and one very long arm. Acrocentric chromosome Biomolecules . Cell Cycle and Cell Division . The 19 chapters of Class 11 Biology . CBSE does not give marks to one chapter. It prints 15 marks for Unit III, Cell: Structure and Function, which includes Cell: The Unit of Life. No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed. Biomolecules. SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works. - Ch 8 NCERT book - 15 marks, Unit III - 3 quick checks - Adding subunits directly to obtain total ribosome sedimentation coefficient (e.g., 50S + 30S = 80S) . S stands for Svedberg unit, which is indirectly a measure of density and size rather than simple mass. Remember that 50S + 30S gives 70S, and 60S + 40S gives 80S. - Including mitochondria and chloroplasts in the endomembrane system . Only include organelles whose functions are coordinated with each other (ER, Golgi body, lysosomes, and vacuoles). Mitochondria and chloroplasts are not part of the endomembrane system. - Confusing the 9 + 2 arrangement of cilia with the 9 + 0 arrangement of centrioles . Cilia and eukaryotic flagella contain peripheral doublets and central singlets (9 + 2 array). Centrioles and basal bodies have peripheral triplets and no central microtubules (9 + 0 array). - Believing prokaryotes have 80S ribosomes in their cytoplasm . Prokaryotes contain only 70S ribosomes. Eukaryotes have 80S ribosomes in the cytoplasm, but their mitochondria and plastids contain 70S ribosomes. ## Key Links - [CBSE](https://www.swavid.com/cbse) - [Class 11](https://www.swavid.com/cbse/class-11) - [Biology](https://www.swavid.com/cbse/class-11/biology/chapters) - [Start free →](https://www.swavid.com/signup) - [All 19 chapters](https://www.swavid.com/cbse/class-11/biology/chapters) - [NCERT Biology (Reprint 2026-27)](https://ncert.nic.in/textbook.php) - [Open notes](https://www.swavid.com/cbse/class-11/biology/chapter/biomolecules) - [Open notes](https://www.swavid.com/cbse/class-11/biology/chapter/cell-cycle-and-cell-division) - [Class 11 Biology](https://www.swavid.com/cbse/class-11/biology/chapters) - [Start free →](https://www.swavid.com/signup)