Chapter 2: Cells and Organelles

Table of Contents:

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The cell theory says living things contain one or more cells; therefore, the cell is the basic unit of life. It also says that new cells must arise from pre-existing cells. The coordinated effort of cells allows living organisms to carry out all their amazing functions.

Cells act like factories that make proteins. In cellular factories, the cell membrane acts as the building, the DNA acts as the instruction manual for building the products, and ribosomes act like workers.

In this chapter, we will mainly discuss eukaryotic cells, which make up animals, plants, fungi, and protists. These types of cells contain many smaller membrane-bound organelles inside them, which are like different rooms in the factory.

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Cell Membrane

Cell membranes are boundaries that hold all of the critical cellular contents inside, protecting them from the surrounding environment. In general, cell membranes contain three main things: phospholipids, cholesterol, and proteins.


  1. Phospholipids are a unique type of lipid (fat) in cell membranes. Each phospholipid has a three-carbon glycerol backbone, attached to one phosphate group and two fatty acid tails. Phosphate groups are polar and hydrophilic (water-loving) because they have negative charges. Fatty acids are nonpolar, so they do not mix well with water (hydrophobic).