3.1 Chemical elements & water IB Biology

Chemistry Recap Element - pure substance, made of one kind of atom, unique chemical and physical properties Molecules - two or more atoms chemically combined through a covalent bond Ion - an atom or molecule with an electric charge

Elements Most common elements in living things Carbon (C) Hydrogen (H) Oxygen (O) Nitrogen (N) C, H, N, O found in proteins and nucleic acid (DNA) C, H, O found in carbohydrates and lipids

Elements found in small amounts Sulfur (S) Needed for some proteins in all organisms Form disulphide bonds Phosphorus (P) In DNA and ATP Calcium (Ca/Ca+) Bone structure, muscle contraction, cell division, regulation of cell processes Iron (Fe) Aerobic cellular respiration Sodium (Na/Na+) Nerve signals (animals), controls amount of water in cytoplasm

Bonding Ionic Bond - Gain / loss of electrons Covalent Bond - Sharing electrons

Polar Covalent Bonds Covalent bond - bond within molecule Sometimes atoms in a covalent bond do not share electrons. Sometimes atoms in a covalent bond do not share electrons equally. The result is a bond with a as seen in water molecules. The result is a bond with a slightly positive end and a slightly negative end as seen in water molecules.

Hydrogen Bonding in Water Intermolecular force Since water is, the positive ends attract the negative ends. Since water is polar, the positive ends attract the negative ends. This attraction creates This attraction creates hydrogen bonds. Hydrogen bonds are individually, but together lead to the unique properties of water Hydrogen bonds are weak individually, but together lead to the unique properties of water

Demo: Strength of hydrogen bond Immerse two glass microscope slides in water Place together lengthways so bottom slide forms a lip Pile 25 fil coins onto the lip of bottom slide How many can it hold before the hydrogen bond breaks? **Safety - slide may break**

Water H 2 O - two hydrogen atoms, one oxygen atoms Molecule formed by polar covalent bond Unequal sharing of electrons Forms a charge distribution Partial positive and partial negative Hydrogen bond gives water unique properties

Properties of Water Cohesion Water molecules stick to each other due to hydrogen bonds between them Surface tension

Cohesion Activity Obtain a 1 dirham coin Use an eyedropper to place water onto coin, 1 drop at a time Record # of drops and qualitative observation Repeat with a small amount of dish soap on coin Discuss results

Cohesion - Water used as a transport medium Many substances can be dissolved and therefore carried in water The of water lets it be pulled to a great height in plants, The cohesion of water lets it be pulled to a great height in plants, transporting dissolved substances Water can also due to its high heat capacity (blood carries from one body part to another, etc.) Water can also transport heat due to its high heat capacity (blood carries from one body part to another, etc.)

Properties of Water Versatile solvent Because water has areas of partial positive and negative charge, it can many substances that are Because water has areas of partial positive and negative charge, it can dissolve many substances that are polar, positively charged, or negatively charged non-polar, uncharged substances (lipids / fats / oils) Water does NOT dissolve non-polar, uncharged substances (lipids / fats / oils) Medium for most in living organisms Medium for most chemical reactions in living organisms

Solvent: Water as a medium for metabolic reactions most reactions of life happen with the substances dissolved in water (cytoplasm is mostly water) Solvent: most reactions of life happen with the substances dissolved in water (cytoplasm is mostly water) Ex. Oxygen from the air must dissolve into the water on the inside of the lungs : the state allows substances to stay in the liquid but enough to come in contact and react State: the liquid state allows substances to stay in the liquid but move around enough to come in contact and react Excellent for metabolic reactions

Properties of Water Thermal properties Heat capacity (high specific heat): large amounts of are needed to raise the temperature of water Heat capacity (high specific heat): large amounts of energy are needed to raise the temperature of water State changes (high heat of vaporization): water boils at a high temperature and has a as a liquid State changes (high heat of vaporization): water boils at a high temperature and has a large temperature range as a liquid Evaporative cooling (high heat of vaporization): energy taken to and free water molecules as they evaporate, cools remaining water Evaporative cooling (high heat of vaporization): energy taken to break hydrogen bonds and free water molecules as they evaporate, cools remaining water

Thermal properties: Water as a coolant : Terrestrial organisms may to remove excess heat Evaporative cooling: Terrestrial organisms may sweat or pant to remove excess heat : Water organisms may transfer heat to the environment without raising the water temperature by much Heat capacity: Water organisms may transfer heat to the environment without raising the water temperature by much

Video Properties of water t/animations/content/propertiesofwater/ water.html

Homework Pg 42 Thinking about science