Cell: The Unit of Life - Summary Notes

Cells are the basic structural and functional units of all living organisms.
Unicellular organisms can exist independently and perform essential life functions.
Antonie Von Leeuwenhoek first observed live cells; Robert Brown discovered the nucleus.

Schleiden and Schwann proposed that all living organisms are composed of cells and their products.
Rudolf Virchow added that all cells arise from pre-existing cells (Omnis cellula-e cellula).
Modern cell theory states:
- All living organisms are composed of cells and their products.
- All cells arise from pre-existing cells.

Cells have a plasma membrane, cytoplasm, and genetic material (DNA).
Eukaryotic cells have membrane-bound nuclei; prokaryotic cells do not.
Cytoplasm contains organelles and is the site of cellular activities.
Ribosomes are present in all cells; animal cells have centrosomes for cell division.
Cell size and shape vary.

Include bacteria, blue-green algae, mycoplasma, and PPLO.
Smaller and multiply faster than eukaryotic cells.
Lack a well-defined nucleus and membrane-bound organelles (except ribosomes).
Genetic material is naked (not enclosed by a nuclear membrane); may contain plasmids.
Cell envelope includes glycocalyx, cell wall, and plasma membrane.
Gram-positive bacteria retain Gram stain; Gram-negative do not.
Motile bacteria have flagella composed of filament, hook, and basal body.
Pili and fimbriae are surface structures for attachment.
Inclusion bodies store reserve materials.

Include protists, plants, animals, and fungi.
Have compartmentalized cytoplasm with membrane-bound organelles.
Possess an organized nucleus with a nuclear envelope.
Plant cells have cell walls, plastids, and a large central vacuole (absent in animal cells).
Animal cells have centrioles (absent in most plant cells).

Composed mainly of lipids (phospholipids and cholesterol) and proteins.
Lipids arranged in a bilayer with polar heads outward and hydrophobic tails inward.
Proteins can be integral (buried) or peripheral (on the surface).
Fluid mosaic model describes the membrane's quasi-fluid nature, allowing lateral movement of proteins.
Selectively permeable; transports molecules via passive (simple diffusion, osmosis) or active transport (requires energy, e.g., Na^+/K^+ pump).

A non-living, rigid outer covering in fungi and plants.
Provides shape, protection, and cell-to-cell interaction.
Composed of cellulose, hemicellulose, pectins, and proteins (plant cells); may contain calcium carbonate (algae).
Middle lamella (calcium pectate) glues neighboring cells together.
Plasmodesmata connect the cytoplasm of neighboring cells.

Coordinates functions of endoplasmic reticulum (ER), Golgi complex, lysosomes, and vacuoles.
Endoplasmic Reticulum (ER): Network of tubular structures in the cytoplasm; divides into luminal and extra-luminal compartments.
- Rough ER (RER) has ribosomes for protein synthesis.
- Smooth ER (SER) synthesizes lipids and steroidal hormones.
Golgi Apparatus: Packages and delivers materials; modifies proteins and forms glycoproteins and glycolipids.
Lysosomes: Vesicular structures with hydrolytic enzymes for digesting cellular materials.
Vacuoles: Membrane-bound spaces for storage, excretion, and osmoregulation.

Double membrane-bound organelles; sites of aerobic respiration and ATP production (“powerhouses” of the cell).
Inner membrane forms cristae to increase surface area.
Contain their own DNA, RNA, ribosomes (70S), and divide by fission.

Found in plant cells and euglenoids; contain pigments.
- Chloroplasts: Chlorophyll and carotenoids for photosynthesis.
- Chromoplasts: Fat-soluble carotenoids (carotene, xanthophylls) for yellow, orange, or red color.
- Leucoplasts: Colourless; store nutrients (amyloplasts for starch, elaioplasts for oils/fats, aleuroplasts for proteins).
Chloroplasts are double membrane-bound; inner membrane encloses stroma with thylakoids arranged in grana.
Contain enzymes for carbohydrate and protein synthesis, DNA, and ribosomes (70S).

Granular structures composed of RNA and proteins; not membrane-bound.
Eukaryotic ribosomes are 80S (60S and 40S subunits); prokaryotic ribosomes are 70S (50S and 30S subunits).
Site of protein synthesis.

Network of filamentous proteinaceous structures (microtubules, microfilaments, intermediate filaments) in the cytoplasm.
Provides mechanical support, motility, and maintains cell shape.

Centrosome contains two centrioles surrounded by pericentriolar material.
Centrioles are cylindrical structures made of nine triplet fibrils of tubulin.
Form basal bodies of cilia/flagella and spindle fibers during cell division (animal cells).

Contains chromatin (DNA, histones, non-histone proteins, RNA), nuclear matrix, and nucleoli.
Nuclear envelope: Double membrane with perinuclear space.
Chromosomes: Condensed chromatin visible during cell division; contain a centromere and kinetochores.
Classified based on centromere position: metacentric, sub-metacentric, acrocentric, telocentric.

Membrane-bound vesicles containing various enzymes; present in plant and animal cells.