Building Directory
Cell & Co. HQ🏢 About Cell & Co.
Cell & Co. is a fully self-contained corporate headquarters operating 24/7. Every department is essential, every role is specialised, and absolutely nothing happens by accident. The building has two versions — Animal Cell HQ and Plant Cell HQ (ground floor has extra features). Click any floor to meet the team.
🧬 The CEO (Nucleus)
Contains all the DNA — the company's complete instruction manual. Controls which proteins get made and when. Nothing happens without its approval.
📋 The Reception Desk (Nuclear Membrane)
Double-layered envelope with nuclear pores — controls what enters and exits the nucleus. mRNA leaves here to deliver instructions to the factory floor.
📁 The Filing Room (Chromatin/Chromosomes)
DNA wound around histone proteins — loosely stored as chromatin when the cell is resting, condensed into chromosomes during division.
🖨️ The Copy Room (Nucleolus)
Produces ribosomal RNA (rRNA). Assembles the components of ribosomes before shipping them out to the cytoplasm for use.
🔋 Energy Production
Site of aerobic cellular respiration. Converts glucose + oxygen into ATP (adenosine triphosphate) — the cell's usable energy currency.
🌀 The Inner Folds (Cristae)
Folded inner membrane — increases surface area for ATP production. More folds = more energy output. Highly active cells (muscle, liver) have more cristae.
💧 The Inner Fluid (Matrix)
Contains enzymes for the Krebs cycle, mitochondrial DNA, and ribosomes. Yes — mitochondria have their own DNA. This supports the endosymbiotic theory.
🏠 Double Membrane
Outer membrane is smooth. Inner membrane is folded (cristae). The intermembrane space between them is critical for the electron transport chain.
⚙️ What They Do
Translate mRNA instructions into proteins. Every protein in the cell — structural, enzymatic, hormonal — is built here. The most abundant organelle in active cells.
📍 Where They Work
Found free in cytoplasm (making proteins for internal use) or attached to rough ER (making proteins for export or membranes). Not membrane-bound.
🔩 Their Structure
Made of rRNA + protein. Two subunits — large and small. No membrane surrounding them — making them the only organelle that isn't membrane-bound.
📦 The Assembly Line
Read mRNA codon by codon. Match each codon to a tRNA carrying the correct amino acid. Chain the amino acids — protein complete. Efficient and non-stop.
🪨 Rough ER
Studded with ribosomes — hence "rough". Modifies and transports proteins made by ribosomes. Packages them into vesicles for delivery to the Golgi apparatus.
🌊 Smooth ER
No ribosomes. Synthesises lipids and steroid hormones. Detoxifies drugs and poisons in liver cells. Also stores calcium ions in muscle cells.
📬 The Delivery Vesicles
Proteins are packaged into membrane-bound vesicles that bud off the ER and travel to the Golgi apparatus for further processing and export.
🔗 Connected to Nuclear Membrane
The ER is continuous with the outer nuclear membrane — forming an interconnected network through the cytoplasm for internal transport.
📥 Receiving (Cis Face)
Receives vesicles from the ER containing proteins and lipids. The cis face (entry side) faces the ER. Cargo is accepted and processing begins.
✏️ Processing (Cisternae)
Stack of flattened membrane sacs (cisternae). Modifies proteins — adds carbohydrate chains (glycoproteins), lipids (lipoproteins), and sorts them by destination.
📤 Dispatch (Trans Face)
The trans face (exit side) buds off vesicles labelled for specific destinations — cell membrane, lysosomes, or secretion outside the cell.
🏷️ Makes Lysosomes
Packages digestive enzymes into lysosomes — the cell's waste management units. Without the Golgi, lysosomes couldn't form and cellular waste would accumulate.
🧪 Digestive Enzymes
Contain hydrolytic enzymes that work best at pH 4.5–5 (acidic). Break down old organelles, foreign particles, and cellular debris. Found only in animal cells.
♻️ Autophagy
Can digest the cell's own worn-out organelles — a process called autophagy ("self-eating"). Recycles components back into the cytoplasm for reuse.
🛡️ Defence
In white blood cells, lysosomes destroy bacteria and viruses that have been engulfed by phagocytosis. Front-line defenders of the cellular immune response.
⚠️ When They Burst
If a lysosome ruptures, its enzymes digest the cell from the inside — contributing to programmed cell death (apoptosis). They are carefully membrane-bound for this reason.
☀️ Photosynthesis
Site of photosynthesis — converts CO₂ + H₂O + light energy into glucose + O₂. The only organelle that can capture light energy and convert it to chemical energy.
🥞 Grana (Thylakoids)
Stacks of membrane sacs (thylakoids) called grana. Contain chlorophyll — the green pigment that absorbs light. Light reactions happen here.
🧃 Stroma
The fluid surrounding the grana. Contains enzymes for the Calvin cycle (dark reactions / light-independent reactions). CO₂ is fixed into glucose here.
🧬 Own DNA + Ribosomes
Like mitochondria, chloroplasts have their own DNA and ribosomes. Further evidence for endosymbiotic theory — once free-living cyanobacteria.
💧 Turgor Pressure
Filled with cell sap (water + dissolved substances). Pushes against the cell wall — creating turgor pressure that keeps plant cells rigid. Lose water = cell wilts.
🗃️ Storage
Stores water, ions, nutrients, pigments (anthocyanins — red/purple colours in flowers), and waste products. Acts as the cell's long-term storage unit.
🧹 Cleanup Crew
Contains hydrolytic enzymes in plant cells — performs some lysosome-like functions. Breaks down waste materials and recycles cell components.
📏 Size Matters
Plant cells have ONE large central vacuole. Animal cells have several small, temporary vacuoles used for food digestion or water balance — not permanent structures.
🌾 Cellulose Structure
Made of cellulose microfibrils — tough, rigid polysaccharide. Provides structural support and shape. Prevents cells from bursting when turgor pressure is high.
🚪 Fully Permeable
Unlike the cell membrane, the cell wall is fully permeable — it does NOT control what enters or exits. The cell membrane just inside it handles all selective transport.
🔗 Plasmodesmata
Tiny channels through the cell wall connecting adjacent plant cells. Allow direct cytoplasm-to-cytoplasm communication and transport between cells.
🚫 Animal Cells
Animal cells have NO cell wall — only a flexible cell membrane. This is why animal cells can change shape, form pseudopods, and undergo phagocytosis.
Plant vs Animal Cell
The Key DifferencesThis comparison comes up in virtually every Grade 11 exam. Know it cold.
| Feature | 🐾 Animal Cell | 🌿 Plant Cell |
|---|---|---|
| Cell wall | ✗ Absent | ✓ Present — cellulose |
| Cell membrane | ✓ Present | ✓ Present (inside wall) |
| Chloroplasts | ✗ Absent | ✓ Present — photosynthesis |
| Central vacuole | ✗ Small, temporary | ✓ Large, permanent |
| Lysosomes | ✓ Present | ✗ Vacuole performs similar role |
| Centrioles | ✓ Present — cell division | ✗ Absent in most plant cells |
| Nucleus | ✓ Present | ✓ Present (often pushed to side) |
| Mitochondria | ✓ Present | ✓ Present |
| Ribosomes | ✓ Present | ✓ Present |
| Golgi apparatus | ✓ Present | ✓ Present |
| ER (rough + smooth) | ✓ Present | ✓ Present |
| Shape | Irregular, flexible | Regular, fixed (cell wall) |
| Starch storage | ✗ Stores glycogen | ✓ Stores starch in plastids |
💡 The 3 things plant cells have that animal cells don't
Memory Hooks
Stick It in Your BrainThese are the connections and mnemonics that make the organelles impossible to forget.
The Secretory Pathway — "Ribosomes → Rough ER → Golgi → Out"
Think of it as writing and posting a letter: the ribosome writes the letter (makes the protein), the rough ER puts it in an envelope, the Golgi adds the address label and stamps it, and the secretory vesicle delivers it. This sequence is non-negotiable in your exam answers.
More mitochondria = harder working cell
Muscle cells, liver cells, and sperm cells have the most mitochondria — and the most cristae per mitochondrion. When an exam shows you a diagram of a very active cell, look for more mitochondria. When it shows highly folded cristae, think: maximum ATP output needed.
"Rough = Ribosomes = pRotein. Smooth = no Ribosomes = lipidS"
The capital letters: Rough = Ribosomes = pRotein processing. Smooth = no ribosomes = lipid Synthesis. Say it three times. Never forget it.
Plant cells: "Wall, Chloro, Vac" — the 3 extras
Every time you see "plant cell" in an exam — think Wall (cell wall), Chloro (chloroplasts), Vac (large central vacuole). These are the three structures plants have that animal cells don't. Three words. Three marks.
Nucleus: "Double door with a security guard"
The nuclear envelope is double-layered (two membranes) with nuclear pores acting as security — only certain molecules (like mRNA) can pass through. The nucleolus inside makes ribosomes. Picture a government building: the DNA is the classified files inside, and nothing gets in or out without being checked.
Lysosomes: "The building's controlled demolition team"
Lysosomes contain 40+ digestive enzymes at pH 4.5 — acidic enough to dissolve cellular debris. They're membrane-bound for good reason: if they burst, they digest the cell. This is actually used in programmed cell death (apoptosis). Animal cells only — plant cells use their vacuole instead.
Mitochondria + Chloroplasts both have own DNA — endosymbiotic theory
Both mitochondria and chloroplasts have their own circular DNA and ribosomes, divide by binary fission, and have double membranes. This is the evidence for the endosymbiotic theory — they were once free-living prokaryotes engulfed by a larger cell. IEB loves asking you to list this evidence.
🎯 Cell & Co. Staff Assessment
Prove you know who does what in the building.