Chapter 8 — Cell: The Unit of Life

Cell is the basic structural and functional unit of all living organisms. All organisms are composed of cells, which vary in shape, size, and function, and are governed by cell theory stating that all cells arise from pre-existing cells.

Chapter 8 covers the fundamental concept of cells as the unit of life. Cell theory, established by Schleiden, Schwann, and Virchow, explains that all organisms are composed of cells and new cells arise from pre-existing cells. The chapter describes prokaryotic and eukaryotic cell structures, including the plasma membrane, organelles like mitochondria and chloroplasts, the nucleus containing genetic material, and specialized structures like ribosomes, lysosomes, and the Golgi apparatus. Cell size ranges from 0.3 µm in Mycoplasmas to the ostrich egg, with shapes varying from disc-like to thread-like depending on function. The cell membrane regulates molecular transport through passive and active mechanisms.

1. 01Cell is the fundamental structural and functional unit of all living organisms composed of cytoplasm, nucleus (in eukaryotes), and cell membrane.
2. 02Prokaryotic cells lack a membrane-bound nucleus and organelles; eukaryotic cells possess a nucleus and compartmentalized organelles like mitochondria, ER, and Golgi apparatus.
3. 03The cell membrane is selectively permeable with lipid bilayer and proteins, facilitating transport of molecules via passive transport (diffusion, osmosis) and active transport (ATP-dependent).
4. 04Double membrane-bound organelles include mitochondria (ATP production via aerobic respiration) and chloroplasts (photosynthesis in plant cells).
5. 05The endomembrane system includes endoplasmic reticulum (protein and lipid synthesis), Golgi apparatus (packaging and secretion), lysosomes (digestion), and vacuoles (storage and osmoregulation).