Study GuideBiology–Cell and Energy1. The Laws of ThermodynamicsLife depends on order. Inside every cell, molecules must stay organized for the cell to survive andfunction properly. To keep this order, cells need a constant supply ofenergy. In science,energyisdefined as the ability to do work. For living things, that “work” includes growing, moving, thinking, andstaying alive.To understand how energy behaves, scientists rely on a set of well-tested rules called thelaws ofthermodynamics. There are two main laws that are especially important for biology.1.1 The First Law of Thermodynamics: Energy Is ConservedThefirst law of thermodynamicsstates thatenergy cannot be created or destroyed. It can onlychange from one form to another.This means that in aclosed system—one where no energy enters or leaves—the total amount ofenergy always stays the same. A good example of a closed system is the universe as a whole.Even though the total energy stays constant, thetypeof energy can change. For example, whengasoline burns in a car engine, itschemical energyis transformed into other forms of energy, suchasheat,sound, andmotion. The energy was not lost—it just changed form.1.2 The Second Law of Thermodynamics: Energy Becomes Less UsefulThesecond law of thermodynamicsexplains why energy transformations are never perfectlyefficient. It states that the amount ofusable energyin a closed system is constantly decreasing.This happens because ofentropy, which refers to the level of disorder or randomness in a system.Over time, entropy always increases in a closed system. In simple terms, systems naturally tend tomove from order to disorder.Preview Mode
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