Lakes and ponds are inland bodies of standing or slowly moving water. Although lakes and ponds cover only 2 percent of the world's land surface, they contain most of the world's fresh water.
Jean-Baptiste Lamarck is best remembered for the incorrect hypothesis that evolutionary change occurs due to the inheritance of acquired characteristics. However, Lamarck's contributions to biological thought are much more important than being the champion of a failed idea.
Landscape ecology is the study of the causes and ecological consequences of spatial pattern in landscapes. While there is no specific spatial extent that defines a landscape, most landscape ecologists are interested in large areas ranging from a few square kilometers to entire continents.
The Leakey family has been the most famous and one of the world's most productive groups of paleoanthropologists, scientists who study human origins. Over the span of more than seventy years, they have made major discoveries proving that humans originated in Africa, and that human ancestors were much older than previously believed.
Learning produces a relatively long-lasting change in behavior as a result of experience. The ability to learn, to gain from experience, allows animals to adapt to and cope with variable environments and therefore contributes to reproductive fitness.
Leaves are plant organs primarily adapted for photosynthesis, although many species have modified leaves that serve a variety of functions besides photosynthesis. Imagine walking through a forest on a summer day surrounded by the green leaves attached to the branches of trees, shrubs, and herbs.
Antony van Leeuwenhoek is often credited with inventing the microscope. In actuality, Galileo, Robert Hooke, and Jan Swammerdam had built microscopes before him; compound (double-lens) microscopes were invented nearly forty years before Leeuwenhoek was born.
A lichen is a compound organism built of a fungus intimately entwined about cyanobacteria or cells of an alga. From a distance, a lichen is a brightly colored coat on a tree, a low, bushlike structure, or greenish growths hanging from branches.
The human life cycle begins at fertilization, when an egg cell inside a woman and a sperm cell from a man fuse to form a one-celled zygote. Over the next few days, the single, large cell divides many times to form a hollow ball of smaller cells.
A life cycle describes the series of stages that an individual organism passes through between the time it is conceived until the time it produces offspring of its own. This series of stages is referred to as a life cycle because offspring pass through the same series before they produce their own offspring.
"Is it alive?" Children ask that question when they see a bug or perhaps a mouse that is very quiet. Then they poke it, and if it moves they say, "It's alive!" But single-celled organisms such as yeast cannot move.
A light microscope (LM) is an instrument that uses visible light and magnifying lenses to examine small objects not visible to the naked eye, or in finer detail than the naked eye allows. Magnification, however, is not the most important issue in microscopy.
In an era when most of the world's population lacks access to clean drinking water, the science of limnology (the study of bodies of fresh water) is making a resurgence in both the scientific and political communities. Earth's water supply is limited, with no new sources in sight.
Linkage refers to the presence of two different genes on the same chromosome. Two genes that occur on the same chromosome are said to be linked, and those that occur very close together are tightly linked.
Carolus Linnaeus developed the binomial system for naming organisms. Born Carl von Linné in Sweden, Linnaeus developed an early interest in botany and classification and later developed a new classification scheme for the growing numbers of plants and animals being discovered throughout the world.
Lipids are uniquely biological molecules, and they are synthesized and used by organisms in a variety of important ways. Unlike proteins, polysaccharides, and nucleic acids, lipids are much smaller, water-insoluble molecules.
The liver is the largest organ in the abdominal cavity and is located under the right and central portions of the diaphragm. It performs over two hundred functions including digestive, metabolic, storage, and other functions.
Locomotion is the active movement from one place to another. It does not include passive movements such as falling or drifting in currents of air or water.
The lymphatic system plays a vital role as one of the organ systems of the body. This system functions with the digestive system to absorb dietary lipids, which enter lymphatic vessels rather than blood vessels for transport.
Lysosomes are membrane-bound organelles that function as the "stomachs" of eukaryotic cells. They contain about fifty different enzymes that break down all types of biological molecules including proteins, nucleic acids, lipids, and carbohydrates.
Reproduction is essential for any species to sustain its population. In the simplest sense, the most important function of every living organism is reproduction.
Mammals are taxonomically separated from other animals at the class level (kingdom Animalia, phylum Chordata, subphylum Vertebrata, class Mammalia). Modern mammals are readily differentiated from other animals by the following characteristics: hair; a four-chambered heart with the aorta descending on the left; red blood cells that lack a nucleus (allowing for increased surface area for oxygen transport); a muscular diaphragm separating the abdominal and thoracic cavities that aids in breathing; descent of the testes into a scrotum to achieve a temperature environment amenable to sperm development; a variety of skin glands including sebaceous, sweat, and milk or mammary (the characteristic giving mammals their name); and elaborate dermal musculature (controlling the skin), particularly in the face (associated with suckling in young).