Cell: The Unit of Life — Revision Notes

⚡ 30-Second Revision

Cell Theory: — All organisms are cells; cell is basic unit; cells from pre-existing cells.
Prokaryotes: — No true nucleus, no membrane-bound organelles, 70S ribosomes, circular DNA, binary fission. E.g., Bacteria.
Eukaryotes: — True nucleus, membrane-bound organelles, 80S ribosomes (cytoplasm), linear DNA, mitosis/meiosis. E.g., Plants, Animals.
Plasma Membrane: — Fluid Mosaic Model (phospholipid bilayer + proteins), selectively permeable.
Cell Wall: — Plants (cellulose), Fungi (chitin), Bacteria (peptidoglycan). Provides support & protection.
Nucleus: — Contains DNA (chromosomes), nuclear envelope with pores. Nucleolus for rRNA synthesis.
Mitochondria: — 'Powerhouse', cellular respiration, ATP synthesis. Double membrane, own DNA (70S ribosomes).
Chloroplasts: — Photosynthesis (plants/algae). Double membrane, own DNA (70S ribosomes).
ER: — RER (ribosomes, protein synthesis/modification), SER (lipid synthesis, detoxification).
Golgi: — Modifies, sorts, packages proteins/lipids.
Ribosomes: — Protein synthesis (70S in prokaryotes/organelles; 80S in eukaryotic cytoplasm).
Lysosomes: — 'Suicidal bags', digestive enzymes.
Vacuoles: — Storage, turgor (large central in plants).
Cytoskeleton: — Microtubules, microfilaments, intermediate filaments. Shape, movement, transport.

2-Minute Revision

The cell is the fundamental unit of life, a concept formalized by the Cell Theory (Schleiden, Schwann, Virchow). Cells are broadly categorized into prokaryotic and eukaryotic. Prokaryotes (like bacteria) are simpler, lacking a true nucleus and membrane-bound organelles, with their genetic material in a nucleoid.

Eukaryotes (plants, animals, fungi) are complex, possessing a true nucleus and specialized membrane-bound organelles. Key eukaryotic organelles include the plasma membrane (a selectively permeable phospholipid bilayer with embedded proteins, described by the Fluid Mosaic Model), the nucleus (housing DNA and controlling cell activities, with the nucleolus synthesizing rRNA), and the cytoplasm (where many metabolic reactions occur).

Energy production occurs in mitochondria (cellular respiration) and chloroplasts (photosynthesis in plants), both of which have their own DNA and ribosomes, supporting the Endosymbiotic Theory. The Endoplasmic Reticulum (ER) comes in two forms: Rough ER (protein synthesis with ribosomes) and Smooth ER (lipid synthesis, detoxification).

The Golgi apparatus modifies, sorts, and packages these products. Lysosomes act as the cell's digestive system, while vacuoles handle storage and maintain turgor. Ribosomes, found in both cell types, are the sites of protein synthesis.

Understanding these structures and their functions is crucial for NEET.

5-Minute Revision

Let's quickly recap the 'Cell: The Unit of Life' – a cornerstone of biology. Remember, the cell is the basic structural and functional unit of all living organisms, a principle established by the Cell Theory (Schleiden, Schwann, Virchow). This theory states that all life is cellular, and all cells arise from pre-existing cells.

We classify cells into two main types: Prokaryotic and Eukaryotic. Prokaryotes (e.g., bacteria) are simpler; they lack a true nucleus (DNA is in a nucleoid) and membrane-bound organelles. They have 70S ribosomes, a cell wall (peptidoglycan), and a plasma membrane. Eukaryotes (e.g., plants, animals) are more complex, featuring a true nucleus (DNA enclosed in a nuclear envelope) and numerous membrane-bound organelles, along with 80S ribosomes in the cytoplasm.

Key eukaryotic organelles and their functions:

Plasma Membrane: — The outer boundary, a selectively permeable phospholipid bilayer with embedded proteins (Fluid Mosaic Model). Controls substance movement.
Cell Wall (plants/fungi): — Rigid outer layer for support and protection. Cellulose in plants, chitin in fungi.
Cytoplasm: — Jelly-like substance, site of many metabolic reactions.
Nucleus: — Contains genetic material (DNA in chromosomes), controls cell. Nucleolus inside synthesizes rRNA and assembles ribosomes.
Endoplasmic Reticulum (ER): — Network of membranes. Rough ER (RER) has ribosomes, synthesizes/modifies proteins. Smooth ER (SER) lacks ribosomes, synthesizes lipids, detoxifies drugs.
Golgi Apparatus: — Modifies, sorts, and packages proteins and lipids from ER for secretion or delivery.
Mitochondria: — 'Powerhouses' – site of cellular respiration, ATP production. Double-membraned, contain their own circular DNA and 70S ribosomes (evidence for Endosymbiotic Theory).
Chloroplasts (plants/algae): — Site of photosynthesis. Double-membraned, contain their own circular DNA and 70S ribosomes (also Endosymbiotic Theory).
Ribosomes: — Non-membrane-bound, synthesize proteins. 70S in prokaryotes/organelles, 80S in eukaryotic cytoplasm.
Lysosomes: — 'Suicidal bags' – contain digestive enzymes for waste breakdown and cellular recycling.
Vacuoles: — Storage sacs. Large central vacuole in plants maintains turgor pressure.
Cytoskeleton: — Network of protein filaments (microtubules, microfilaments, intermediate filaments) providing shape, support, and aiding movement.
Centrosome (animals): — Organizes microtubules, involved in cell division.

Remember to compare and contrast prokaryotic vs. eukaryotic, and plant vs. animal cells. Focus on the 'why' behind each structure's function. For instance, why do muscle cells have many mitochondria? Because they need a lot of ATP for contraction. This chapter is foundational for almost all other biology topics, so a solid grasp is indispensable.

Prelims Revision Notes

Cell: The Unit of Life - NEET Revision Notes

I. Cell Theory:

Robert Hooke (1665): — First observed 'cells' in cork.
Anton von Leeuwenhoek: — First saw living cells (bacteria, protozoa).
Schleiden (1838): — All plants made of cells.
Schwann (1839): — All animals made of cells; cell is basic unit.
Virchow (1855): — 'Omnis cellula e cellula' (all cells arise from pre-existing cells).
Modern Cell Theory: — 1. All organisms composed of cells. 2. Cell is basic unit of life. 3. All cells from pre-existing cells.

II. Types of Cells:

Prokaryotic Cells (e.g., Bacteria, Archaea):

* No true nucleus (DNA in nucleoid). * No membrane-bound organelles. * 70S ribosomes. * Single, circular DNA (no histones). * Cell wall (peptidoglycan in bacteria). * Plasma membrane, cytoplasm, mesosomes (respiration). * Reproduction: Binary fission.

Eukaryotic Cells (e.g., Plants, Animals, Fungi, Protists):

* True nucleus (DNA in nuclear envelope). * Membrane-bound organelles present. * 80S ribosomes (cytoplasm), 70S in mitochondria/chloroplasts. * Multiple, linear DNA (with histones). * Cell wall (cellulose in plants, chitin in fungi); absent in animals. * Reproduction: Mitosis/Meiosis.

III. Eukaryotic Cell Organelles & Functions:

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Plasma Membrane:

* Fluid Mosaic Model (Singer & Nicolson). * Phospholipid bilayer, integral & peripheral proteins, cholesterol. * Selectively permeable, cell recognition, transport.

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Cell Wall (Plants): — Cellulose. Provides structural support, protection, prevents bursting.
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Cytoplasm: — Cytosol + organelles. Site of glycolysis, many metabolic reactions.
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Nucleus:

* Nuclear Envelope: Double membrane with nuclear pores. * Nucleoplasm: Contains chromatin (DNA + histones). * Nucleolus: Non-membrane-bound, site of rRNA synthesis & ribosome assembly.

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Endoplasmic Reticulum (ER): — Network of cisternae, tubules.

* Rough ER (RER): Ribosomes present. Protein synthesis, folding, modification (for secretion/membranes). * Smooth ER (SER): No ribosomes. Lipid synthesis (steroids), detoxification, Ca2+ storage.

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Ribosomes: — Non-membrane-bound. Protein synthesis (translation).

* 70S (prokaryotes, mitochondria, chloroplasts). * 80S (eukaryotic cytoplasm, RER).

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Golgi Apparatus (Golgi complex): — Stack of cisternae.

* Modifies, sorts, packages proteins/lipids from ER. * Forms lysosomes, secretory vesicles.

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Lysosomes: — 'Suicidal bags'. Contain hydrolytic enzymes (acid hydrolases). Digestion, autophagy.
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Vacuoles: — Membrane-bound sacs.

* Plant cells: Large central vacuole (tonoplast membrane). Stores water, nutrients, waste; maintains turgor. * Animal cells: Smaller, temporary.

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Mitochondria: — 'Powerhouse'. Double membrane (outer smooth, inner folded into cristae).

* Site of aerobic respiration, ATP synthesis. * Own circular DNA, 70S ribosomes (Endosymbiotic Theory).

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Chloroplasts (Plants/Algae): — Site of photosynthesis. Double membrane (stroma, thylakoids, grana).

* Own circular DNA, 70S ribosomes (Endosymbiotic Theory).

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Cytoskeleton: — Network of protein filaments.

* Microtubules (tubulin): Cell shape, cilia/flagella, spindle fibers. * Microfilaments (actin): Muscle contraction, amoeboid movement. * Intermediate filaments: Structural support.

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Centrosome (Animal cells): — Two centrioles (9+0 arrangement). Microtubule organizing center, forms spindle fibers.
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Cilia & Flagella: — Hair-like outgrowths. Locomotion, movement of substances. (9+2 arrangement of microtubules).

IV. Plant vs. Animal Cell Differences:

Plant: — Cell wall, chloroplasts, large central vacuole, plasmodesmata, no centrioles.
Animal: — No cell wall, no chloroplasts, small/no vacuoles, centrioles present, various cell junctions.

Vyyuha Quick Recall

Can People Not Eat Really Good Large Mangoes Very Carefully?

Cell Wall (Plants)
Plasma Membrane
Nucleus
Endoplasmic Reticulum (RER & SER)
Ribosomes
Golgi Apparatus
Lysosomes
Mitochondria
Vacuoles
Chloroplasts (Plants)

This mnemonic helps recall the major organelles and structures of a eukaryotic cell, especially useful for remembering the components to describe or compare.