How cell parts and membranes keep cells working
Cells are like tiny factories, each part doing a special job. In Class 6-8 you learn that every cell has a cell membrane, cytoplasm and usually a nucleus. Plant cells also have a cell wall, chloroplasts and a large vacuole, while animal cells do not. Cells come in many shapes: nerve cells are long and branched to carry messages, and red blood cells are disc-shaped to carry oxygen.
In Class 11-12, cells are grouped as prokaryotic, such as bacteria, with no membrane-bound nucleus and 70S ribosomes, or eukaryotic, with a true nucleus and membrane-bound organelles. The fluid mosaic model describes the plasma membrane as a lipid bilayer with proteins floating in it. Substances cross it by simple diffusion, by facilitated diffusion through carrier proteins, or by active transport using ATP. The endomembrane system, made of the endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles, works together. Mitochondria and chloroplasts have their own DNA, and the cytoskeleton gives shape and helps movement.
Why it matters
Cell structure explains how antibiotics can kill bacteria without harming human cells, how nerve and muscle cells are suited to their jobs, and how medicines cross membranes. Knowing about active transport helps explain how kidneys reabsorb useful substances. This knowledge is the basis for physiology, cell division and molecular biology.
Key terms
- Prokaryotic cell
- A cell without a membrane-bound nucleus, such as a bacterium.
- Fluid mosaic model
- A model describing the cell membrane as a lipid bilayer with embedded, moving proteins.
- Active transport
- Movement of substances across a membrane against a concentration gradient using energy from ATP.
- Chloroplast
- A green plastid in plant cells where photosynthesis takes place.