Rucete ✏ Campbell Biology In a Nutshell
At the most fundamental level, life is chemistry in motion. Every breath you take, every meal you digest, and every thought in your brain involves chemical reactions—the breaking and forming of chemical bonds that rearrange matter. Without these reactions, life as we know it simply wouldn’t exist.
Unit 1 THE CHEMISTRY OF LIFE
Concept 2.4 Chemical reactions make and break chemical bonds
What is a Chemical Reaction?
A chemical reaction occurs when atoms or molecules break existing bonds and form new ones, leading to a change in the composition of matter.
For example, when hydrogen gas (H₂) reacts with oxygen gas (O₂), it forms water (H₂O):
In this reaction:
✔ Old bonds break (between hydrogen and oxygen molecules).
✔ New bonds form (to create water molecules).
✔ Matter is conserved—no atoms are lost, just rearranged.
The Law of Conservation of Matter
One of the fundamental rules of chemistry is that matter cannot be created or destroyed in a chemical reaction—it can only be rearranged. This is why the number and types of atoms on both sides of a chemical equation must always be balanced.
The Role of Chemical Reactions in Life
Biology is powered by chemical reactions, and one of the most essential is photosynthesis, which fuels almost all ecosystems.
☀️ Photosynthesis: A Life-Sustaining Reaction
Plants use sunlight to transform carbon dioxide and water into glucose (sugar) and oxygen:
✔ Reactants: Carbon dioxide (CO₂) and water (H₂O)
✔ Products: Glucose (C₆H₁₂O₆) and oxygen (O₂)
This reaction stores solar energy in chemical bonds, making it available for other organisms to use. Without photosynthesis, there would be no food, no oxygen, and no complex life on Earth.
All Reactions Are Reversible
Every chemical reaction can, in theory, go in both directions. Just as water can be formed from hydrogen and oxygen, it can also be broken apart into these gases under the right conditions.
The double arrow (↔) means this reaction can go both forward and backward. When the rates of both directions become equal, the system reaches chemical equilibrium.
🔄 Chemical Equilibrium: A state where reactants and products exist in a stable ratio, with no overall change in concentrations.
This is important in biological systems, where many reactions don’t go to completion but instead fluctuate dynamically, allowing cells to regulate biochemical pathways efficiently.
What Affects the Speed of Chemical Reactions?
Reactions don’t all happen at the same rate—some occur instantly, while others take centuries.
⏳ Factors that affect reaction rates:
✔ Concentration of Reactants: More reactants mean more frequent collisions, speeding up the reaction.
✔ Temperature: Higher temperatures increase molecular motion, leading to more collisions.
✔ Catalysts: Special molecules (like enzymes in biology) speed up reactions without being consumed.
In living organisms, enzymes act as biological catalysts, ensuring that crucial reactions happen quickly and efficiently to sustain life.
In a nutshell
✔ Chemical reactions break and form bonds, transforming substances.
✔ Matter is never lost, only rearranged—a core principle in chemistry.
✔ Photosynthesis is a key example of how chemical reactions sustain life.
✔ Reactions can go forward or backward, and many reach chemical equilibrium.
✔ Factors like temperature and enzymes control reaction speed, ensuring life functions smoothly.
Life is built on chemistry, and every moment of existence is a testament to the power of chemical reactions—the silent forces shaping everything from the food we eat to the air we breathe.