The Biological Importance of Water

Major component of all living systems and our planet. Why is water important? Major component of all living systems and our planet. Occupies most of a cell’s volume. Has major properties that living systems require. http://viewpure.com/0eNSnj4ZfZ8?start=0&end=0

Water is dipolar- made up of two elements, hydrogen and oxygen Neutral in charge and polar covalent. Polarity: unequal sharing of electrons, leading to a partially positive and partially negative charge. The oxygen atom is slightly negative and the hydrogen atoms are slightly positive. Covalent bonds are between the hydrogen and oxygen atoms, resulting in an uneven sharing of electrons = polarity. Water molecules form hydrogen bonds with other neighboring water molecules. Each H2O molecule can form 4 hydrogen bonds with four other water molecules. Groups of hydrogen bonds are very strong, but bonds by themselves are weak. Also find hydrogen bonds holding our DNA and proteins together.

Label the hydrogen and covalent bond

Covalent Bond

Polarity Polar Nonpolar Water soluble Asymmetrical: uneven electron distribution, do not share electrons Examples: water, sugar, salt, ethanol, hydrogen sulfide The electrons of the polar covalent bonds spend more time near the oxygen than the hydrogen. Polarity allows water to form hydrogen bonds with each other. Ionic compounds dissolve in water to form ions: for most biological reactions to occur the reactants MUST dissolve in water. Fat soluble Symmetrical: electrons are evenly distributed. Strongly covalently bonded Examples: fats, oils, cell membranes and cell walls, carbon dioxide, gasoline.

Water, The Universal Solvent Dissolves almost all substances (mostly polar), and provides a medium in which other molecules can interact. Soluble: able to be dissolved, especially in water. Solution: uniform mixture of two or more substances. Solvent: liquid in which a solute dissolves Important solutions in our body (water = solvent): blood plasma, sweat, urine, and tears Solute: substance that dissolves in a solvent Important solutes in our body: oxygen, salt, sugars, and calcium Examples: water= solvent, Kool-Aid powder / sugar= solute, Kool-Aid= solution

Hydrophilic Hydrophobic Amphipathic “water loving” Molecules dissolve in water. “water fearing” Nonpolar molecules separate in water. Molecules have both polar and nonpolar regions. Ex- Cell Membrane

Recall Questions Take 5- 10 minutes and answer the questions in your notes.

The Properties of Water

Cohesion & Surface Tension Water molecules stick together Why? Hydrogen bonding Causes: surface tension, which means how difficult it is to break the surface. Surface tension: creates a skin on the surface of the water. Examples: Skipping rocks, rain drops beading up on a car, water droplets on a penny, spider walking on water http://viewpure.com/45yabrnryXk?start=0&end=0

Adhesion Water molecules stick to other objects Examples: Meniscus (graduated cylinder), wet microscope slides sticking together

Capillary Action Movement of liquid through a narrow passage / H2O molecules stick to tubes of small diameter. Result of the cohesion of water molecules sticking to each other, and adhesion of water molecules sticking to another surface. Examples: Drinking straw Food coloring added to water to dye flowers Plants transporting water from roots to leaves

High Specific Heat Water resists changes in temperature; therefore water must absorb more heat energy to increase temperature. Very important because our cells release a lot of heat, and water absorbs that heat, which allows us to regulate cell temperatures= HOMEOSTASIS Specific heat is the energy required to raise 1g of water by 1ºC. Examples: oceans cool slower than land due to the high heat capacity of water.

High Heat of Vaporization Vaporization = evaporation & boiling Water is changing from a liquid to a gas Liquid molecules enter the air Evaporation produces a cooling effect Hydrogen bonds must be broken before water can evaporate and this requires a lot of energy. Example: sweating (humans) or panting in dogs= dogs can’t sweat through their skin, they pant to circulate air through their bodies to cool down= evaporative cooling.

Lower Density When Solid Water freezes = crystalline structure maintained by hydrogen bonding O C / 32F = Freezing Ice is less dense than liquid water because the hydrogen bonds are positioned in a way that pushes the molecules apart= lowers density. When ice melts to liquid water, the structure collapses and the density of the liquid increases. Ecosystems: Advantages: protects aquatic ecosystems. If ice filled an entire lake or ocean, from bottom to top, all of the living organisms would die. Also allows turnover of nutrients. In the spring, the ice melts; water sinks and pushes up the nutrient rich water.

Guess the property

https://www. google. com/url https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiohO3Lht3KAhVDHR4KHYMACMIQjB0IBg&url=http%3A%2F%2Fwww.britannica.com%2Fscience%2Fcohesion&psig=AFQjCNEtkP_qaT6q30R8TugoqoSA6HZnsA&ust=1454638963545832

Videos http://viewpure.com/HP5dDJGz8b4?start=0&end=0 https://vimeo.com/83880203

Review Table Complete the review table without looking back in your notes! You can do it, have faith in yourself!