Chapter 3: Water and the Fitness of the Environment IB HL Biology Douglas County HS Mr. Spoor Topic 2: The Chemistry of Life

Essential Elements of Life- Topic About 25 of the 92 elements are essential to life Carbon, hydrogen, oxygen, and nitrogen make up 96% of living matter Most of the remaining 4% consists of calcium, phosphorus, potassium, and sulfur Trace elements are those required by an organism in minute quantities, such as iodine.

Other Biologically Important Elements and their functions- Topics & Calcium (Ca): Formation of bones and shells in animals, involved with muscle contraction and neuron activity in animals. Phosphorous (P): Forms energy storing compounds ATP, Nucleotides (A,T, G, C, U), and membrane building molecules (phospholipids). Sulfur (S): amino acids and protein structure Sodium (Na): Neuron activity, water balance, and membrane transport Potassium (K): membrane transport and muscle activity Iron (Fe): oxygen transport of red blood cells as a component of hemoglobin. Magnesium (Mg): light activated atom component of chlorophyll molecules. This is important!

Overview: The Molecule That Supports All of Life 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Did you know that… Water is the most common chemical compound in the world Contributes to global warming and the greenhouse effect? Is found in large quantities in tumors and other cancers? Was found in significant quantities in the levees breached during Hurricane Katrina? Is ingested by cows in large quantities, leading to increased milk production?

Properties of Water Let’s look at the major properties of water and how they are important to living things

1. Polar Properties Water is Polar Because of the uneven balance of extra electrons possessed by oxygen, water has a slightly negative charge The hydrogen end is slightly positive

Topic Draw and label water molecules to show their polarity and hydrogen bond formation (add the charges and bond types) Hydrogen Bonding Water has hydrogen bonding between molecules. This causes the molecules to “stick” together. Each molecule can attract 4 other water molecules. This gives water some of its unique characteristics. Important

2. Solvent Properties The polar properties of water make it a good solvent for: Polar molecules (e.g. sugars and alcohols) These form hydrogen bonds with the water molecules Ionic compounds (e.g. salts, acids and bases) These dissociate into their component ions

Solvent properties and life Water is a very important transport medium for living organisms, because of its solvent properties and... Water is also an important medium for biochemical reactions because it remains a liquid over a large range of temperatures

3. Cohesive Properties a. Water has Cohesion: -Water molecules stick to each other due to hydrogen bonding Important in fluid transport of plants, such as tall trees The water forms a tall column that rarely breaks

b. Surface Tension Surface tension is a measure of how hard it is to break the surface of a liquid This is strong enough for some organisms to be supported Surface tension is related to cohesion

c. Adhesion Water also exhibits adhesion- an attraction to other substances. Together with cohesion, this helps water reach the tops of the tallest trees. Giant red wood Sequoiadendron giganteum N. California

4. Thermal Properties  a. Water has a very high thermal capacity (4.2 J°C -1 g -1 ) and a high heat of vaporization.  b. Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to gas.  Water absorbs heat from warmer air and releases stored heat to cooler air  Water can absorb or release a large amount of heat with only a slight change in its own temperature

High Specific Heat c. The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC The specific heat of water is 1 cal/g/ºC Water resists changing its temperature because of its high specific heat

High Heat Capacity and Life Blood acts as a transport medium for heat in living things Since blood is made up of mostly water, it can carry warmth to cooler locations in the body Very low or very high temperatures may damage enzymes or slow down important chemical reactions Because the human body is mostly water, a sunbather can absorb a lot of heat energy without sending her/his body temperature soaring

Water is a great coolant d. Evaporative cooling helps to moderate temperatures in bodies of water as well as in the bodies of land organisms. This is why sweating cools you off. Transpiration in plants also acts as a coolant This helps keep global temperatures in check.

African elephants (Loxodonta africana) bathing © Shirley Burchill 2007

e. High Boiling Point Water’s boiling point is very high (100 C) compared to other liquids A large amount of energy is required to break the hydrogen bonds between water molecules

5. Other properties: Density Less dense as solid than liquid due to hydrogen bonding Crystalline lattice keeps molecules at a distance

Density This allows ice to float atop bodies of water, serving as an insulator for life below

Other properties: Transparency Water is transparent and translucent Allows light to penetrate bodies of water so producers can photosynthesize

Hydrophilic and Hydrophobic Substances A hydrophilic substance is one that has an affinity for water A hydrophobic substance is one that does not have an affinity for water Oil molecules are hydrophobic because they have relatively nonpolar bonds