10 résultats pour "shark"
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Shark - biology.
Sharks have two-chambered hearts that are relatively small compared to the rest of their bodies. Blood flows from the heart to the gills, where it collects oxygen fromwater and then distributes it to the other organs and tissues. The small heart produces weak blood pressure, and many sharks must swim continuously to create themuscular contractions needed to circulate blood throughout their bodies. Most sharks are cold-blooded—that is, they do not generate heat by digesting food. Instead, the bod...
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Great White Shark - biology.
The great white shark is a rare species that takes long to reach sexual maturity and that reproduces slowly. Populations cannot easily increase if depleted. The biggestthreat to great whites comes from being unintentionally caught in fishing nets. Some targeted fisheries and sport fishing for great white sharks also occur. Trade ingreat white shark products includes the jaws (which can sell for thousands of dollars as curios), individual teeth, and leather from its skin. Fins from all sharks, in...
- Whale Shark - biology.
- Jaws Jaws, motion picture about a killer shark, based on the popular novel by Peter Benchley.
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Fish - biology.
pectoral fins provide fine movements, add forward thrust, or, together with the pelvic fins, serve as brakes. Typically, fins consist of a thin membrane stretched over afanlike series of thin rods called spines or rays. Most fish breathe underwater with the help of special respiratory organs called gills. Gills are made of a series of thin sheets or filaments through which blood circulates.As water moves into a fish’s mouth and passes over the gills, dissolved oxygen passes across the thin gill...
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Seal (mammal) - biology.
remote lakes by swimming thousands of kilometers up rivers from the Arctic Ocean. A few other species such as ringed seals and harbor seals have been found livingyear-round in lakes and rivers near the coasts of Russia, Canada, and Alaska. IV DIET OF SEALS Most seals eat fish and sometimes squid. The leopard seal, an Antarctic species, may have the most diverse diet of all, commonly hunting penguins and other seabirds,smaller seals, as well as fish, squid, krill (small shrimplike crustaceans),...
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Comparative Anatomy.
In comparing two species, anatomists have to be careful to differentiate between homologous structures, which are ones that have evolved from a shared ancestor, andanalogous structures, which have developed from different origins. Homologous structures are built on the same underlying plan. A human arm, a bat’s wing, and awhale’s flipper look quite different from the outside, but the bones inside reveal that these limbs all have the same basic structure. Analogous structures, by contrast,often l...
- Le requin noir
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Animals.
All animals must breathe oxygen to stay alive. They must breathe out a waste gas called carbon dioxide. Some animals breathe through lungs. Lungs take oxygen out of air. Cattle, dogs, cats, whales, people,and other mammals breathe through lungs. Birds and reptiles also breathe air through lungs. Lungs cannot take air from water. Seals, whales, dolphins, and other mammals that live in waterbreathe through lungs. They can stay underwater a long time because they can hold their breath for along tim...
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Coral Reef.
sensitive to particles of mud or sediment settling on them, which means that corals rarely grow close to rivers or other sources of sediment. In the sea, light is filteredout by depth, so reef-building corals can only grow in relatively shallow water. Even in the clearest oceans few reef-building corals grow below a depth of 80 to 100 m(260 to 328 ft). Although corals need nutrients, they cannot thrive in areas where there are large amounts of nutrients. Typically, microscopic organisms in the p...