What is energy? CellEnergetics 1. Energy Energy is the ability to do work. Energy is a phenomenon, not a material. Two broad categories of energy: Potential.

What is energy?

Cell Energetics 1

Energy

Energy is the ability to do work.

Energy is a phenomenon, not a material.

Two broad categories of energy:

Potential

Kinetic

Potential Energy

Potential energy is stored energy.

Examples: coiled spring, bonds between atoms

Kinetic Energy

Kinetic energy is energy that has been released to do work.

Examples: car in motion, heat, light.

Examples of Energy

PotentialPotential KineticKinetic

Magnetic Radiant (Light)

Gravity Electrical

Chemical Sound

Nuclear Motion

Stored mechanical Thermal (heat)

First Law of Thermodynamics

Assuming there is no input of energy, the total energy within a given system remains constant. Energy is conserved.

Energy can change form (example: chemical energy in cells may be converted to heat, motion, etc.)

Energy Transformations

PotentialPotential KineticKinetic

Chemical: Energy stored in chemical bonds in food. Motion: Muscles in motion

Chemical: Energy stored by photosynthesis. Radiant: Sunlight

Electrical: Current used by an electric heater.

Thermal: Heat produced by the heater.

Chemical: Gasoline Motion: Car powered by burning gasoline.

Second Law of Thermodynamics

Assuming there is no input of energy (closed system), when energy is converted from one form to another, the amount of useful energy in the system decreases.

Entropy is the tendency toward an increase in randomness and disorder in a closed system.

Thinking Question

Write out an answer to this question:

Do living systems violate the second law of thermodynamics? Why or why not?

Share your response with a partner and discuss what you have written.

Exergonic Reactions

Exergonic (exothermic) reactions release energy.

In exergonic reactions, the reactants have more energy than the products.

However, all chemical reactions require an input of energy to get them started.

Exergonic Reaction

Exergonic Reactions: Living systems

In living systems, exergonic reactions are carried out by enzymes.

Enzymes lower the activation energy required to get these reactions started, so there is more net energy at the end.

Enzymes also control the rate of the reaction so that heat is controlled.

Endergonic Reactions

Endergonic (endothermic) reactions require an input of energy.

Products of the reactions have more energy than the reactants.

Endergonic Reaction

Ammonium thiocyanate + Barium hydroxide

Coupled Reactions

Living organisms use energy from exergonic reactions to drive endergonic reactions.

The reactions may occur in different places. Energy may be transferred by energy-carrier molecules such as ATP.

ATP

Adenosine triphosphate (ATP) is the universal energy molecule.

ATP is made up of adenine, a ribose sugar, and three phosphate groups.

ATP and Energy

ATP is synthesized from ADP (Adenosine diphosphate) and a phosphate group, using energy released from the breakdown of glucose, fats, and amino acids.

When the terminal phosphate bond in ATP is broken, energy is released.

ATP is a very unstable molecule.

ATP and Living Organisms

ATP is used by all living organisms.

In plants, the chloroplasts harvest light to make ATP and use it to make glucose and other carbon compounds.

Plants, animals, and all other eukaryotes break down glucose and other compounds to make ATP for their metabolic needs.

Thinking Question

Think about all the things going on in your cells right now.

List as many things as you can think of that probably require ATP to run them.