Cells and Life Processes - Cell Theory

The Cell Theory consists of three main principles: 1. All living organisms are composed of one or more cells. 2. The cell is the basic unit of structure and organization in organisms. 3. Cells arise from pre-existing cells.

All living things perform seven basic life processes, often remembered by the acronym $MR\ H\ GREN$: Metabolism, Reproduction, Homeostasis, Growth, Response (Sensitivity), Excretion, and Nutrition.

Metabolism refers to the sum of all chemical reactions within a cell, including the release of energy through $ATP$ production.

Cells are measured in micrometers ($\mu m$) and nanometers ($nm$). Conversion: $1\ mm = 1,000\ \mu m$ and $1\ \mu m = 1,000\ nm$.

The surface area to volume ratio ($SA:V$) is a limiting factor for cell size. As a cell grows, its volume ($V$) increases faster than its surface area ($SA$), making it harder to move materials like $O_2$ and $CO_2$ efficiently across the membrane.

Unicellular organisms, such as $Paramecium$ or $Chlamydomonas$, must perform all functions of life within a single cell.

Multicellular organisms exhibit emergent properties, where the whole organism is more than the sum of its cellular parts due to cellular differentiation and specialization.