The Chemistry of Life

Characteristics of Living Things All living things  Are made of one or more cells  Have a way to reproduce  Grow and develop  Share a universal genetic code  Must obtain material and use the energy from it  Maintain a fairly stable internal environment  Are able to respond to changes in their environment over time

So why do we need to know about chemistry in a biology class?  All living things are made up of chemicals. The chemistry of living things is called biochemistry and includes concepts of atomic structure, chemical bonding, and pH.

Chemistry Basics  Chemistry is the study of matter, its structure and composition and interactions.  All matter is made up of either elements or compounds or a mixture of elements or a mixture of compounds or a mixture of elements and compounds.  Elements are the chemical alphabet.

More Basics…  Element - substance that can't be broken down into simpler substances.  90 elements occur naturally, and about 25 are essential to life.  4 elements make up 96% of human mass.  Oxygen, Carbon, Hydrogen, Nitrogen  Elements that occur in tiny amounts (such as iron and magnesium) are called trace elements.

Chemical Bonding  Two or more elements joined chemically make a compound. The way they are joined is by a chemical bond.  There are 3 types of chemical bonds we are interested in for biology: Covalent Covalent Ionic Ionic Hydrogen Hydrogen

Atomic Structure  Protons, neutrons, electrons, nucleus, energy levels, electron shells

Ionic Bonds  Ionic bonds are the result of two atoms that gain or lose electrons.  Ions have either a positive or negative charge.  Unlike charges attract each other so that electrical attraction holds the atoms together.  ule_viewer.php?mid=57 ule_viewer.php?mid=57 ule_viewer.php?mid=57

Ionic Bonding

Covalent Bonds  Form when electrons are shared between 2 atoms.  Atoms that share electrons form molecules.  Organic compounds which are molecules that make up living tissues are also formed with covalent bonds.  Organic molecules have one or more carbon atoms, whose symbol is (C), combined with hydrogen (H), combined with oxygen (O) and or nitrogen (N).

Covalent bonds

Water  Water has many qualities that make it important to living things: It is transparent so sunlight passes through it to reach plants that live underwater. It is transparent so sunlight passes through it to reach plants that live underwater. It can form positive or negative charged particles called ions. It can form positive or negative charged particles called ions. It is an universal solvent that can dissolve many substances easily so that they can be transported by the blood or other body fluids. It is an universal solvent that can dissolve many substances easily so that they can be transported by the blood or other body fluids. It is found inside our cells and outside our cells It is found inside our cells and outside our cells  ewer.php?mid=57 ewer.php?mid=57 ewer.php?mid=57

 It exists as a liquid at room temperature, and its solid state floats and does not sink. 

Water is polar  The oxygen side of the molecule has a slightly negative charge and the hydrogen side of the molecule has a slightly positive charge which makes water a polar molecule.

Hydrogen bonding-  Attraction between the H + and the O -  Water attracts other water molecules  Water molecules can form weak bonds called hydrogen bonds.  They make water cohesive - a few molecules stick together.

This allows animals like a water strider to be able to “walk” on the surface.     

Hydrogen bonds cause capillary action: Water creeps up in thin tubes Hydrogen bonds cause capillary action: Water creeps up in thin tubes  Water molecules can form weak bonds called hydrogen bonds. They make water cohesive - a few molecules stick together.

 A. Water has a high surface tension  Cohesion-Attraction between molecules  Surface tension- surface of H 2 O molecules act like a film on surface

Copy and answer questions:  How many covalent bonds does water have?  Draw a water molecule and label the charges.  What is a hydrogen bond?  What gives water it unique properties?  Why does water cling to surfaces?  Why can a Jesus lizard walk on water?

 3. Plants take advantage of this to get water  4. Water travels from roots to leaves

Water has a high heat of vaporization  Takes more energy to break attraction and cause it to evaporate  This property helps cool human body

Water resists temperature change Requires more heat to change temperature Requires more heat to change temperature Coastal areas have less fluctuation in temperature than other areas of the same latitude Coastal areas have less fluctuation in temperature than other areas of the same latitude

 Water makes up 60 to 80 % of all living organisms and 65 to 70 % of the human body.

pH  Water is important because of its ability to form ions. It forms positive H ions and negative OH ions.  The pH scale is a measure of the amount of H ions in a solution.  The scale ranges from 0 to 14 with 7 being neutral.  Pure water has a pH of 7.  A pH of 0 to 6.9 is an acid, while a pH of 7.1 to 14 is a base or alkaline.

 Your body is designed so that each system works best within a certain pH range.  Acids form positive H ions in solution.

pH of common substances  Stomach acid 1.0 to 4.4  Lemon juice 2.5  Soft drinks 2.0 – 3.5  Acid rain 4.5  Pure water 7.0  Urine 7.2  Saliva 7.4  Blood 7.4  Ocean water 8.5  Soap 10  Oven cleaner 14