Click any organelle to learn its function · Compare cell types
BIO 111 — Chapter 3
The cell is the basic unit of life — but not all cells are created equal. Prokaryotes had a billion-year head start on eukaryotes, and plant cells built a wall.
👆 Click any organelle
Tap or click any part of the cell above to learn what it does, why it matters, and how to remember it.
All labeled structures are clickable
👆 Click any organelle
Tap or click any part of the plant cell above to learn what it does.
Plant cells have 3 things animal cells don't: cell wall, chloroplasts, large central vacuole
👆 Click any structure
Prokaryotes are simpler than eukaryotes — no membrane-bound nucleus, no organelles. But they ruled Earth for over 2 billion years before eukaryotes evolved.
Key difference from eukaryotes: no membrane-bound nucleus or organelles
The two biggest comparisons in cell biology — know both cold for exams.
Prokaryote vs. Eukaryote
Prokaryote
Bacteria, Archaea — appeared ~3.5 billion years ago
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Nucleus: No membrane-bound nucleus — DNA floats in nucleoid region
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Organelles: No membrane-bound organelles
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Ribosomes: Yes — 70S (smaller)
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Cell wall: Usually yes — peptidoglycan in bacteria
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DNA: Circular, often with plasmids
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Size: 1–10 μm — much smaller
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Flagella: Sometimes — simpler structure
Eukaryote
Animals, Plants, Fungi, Protists — appeared ~1.5–2 billion years ago
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Nucleus: Yes — membrane-bound, contains DNA
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Organelles: Yes — mitochondria, ER, Golgi, etc.
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Ribosomes: Yes — 80S (larger)
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Cell wall: Plants/fungi yes, animals no
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DNA: Linear chromosomes, no plasmids
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Size: 10–100 μm — much larger
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Flagella: Sometimes — complex (9+2) structure
Plant vs. Animal Cell
Plant cell
Has three structures animal cells don't
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Cell wall: Yes — cellulose, rigid structure
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Chloroplasts: Yes — photosynthesis
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Central vacuole: Yes — large, takes up 90% of cell
ChloroplastSite of photosynthesis. Contains chlorophyll. Has its own DNA.
Central vacuoleGiant water-filled sac. Maintains turgor pressure. Stores waste.
Cell theory wasn't discovered by one person — it took a chain of scientists over two centuries. Click each scientist to see their specific contribution.
The three tenets of Cell Theory
1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of life.
3. All cells arise from pre-existing cells (omnis cellula e cellula).
The endomembrane system is the cell's protein sorting and shipping network. ER = factory → Golgi = post office → vesicles = delivery trucks → plasma membrane = destination.
Interactive pathway — click each station
Click any step in the pathway above to learn what happens there
The cytoskeleton is a dynamic network of protein fibers — the cell's skeleton, muscle, and highway all in one. And the endosymbiotic theory explains why your mitochondria have their own DNA.
Cytoskeleton components — click to explore
Cilia vs Flagella
Cilia
Short and numerous · Wave-like motion · Move substances past the cell · Examples: mucus in respiratory tract, egg toward uterus in fallopian tubes · 9+2 microtubule arrangement
Flagella
Long and few (1–2) · Whip-like motion · Propel the cell itself · Examples: sperm, some protists · 9+2 in eukaryotes · Prokaryotic flagella rotate like a propeller (simpler structure)
Endosymbiotic Theory
Ancient prokaryote
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Engulfs smaller bacteria
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Symbiosis, not digestion
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Modern eukaryote
Lynn Margulis (1967) proposed that mitochondria and chloroplasts were once free-living prokaryotes engulfed by a larger cell. Instead of being digested, they formed a mutually beneficial (symbiotic) relationship. The host provided shelter; the engulfed bacteria provided energy (mitochondria) or food via photosynthesis (chloroplasts).