B1.1 Introduction
In a sample having non-uniform composition of certain kind of atoms, a concentration gradient is set in, which leads to migration of atoms from region of their higher concentration to the region of lower concentration. This phenomenon is referred to as Diffusion and continues till atomic distribution becomes homogeneous throughout.
The diffusion process plays an important role in the field of metallurgy and fabrication of extrinsic semiconductors. The technology of controlled diffusion plays a sensitive role in accomplishment of desired devices. The metals, in their pure form, are soft and do not possess large tensile strength. Their properties can be modified by the process of alloying in a controlled manner. The
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For example diffusion of copper in copper (b) Inter-diffusion in which the solute atoms are different from the solvent atoms as in the case steel where solvent is iron whereas solute atoms are those of carbon and many other elements.
The phenomenon of diffusion of solute atoms into the solvent environment may occur through the following mechanisms:
(a) Vacancy mechanism where the solute atoms lie in the vacancy and moves to other available vacancy. Atoms can move from one site to another if there are vacancies and the atom has sufficient energy to overcome a local activation energy barrier. The activation energy for diffusion is the sum of energy required to form a vacancy and further cause its motion.
(b) Interstitial Mechanism is applicable in case of small atoms like hydrogen, helium, carbon, nitrogen diffuse through the interstitial spaces in a crystal. The activation energy for diffusion is the energy required for these atoms to squeeze through the small voids between the host lattice atoms.
B1.3 Macroscopic Model of Diffusion
B1.3.1 Steady State Diffusion: Fick’s I Law
The process of diffusion is time dependent which implies that one needs to study the quantity of solute material that gets transported in solvent is a function of time. This time dependent mass transfer is often represented by a quantity called diffusion flux (J) which is defined as the solute mass transferred in unit time through a unit cross-sectional area placed perpendicular to the
Cells and molecules in the environment are constantly moving and changing, for cells to function properly there is a need for equilibrium to be met. The size of the cell and the solution outside of the cell affects the rate of diffusion and osmosis in the cell. Cells are constantly trying to reach an equilibrium with the molecules and substances around it, which is why there are such terms as: hypertonic, hypotonic and isotonic. The procedures allowed testing of whether or not surface area or volume increased diffusion and how different substance control diffusion. Cells are constantly moving to reach equilibrium through diffusion and osmosis.
2. Explain your observations in detail in terms of concentration gradient, diffusion, osmosis, osmotic pressure, passive transport, and active transport.
One way in which osmosis is similar to simple diffusion is that both mechanisms are
Expansion diffusion- the spread of a feature from one place to another in a snowballing process. Three types:
diffusion is one of the passive transport processes. it is used in oxygen entering a cell and carbon dioxide leaving a cell. diffusion is the movement of particles such as atoms or molecules from a high concentration place in an area of a low concentration. this shows that they diffuse down the concentration gradient. the concentration gradient is a gradual change in the concentration of solutes in a solution as a function of distance through a solution. in biology a gradient results from an unequal distribution of particles across the cell membrane. When this happens solutes move along the concentration gradient until the concentration of the
A major determinant of diffusion in a biological system is membrane permeability. Small, uncharged molecules pass through cellular membranes easily, while most and/or charged molecules cannot pass through the membrane. The movement of water across a selectively permeable membrane, like the plasma membrane
Diffusion is the movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached. Osmosis, however, is the movement of water according to its own concentration gradient across a selectively
The following hypothesis was made in regard to effect of the concentration gradient on the rate of diffusion: The higher the concentration gradient, the faster the rate of diffusion.
Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration. The rate at which molecules diffuse can be determined by the relationship of molecular weight and that rate of diffusion through a membrane. Hypothesis of this experiment is that the fluid with higher molecular weight will diffuse at a slower rate and distance.
A cell needs to perform diffusion in order to survive. Substances, including water, ions, and molecules that are required for cellular activities, can enter and leave cells by a passive process such as diffusion. Diffusion is random movement of molecules in a net direction from a region of higher concentration to a region of lower concentration order to reach equilibrium. Diffusion does not require any energy input. Diffusion is needed for basic cell functions - for example, in humans, cells obtain oxygen via diffusion from the alveoli of the lungs into the blood and in plants water
Diffusion is an automated process by where the levels of oxygen, water and carbon dioxide pass over a ‘semi-permeable membrane’ between the walls of the cells and blood vessels to create a level environment. This membrane only allows these three elements to pass whilst retaining other elements such as blood cells, hence semi-permeable. The high concentration on one side of the cells transfers through this membrane until the level is equal on both sides.
All cells contain membranes that are selectively permeable, allowing certain things to pass into and leave out of the cell. The process in which molecules of a substance move from an area of high concentration to areas of low concentration is called Diffusion. Whereas Osmosis is the process in which water crosses membranes from regions of high water concentration to areas with low water concentration. While molecules in diffusion move down a concentration gradient, molecules during osmosis both move down a concentration gradient as well as across it. Both diffusion, and osmosis are types of passive transport, which do not require help.
A concentration gradient is a gradual change in solute concentration between two areas, these areas are usually separated by a membrane. A gradient result from an unequal distribution across the cell membrane. When this happens, the solutes travel along the concentration gradient (Seeley, Stephens, Tate, 2005). This type of movement is called diffusion. Diffusion is the tendency of molecules to move from a higher concentrated environment to a lower concentrated environment. This movement continues until both sides are even. Diffusion across a cell membrane is a type of passive transport, a transport that does not require energy (Karp, 2010).
2.1. Diffusion is the spontaneous kinetic movement by which molecules move from an area of a high concentration to an area of low concentration. Diffusion continues until it reaches equilibrium. Osmosis is similar to Diffusion but it’s the process in which water moves across a semi-permeable membrane and goes to the higher concentration of solute.1
Diffusion is the passage of solute molecules from an area of high concentration to an area of low concentration (Campbell & Reece, 2005). An example is ammonia diffusing throughout a room. A solute is one of two components in a chemical solution. The solute is the substance dissolved in the solution. The solvent, the other component, is any liquid in which the solute can be dissolved (Anderson, 2002). Diffusion requires little or no energy because molecules are always randomly moving; this is due to their kinetic energy. Diffusion occurs only when there is an imbalance in the areas of