Cell organelles and their functions

Cell organelles and their functions chart

Every structure an introductory biology course asks you to label, with its main job and whether you will find it in an animal cell, a plant cell, or both. Membranes are the quickest way to sort them: two membranes point to an organelle that began as a captured bacterium (mitochondria and chloroplasts) or to the envelope around the genome; one membrane marks the endomembrane system that trades vesicles between the ER, Golgi, lysosomes, and cell membrane; ribosomes have none, which is why bacteria have them too.

Bacteria and archaea (prokaryotes) have a cell membrane, cytoplasm, ribosomes, and often a cell wall, but none of the membrane-bound organelles in this chart. Their DNA sits in the cytoplasm as a nucleoid, and their smaller 70S ribosomes are the reason many antibiotics can hit them without harming ours.

Animal cell vs plant cell

A flexible, roughly rounded cell 10–30 µm across, bounded only by its membrane. It has a pair of centrioles near the nucleus and many lysosomes, but no wall, no chloroplasts, and no large central vacuole. A boxy cell 10–100 µm across held rigid by a cellulose wall outside the membrane. A large central vacuole fills most of the interior, chloroplasts line the cytoplasm, and there are no centrioles or true lysosomes. Both share the nucleus, mitochondria, ribosomes, ER, Golgi apparatus, and cell membrane; the five differences below are what an exam usually asks for.

• Cell wall. Plant cells build a rigid cellulose wall outside the membrane, typically 0.1–10 µm thick. Animal cells have only their flexible membrane, so they can crawl, engulf food, and change shape.
• Chloroplasts. Green plant tissues carry 30–100 chloroplasts per cell to run photosynthesis. Animal cells have none and must eat sugar that plants made.
• Central vacuole. A mature plant cell keeps one water-filled vacuole that can fill 80–90% of its volume; its pressure against the wall (turgor) is what holds a plant upright. Animal cells have only small, short-lived vacuoles and vesicles.
• Centrioles. Animal cells organize the spindle for cell division from a pair of centrioles beside the nucleus. Flowering plants and conifers have no centrioles and build their spindle without them.
• Shape. The wall gives plant cells a fixed, boxy outline that fits neighbors like bricks. Animal cells are rounded or irregular, and their shape follows the cytoskeleton and whatever they are attached to.
• Bonus: lysosomes and storage. Animal cells digest with many lysosomes and store glucose as glycogen; plant cells digest mostly inside the vacuole and store glucose as starch grains.