Click image to open full size
The Human Cell
Structure and Organelle Functions
Related Tools
Related Worksheets
Related Cheat Sheets
The human cell is the basic structural and functional unit of the body, and understanding its parts is essential for medical science. Every tissue, organ, and physiological process depends on cells carrying out specialized tasks. A clear picture of cell structure helps students connect anatomy, physiology, pathology, and pharmacology. Many diseases begin with cell injury, organelle dysfunction, or abnormal signaling inside and between cells.
A typical human animal cell contains membrane-bound organelles that divide labor efficiently. The nucleus stores genetic information, ribosomes and rough endoplasmic reticulum build proteins, mitochondria generate most ATP, and the Golgi apparatus modifies and packages cellular products. Lysosomes digest waste, peroxisomes handle oxidative reactions, and the cytoskeleton maintains shape and transport. In medicine, these structures matter because defects in organelles can lead to cancer, metabolic disease, neurodegeneration, and inherited disorders.
Key Facts
- Plasma membrane structure follows the fluid mosaic model and is mainly a phospholipid bilayer with embedded proteins.
- Nucleus function: stores DNA and controls gene expression; the nucleolus produces rRNA and assembles ribosomal subunits.
- Protein secretion pathway: ribosome -> rough ER -> Golgi apparatus -> secretory vesicle -> plasma membrane.
- ATP hydrolysis releases usable energy: ATP + H2O -> ADP + Pi + energy.
- Mitochondria generate most cellular ATP by aerobic respiration; overall equation: C6H12O6 + 6O2 -> 6CO2 + 6H2O + ATP.
- Cell size is usually measured in micrometers, and most human cells are about 10 to 30 um in diameter.
Vocabulary
- Organelle
- An organelle is a specialized structure inside a cell that performs a specific function.
- Plasma membrane
- The plasma membrane is the selectively permeable outer boundary of the cell that controls movement of substances in and out.
- Cytoplasm
- The cytoplasm is the material between the plasma membrane and nucleus that contains organelles suspended in cytosol.
- Mitochondrion
- A mitochondrion is an organelle that produces most of the cell's ATP through aerobic respiration.
- Lysosome
- A lysosome is a membrane-bound organelle containing digestive enzymes that break down waste and worn-out cell parts.
Common Mistakes to Avoid
- Confusing ribosomes with rough endoplasmic reticulum, because ribosomes can be free in the cytosol or attached to rough ER, but the rough ER is the membrane network itself.
- Assuming all cells have the same number of organelles, which is wrong because organelle abundance depends on cell function, such as many mitochondria in muscle cells.
- Thinking the Golgi apparatus makes proteins, which is wrong because proteins are synthesized by ribosomes and then modified, sorted, and packaged by the Golgi.
- Believing lysosomes and peroxisomes do the same job, which is wrong because lysosomes mainly digest macromolecules while peroxisomes carry out oxidative reactions and detoxification.
Practice Questions
- 1 A skeletal muscle cell has 2000 mitochondria, and each mitochondrion produces 5 x 10^4 ATP molecules per second. How many ATP molecules are produced per second by all the mitochondria together?
- 2 A cell is 24 um wide. Convert this width to millimeters and to meters.
- 3 A toxin blocks the Golgi apparatus in a secretory cell. Explain how this would affect the production and release of a protein hormone.