Interactive Learning Experience

Cell Biology

Explore the building blocks of life through interactive simulations, animated diagrams, and hands-on experiments. From prokaryotes to photosynthesis, discover how cells work.

8 Interactive Modules
6 Live Simulations
20 Quiz Questions
Start Exploring
Module 1

Prokaryotic vs Eukaryotic Cells

Life on Earth is built from two fundamentally different cell architectures. Prokaryotes (Bacteria, Archaea) appeared 3.5 billion years ago. Eukaryotes emerged ~2 billion years ago through endosymbiosis.

Prokaryotic Cell

  • No true nucleus - DNA in nucleoid region
  • Size: ~1 micrometer
  • Circular DNA molecule + plasmids
  • Cell wall, cytoplasmic membrane, ribosomes
  • May have capsule, fimbriae, flagellum
  • 3 domains: Bacteria, Archaea

Eukaryotic Cell

  • True nucleus with double membrane + pores
  • Size: 10-100 micrometers
  • Linear DNA molecules with histones = chromatin
  • Numerous membrane-bound organelles
  • Largest: ostrich egg yolk (~8 cm diameter)
  • Longest: whale neurons (up to 30 m)

Endosymbiotic Theory

  • Proposed by Lynn Margulis
  • Mitochondria arose from bacteria (~2 BYA)
  • Chloroplasts arose from cyanobacteria (~1 BYA)
  • Evidence: own DNA, double membranes, independent division
  • These organelles function semi-autonomously
Module 2

Cytoplasmic Membrane

The cytoplasmic membrane is found on the surface of all cell types. It consists of a phospholipid bilayer with embedded proteins and sterols. It is semi-permeable, controlling what enters and exits the cell.

Phospholipids

  • Foundation of the membrane
  • 2 fatty acid chains (hydrophobic tails)
  • Glycerol + phosphate group (hydrophilic head)
  • Form a bilayer spontaneously in water

Membrane Proteins

  • Transmembrane: span entire membrane, act as channels/pumps
  • Active transport: uses ATP energy (e.g., Na-K pump)
  • Passive transport: channels using concentration gradient
  • Peripheral: receive signals from environment

Sterols (Cholesterol)

  • Inserted between phospholipids
  • Bind to fatty acids, limiting movement
  • Regulate membrane fluidity
  • Excess dietary cholesterol can deposit in blood vessel walls
Module 3

Osmosis & Membrane Transport

Water moves spontaneously across semi-permeable membranes toward higher solute concentration. This process - osmosis - determines whether cells swell, shrink, or maintain their shape.

Isotonic Solution

Equal solute concentration inside and outside the cell. Normal physiological state. Example: 0.9% NaCl solution (saline). Isotonic sport drinks.

Hypertonic Solution

Higher external solute concentration. Water leaves the cell. Animal cells shrivel (crenation/plasmorrhiza). Plant cells undergo plasmolysis - membrane pulls away from cell wall.

Hypotonic Solution

Lower external solute concentration. Water floods into the cell, increasing internal pressure (turgor). Animal cells may burst (plasmoptysis). Plant cells become turgid.

Module 4

Cell Organelles

Eukaryotic cells contain specialized compartments called organelles. Click on each organelle to learn about its structure and function.

Single-Membrane Organelles

  • Golgi apparatus: post-translational protein modification
  • Lysosomes: enzymatic digestion of ingested material
  • ER (smooth): cholesterol & phospholipid synthesis, Ca2+ storage
  • ER (rough): protein synthesis (ribosomes attached)
  • Vacuole: storage, turgor pressure, defense compounds

Semi-Autonomous Organelles

  • Mitochondria: ATP production, double membrane with cristae
  • Chloroplasts: photosynthesis, thylakoids contain chlorophyll
  • Both have their own DNA and divide independently
  • Evidence for endosymbiotic origin

Cell Wall

  • Plants: cellulose + hemicellulose + pectin + lignin
  • Fungi: chitin (same as arthropod exoskeletons)
  • Bacteria: peptidoglycan (Gram+ thick, Gram- thin + outer membrane)
  • Animal cells lack cell walls (have glycocalyx instead)
Module 5

Photosynthesis & Cellular Respiration

Life runs on energy transformations. Photosynthesis captures light energy into glucose. Cellular respiration breaks glucose down to release ATP. These two processes are complementary.

Photosynthesis 6CO2 + 6H2O + light energy → C6H12O6 + 6O2
Cellular Respiration C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP)

Photosynthesis

  • Location: chloroplast
  • Primary reactions: thylakoid membranes - photolysis of water, ATP production
  • Secondary reactions: stroma - Calvin cycle, CO2 fixation into glucose
  • Light spectrum: 400-700 nm (visible light)

Cellular Respiration

  • Location: mitochondria
  • Glycolysis: glucose → pyruvate → acetyl-CoA
  • Krebs cycle: oxidation releases electrons and H+ ions
  • Electron transport chain: produces most ATP

Fermentation

  • Anaerobic (without oxygen), occurs in cytoplasm
  • Alcoholic: glucose → ethanol + CO2 + energy
  • Lactic acid: glucose → lactic acid + energy
  • Used by bacteria, yeast, and in muscle cells
Module 6

Cytoskeleton

The cellular skeleton is a dynamic network of protein filaments that gives cells shape, enables movement, and organizes internal transport. Three types of filaments form this system.

Microtubules

  • Thickest filaments (~25 nm diameter)
  • Made of tubulin protein subunits forming hollow tubes
  • Form mitotic spindle for chromosome separation
  • Form flagella and cilia
  • Serve as tracks for organelle transport

Microfilaments (Actin)

  • Thinnest filaments (~7 nm)
  • Chains of globular actin protein
  • Network beneath membrane - enables phagocytosis
  • Most abundant in muscle cells
  • Power cell crawling and shape changes

Intermediate Filaments

  • Medium thickness (~10 nm), very stable
  • Most famous: keratins (in skin cells)
  • Form hair, nails, and other skin structures
  • Keratin is hydrophobic - water-repellent skin surface
  • Provide mechanical strength to cells
Test Your Knowledge

Cell Biology Quiz

Put your understanding to the test with these questions drawn directly from the course material.

Question 1 / 20