Water and Life on Earth AP Biology Chapter 3:
Life on Earth is based on WATER Water is the Biological medium on Earth All living organisms require water more than any other substance Most cells are surrounded by water, and cells themselves are about 70–95% water The abundance of water is the main reason the Earth is habitable
Figure 3.1 Figure 3.1 How does the habitat of a polar bear depend on the chemistry of water? 3
Polar covalent bonds in water molecules result in hydrogen bonding The water molecule is a polar molecule: the opposite ends have opposite charges Polarity allows water molecules to form hydrogen bonds with each other © 2011 Pearson Education, Inc.
Figure 2.16 A hydrogen bond
Special Properties of Water Cohesion Is the attraction of like substances Occurs in water because of hydrogen bonding between water molecules Is the ability to resist rupture Allows for organisms to “walk on water surfaces” Allows for water to be drawn up to the tops of plants (p35)
Adhesion Water are often attracted to other polar substances YET Adheres to other unlike molecules (non-polar substances) When water adheres to the walls of narrow tubing or to absorbent solids like paper, it demonstrates capillary action. (Model with capillary tube)***
Transport in plant Adhesion + Cohesion
Water Transportation in Plants Video Clip…
Figure 3.4 10/3/17 Figure 3.4 Walking on water. 11
Surface Tension The hydrogen bonds of water provide for good high surface tension which is the difficulty to stretch or break the surface of a liquid
Activities See how many drops of water you can get on the head of a penny! What property of water is this illustrating? Use the capillary tube to and red solution to see what happens!
Demo Ice in Water???? Why does it float??? Why does it not float?
Density of Water –Ice Floats Water molecules are most dense at 4C, which means that solid water is less dense than liquid water, or ice floats. ICE WATER STEAM
Water is significant How are these properties of water so very important for life on this planet? Site examples… with explanation Share! ???
Heat and Temperature Kinetic energy is the energy of motion Heat is a measure of the total amount of kinetic energy due to molecular motion Temperature measures the intensity of heat due to the average kinetic energy of molecules © 2011 Pearson Education, Inc.
Hydrogen Bonding Because water has hydrogen bonding it has: A High Specific Heat, the amount of energy needed to increase the temperature of 1 gram of a substance 1 degree Celsius (changes temp slowly) A High Heat of Vaporization, the amount of heat energy needed to change a liquid to a gas (or evaporate) A High Heat of Fusion, the energy needed to convert a substance from a liquid to a solid (freezing, in the case of water)
Because of Specific Heat: The temperatures of large bodies of water are very stable in response to the temperature changes of the surrounding air. You must add a large amount of energy to warm water or remove a large amount of energy to cool water. When sweat evaporates from your skin, large amounts of heat are taken with it and you are cooled.
What About Water’s Temp? Water provides a more stable environment, in terms of temperature, for cells and ecosystems Life can occur in temperate lake areas, since the frozen ice serves to insulate the water below. P50… what about the shrimp?
What does this tell us?
Water is an excellent solvent - Universal Solvent Solvent Properties Water is an excellent solvent - Universal Solvent Ionic substances are soluble in water because the poles of the polar water molecule interact with the ionic substances and separate them into ions The ionic compound is said to dissociate. (such as NaCl)
Na Na Cl Cl Figure 3.7 Figure 3.7 Table salt dissolving in water. 25
What about Covalent molecules? Will covalent bonded molecules dissolve in water? Why or why not? Note examples and explain why? ???
Hydrophobic/Hydrophilic Substances that dissolve in water are called Hydrophilic (water loving) Substances that lack charged poles, (nonpolar covalent substances) do not dissolve in water. These are called Hydrophobic (water fearing)
Figure 3.8 + + Figure 3.8 A water-soluble protein. 28
Amphipathic Some molecules have both hydrophobic and hydrophilic ends. Such molecules are said to be AMPHIPATHIC.
Solutions Solute (substance that is dissolved… example – salt, NaCl) Solvent (substance that does the dissolving… usually WATER)
Universal Solvent How are the terms – solute, solvent and solution related? How would you go about making one Liter of a 1M solution of sucrose? What do you need to know? How would you calculate it? Volunteers???
Important Water Properties Polar Hydrogen Bonds Cohesion Adhesion Surface Tension High Specific Heat Universal Solvent
Making solutions What would happen if you added 342 g of sucrose to 1000 ml of Distilled Water? Would it be a 1M solution? How many molecules of sucrose is in 1M solution? How much sucrose would you need to make 500ml of 1M sucrose solution? …1000ml of a 0.5M sucrose solution?
Calculate & Make Your solution?... 342g of Sucrose = total mass of 1 mole of Sucrose (sugar) molecules 1M = 1 mole of sucrose in 1000mL (1L) of solution Calculate for your solution (note board)
Make Solutions of Sucrose 10/3/17 or 10/4/17 We need 1 liter solution of the following molarities of Sucrose 1M Sucrose 0.8 M Sucrose 0.6 M Sucrose 0.4 M Sucrose 0.2 M Sucrose Your lab station cup indicates your molarity
Before talking about Acids and Bases, etc Begin by doing the following: Acquire a beaker with your solution & dropper (add liquid to beaker, if needed) Grab one of the pH items on front table Make your prediction on white board for your solution
Go to Acid/Base PP
Water: Acids and Bases At any given time, a fixed proportion of a volume of water will be: H+ (hydrogen ions) Acids OH- (hydroxide ions) Bases And the rest will be H2O
ACIDS and BASES ACIDS: BASES: A substance which liberates H+ in solution Contains more H+ ions than OH- BASES: A substance which combines with H+ in solution A substance which donates OH- to solution Contains more OH- ions that H+
pH (power of Hydrogen) Reactions of living organisms are very sensitive to levels of pH It is critical to maintain proper pH in an environment where cells and tissues present An optimum pH is essential for cellular metabolism (10 x -7)
Acidic solutions have pH values less than 7 Basic solutions have pH values greater than 7 Most biological fluids have pH values in the range of 6 to 8 © 2011 Pearson Education, Inc.
pH Scale 1 2 Increasingly Acidic [H+] > [OH] 3 4 Acidic solution 5 Figure 3.10 pH Scale 1 Battery acid 2 Gastric juice, lemon juice H+ H+ H+ Vinegar, wine, cola H+ OH 3 Increasingly Acidic [H+] > [OH] OH H+ H+ H+ H+ 4 Acidic solution Tomato juice Beer Black coffee 5 Rainwater 6 Urine OH OH Neutral [H+] = [OH] Saliva OH 7 H+ H+ Pure water OH OH Human blood, tears H+ H+ H+ 8 Seawater Neutral solution Inside of small intestine 9 Figure 3.10 The pH scale and pH values of some aqueous solutions. 10 Increasingly Basic [H+] < [OH] Milk of magnesia OH OH 11 OH H+ OH OH Household ammonia OH H+ OH 12 Basic solution Household bleach 13 Oven cleaner 14 46
Buffers The internal pH of most living cells must remain close to pH 7 Buffers are substances that minimize changes in concentrations of H+ and OH– in a solution Most buffers consist of an acid-base pair that reversibly combines with H+ © 2011 Pearson Education, Inc.