Cell Structure and Membranes
Cell Theory and Organelles
Cell organization
Cells are the basic units of life, but they are not simple bags of fluid. Eukaryotic cells compartmentalize functions into organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes.
Why compartments matter
Compartmentalization allows incompatible reactions to occur in the same cell without interfering with each other.
Membrane structure
Biological membranes are phospholipid bilayers with embedded proteins. The fluid mosaic model explains why membranes are dynamic and selectively permeable. Cholesterol can tune membrane fluidity.
What property most directly makes the plasma membrane selectively permeable?
The lipid bilayer blocks many polar molecules, while proteins provide regulated pathways for transport.
Correct answer: Its phospholipid bilayer and embedded transport proteins
Why are mitochondria important for many eukaryotic cells?
Mitochondria convert energy from nutrients into ATP, the cell's main energy currency.
Correct answer: They generate ATP through aerobic respiration and support energy metabolism.
Selected organelles
| Organelle | Primary function |
|---|---|
| Nucleus | Stores DNA and controls transcription |
| Ribosome | Protein synthesis |
| Golgi apparatus | Modifies and sorts proteins |
| Lysosome | Macromolecule digestion |
| Mitochondrion | ATP production |
Which organelle is most associated with protein synthesis?
Ribosomes translate mRNA into polypeptides.
Correct answer: Ribosome