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Prokaryotic Cell Structure

Prokaryotic cells are about 10 times smaller than eukaryotic cells. A typical E. coli cell is about 1 μm wide and 2 to 3μm long. Structurally, prokaryotes are very simple cells when compared with eukaryotic cells, and yet they are able to perform the necessary processes of life. Reproduction of prokaryotic cells is by binary fission—the simple division of one cell into two cells, after DNA replication and the formation of a separating membrane and cell wall. All bacteria are prokaryotes, as are the archaea. Embedded within the cytoplasm of prokaryotic cells are a chromosome, ribosomes, and other cytoplasmic particles (Fig. 1). Unlike eukaryotic cells, the cytoplasm of prokaryotic cells is not filled with internal membranes. The cytoplasm is surrounded by a cell membrane, a cell wall (usually), and sometimes a capsule or slime layer. These latter three structures make up the bacterial cell envelope. Depending on the particular species of bacterium, flagella, pili (description follows

Coastal Ecosystems Border the Oceans

Salt marshes, discussed previously, and also mudflats and mangrove swamps, featured in Figure 1, are ecosystems that occur at a delta. Mangrove swamps develop in subtropical and tropical zones, while marshes and mudflats occur in temperate zones. These ecosystems are often designated as an estuary. So are coastal bays, fjords (an inlet of water between high cliffs), and some lagoons (a body of water separated from the sea by a narrow strip of land). Therefore, the term estuary has a very broad deﬁ nition. An estuary is a partially enclosed body of water where fresh water and seawater meet and mix as a river enters the oceans. Organisms living in an estuary must be able to withstand constant mixing of waters and rapid changes in salinity. But those organisms adapted to the estuarine environment ﬁ nd an abundance of nutrients. An estuary acts as a nutrient trap because the sea prevents the rapid escape of nutrients brought by a river. As the result of usually warm, calm waters and plenti

Crustaceans

The most common type of arthropod on the reef is the crustacean. Crustaceans include shrimp, lobsters, and crabs. As shown in Figure below, the body segments of crustaceans are grouped into three specialized areas: head, thorax, and abdomen. Crustaceans have paired appendages attached to each segment that are used for walking, sensing, feeding, and defense. In a number of species, appendages form claws that are capable of exerting hundreds of pounds of pressure. The biggest reef crustacean is the lobster. Even though the first pair of appendages are modified as claws in several lobster species, most reef lobsters are clawless. The appendages on the thorax of lobsters are adapted for walking along the reef floor and for swimming. Several lobster species make their homes on the reef. Two common ones are the spiny lobster (Panulirus argus) and the slipper lobster (Parribacus antarcticus). The body of a crustacean is divided into three areas: head, thorax, and abdomen. The head

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