Cell Biology - Introduction to cells

The Cell Theory states: 1. All living organisms are composed of cells. 2. The cell is the smallest unit of life. 3. Cells arise from pre-existing cells.

Exceptions to the Cell Theory include: Striated muscle fibers (multiple nuclei in a single cell), Aseptate fungal hyphae (lacks septa/walls separating nuclei), and Giant Algae ($Acetabularia$, which is a very large single cell with one nucleus).

All organisms perform the seven functions of life: Metabolism, Reproduction, Homeostasis, Growth, Response, Excretion, and Nutrition ($MR\ H\ GREN$).

The Surface Area to Volume ratio ($SA:Vol$) limits cell size. As a cell grows, volume increases at a rate of $x^3$ while surface area increases at $x^2$. If the ratio is too small, substances cannot enter/exit quickly enough to sustain metabolic needs.

Multicellular organisms show emergent properties: 'The whole is greater than the sum of its parts,' meaning interaction between individual components produces new, complex functions.

Differentiation involves the expression of some genes and not others in a cell's genome to develop specialized tissues.

Stem cells are characterized by their capacity to divide indefinitely and their potency to differentiate into specialized cell types. They are used to treat $Stargardt's$ disease (replacing retinal cells) and Leukemia (replacing white blood cells).