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Life depends on energy, which is governed by the laws of thermodynamics and transferred through redox reactions. Cells use ATP (adenosine triphosphate) as their primary energy currency, storing and releasing energy for biological processes. Enzymes speed up reactions by lowering activation energy, and metabolic pathways regulate energy use through anabolic (building) and catabolic (breaking down) reactions.
Robert Caputo/Aurora Photos/Cavan images
Energy in Living Systems
Energy in Living Systems
Energy exists as kinetic (motion) or potential (stored) energy.
The Sun is the primary energy source for life, with photosynthesis storing solar energy in chemical bonds.
Redox reactions (oxidation & reduction) transfer energy in cells.
Laws of Thermodynamics & Free Energy
Laws of Thermodynamics & Free Energy
First Law: Energy cannot be created or destroyed, only converted.
Second Law: Energy transfers increase disorder (entropy).
Free energy (ΔG) determines whether a reaction is spontaneous (exergonic) or requires energy input (endergonic).
ATP: The Cell’s Energy Currency
ATP: The Cell’s Energy Currency
ATP consists of adenine, ribose sugar, and three phosphate groups.
ATP hydrolysis (breaking a phosphate bond) releases energy for cellular work.
ATP is constantly recycled between ATP ↔ ADP + P.
Water: The Essential Molecule of Life
Water: The Essential Molecule of Life
Water is a polar molecule, meaning it has a partial positive charge (H side) and a partial negative charge (O side). This allows for hydrogen bonding, leading to water’s unique properties:
Cohesion & Adhesion: Water molecules stick to each other (cohesion) and to other surfaces (adhesion), allowing capillary action in plants.
High Specific Heat: Water absorbs heat slowly and retains heat longer, helping regulate body temperature and climate stability.
High Heat of Vaporization: It takes a lot of energy to evaporate water, allowing for cooling effects like sweating.
Density of Ice: Ice is less dense than liquid water, meaning it floats and insulates aquatic ecosystems.
Water as a Solvent: Water dissolves polar and ionic substances, making it the "universal solvent" in biological systems.
Acids, Bases, and pH
Acids, Bases, and pH
source: https://www.sciencelearn.org.nz/images/4557-ph-scale
Acids donate H⁺ ions, increasing hydrogen ion concentration (pH < 7).
Bases remove H⁺ ions or add OH⁻ ions, decreasing hydrogen ion concentration (pH > 7).
Buffers help maintain a stable pH in organisms by neutralizing acids or bases.
Why This Matters?
Why This Matters?
Understanding chemical interactions helps explain how life works at the molecular level, from DNA replication to digestion.
Water’s unique properties make it essential for all biological processes.
Biological Importance : Cells must maintain a pH balance to prevent damage to proteins and enzymes. Blood uses bicarbonate buffers to maintain a stable pH (~7.4).
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