BIOLOGY: :BIOLOGY: Properties of Water


Water :Water Makes up 70-90% of all living things. ¾ of the earth’s surface is covered with water; if the earth’s surface were smooth, all of it would be under 2.5 km (1.5 mi.) of water.


Water :The water molecule is polar—shared electrons spend most of the time around the oxygen atom Thus water molecules form weak hydrogen bonds that are constantly broken and reformed. Water


Properties of Water :Properties of Water Water has a high heat capacity. specific heat—the amount of heat a given amount of a substance requires for an increase in temperature. Examples: water = 1 ethyl alcohol = 0.6 sucrose = 0.3 liquid ammonia = 1.23


Slide 5:Why does water have a high heat capacity? The many hydrogen bonds linking water molecules help it to absorb heat without a great change in temperature. What are the consequences of this property to living things? Because the temperature of water rises and falls slowly, organisms are better able to maintain their normal internal temperatures.


Properties of Water :Properties of Water Water has a high heat of vaporization. It requires 540 calories of heat energy to convert 1 g of the hottest water to a gas calorie—the amount of heat that will raise the temperature of 1 g (1 mL or 1 cc) of water 1o Celsius.


Slide 7:Why does water have this high heat of vaporization? Hydrogen bonds must be broken before water boils and water molecules vaporize. What are the consequences to living things? Organisms have a way to release excess body heat. When it sweats, body heat is used to vaporize water and cool it.


Properties of Water :Properties of Water Water is an excellent solvent. Water is often called the universal solvent, because it can dissolve both hydrophilic and hydrophobic molecules.


Slide 9:What causes water to be such a good solvent? It is because water is a polar molecule; the positive and negative portions are attracted to charged regions of other polar molecules.


Slide 10:How does the fact that water is an excellent solvent help living things? Many substances can be carried throughout an organism’s body dissolved in the water of its blood.


Properties of Water :Properties of Water 4. Water molecules are cohesive and adhesive. Cohesion—water molecules stick together. Adhesion—water molecules stick to other polar surfaces.


Slide 12:How do adhesion and cohesion help living things? Allows water to transport nutrients and wastes in the bloodstream of animals and from the roots of plants through their stems to their leaves.


Properties of Water :Properties of Water Water has high surface tension. Hydrogen bonding causes water to have a high surface tension.


Slide 14:What are the consequences of high surface tension to life on earth? Some animals such as the Jesus lizard and water striders can walk on the surface of water.


Properties of Water :Properties of Water Frozen water (ice) is less dense than liquid water. As water cools the molecules come closer together. Below 4o hydrogen bonding becomes more rigid and open.


Slide 16:How do living things benefit from water expanding when freezing? a. Ice in rock crevices can break a rock into pieces making soil. b. Ice forms from the top down and acts as an insulator to keep the water underneath from freezing.


Water’s pH :Water’s pH Most life can only exist in a narrow pH range. Acids have a pH of 0-6. Bases have a pH of 8-14. When water ionizes it releases an equal number of hydrogen ions (H+) and hydroxide ions (OH-) making it neutral.


Figure 3.10 The effects of acid precipitation on a forest :Figure 3.10 The effects of acid precipitation on a forest