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- Motility is the ability of a cell or organism to move of its own accord by expending energy. Means of motility can range from animals’ use of muscles to single cells which may have microscopic structures that propel the cell along.
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For an organism to function, substances must move into and out of cells. Three processes contribute to this movement – diffusion, osmosis and active transport. Part of Biology (Single Science...
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locomotion, in ethology, any of a variety of movements among animals that results in progression from one place to another.
To locomote, all animals require both propulsive and control mechanisms. The diverse propulsive mechanisms of animals involve a contractile structure—muscle in most cases—to generate a propulsive force. The quantity, quality, and position of contractions are initiated and coordinated by the nervous system: through this coordination, rhythmic movements of the appendages or body produce locomotion.
Animals successfully occupy a majority of the vast number of different physical environments (ecological niches) on Earth; in a discussion of locomotion, however, these environments can be divided into four types: aerial (including arboreal), aquatic, fossorial (underground), and terrestrial. The physical restraints to movement—gravity and drag—are the same in each environment: they differ only in degree. Gravity is here considered as the weight and inertia (resistance to motion) of a body, drag as any force reducing movement. Although these are not the definitions of a physicist, they are adequate for a general understanding of the forces that impede animal locomotion.
To counteract the force of gravity, which is particularly important in aerial, fossorial, and terrestrial locomotion, all animals that live in these three environments have evolved skeletal systems to support their body and to prevent the body from collapsing upon itself. The skeletal system may be internal or external, and it may act either as a rigid framework or as a flexible hydraulic (fluid) support.
To initiate movement, a sufficient amount of muscular work must be performed by aerial, fossorial, and terrestrial animals to overcome inertia. Aquatic animals must also overcome inertia; the buoyancy of water, however, reduces the influence of gravity on movement. Actually, because many aquatic animals are weightless—i.e., they possess neutral buoyancy by displacing a volume of water that is equal in weight to their dry weight—little muscular work is needed to overcome inertia. But not all aquatic animals are weightless. Those with negative buoyancy sink as a result of their weight; hence, the greater their weight, the more muscular energy they must expend to remain at a given level. Conversely, an animal with positive buoyancy floats to and rests on the surface and must expend muscular energy to remain submerged.
In water, the primary force that retards or resists forward movement is drag, the amount of which depends upon the animal’s shape and how that shape cleaves the water. Drag results mainly from the friction of the water as it flows over the surface of the animal and the adherence of the water to the animal’s surface (i.e., the viscosity of the water). Because of the water’s viscosity, its flow tends to be lamellar; i.e., different layers of the water flow at different speeds, with the slowest layer of flow being the one adjacent to the body surface. As the flow speed increases, the lamellar pattern is lost, and turbulence develops, thereby increasing the drag.
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Most motile protozoans, which are strictly aquatic animals, move by locomotion involving one of three types of appendages: flagella, cilia, or pseudopodia. Cilia and flagella are indistinguishable in that both are flexible filamentous structures containing two central fibrils (very small fibres) surrounded by a ring of nine double fibrils. The peri...
Nov 13, 2022 · In biology, transport refers to the act or the means by which a molecule or ion is moved across the cell membrane or via the bloodstream. There are two types of transport in this regard: (1) passive transport and (2) active transport .
Often, substances have to be moved from a low to a high concentration - against a concentration gradient. Active transport is a process that is required to move molecules against a...
Active transport is the movement of dissolved molecules into or out of a cell through the cell membrane, from a region of lower concentration to a region of higher concentration. The particles...
May 16, 2020 · 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.
Mar 2, 2017 · Motility is the ability of a cell or organism to move of its own accord by expending energy. Means of motility can range from animals’ use of muscles to single cells which may have microscopic structures that propel the cell along.
