Energy and Thermodynamics Overview (Exam 2)

Energy: The Capacity to Do Work

• Energy is the capacity to bring about movement against an opposing force; the ability to do work.
• Potential energy is stored energy (e.g., chemical energy in food, hydroelectric dam).
• Kinetic energy is energy in motion (e.g., running, biking, flying).

Thermodynamics

• First Law of Thermodynamics: energy cannot be created or destroyed, only transformed. Excess energy is released as heat.
• Second Law of Thermodynamics: energy moves from order to disorder (entropy). Entropy is the measure of disorder.

Exergonic and Endergonic Reactions

• Exergonic reactions release energy because reactants have more energy than products (e.g., cellular respiration).
• Endergonic reactions require energy because products have more energy than reactants (e.g., photosynthesis).

Cellular Respiration and Photosynthesis

• Photosynthesis is the conversion of light energy to chemical energy:
  • 6H2O + 6CO2 → C6H12O6 + 6O2
  • Water + Carbon dioxide → Glucose + Oxygen
• Cellular Respiration is the process where living things extract energy stored in molecules:
  • C6H12O6 + 6O2 → 6CO2 + 6H2O + 36ATP + Heat
  • Glucose + Oxygen → Carbon dioxide + Water + 36 ATP + Heat

ATP: The Energy Transfer Molecule

• Adenosine triphosphate (ATP) is the main molecule for energy transfer in living things.
• Adenosine diphosphate (ADP) is the lower-energy form of ATP.
• Phosphorylation is the addition of a phosphate group to a molecule, which increases its energy level.

Oxidation-Reduction Reactions

• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• Redox reactions involve the transfer of electrons between molecules.

NAD: Electron Carrier

• Nicotinamide adenine dinucleotide (NAD+) is an electron carrier that transfers electrons from hydrogen atoms.

Cellular Respiration: Four Stages

• Cellular respiration breaks down glucose into 36 ATP in four stages:
  • Glycolysis: 2 ATP produced in the cytosol.
  • Transition Phase: No ATP produced, takes place in the mitochondria.
  • Krebs Cycle: 2 ATP produced in the mitochondria.
  • Electron Transport Chain: 32 ATP produced in the mitochondria.

Macromolecules and Energy

• We eat food to obtain energy stored in the chemical bonds of macromolecules (e.g., sugars).
• This energy is captured and converted into ATP during cellular respiration.
• ATP is used for the production of tissue and cell activities, or excreted as waste.

Glycolysis: Breakdown of Glucose

• Glycolysis breaks down one glucose molecule into two pyruvate molecules.
• Occurs in the cytosol (outside mitochondria) and is present in all living things.
• Two stages:
  • Energy Investment Stage: Requires 2 ATP.
  • Energy Harvesting Stage: Produces 4 ATP and 2 NADH.

Transition Phase: Acetyl CoA Formation

• Coenzyme A (acetyl CoA) is added to pyruvate to produce Acetyl Coenzyme A.
• Carbon dioxide is a byproduct.
• One NADH molecule is produced per pyruvate molecule.
• Takes place in the inner compartment of mitochondria.

Krebs Cycle: Energy Production

• Takes place in the inner compartment of mitochondria.
• One glucose molecule (2 pyruvate) produces:
  • 4 CO2
  • 6 NADH
  • 2 ATP
  • 2 FADH2
• Each turn of the Krebs Cycle involves a sequence of reactions:
  • Acetyl CoA combines with 4-carbon oxaloacetic acid to form 6-carbon citric acid.
  • Citric acid undergoes oxidation steps, releasing CO2 and producing NADH.
  • The 4-carbon compound is regenerated, completing the cycle.

Electron Transport Chain: ATP Synthesis

• Energy from electrons is used to pump H+ ions from the inner to the outer compartment of mitochondria, creating a gradient.
• Oxygen is the final electron acceptor.
• Chemiosmosis is the movement of ions across a semipermeable membrane down their electrochemical gradient.
• ATP synthase uses energy from H+ ions to add phosphate to ADP, producing ATP.

Anaerobic Pathways: Energy Production Without Oxygen

• Anaerobic pathways occur without oxygen:
  • Glycolysis: produces 2 ATP.
  • Fermentation: regenerates NAD+ from NADH to allow glycolysis to continue.
• Aerobic pathways occur with oxygen:
  • Cellular Respiration: produces 36 ATP.

Fermentation: Anaerobic Energy Production

• Fermentation regenerates NAD+ from NADH, enabling continued glycolysis in the absence of oxygen.
• Alcohol fermentation: occurs in yeast, producing ethanol.
• Lactic acid fermentation: occurs in animals when oxygen supply is limited, producing lactic acid.

Summary of Cellular Respiration Steps

Lactic Acid Fermentation

• Lactic acid is produced when pyruvate accepts electrons from NADH
• Occurs when oxygen delivery to cells is lagging, causing a burning sensation in muscles

Anaerobic and Aerobic Contributions

• Energy from anaerobic respiration is used for short bursts of activity

Cellular Respiration Review

• NAD+ becomes reduced when it gains an electron
• Oxygen is required to make ATP
• Cellular respiration is considered an exergonic reaction because it releases energy
• The Krebs cycle produces the most electron carriers
• 2 ATPs are generated per glucose molecule processed through the Krebs cycle
• The electron transport chain uses energy from electrons to power the active transport of hydrogen ions
• The electron transport chain uses energy from electrons to attach phosphate groups to ADP
• Oxygen acts as the final electron acceptor in the electron transport chain

Homeostasis

• Homeostasis is the physiological state of internal stability
• Regulators use internal mechanisms to control external fluctuations
• Conformers allow internal conditions to change in response to external fluctuations

Thermoregulation

• Thermoregulation is the process by which animals maintain their body temperature within a normal range
• Endotherms maintain their body temperature through metabolic heat, including birds, mammals, and some insects
• Ectotherms rely on external sources to regulate their body temperature, including most reptiles, fish, and invertebrates
• Poikilotherms are animals whose body temperature fluctuates with the environment
• Homeotherms are animals with a relatively constant body temperature

Heat Exchange with the Environment

• Conduction is the direct transfer of heat
• Convection is the transfer of heat by the movement of air or water across a surface
• Radiation is the emission of electromagnetic waves
• Evaporation is the loss of heat when a liquid changes into a gas

Adaptations for Thermoregulation

• Insulation includes hair, feathers, and fat (blubber)
• Behavior responses include basking, huddling, burrowing, and hot tubbing
• Evaporative heat loss includes sweating, panting, and defecation

Energy Conservation

• Torpor is a physiological state of decreased activity and metabolism
• Hibernation is long-term torpor with decreased body temperature in response to winter cold and food scarcity
• Estivation is decreased metabolic rate and activity during hot summer months

Vasodilation and Vasoconstriction

• Vasodilation is the widening of superficial blood vessels, increasing heat transfer
• Vasoconstriction is the decreasing of the diameter of superficial blood vessels, decreasing heat transfer

Counter-current Heat Exchange

• Warm arterial blood from the core comes in close contact with veins returning from extremities
• Arterial blood remains slightly warmer than venous blood, resulting in heat transfer
• Returning blood is almost as warm as arterial blood

Animal Diets

• All animals are heterotrophic
• Herbivores eat plants
• Carnivores eat meat
• Omnivores eat both plants and meat
• Insectivores eat insects
• Three nutritional needs for animals include:
  • Chemical energy for cellular processes
  • Organic building blocks for macromolecules
  • Essential nutrients

Trade-offs of Thermoregulatory Strategies

• Endotherms

  • Pros:
    • Can be active in cold environments
    • Can maintain a stable body temperature
  • Cons:
    • Require more energy than ectotherms
    • Can overheat in hot environments

• Ectotherms

  • Pros:
    • Low energy requirements
    • Can survive in environments with limited food resources
  • Cons:
    • Not active in cold environments
    • Vulnerable to temperature fluctuations

• Smaller endotherms have a greater surface area to volume ratio

• Smaller endotherms lose heat to the environment more easily, requiring more energy to maintain a constant body temperature