Characteristics of Aquatic Life

Characteristics of Aquatic Life There are thousands of species of marine life, from tiny zooplankton to enormous whales. Each is adapted to its specific habitat. Throughout the oceans, marine organisms must deal with several problem we avoid on land: Regulating salt intakeObtaining oxygenAdapting to water pressureDealing with wind, waves, and changing temperaturesGetting enough light There are many ways marine life survive in this environment that is so different from ours. Salt Regulation Fish can drink salt water, and eliminate the salt through their gills. Seabirds also drink salt water, and the excess salt is eliminated via the nasal, or â€Å"salt glands† into the nasal cavity, and then is shaken, or sneezed out by the bird. Whales don’t drink salt water, instead, they get the water they need from the organisms they eat. Oxygen Fish and other organisms that live underwater can take their oxygen from the water, either through their gills or their skin. Marine mammals need to come to the water surface to breathe, which is why the deep-diving whales have blowholes on top of their heads, so they can surface to breathe while keeping most of their body underwater. Whales can stay underwater without breathing for an hour or more because they make very efficient use of their lungs, exchanging up to 90% of their lung volume with each breath, and also store unusually high amounts of oxygen in their blood and muscles when diving. Temperature Many ocean animals are cold-blooded (ectothermic) and their internal body temperature is the same as their surrounding environment. Marine mammals, however, have special considerations because they are warm-blooded (endothermic), meaning they need to keep their internal body temperature constant no matter the water temperature. Marine mammals have an insulating layer of blubber (made up of fat and connective tissue) under their skin. This blubber layer allows them to keep their internal body temperature about the same as ours, even in the cold ocean. The bowhead whale, an arctic species, has a blubber layer that is 2-feet-thick. Water Pressure In the oceans, water pressure increases 15 pounds per square inch for every 33 feet of water. While some ocean animals do not change water depths very often, far-ranging animals such as whales, sea turtles, and seals sometimes travel from shallow waters to great depths several times in a single day. How can they do it? The sperm whale is thought to be able to dive more than 1 1/2 miles below the ocean surface. One adaptation is that lungs and rib cages collapse when diving to deep depths. The leatherback sea turtle can dive to over 3,000 feet. Its collapsible lungs and flexible shell help it stand the high water pressure. Wind and Waves Animals in the intertidal zone do not have to deal with high water pressure  but need to withstand the high pressure of wind and waves. Many marine invertebrates and plants in this habitat have the ability to cling onto rocks or other substrates so they are not washed away  and have hard shells for protection. While large pelagic species like whales and sharks may not be impacted by rough seas, their prey can be moved around. For example, right whales prey on copepods, which can get spread to different areas during a time of high wind and waves. Light Organisms that need light, such as tropical coral reefs and their associated algae, are found in shallow, clear waters that can be easily penetrated by sunlight. Since underwater visibility and light levels can change, whales do not rely on sight to find their food. Instead, they locate prey using echolocation and their hearing. In the depths of the ocean abyss, some fish have lost their eyes or pigmentation because they are just not necessary. Other organisms are bioluminescent, using light-giving bacteria or their own light-producing organs to attract prey or mates.

Definition of Descent With Modification

Definition of Descent With Modification Descent with modification refers to the passing on of traits from parent organisms to their offspring. This passing on of traits is known as heredity, and the basic unit of heredity is the gene. Genes are the blueprints for making an organism, and, as such, hold information about its every conceivable aspect: its growth, development, behavior, appearance, physiology, and reproduction. Heredity and Evolution According to Charles Darwin, all species descended from only a few lifeforms that had been modified over time. This descent with modification, as he called it, forms the backbone of his Theory of Evolution, which posits that the development of new types of organisms from preexisting types of organisms over time is how certain species evolve. How It Works The passing on of genes is not always exact. Parts of the blueprints may be copied incorrectly, or in the case of organisms that undergo sexual reproduction, genes of one parent are combined with the genes of another parent organism. That is why children are not exact carbon copies of either of their parents. There are three basic concepts that are helpful in clarifying how descent with modification works: Genetic mutationIndividual (or natural) selectionEvolution of the population (or species as a whole) It is important to understand that genes and individuals do not evolve, only populations as a whole evolve. The process looks like this: Genes mutate and those mutations have consequences for the individuals within a species. Those individuals either thrive or die out due to their genetics. As a result, populations change (evolve) over time. Clarifying Natural Selection Many students confuse natural selection with descent with modification, so its worth repeating, and further clarifying, that natural selection is part of the process of evolution, but not the process itself. Natural selection comes into play, according to Darwin, when a species as a whole adapts to its environment, thanks to its specific genetic makeup. Say at some point in time two species of wolves lived in the Arctic: those with short, thin fur and those with long, thick fur. Those wolves with long, thick fur were genetically capable of living in the cold. Those with short, thin fur were not. Therefore, those wolves whose genetics allowed them to live successfully in their environment lived longer, bred more frequently, and passed on their genetics. They were naturally selected to thrive. Those wolves who were not genetically adapted to the cold eventually died out. Furthermore, natural selection doesnt create variation or give rise to new genetic traits- it selects for the genes already present in a population. In other words, the Arctic environment in which our wolves lived did not prompt a series of genetic traits that didnt already live in certain of the wolf individuals. New genetic strains are added to a population through mutation and horizontal gene transmission- e.g., the mechanism by which bacteria become immune to certain antibiotics- not natural selection. For instance, a bacterium inherits a gene for antibiotic resistance and therefore has a greater chance of survival. Natural selection then spreads that resistance through the population, forcing scientists to come up with a new antibiotic.