Chapter 9. Cells: The Units of Life

Cell theory. All living things are made of cells; the cell is the basic unit of life; new cells come from existing cells [10][11].

Characteristics of life: organization, metabolism, growth, response to stimuli, reproduction, homeostasis and evolution.

Two cell types

Organelles (eukaryotes): nucleus (DNA), mitochondria (energy release), ribosomes (protein synthesis), endoplasmic reticulum, Golgi apparatus (processing and packaging), lysosomes. Plant cells also have a cell wall and chloroplasts, and a large central vacuole.

Cell membrane. A selectively permeable boundary made of a phospholipid bilayer. Materials cross by diffusion, osmosis, facilitated diffusion and active transport (which needs energy).

Energy in cells

Photosynthesis: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

Cellular respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)

Cell division. Mitosis makes two identical body cells for growth and repair; meiosis makes four genetically varied sex cells with half the chromosomes [10].

Review: Which organelle is the main site of ATP production in eukaryotes? (Answer: the mitochondrion.)