3: Cell Structure and Function

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3.1: How Cells Are Studied
In multicellular organisms, several cells of one particular kind interconnect with each other and perform shared functions to form tissues (for example, muscle tissue, connective tissue, and nervous tissue), several tissues combine to form an organ (for example, stomach, heart, or brain), and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems functioning together form an organism (such as an elephant, for example).
3.2: Comparing Prokaryotic and Eukaryotic Cells
Cells fall into one of two broad categories: prokaryotic and eukaryotic. The predominantly single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes (pro- = before; -karyon- = nucleus). Animal cells, plant cells, fungi, and protists are eukaryotes (eu- = true).
3.3: Eukaryotic Cells
At this point, it should be clear that eukaryotic cells have a more complex structure than do prokaryotic cells. Organelles allow for various functions to occur in the cell at the same time. Before discussing the functions of organelles within a eukaryotic cell, let us first examine two important components of the cell: the plasma membrane and the cytoplasm.
3.4: The Cell Membrane
The plasma membrane is referred to as the fluid mosaic model and is composed of a bilayer of phospholipids, with their hydrophobic, fatty acid tails in contact with each other. The landscape of the membrane is studded with proteins, some of which span the membrane. Some of these proteins serve to transport materials into or out of the cell. Carbohydrates are attached to some of the proteins and lipids on the outward-facing surface of the membrane. These function to identify other cells.
3.A: Cell Structure and Function (Exercises)

Thumbnail: A diagram of a typical prokaryotic cell. (Public Domain; LadyofHats).