Cell is the basic structural and functional unit of life. Cell Theory: Schleiden (1838, plants) + Schwann (1839, animals) → all living things are made of cells. Virchow (1855): 'Omnis cellula e cellula' — all cells arise from pre-existing cells. Two types: Prokaryotic (no nuclear membrane — bacteria, blue-green algae) and Eukaryotic (definite nuclear membrane — plants, animals, fungi).

Cell organelles and functions: Nucleus (control center, contains DNA), Cell Membrane (semi-permeable, controls entry/exit), Cell Wall (only in plants — provides rigidity, made of cellulose), Mitochondria ('powerhouse of cell' — ATP production through cellular respiration), Chloroplast (only in plant cells — photosynthesis, contains chlorophyll), Endoplasmic Reticulum (Rough ER = protein synthesis with ribosomes, Smooth ER = lipid synthesis), Golgi Apparatus (packaging and secretion), Lysosomes ('suicide bags' — contain digestive enzymes), Vacuoles (large in plant cells for storage, small in animal cells).

Plant cell vs Animal cell: Plant has cell wall, chloroplasts, large central vacuole; Animal has centrioles, small vacuoles, no cell wall. Cell division: Mitosis (2 identical daughter cells, for growth and repair) and Meiosis (4 daughter cells with half chromosomes, for gamete/sex cell production). Human body: 46 chromosomes (23 pairs) — 22 pairs autosomes + 1 pair sex chromosomes (XX=female, XY=male).

REET Exam Tips: Focus on Cell Theory contributors with dates (Schleiden 1838, Schwann 1839, Virchow 1855), organelle-function matching ('powerhouse'=mitochondria, 'suicide bags'=lysosomes), and plant vs animal cell differences.