Water

Water 70% - 95% of most organisms 70% - 95% of most organisms Water is one of the most important compounds in living organisms because… Water is one of the most important compounds in living organisms because… –Molecules and ions are dissolved in water so that they are free to move and collide with one another –Transports materials

Water is Polar Shared electrons are more attracted to the oxygen nucleus than the hydrogen nuclei – so they spend more time with Oxygen. Shared electrons are more attracted to the oxygen nucleus than the hydrogen nuclei – so they spend more time with Oxygen. This is a polar bond This is a polar bond Polar molecules have a positive end and a negative end. Polar molecules have a positive end and a negative end. This is why water can dissolve many This is why water can dissolve many –Ionic compounds (Salt) –Polar molecules (sugar)

Hydrogen bond The attraction between H and O forms a weak bond called a HYDROGEN BOND The attraction between H and O forms a weak bond called a HYDROGEN BOND

Properties of Water 1. Creeps up thin tubes (Adhesion) 2. Resists temperature change (High Heat Capacity) 3. Expands when freezes 4. High surface tension (Cohesion) 5. Takes the shape of its container (Adhesion)

1. Creeps up thin tubes Called Capillary Action Called Capillary Action

2. Resists temperature change Water requires more heat to increase its temperature than other liquids Water requires more heat to increase its temperature than other liquids

3. Expands when freezes Ice is less dense than liquid water - so it floats Ice is less dense than liquid water - so it floats

4. High Surface Tension

5. Takes the shape of its container

Robert Brown Scottish scientist Scottish scientist Used a microscope to observe pollen grains suspended in water. Used a microscope to observe pollen grains suspended in water. –The pollen grains seemed to jerk –He used dye particles and observed the same –This is Brownian Motion

Diffusion All objects in motion have kinetic energy – particles are in constant motion, colliding with each other. All objects in motion have kinetic energy – particles are in constant motion, colliding with each other. Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration This is the random motion observed by Brown This is the random motion observed by Brown This is a slow process! This is a slow process!

3 factors affect rate of diffusion 1. Concentration more particles/more motionmore particles/more motion 2. Temperature increased temperature increases energy and the faster the particles moveincreased temperature increases energy and the faster the particles move 3. Pressure Increased pressure, increases particle motionIncreased pressure, increases particle motion

Results of Diffusion Dynamic Equilibrium will result – concentration remains the same, even though particles are still in motion Dynamic Equilibrium will result – concentration remains the same, even though particles are still in motion

How does diffusion apply to Biology? Diffusion is one of the methods cells move substances into and out of the cell. Diffusion is one of the methods cells move substances into and out of the cell. The diffusion of oxygen gas occurs in the lungs – Not just a liquid process The diffusion of oxygen gas occurs in the lungs – Not just a liquid process

Review 1. Explain why water is a polar molecule. The O and two H atoms do not share the electrons equally. As a result, the O is negatively charged and the H are positively charged.

2. How does a hydrogen bond compare to a covalent bond? Hydrogen bonds are very weak compared to covalent bonds Hydrogen bonds are very weak compared to covalent bonds

3. What property of water explains why it can travel to the tops of trees? Capillary Action Capillary Action 4. What is the eventual result of the cellular process of diffusion? Particles will move from an area of higher concentration to an area of lower concentration until dynamic equilibrium is reached. After equilibrium is reached, the concentration stays the same, but particle motion continues. Particles will move from an area of higher concentration to an area of lower concentration until dynamic equilibrium is reached. After equilibrium is reached, the concentration stays the same, but particle motion continues.