Definition Active transport is the process of transferring substances into, out of, and between cells, using energy. In some cases, the movement of substances can be accomplished by passive transport, which uses no energy. However, the cell often needs to transport materials against their concentration gradient. In these cases, active transport is required. Process of … Read more
Sympathetic Nervous System Definition The sympathetic nervous system is part of the autonomic nervous system, an extensive network of neurons that regulate involuntary processes. Specifically, the sympathetic nervous system controls aspects of the body related to the flight-or-fight response, such as mobilizing fat reserves, increasing the heart rate, and releasing adrenaline. Sympathetic Nervous System Overview … Read more
Ecological Pyramid Definition An ecological pyramid is a graphical representation of the relationship between different organisms in an ecosystem. Each of the bars that make up the pyramid represents a different trophic level, and their order, which is based on who eats whom, represents the flow of energy. Energy moves up the pyramid, starting with … Read more
Hydrophilic Definition A hydrophilic molecule or substance is attracted to water. Water is a polar molecule that acts as a solvent, dissolving other polar and hydrophilic substances. In biology, many substances are hydrophilic, which allows them to be dispersed throughout a cell or organism. All cells use water as a solvent that creates the solution … Read more
Definition of Speciation Speciation is a process within evolution that leads to the formation of new, distinct species that are reproductively isolated from one another. Anagenesis, or ‘phyletic evolution’, occurs when evolution acts to create new species, which are distinct from their ancestors, along a single lineage, through gradual changes in physical or genetic traits. … Read more
Xylem Definition Xylem is a type of tissue in vascular plants that transports water and some nutrients from the roots to the leaves. Phloem is the other type of transport tissue; it transports sucrose and other nutrients throughout the plant. Xylem and phloem give vascular plants their classification; they are the vascular tissues that transport … Read more
Frenulum Definition A frenulum is a small ridge or fold of skin that helps to anchor a semi-mobile body part. In the human body, frenulums are found on the penis, under the tongue, inside the lips, as part of the female genitalia, and internally in the brain and digestive tract. Because the two most important … Read more
Sexual Intercourse Definition Sexual intercourse, or copulation, is the deposition of sperm into a female via a male intromittent organ. In humans, the intromittent organ is the penis, and sperm are deposited into the vagina, where they make their way to towards the uterus to fertilize an egg. However, sexual intercourse is almost as varied … Read more
Central Vacuole Definition The central vacuole is a large vacuole found inside of plant cells. A vacuole is a sphere filled with fluid and molecules inside a cell. The central vacuole stores water and maintains turgor pressure in a plant cell. It also pushes the contents of the cell toward the cell membrane, which allows … Read more
Nuclear Membrane Definition Known also as the nuclear envelope, the nuclear membrane separates the nucleus from the rest of the cell. Cells of both animals and plants contain it. Cells build proteins, convert molecules into energy, and remove waste products. Cells protect their genetic material from chemical reactions taking place outside their nucleus by using … Read more