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Chapter 5

BGYB30 Chapter 5 textbook notes

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University of Toronto Scarborough
Biological Sciences

Chapter 5 Membrane Dynamics BGYB30 Mass Balance & Homeostasis: - The law of mass balance: if the amount of a substance in the body is to remain constant, any gain must be offset by an equal loss. - Total amount (or load) of substance x in the body = intake + production excretion metabolism - Mass Balance = Existing body load + Intake or metabolic production Excretion or metabolic removal. - The rate at which a molecule disappears from the body by excretion, metabolism, or both is called the molecules clearance. - Mass Flow (amount xmin) = concentration (amount xvol) volume flow (volmin) - Because of the free movement of water, the extracellular and intracellular compartments can reach a state f osmotic equilibrium, in which the total amount of solute per volume of fluid is equal on the two sides of the cell membrane. At the same time, however, the body is in a state of chemical disequilibrium, in which the major solutes are more concentrated in one of the two body compartments than in the other. Example: -> Na , Cl and HCO are3more concentrated in extracelullar fluid than in intracellular fluid. -> Whereas, K are more concentrated inside the cell. -> Ca is more concentrated in the extracelullar fluid than in the cytosol, although many 2+ cells store Ca inside organelles such as the endoplasmic reticulum and mitochondria. - The inside of the cell is slightly negative relative to the extracelullar fluid. - Homeostasis is not the same as equilibrium. The intracellular and extracelullar compartments of the body may be in osmotic equilibrium, but they are also in chemical and electrical disequilibrium. * The intracellular fluid can be distinguished from the extracelullar fluid by the ICFs high concentration of K ion and low concentration of Na , and Cl ions.- Diffusion: - Cell membranes are selectively permeable; the lipid and protein composition of a given cell membrane determines which molecule will enter the cell and which will leave. - The size of the molecule and its lipid solubility influence its movement across cell membranes. - Passive transport doesnt require the input of energy Active transport requires the input of energy (e.g. high-energy phosphate bond of ATP) - Diffusion is the movement of molecules from an area of higher concentration of the molecules to an area of lower concentration of the molecules. www.notesolution.com
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