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University of Toronto St. George
Human Biology

Pages 22-25 Animal Physiology Lecture 2 readings Food webs transfer energy: Most biological processes are transfers of energy from one form to another. (Like when you smell a flower, chemical and electrical energies are transferred between the sensory systems and the brain) - Plants also catch the energy of photons from the sun and it uses it to create sugars (Photosynthesis) - When herbivores eat plants and when carnivores eat those herbivores, potential energy is produced and this energy could be converted to heat and its either lost to the environment or just stays in the animal. - Also some of this potential energy is changed to kinetic energy to use it as fuel from nutrients. !! Light is the biggest source of nutritional energy for most animals that gives them vision and identify color. Energy is stored in electrochemical gradients: The usual: Molecules that exist in the system disperse (DIFFUSE) in the empty space everywhere. Two aspects of diffusion: 1) It leads to a random distribution of molecules but keep in mind, THE rate of diffusion is SLOW! 2) When molecules diffuse, they give out energy that the cells use to drive other processes. There are gradients in our systems that were created by the cells that control our bodies and its processes. Chemical gradient: Arises when type of molecule occurs at a higher concentration on one side of a membrane. (When 10-fold more concentrated outside the cell rather than the inside so its higher concentration outside than inside) Electrical gradient: happens when the distribution of charged molecules is unequal on both sides of an electrical barrier in a circuit. (It depends on the distribution of all charged molecules and this is expressed in volts) The combination of both electrical gradient and the chemical gradient is called membrane potential! NOTE! - if a molecule is uncharged, then It can only form a chemical gradient - if a molecule is charged, then it can form a chemical gradient and influence the electrical gradient. Example: if the concentration of Na+ is greater outside the cell than inside, then there is both an electrical and chemical gradient (More positive charges outside) This is called electrochemical gradients. Thermal energy is the movement of molecules: When a system gains thermal, there is an increase in the movement of molecules in the system. Most chemical reactions involve in thermal energy: Exergonic reactions: Releases energy Endergonic reactions: absorbs energy Pages 29-31 Solutes move through water by diffusion: Concentration gradient controls the direction of diffusion of molecules in a solution. If solute molecules are large, they have a more difficult time moving through the structure of water! It’s big that it can’t go through. Large molecules like proteins and lipids diffuse really slowly than small molecules that can enter faster. There are factors that can restrict the entering of the molecules through the concentration gradient: (Diffusion) 1) There is a hydration shell that forms around many molecules and enlarges its functional size and restricts its movement. 2) Charge and solubility also affects it. Solutes can impose osmotic pressure:
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