Energy unit 2 bio
Energy Transformation in Living Things – Notes
A firefly’s light is produced by bioluminescence.
Bioluminescence is a chemical reaction that converts chemical energy into light energy.
This reaction happens in special cells in the firefly’s lower abdomen.
Living things carry out thousands of chemical reactions every day.
These reactions require or release energy.
Life is energy-intensive because organisms constantly use and transform energy.
Energy transformation = the consumption and release of energy.
Energy transformations occur continuously throughout an organism’s life.
Energy can change from one form to another (example: chemical → light).
Metabolism – Notes
Metabolism is the term that describes all chemical reactions in living organisms.
Metabolism is constant:
Begins at conception
Ends only when an organism dies
Two Types of Metabolic Reactions
Energy-producing reactions (catabolic reactions)
Break down complex molecules into simpler molecules
Release energy
Energy-consuming reactions (anabolic reactions)
Build complex molecules from simpler molecules
Require energy
Example of Metabolism
Eating sugar:
Sugar molecules are broken down into simpler molecules
This process releases energy
The released energy is used to:
Pump blood
Heal tissue
Form muscle
Support growth
Metabolic Rate
Children have higher metabolic rates than adults
Because they are growing
Younger children have even higher metabolic rates
Because they grow faster
Metabolic Pathways – Notes
Metabolic pathways are the ordered sequences of chemical reactions that occur during metabolism.
There are two types of metabolic pathways:
Catabolic pathways
Anabolic pathways
How a Metabolic Pathway Works
A pathway starts with a specific molecule from food, called a reactant.
The reactant is changed through several steps.
These steps result in a final product.
Each step involves a chain of chemical reactions.
Role of Enzymes
Reactions occur in the presence of a catalyst.
A catalyst speeds up chemical reactions without being used up.
Enzymes are the catalysts in living organisms.
Purpose of Metabolism
Metabolism manages the cell’s material and energy resources.
It ensures cells have:
Enough energy
Necessary materials to function and grow
Catabolic and anabolic pathways work together to keep cells alive.
Catabolic and Anabolic Pathways – Notes
Catabolic Pathways
Catabolic pathways break down complex molecules into simpler compounds.
This process releases energy.
Example:
Cellular respiration
Glucose and other fuels → carbon dioxide + water
Energy is released
Anabolic Pathways
Anabolic pathways build complex molecules from simpler molecules.
These pathways consume (absorb) energy.
Example:
Protein synthesis
Thousands of amino acids join to form a protein
Relationship Between Catabolic and Anabolic Pathways
Catabolic pathways = downward paths
Release energy
Anabolic pathways = upward paths
Require energy
Energy released from catabolic reactions is:
Captured
Stored
Used to drive anabolic reactions
Example: Digestion
Digestion is a catabolic process:
Food breaks down into simpler compounds
Energy is released and stored
Anabolic processes then use this energy:
To build complex molecules from simpler ones
Gibbs Free Energy (ΔG) – Notes
Gibbs free energy measures the amount of energy in a system that is available to do work.
It applies when temperature and pressure are constant, such as in a living cell.
It was defined in 1878 by J. Willard Gibbs, a professor at Yale University.
ΔG and Spontaneous Reactions
ΔG (change in free energy) helps predict whether a reaction:
Is spontaneous (occurs without extra energy)
Or requires energy input to begin
Biologists use ΔG to:
Predict which metabolic reactions happen without help
Identify reactions that release energy
Identify reactions that consume energy
Types of Metabolic Reactions
Exergonic reactions:
Release free energy
Occur spontaneously
ΔG is negative
Endergonic reactions:
Absorb free energy from surroundings
Require energy input
ΔG is positive
Exergonic Reactions & Activation Energy – Notes
ΔG in Exergonic Reactions
In an exergonic reaction, the system loses free energy.
Because free energy (G) decreases:
ΔG is negative
Example: Cellular Respiration
Cellular respiration is an exergonic reaction.
One mole of glucose (180 g) releases 686 kcal of energy.
Energy is conserved, so:
Products have less free energy than reactants
Therefore, ΔG is negative
Chemical equation:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
ΔG = –686 kcal/mol
Activation Energy (Eₐct)
Most exergonic reactions are spontaneous, but:
Some require an initial input of energy to start
Activation energy (Eₐct):
The minimum energy needed to start a reaction
Once Eₐct is supplied:
The reaction proceeds spontaneously
Example: Marshmallow
Marshmallow on a table:
No reaction → no energy released
Marshmallow in a fire:
Heat provides activation energy
Reaction begins and releases energy
Free Energy Diagram (Exergonic Reaction)
Reactants start at higher free energy
A small energy hill represents Eₐct
Products end at lower free energy
Net energy change is negative (ΔG < 0)
Endergonic Reactions – Notes
An endergonic reaction:
Absorbs free energy from its surroundings
Stores free energy in molecules
Because free energy (G) increases:
ΔG is positive
Example of an Endergonic Reaction
Building glycogen from glucose units
Multiple glucose molecules are joined to form a glycogen molecule
Energy is required to build these bonds
Spontaneity and Energy Source
Endergonic reactions are not spontaneous
They always require an outside energy source to begin
The magnitude of ΔG:
Represents the amount of energy needed to drive the reaction
Energy Coupling
Endergonic reactions are driven by coupling them with exergonic reactions
Energy released from an exergonic reaction is used to:
Power the endergonic reaction
Activation Energy
Endergonic reactions have:
A much higher activation energy
They rely on:
Exergonic reactions with lower activation energy
To provide the needed energy
Energy Coupling & ATP – Notes
Cells store energy released from exergonic reactions.
This stored energy is later used to drive endergonic reactions.
Metabolic pathways and chemical reactions help supply energy to cells.
Energy Coupling
Energy coupling is the transfer of energy:
From an exergonic reaction
To an endergonic reaction
Energy coupling allows non-spontaneous reactions to occur.
ATP (Adenosine Triphosphate)
ATP is a universal energy molecule found in all living organisms.
It performs the same function in:
Bacteria
Humans
All other living things
ATP is usually the immediate source of energy for:
Cellular work
Chemical reactions
Movement, growth, and maintenance
ATP Structure and Function – Notes
What is ATP?
ATP (adenosine triphosphate) is a multifunctional molecule.
It transports chemical energy so metabolism can occur.
ATP is the main energy currency of the cell.
Structure of ATP
ATP consists of:
Adenosine (an organic molecule)
Three phosphate groups
Adenosine includes:
The sugar ribose
The nitrogenous base adenine
Phosphate Bonds
The first phosphate is attached by a simple covalent bond.
The second and third phosphates are attached by high-energy bonds.
ATP Hydrolysis
Hydrolysis breaks the bond between phosphate groups.
When the terminal phosphate is removed:
ATP → ADP (adenosine diphosphate) + inorganic phosphate (Pi)
This reaction is exergonic.
Energy released:
7.3 kcal per mole of ATP (standard conditions)
ATP in Bioluminescence
Fireflies use ATP hydrolysis:
ATP → ADP
Energy released produces light in the presence of oxygen
ATP Regeneration (Phosphorylation)
Phosphorylation adds a phosphate group to ADP:
ADP + Pi → ATP
This process requires energy.
Animals use energy from glucose breakdown to regenerate ATP.