Rotate the cell and click any structure — or use the buttons and colored legend on the right — to see its job. Each part of the cell handles a specialized task.
Think of an animal cell as a busy factory sealed inside a soft, water-filled bag. The bag is the cell membrane, and the watery space inside is the cytoplasm. A typical animal cell is only about $10$–$30\,\mu\mathrm{m}$ wide — far too small to see without a microscope — yet inside it dozens of little machines are all working at once. Each machine is an organelle ("little organ"), and just like the organs in your body, every organelle has one main job.
At the center sits the nucleus, the manager: it holds the cell's DNA and the instructions for every protein. Scattered around it are the mitochondria, the power plants that burn fuel to make ATP energy. A folded membrane network called the endoplasmic reticulum (ER) builds proteins (on its ribosome-studded rough region) and lipids (on its smooth region). The Golgi apparatus is the shipping department, and the lysosomes are the recycling crew. Click each one in the sim to meet it.
The big idea is compartmentalization: by wrapping jobs in separate membranes, one cell can run many chemical processes that would interfere with each other if mixed. A lysosome can stay acidic while the cytoplasm stays neutral; a mitochondrion can build a steep proton gradient; the nucleus can keep its DNA safe. Folded membranes also pack in enormous surface area — the ratio $\frac{\text{surface area}}{\text{volume}}$ is what lets a mitochondrion's cristae and the sprawling ER host so many reactions. The parts also form a pathway: nucleus → ribosome/rough ER → Golgi → vesicle → destination.
Rotate the cell and click the nucleus, then the rough ER and Golgi right next to it — that cluster is the cell's protein production line. Turn off "Cell membrane" to see the crowded interior, toggle "Labels" to test yourself, and use the dropdown to hunt down the smaller parts like the centrosome and peroxisome.
| Organelle | Main job | Membrane? |
|---|---|---|
| Cell membrane | Selectively controls what enters and leaves; the cell's boundary | Single bilayer |
| Nucleus | Stores DNA and directs protein synthesis (the control center) | Double (nuclear envelope) |
| Nucleolus | Makes ribosomal RNA and assembles ribosome subunits | None (region in nucleus) |
| Mitochondrion | Aerobic respiration → ATP energy; has its own DNA | Double (inner = cristae) |
| Rough ER | Synthesizes and folds proteins (ribosome-studded) | Single |
| Smooth ER | Makes lipids, stores calcium, detoxifies | Single |
| Golgi apparatus | Modifies, sorts, and ships proteins and lipids in vesicles | Single (stacked sacs) |
| Lysosome | Digests and recycles waste with acidic enzymes | Single |
| Ribosome | Reads mRNA and builds proteins | None |
| Centrosome | Organizes microtubules and the spindle in cell division | None |
| Peroxisome | Breaks down fatty acids; neutralizes hydrogen peroxide | Single |
Many of these organelles are physically connected as one team called the endomembrane system. The nuclear envelope is continuous with the rough ER; a gene is copied into mRNA in the nucleus, that mRNA is read by a ribosome on the rough ER, and the new protein is folded inside the ER. Vesicles then bud off and carry the protein to the Golgi, which tags and sorts it before shipping it onward — to a lysosome, to the membrane, or out of the cell entirely. This is why the rough ER, Golgi, and nucleus sit so close together in the sim.
The energy reactions of respiration happen on the inner mitochondrial membrane. By folding that membrane into cristae, the mitochondrion packs far more membrane — and therefore far more of the protein machinery — into the same small volume, boosting ATP output. Mitochondria also carry their own small circular DNA and replicate on their own, evidence for the endosymbiotic theory that they descend from ancient free-living bacteria.
An organelle is a specialized structure inside a cell that performs a specific job, much like an organ does for the whole body. Most organelles in an animal cell are wrapped in their own membrane — the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes are examples. A few important structures, like ribosomes, are not membrane-bound.
Key takeaway: organelles divide the cell's work into specialized, often membrane-enclosed compartments.The nucleus is the control center of the cell. It stores the cell's DNA, and the genes in that DNA direct which proteins the cell makes. A double membrane called the nuclear envelope surrounds it, and pores in that envelope let messenger RNA and other molecules pass in and out. Inside is the nucleolus, where ribosomes are assembled.
Key takeaway: the nucleus protects the DNA and directs the cell by controlling protein synthesis.Mitochondria carry out aerobic cellular respiration: they use oxygen to release the energy stored in glucose and capture it in molecules of ATP, the cell's usable energy currency. Their inner membrane is folded into cristae that increase the surface area for the reactions of the electron transport chain. Cells that need lots of energy, like muscle cells, contain thousands of mitochondria.
Key takeaway: mitochondria make most of the cell's ATP through aerobic respiration.The rough endoplasmic reticulum, studded with ribosomes, makes and folds proteins, while the smooth ER makes lipids. Both pinch off vesicles that carry their cargo to the Golgi apparatus. The Golgi then modifies, sorts, and packages those molecules and ships them in new vesicles to their destinations inside or outside the cell.
Key takeaway: the ER manufactures proteins and lipids, and the Golgi finishes, labels, and ships them — an assembly line.A lysosome is a membrane sac filled with acidic digestive (hydrolytic) enzymes. It breaks down worn-out organelles, food particles brought into the cell, and invading bacteria, then recycles the useful building blocks. Its membrane keeps those powerful enzymes safely separated from the rest of the cell.
Key takeaway: lysosomes are the cell's recycling and waste-disposal centers.Animal and plant cells share most organelles — nucleus, mitochondria, ER, Golgi, and ribosomes. Plant cells additionally have a rigid cell wall outside the membrane, chloroplasts for photosynthesis, and a large central vacuole. Animal cells lack all three, but they have centrioles and typically many small lysosomes.
Key takeaway: plant cells add a cell wall, chloroplasts, and a big vacuole; animal cells rely on centrioles and lysosomes.Membranes let the cell create separate compartments, each with its own chemistry. The acidic interior of a lysosome, the energy-converting space inside a mitochondrion, and the protected DNA of the nucleus all depend on a membrane keeping conditions different from the surrounding cytosol. Membranes also vastly increase usable surface area for reactions, which is why the inner mitochondrial membrane and the ER are so folded.
Key takeaway: membranes create specialized compartments and add reaction surface area, letting one cell run many incompatible processes at once.