Energy for Life

• All living things need energy for survival and reproduction including bacteria, plants, and animals
• Energy means the ability to do work
• Work occurs when a force moves an object

Energy Source

• The sun is the primary source of energy
• Plants conduct photosynthesis, using energy to make sugar and oxygen from carbon dioxide and water
• Other organisms obtain energy by consuming plants
• Sugar is then used as an energy source to do work

Capturing and Using Energy

• Energy is defined by physicists as the ability to do work
• Energy is crucial for life, as many cellular processes depend on it
• The total energy in an object is the sum of its kinetic and potential energy
• Potential energy: This is stored energy available to do work
• Covalent bonds within molecules have a form of potential energy called chemical energy
• Kinetic Energy: energy is being used to do work
• Any moving object possesses kinetic energy

Measuring Energy

• Calories are units used to measure energy
• One calorie (cal) is the amount of energy required to raise the temperature of 1 gram of water by 1°C
• The most common unit for measuring the energy content of food is kilocalories
• 1 kcal is equal to 1000 calories

Energy Conversion

• During photosynthesis, plants convert kinetic energy from sunlight into potential energy stored in chemical bonds of sugars
• In respiration, organisms release potential energy, with heat being lost in the process

Thermodynamics and Energy Transfer

• Thermodynamics: The study of energy transformations
• Energy conversions are vital for both living and non-living systems and are described by the 1st and 2nd laws of thermodynamics
• First Law of Thermodynamics (Law of Energy Conservation): Energy cannot be created or destroyed, but converted into other forms; the total energy in the universe remains constant
• Living organisms constantly convert energy from one form to another
• Photosynthesis and respiration are the most important energy transformations

Photosynthesis and Cellular Respiration

• Photosynthesis: Plants and some microbes use CO2, water, and kinetic energy (sun) to produce sugars assembled into glucose and other carbohydrates.
• Cellular respiration: Energy-rich glucose molecules are broken down back into CO2 and water, releasing energy needed to power life

Second Law of Thermodynamics

• The second law states that energy transformations are inefficient, as energy is lost as heat to the surroundings during every reaction
• Heat energy is disordered due to random molecular movements
• Because heat is disordered and all energy transformations become heat, it follows that all energy transformations must head towards increasing disorder

Entropy and Order

• Entropy is the measure of randomness
• The more disordered a system, the higher its entropy
• Organisms maintain organization by using a constant stream of incoming energy and matter, using information in DNA
• The sun constantly provides energy to Earth which keeps life ordered and complex

Chemical Networks and Metabolism

• A great number of chemical reactions occur in cells
• Metabolism: Encompasses chemical reactions in cells that build new molecules and break down existing ones
• Each reaction rearranges atoms into new compounds and either absorbs or releases energy
• Photosynthesis and respiration are parts of metabolism
• Metabolism: Sum of all chemical reactions in an organism, including breaking down, producing, or chemically modifying substances
• Catabolism: The process of breaking down materials in the body
• Anabolism: The process of making larger substances from smaller substances

Metabolism Factors

• Factors affecting metabolism: includes the amount and type of food consumed
• Other factors include age, gender, temperature, and certain diseases can affect metabolism

Energy Input and Release in Reactions

• Biologists classify metabolic reactions based on energy requirements: endergonic and exergonic
• Endergonic reaction: requires energy input to proceed
• The products contain more energy than the reactants
• These reactions build complex molecules from simpler components
• Photosynthesis: Glucose products of photosynthesis contain more potential energy than the CO2 and H2O reactants
• Sunlight serves as the energy source for this reaction
• Exergonic reaction: Releases energy
• Products contain less energy than the reactants
• Breaks down large, complex molecules into smaller, simpler components
• Cellular respiration: An example includes breaking down glucose into CO2 and H2O
• The products contain less energy than glucose

Oxidation-Reduction Reactions and Electron Transport

• Electrons carry energy
• Most energy transformations in organisms occur in Oxidation-Reduction (Redox) reactions, transferring energized electrons from one molecule to another
• Oxidation: The loss of electrons from a molecule, atom, or ion Oxidation reactions are exergonic and release energy as they degrade complex molecules into simpler products
• Reduction: A gain of electrons Reduction reactions are endergonic and need a net input of energy
• Oxidation and reduction occur at the same time
• Electrons that are removed from one molecule during oxidation must join another molecule and reduce it
• One molecule is reduced (gains electrons), then another must be oxidized (loses electrons)
• An electron donor has more potential before it is oxidized than after reaction is complete
• The reduction half is endergonic: The acceptor molecule gains energy-rich electrons and ends up with more potential energy than had before reaction started