Chemistry of Organisms

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Composition of Matter

Ø  Everything in the universe is made of matter

Ø  Matter takes up space & has mass

Ø  Mass is a measure of the amount of matter in the substance

Ø  Mass & weight are NOT the same

Ø  Weight is a measure of the pull of gravity on an object

Question: Is the mass of an object the same on the moon as it is on the Earth? Is its weight the same? (Hint: Gravitational pull on the moon is 1/6 of that on the Earth.)

Ø  Matter exists in 4 states – solid, liquid, gas, & plasma

Ø  Solids have both a definite volume & definite shape (rock)

Ø  Liquids have a definite volume but no definite shape; they can be    poured (water)

Ø  Gases do not have a definite volume or definite shape, but they take the  volume & shape of their container

Ø  Plasmas have no definite volume, no definite shape, and only exist at extremely high temperatures such as the sun

Ø  Chemical Changes in matter are essential to all life processes

Ø  Biologists study chemistry because all living things are made of the same kinds of matter that make up nonliving things


Ø     Elements are pure substances which cannot be chemically broken down into simpler kinds of matter

Ø     More than 100 elements have been identified, but only about 30 are important in living things

Ø     All of the Elements are arranged on a chart known as the Periodic Table

Ø     Periodic charts tell the atomic number, atomic mass, & chemical symbol for every element

Ø     Four elements, Carbon – C, Hydrogen – H, Oxygen – O, and Nitrogen – N make up almost 90% of the mass of living things

Ø     Every element has a different chemical symbol composed of one to two letters

Ø     Chemical symbols usually come from the first letter or letters of an element like C for Carbon and Cl for Chlorine

Ø     Some chemical symbols come form their Latin or Greek name such as  Na for Sodium (natrium) or K for Potassium (Kalium)

Ø      Elements in the same horizontal period on the periodic table have the same number of energy levels (e.g. H & He in period 1 have only a K energy level)

[Periodic Table]
All Period 2 elements have 2 energy levels
(K & L)

Ø      Elements in the same vertical Family on the periodic table have the same number of electrons in their outermost energy level & react similar (e.g. Family IV, the Carbon family all have 4 electrons in their outermost energy level)


Ø     Atoms are the simplest part of an element that keeps all of the element’s properties

Ø     Atoms are too small to be seen so scientists have developed models that show their structure & properties

Ø     Atoms consist of 3 kinds of subatomic particlesprotons & neutrons in the center or nucleus, and electrons spinning in energy levels around the center

Ø     The nucleus is the center of an atom where most of the mass is concentrated

Ø     Protons are positively charged ( p+ ),  have a mass of 1 amu (atomic mass unit) , are found in the nucleus, and determine the atomic number of the element

Example:  Carbon has 6 protons so its atomic number is 6

Ø     Neutrons are neutral or have no electrical charge (n), have a mass of 1 amu, are found in the nucleus, and when added to the number of protons, determine the atomic mass of the element

Example:  Sodium has 11 protons and 12 neutrons so its atomic mass is 11+12=23 amu

Ø     Electrons (e-) are negatively charged, high energy particles with little mass that spin around the nucleus in energy levels

Ø     Seven energy levels (K, L, M, N, O, P, & Q) exist around the nucleus and each holds a certain number of electrons

Ø     The K energy level is closest to the nucleus & only holds 2 electrons, while the  L – Q energy levels can hold 8 electrons  

Ø     Electrons in outer energy level are traveling faster & contain more energy than electrons in inner levels  

Ø     The number of protons (positive charges) and electrons (negative charges in an atom are equal so the net electrical charge on a atom is zero making it electrically neutral

Ø     Stable or non-reactive atoms have an outer energy level that is filled with electrons  


Ø     Most elements do not exist by themselves; Most elements combine with other elements

Ø      Compounds are made of atoms of two or more elements chemically combined

Ø      Chemical Formulas represent a compound & show the kind & number of atoms of each element  (e.g. H2O has 2 hydrogen & 1 oxygen)

Ø      Compounds have different physical & chemical properties than the atoms that compose them  (e.g. hydrogen & oxygen are gases but H2O is a liquid)

Ø      The number & arrangement of electrons in an atom determines if it will combine to form compounds

Ø      Chemical reactions occur whenever unstable atoms (outer energy level not filled) combine to form more stable compounds

Ø      Chemical bonds form between atoms during chemical reactions

Types of Chemical Bonds

Ø     Covalent bonds form between atoms whenever they share 1 or more pairs of electrons (e.g. H2O)  

Ø     Molecules form from covalent bonding & are the simplest part of a compound (e.g. NaCl, H2O, O2)  

Ø     Ionic bonding occurs between a positively & negatively charged atom or ion  

Ø     Positively charged ions have more electrons (-) than protons (+); negatively charged ions have more protons than electrons

Ø     Table salt (NaCl) forms when the 1 outer electron of Na is transferred to the outer energy level of chlorine that has 7 electrons (e-)

Ø     Sodium (Na) with 1 less e- becomes positively charged, while Chlorine (Cl) with 1 more e- becomes negatively charged; the + and – charges attract & form the ionic bond holding NaCl together

Ø     Other types of chemical bonding include hydrogen bonding


Ø     Energy is the ability to do work

Ø     Energy occurs in several forms & may be converted from one form to another

Ø     Sunlight is the ultimate energy for all life on earth

Ø     Forms of energy include chemical, electrical, mechanical, thermal, light, & sound

Ø     Free energy is the energy available for work (e.g. cells have energy to carry out cell processes)

Ø     Cells convert the chemical energy stored in food into other types of energy such as thermal & mechanical

Ø     Energy is used to change matter form one state into another (e.g. liquid into a gas)

Chemical Reactions

Ø     Living things undergo thousands of chemical reactions

Ø     Chemical equations represent chemical reactions

Ø     CO2 + H20—–goes to—–H2CO3  (carbonic acid) is a sample Chemical Reaction in living things

Ø     Reactants are on the left side of the equation, while products are on the right side

Ø Activation energy is required to start many reactions

Ø     Chemical bonds are broken, atoms rearranged, and new bonds form in chemical reaction

Ø     Plants use sunlight to produce sugars such as C6H12O6 glucose; the chemical energy from the sun is stored in the chemical bonds of glucose

Ø      Organisms eat plants, break down the sugars, and release energy along with CO2 & H2O

Ø      Exergonic reactions involve a net release of energy; while endergonic reactions involve a net absorption of energy

Ø      Energy must be added to the reactants for most chemical reactions to occur; called activation energy

Ø      Enzymes are chemical substances in living things that act as catalysts & reduce the amount of activation energy needed

Ø      Organisms contain thousands of different enzymes

Ø      Most enzymes end with –ase (e.g. lipase is the enzyme that acts on lipids)

Reduction-Oxidation (Redox) reactions

Ø     Reactions in which e- are transferred between atoms is a redox or reduction-oxidation reaction (e.g. formation of table salt NaCl)

Ø     In oxidation reactions, a reactant loses 1 or more e- & becomes positively (+) charged (e.g. Sodium atom becomes a Na+ ion)

Ø     In a reduction reaction, a reactant gains 1 or more e- and becomes negatively (-) charged (e.g. Chlorine atom becomes a Cl- ion)

Ø     REDOX reactions always occur together; the electron(s) from the oxidation reaction are then accepted by another substance in the reduction reaction


Ø     A large percentage of the mass of organisms is water & many of the chemical reactions of life occur in water

Ø     A solution  is a uniform mixture of one substance in anther

Ø     Solutions may be mixtures of solids, liquids, or gases

Ø     The solute is the substance uniformly dissolved in the solution & may be ions, molecules, or atoms

Ø     The solvent is the substance in which the solute is dissolved

Ø     Water is known as the universal solvent 

Ø     Dissolving one substance in another does not alter their chemical properties

Ø     The concentration of a solution is a measure of the amount of solute dissolved in a given volume of solvent

Ø     Increasing the amount of solute increases the solution’s concentration

Ø     Aqueous solutions are solutions in which water is the solvent; these are important in living things (e.g. blood, cytoplasm of cell…)

Acids and Bases

Ø     The degree of acidity or alkalinity (basic) is important in organisms

Ø     The force of attraction between molecules is so strong that the oxygen atom of one molecule can actually remove the hydrogen from other water molecules; called Dissociation

Ø      H20—–GOES TO—– H+  +  OH-

Ø     OH- called hydroxide ion; H+ called hydrogen ion

Ø     Free H+ ion can react with another water molecule to form H3O+  (hydronium ion)

Ø     Acidity or alkalinity is a measure of the relative amount of H+ and OH- ions dissolved in a solution

Ø     Neutral solutions have an equal number of H+ and OH- ions

Ø     Acids have more H3O+ ions than OH- ions; taste sour; and can be corrosive

Ø     Bases contain more OH- ions than H3O+ ions; taste bitter; & feel slippery  


Examples of Common Acids

  • citric acid (from certain fruits and veggies, notably citrus fruits)
  • ascorbic acid (vitamin C, as from certain fruits)
  • vinegar (5% acetic acid)
  • carbonic acid (for carbonation of soft drinks)
  • lactic acid (in buttermilk)
Examples of Common Bases

  • detergents
  • soap
  • lye (NaOH)
  • household ammonia

PH Scale

Ø     Compares the relative concentration of H3O+ ions and OH- ions

Ø     Scale ranges from 0 to 14; 0-3 is very acidic; 7 is neutral; 11-14 is very basic or alkaline


Ø    Litmus paper, phenolphthalein, pH paper, & other indicators that change color can be used to measure pH


Ø     Control of pH is important to organisms

Ø     Enzymes function only within a narrow pH range; usually neutral

Ø     Buffers neutral acids or bases in organisms to help control pH

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