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.
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.