Cellular Structure And Function

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diffusion

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The process of random movement toward a state of equilibrium. It is the net movement from regions of greater(higher) concentration to regions of lesser(lower) concentration. Generally a very slow process in living tissue.

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osmosis

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a process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane.

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semi-permeable

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A membrane that is selectively permeable, i.e. being permeable to only certain molecules and not to all molecules.

An example of such membrane is the cell membrane wherein it allows passage of only certain types of molecules by diffusion and occasionally by facilitated diffusion.

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hypotonic

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Hypotonic comes from the Greek "hypo," meaning under, and "tonos," meaning stretching. In a hypotonic solution the total molar concentration of all dissolved solute particles is less than that of another solution or less than that of a cell.

If concentrations of dissolved solutes are less outside the cell than inside, the concentration of water outside is correspondingly greater. When a cell is exposed to such hypotonic conditions, there is net water movement into the cell. Cells without walls will swell and may burst (lyse) if excess water is not removed from the cell. Cells with walls often benefit from the turgor pressure that develops in hypotonic environments.

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isotonic

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When two environments are isotonic, the total molar concentration of dissolved solutes is the same in both of them.

When cells are in isotonic solution, movement of water out of the cell is exactly balanced by movement of water into the cell. A 0.9% solution of NaCl (saline) is isotonic to animal cells. When exposing animal tissues to solutions, it is common to use an isotonic solution such as Ringer's buffered saline so as to prevent osmotic effects and consequent damage to cells.

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hypertonic

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Hypertonic comes from the Greek "hyper," meaning over, and "tonos," meaning stretching. In a hypertonic solution the total molar concentration of all dissolved solute particles is greater than that of another solution, or greater than the concentration in a cell.

If concentrations of dissolved solutes are greater outside the cell, the concentration of water outside is correspondingly lower. As a result, water inside the cell will flow outwards to attain equilibrium, causing the cell to shrink. As cells lose water, they lose the ability to function or divide. Hypertonic environments such as concentrated brines or syrups have been used since antiquity for food preservation because microbial cells that would otherwise cause spoilage are dehydrated in these very hypertonic environments and are unable to function.

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active transport

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Process that requires the input of metabolic (chemical) energy from an outside source.

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passive transport

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Process that does not require a direct input of metabolic energy.

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homeostasis

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The tendency of an organism or a cell to regulate its internal conditions, usually by a system of feedback controls, so as to stabilize health and functioning, regardless of the outside changing conditions

(2) The ability of the body or a cell to seek and maintain a condition of equilibrium or stability within its internal environment when dealing with external changes

(3) homeostasis is the maintenance of the constant internal environment which include the function of kidney,liver,skin...

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dynamic equilibrium

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A system in a steady state since forward reaction and backward reaction occur at the same rate.

In a dynamic equilibrium, the rate of loss is equal to the rate of gain.

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endocytosis

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A process of cellular ingestion by which the plasma membrane folds inward to bring substances into the cell.

The transport of particles into a living cell by the movement of a filled vacuole that has formed from the folding inward of the part of the cell membrane on which the particles rest

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exocytosis

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The transport of matter out of a living cell by the movement of a filled vacuole to the cell membrane and the extrusion of its contents

(Biochemistry) a process by which material is exported from a biological cell

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phagocytosis

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The ingestion by a cell of a microorganism, cell particle, or other matter surrounded and engulfed by the cell

The process by which a cell, such as a white blood cell, ingests microorganisms, other cells, and foreign particles

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pinocytosis

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Introduction of fluids into a cell by invagination of the cell membrane, followed by formation of vesicles within the cells.

Process by which certain cells can engulf and incorporate droplets of fluid

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carrier proteins & channel proteins

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1. Carrier proteins facilitate the diffusion of different molecules.

2. channel proteins are involved in the movement of ions, small molecules, or macromolecules, such as another protein, across a biological membrane.

3. Carrier proteins are integra lmembrane proteins; that is they exist in and span of the membrane across which they transport substances.

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concentration gradient

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1. a gradual change in the concentration of solutes in a solution as a function of distance through a solution.

2. the gradual difference in the concentration of solutes in a solution between two regions. In biology, a gradient results from an unequal distribution of ions across the cell membrane. When this happens, solutes move along a concentration gradient. This kind of movement is called diffusion.