Section 6.2 Water & Diffusion p

How much (%) water is in the following? Watermelon Watermelon 90% 90% Cucumber Cucumber 97% 97% Tomato Tomato 95% 95% Human Body Human Body 55-60% 55-60%

Water + its Importance Water is perhaps the most important compound in living organisms Water is perhaps the most important compound in living organisms Most of life processes can only occur when molecules and ions are free to move and collide with one another Most of life processes can only occur when molecules and ions are free to move and collide with one another when substances are dissolved in water when substances are dissolved in water water acts as a medium to transport substances in organisms water acts as a medium to transport substances in organisms water makes up 70 to 95 % of most organisms water makes up 70 to 95 % of most organisms

#1 – Water is Polar Definition Definition A molecule with an unequal distribution of charge (“+” end / “-” end) A molecule with an unequal distribution of charge (“+” end / “-” end) Results because… Results because… Electrons are not shared equally in covalent bond Electrons are not shared equally in covalent bond

#1 – Water is Polar Polar molecules attract ions as well as other polar molecules Polar molecules attract ions as well as other polar molecules Water is called the “Universal Solvent” because it can dissolve many ionic compounds (salt) + other polar molecules (sugar) Water is called the “Universal Solvent” because it can dissolve many ionic compounds (salt) + other polar molecules (sugar)

#1 – Water is Polar Water molecules form hydrogen bonds Water molecules form hydrogen bonds Weak bond – easily broken Weak bond – easily broken Occurs because of “+”/”-” charged regions Occurs because of “+”/”-” charged regions

#1 – Water is Polar Plants use capillary action to move water upwards from roots to leaves Plants use capillary action to move water upwards from roots to leaves

#2 Water resists TEMPERATURE CHANGES Requires energy to be gained/lost to increase/decrease its temperature Requires energy to be gained/lost to increase/decrease its temperature Can act like an insulator to maintain homeostasis for cells Can act like an insulator to maintain homeostasis for cells

#3 Water EXPANDS when it freezes Ice is less dense than liquid water so it floats Ice is less dense than liquid water so it floats Can cause cracks in rocks to help form soil Can cause cracks in rocks to help form soil

Diffusion Kinetic energy Kinetic energy Energy of motion – known as Brownian motion Energy of motion – known as Brownian motion

Diffusion Definition Definition Net movement of particles from an area of higher concentration to an area of lower concentration Net movement of particles from an area of higher concentration to an area of lower concentration Results due to Brownian motion Results due to Brownian motion

Diffusion Is a slow process Is a slow process Factors that affect diffusion: Factors that affect diffusion: Concentration Concentration Higher concentration – increases rate of diffusion Higher concentration – increases rate of diffusion Temperature Temperature Higher temperature – increases rate of diffusion Higher temperature – increases rate of diffusion Pressure Pressure Higher pressure – increases rate of diffusion Higher pressure – increases rate of diffusion

Diffusion Eventually the molecules reach dynamic equilibrium and can move randomly throughout the space Eventually the molecules reach dynamic equilibrium and can move randomly throughout the space

Diffusion in living systems Most substances in and around a cell are in a water solution Most substances in and around a cell are in a water solution Called an aqueous solution Called an aqueous solution Concentration gradient Concentration gradient Difference in concentration across a space Difference in concentration across a space

Diffusion in living systems A method by which cells move substances in and out of the cell A method by which cells move substances in and out of the cell Example: Example: Oxygen Oxygen

Review videos Properties of Water Properties of Water Properties of Water Properties of Water Diffusion Diffusion Diffusion