Cell Structure — BIO 111

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

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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

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Centrioles: No (most plants)

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Lysosomes: Rare — vacuole handles waste

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Shape: Regular, box-like (wall enforces shape)

Animal cell

Has two structures plant cells don't

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Cell wall: No — only cell membrane

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Chloroplasts: No — must eat for energy

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Central vacuole: No — small vacuoles only

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Centrioles: Yes — cell division

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Lysosomes: Yes — waste disposal

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Shape: Irregular, flexible

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Key vocabulary

Cell membrane

Phospholipid bilayer surrounding all cells. Controls what enters and exits. Selectively permeable.

Nucleus

Control center of the eukaryotic cell. Contains DNA. Surrounded by nuclear envelope with pores.

Mitochondria

Powerhouse of the cell. Makes ATP via cellular respiration. Has its own DNA — evidence of endosymbiosis.

Ribosome

Makes proteins. Found in all cells. 70S in prokaryotes, 80S in eukaryotes — this difference is why antibiotics can target bacteria without harming us.

Endoplasmic reticulum

Rough ER: protein synthesis (has ribosomes). Smooth ER: lipid synthesis and detox. Connected to nuclear envelope.

Golgi apparatus

The cell's post office. Receives proteins from rough ER, modifies them, packages and ships them.

Exam reminders

Plant cells have 3 extra structures: cell wall, chloroplasts, central vacuole. Animal cells have 2 extra: centrioles, lysosomes.

Prokaryotes have NO membrane-bound nucleus or organelles. They DO have ribosomes (70S), cell walls, and sometimes flagella.

Ribosome size matters: 70S = prokaryote, 80S = eukaryote. This is why antibiotics target 70S ribosomes — they don't affect our 80S ones.

Mitochondria and chloroplasts both have their own DNA. This supports the endosymbiotic theory — they were once free-living bacteria.

The nucleolus is inside the nucleus — it makes rRNA for ribosomes. Nucleus → nucleolus → ribosomes → proteins.

The 3 plant-only structures

Cell wall Rigid cellulose layer outside membrane. Gives shape, prevents bursting.

Chloroplast Site of photosynthesis. Contains chlorophyll. Has its own DNA.

Central vacuole Giant water-filled sac. Maintains turgor pressure. Stores waste.