Skip to main content

Posts

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)…
Recent posts

Marine Mammals: Dugongs

Shy and retiring, dugongs are marine mammals that spend their days feeding in the shallow waters of reefs and along coastlines in the Indian Ocean, the Indonesian archipelago, and the southwestern Pacific around the Philippines. Even though they resemble a cross between a seal and a walrus, dugongs are more closely related to elephants. The slow-moving mammals are easily identified by their triangular, whalelike tails, broad trunklike snouts, and long bodies, which reach 9 feet (2.7 m). Dugongs have a thick layer of blubber under their skin, a feature that gives them a round-shouldered look. Their mouths look like vertical slits on their upper jaws, and their flippers are small and paddle shaped.
Dugongs have unusually slow metabolic rates for mammals but function well in their warm water environments where they float and feed, expending very little energy. With very few predators and plenty of food, migration and other energetic types of behavior are not necessary. Most of their tim…

The minke whale (Balaenoptera acutorostrata)

The minke whale (Balaenoptera acutorostrata) is the second smallest of the baleen whales, measuring about 32.8 feet (10 m) in length. A distinctive triangular head, narrow and pointed snout, and sickle-shaped dorsal fin make this whale easy to identify. Generally, minke whales are black, gray, or brown on their dorsal surface and a light color on their ventral surface. These active, agile whales have good maneuverability and speed, able to travel at 10.4 miles per hour (17 kph) for short periods of time.
As baleen whales, minkes are carnivores whose mouths are equipped with smooth baleen plates for filtering small organisms from gulps of water. Minkes can be found worldwide and are known to live in deep oceans, along coasts, and in coral reefs. Instead of seasonal migration, they only travel to follow their food. Sometimes minkes chase schools of small fish such as sardines and herring, swimming beneath and scooping them up in their open mouths. As in humpbacks, the throats of minkes …

Humpback Whales

The humpback whale (Megaptera novaeangliae) is much bigger than the spinner dolphin, measuring 40 to 50 feet (12.9 to 15.2 m) long and weighing up to 55 tons. The common name humpback describes the motion this whale makes as it jumps out of the water. A typical humpback whale is black on the dorsal side, with a white ventral surface and distinctive 15-foot flippers on the sides of its body.
The head of a humpback whale is large in proportion to the rest of its torpedo-shaped body. This figure below shows that the mouth line runs high along the entire length of head, and the eyes are set above the ends of the mouth. The small ear slits are located behind and below the eyes.
On the top of its head, a humpback has a raised area in front of its two blowholes that functions like a splashguard to keep water from flowing back into the holes where it breathes. Rounded knobs called tubercles are also located on the head, often on the upper and lower jaws. Each tubercle contains a hairlike str…

Spinner Dolphins

Spinner dolphins (Stenella longirostris) are easily spotted as they swim in the clear waters of coral reefs. Named for their ability to spin during acrobatic jumps, these dolphins are slender, with long thin beaks, sloping foreheads, and a stripe that runs from the eyes to the flippers. An adult measures 4.25 to 6.89 feet (1.3 to 2.1 m) long, and weighs between 100 and 165 pounds (45 and 75 kg). There are several varieties of spinners in different geological locations, and they vary slightly in shape and color.
Spinner dolphins feed at night on fish and squid in the deeper waters of the reef, although they will also eat organisms that live on the reef floor. Their mouths are equipped with 45 to 65 pairs of sharp teeth in each jaw. After feeding, spinner dolphins can often be found resting in protected areas of shallow water.
As social animals, spinners depend on interaction with others for hunting, defense, and reproduction and form small, long-lasting social groups called pods. In thi…

Marine Mammals

Mammals are the most obvious group of animals on land, but they are relatively rare in marine environments. There are just a few types of mammals whose bodies have become specialized for marine life. Among these are the cetaceans, a group that includes whales and dolphins, porpoises, and dugongs.
Marine Mammal Anatomy Mammals are warmblooded vertebrates that have hair and breathe air. All females of this group have milk-producing mammary glands with which to feed their young. Mammals also have a diaphragm that pulls air into the lungs and a four-chambered heart for efficient circulation of blood. The teeth of mammals are specialized by size and shape for particular uses.
Marine mammals are subdivided into four categories: cetaceans, animals that spend their entire lives in the ocean; sirenians, herbivorous ocean mammals; pinnipeds, web-footed mammals; and marine otters. Animals in all four categories have the same characteristics as terrestrial mammals, as well as some special adaptat…

Marine Bird Anatomy

Birds are warm-blooded vertebrates that have feathers to insulate and protect their bodies. In most species of birds, feathers are also important adaptations for flying. As a general rule, birds devote a lot of time and energy to keeping their feathers waterproof in a process called preening. During preening, birds rub their feet, feathers, and beaks with oil produced by the preen gland near their tail.
The strong, lightweight bones of birds are especially adapted for flying. Many of the bones are fused, resulting in the rigid type of skeleton needed for flight. Although birds are not very good at tasting or smelling, their senses of hearing and sight are exceptional. They maintain a constant, relatively high body temperature and a rapid rate of metabolism. To efficiently pump blood around their bodies, they have a four-chambered heart.
Like marine reptiles, marine birds have glands that remove excess salt from their bodies. Although the structure and purpose of the salt gland is the s…