1. Metabolic Reactions
SBI4U

2. Maintaining Biological Order
1. Nature tends to form disorder from order.
2. Your cell is a highly ordered system, and as it functions, it tends to get disordered: Organelles start malfunctioning, enzymes are denatured etc.
3. For our cells to function effectively, order must be maintained: New enzymes and organelles must be made
4. This requires energy. The cell, therefore, requires an energy source.
Energy
Utilizes
Maintains
Biological
Organization

3. Messy Room Analogy:

4. Order and Disorder Your clean room is an ordered system
Everything functions properly: Your bed is for sleeping, closet holds clothes, chair is for sitting etc.
Over the course of time, your room becomes disordered: The chair now has clothes on it, your bed may now be the resting place for your latest shopping items etc.
You need to clean it and this requires energy to do all this work!
Your mom also uses energy to yell at you to clean your room. This energy does not do work!

5. Heat: the energy that does no work
In any system we have energy wasted as heat. This is shown by the equation below:
Work = Total Energy - Heat

6. Entropy The measure of the disorder of a system
The same equation is expressed below:
G = H - TS
G = Work, H = Total Energy, T = Temperature and S = Entropy

7. (Energy Available for Work)
Efficiency
If all the energy supplied to a system actually did work, then the system would be 100% efficient.
The table below outlines the efficiency of some systems.
As you can see, cells are pretty efficient.
Complete the table to show what percentage of energy is wasted as heat: 
Table 1: Cells Are More Efficient than Machines
Energy Converter
% Efficiency
(Energy Available for Work)
% Energy Lost as Heat
Steam Engine
Gasoline Engine
Green Plants
Refrigerator
Cells 8 17 25 35 40

8. Metabolism
So all of this entropy stuff is great and all, but what does it have to do with BIOLOGY??!!
Highly organized forms of matter such as living organisms become disordered
Energy is used to maintain their organization.
If you as a form of highly organized matter cease to eat and digest food to provide the energy needed for maintenance, you will die and become disordered.
Living organisms interact with their environments and utilise and convert energy
metabolism

9. Understanding Chemical Reactions
Energy changes occur in chemical reactions because
Old Bonds break
Requires energy
New bonds form
Releases energy
The energy changes during a chemical reaction are the net result of the breaking and formation of bonds.
Bond formation > bond breakage = energy released
Bond breakage > bond formation = energy required

10. Combustion of Hydrogen
2 H O2 → 2 H2O kcal
We will use the table on the right to calculate the energy produced.
Breaking apart 2 H2 requires 2 x 104 kcal = -208
Breaking apart O2 requires 118 kcal = -118
Forming 4 O-H bonds releases 4 x 110 kcal = +440
Total = +114
Table 2: Bond energies represent the energy required to break a bond or the amount of energy released when the bond is formed.
Bonding Atoms
Bond Energy (kcal/mol)
H-H
104
O-H
110
O=O
118

11. Units of Energy
The energy values in the equations are quoted in kilocalories.
You will also see energy expressed in kilojoules (kJ)
From now on, we will only use kilojoules since this is the SI unit for energy.
The conversion factor is: 1 kcal = kJ 

12. Exergonic and Endergonic Rxns
The equations for the combustion of glucose and palmitic acid on your handout are both exergonic.
Energy is released positive value for energy in the chemical equation, but Gibbs free energy is negative. Why?
Entropy (measure of disorder) increases for exergonic rxns.
Big molecules = ordered system, Small molecules = disordered system

13. Classwork Two examples of metabolic reactions are shown below:
C6H12O O2 → 6 CO H2O kcal
palmitic acid O2 → 16 CO H2O kcal
The above equations for the metabolism of glucose and palmitic acid respectively, releases huge amounts of heat energy. Since animals are isothermic (maintains body temperature within a narrow range), what problems will arise when breaking down these molecules?
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Thinking question: How then, do living things break down molecules?