Period+4+Ch.+3+2011


 * AP Biology**
 * Chapter 3 Guided Reading Assignment**

1. Why is water considered a polar molecule? Water is considered a polar molecule because one side of the molecule is a different charge then the other side of the molecule.  2. For each of the below listed properties of water – briefly define the property and then explain how water’s polar nature and polar covalent bonds contribute to the water special property. Include an example in nature of each property also. a. Cohesion Occurs when hydrogen bonds together. This allows water to become more structured. Water molecules that are evaporating from the leaves on plants help pull up new molecules from the roots and ground to help keep the plant supplied with the proper amounts of water.

b. Adhesion The clinging of one substance to another. It occurs because the polar bonds allow the water to cling onto other substances. Water adheres to the walls of cells to help counter the downward pull of gravity when water leaves the roots to go to the leaves.



c. Surface tension A measure of how difficult it is to stretch or break the surface of a liquid. The hydrogen atoms in water bond to the hydrogen atoms in the air, creating a greater surface tension than most other liquids. This describes how some animals can run, walk, or stand on water.



d. High specific heat The amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1 degree Celsius. The specific heat of water is 1 __#|calorie__ per gram per degree Celsius. Water has a high specific heat because of its hydrogen bonding (heat must be absorbed in order to break hydrogen bonds, and heat is released when hydrogen bonds form). In nature, a large body of water can absorb and store a large amount of heat from the sun, which can later be used to warm up the air as it cools down at night and during the winter. This creates a favorable environment for marine life.



e. Heat of vaporization The quantity of heat a liquid must absorb for 1g of it to be converted from the liquid to the gaseous state. To evaporate 1g of water at 25 degree C, about 580 cal of heat is needed. This is another property of hydrogen bonds, which must be broken before the molecule can make a departure from the liquid.

f. Evaporative cooling: the property of a liquid whereby the surface becomes cooler during evaporation, owing to a loss of highly kinetic molecules to the gaseous state. this contributes to the stability of temperature of lakes and ponds which provides organisms from overheating.

3. What is special about water and density? Water is one of the few sunstances of earth that is less dense in its solid form that it is in its liquid form. This why ice floats in water. 4. Define the following terms: a. Solute ~ A solute is a substance that is dissolved in a solution

b. Solvent ~ A solvent is what a solute is dissolved in

c. Aqueous solution ~ An aqueous solution is a solution in which water is the solvent

d. Hydrophilic- any molecule that has an affinity or an attraction to water e. Hydrophobic - any molecule that has no attraction to water f. Colloid- A substance that constists of particles dispersed through another substance, like smoke. g. Hydration shell The hydration shell is the water molecules surrounding a dissolved ion.

h. Molarity Molarity is the amount of solute per each liter of a solution.

5. Label the diagram below to demonstrate the dissociation of the water molecule and then relate this diagram to pH. In this reaction, water is being dissociated into a hydrogen ion and a hydroxide ion. This reaction will eventually reach a state of equilibrium. Changing the concentrations of the hydrogen and hydroxide ions can cause a large change on the cell's proteins and other complex molecules. Adding solutes (acids and bases) disrupt the equal H+ and OH- concentrations, and pH can then be measured.

6. What defines an acid and a base? An acid is something that increases the hydrogen ion concentration of a solution and a base is something that decreases the hydrogen ion concentration



7. Why are “apparently” small changes in pH so important in biology? The pH is measured logarithmically. If pH varies by one it actually varies by 10. So, even a slight change in pH can be harmful to the chemical processes in a cell, killing the cell.



8. What is a buffer and write and explain the carbonic acid buffer system in human blood – yes we are back to the equation AGAIN! Buffers are substances that change the concentrations of H+ and OH- in a solution. The carbonicc acid buffer system keeps blood pH around 7.4 by yeilding a bicarbonate ion and a hydrogen ion. An equation for example would be - H2CO3->HCO3-+H+

9. What is acid precipitation and why is it important to living organisms?

Acid precipitation is rain, snow, or fog with a pH lower (more acidic) than normal precipitation. It is also refereed to as "acid rain". Acid precipitation takes in the sulfur oxides and nitrogen oxides that are are formed by the burning of fossil fuels. The acid rain can fall on land and wash away minerals. Also, it can increase the acidity of the environment if it is too basic. It then balances out. It can also take up pollution.