Biological Molecules
Let’s now understand what kinds of molecules make up living things.
Role of Water in Life
Water is life’s most essential chemical. Life started in water, and it still depends on water to survive.
💧 Facts about Water in Living Things:
- Our body is made up of around 80% water (inside a substance called protoplasm, which fills cells).
- All chemical reactions in the body (like digestion or energy production) happen in water-based solutions, called aqueous solutions.
✅ Example:
- Digestion of food in your stomach happens in a watery solution.
- Plants use water during photosynthesis to make food.
Chemical Composition of Living Organisms
Living things are made of two types of molecules:
1. Organic Molecules – These contain carbon and are made by living cells.
- Examples: Carbohydrates, proteins, lipids (fats), and nucleic acids (DNA/RNA).
2. Inorganic Molecules – These don’t contain carbon (usually).
- Examples: Water, salts, carbon dioxide, acids, and bases.
What are Organic Molecules
Organic molecules are carbon-based compounds made by living organisms. They occur naturally inside plants, animals, humans, and even bacteria.
🧪 Examples:
- Sugar in fruits → a carbohydrate
- Proteins in meat and eggs
- Fats in oil or butter
- DNA in every living cell
These organic compounds are the building blocks of life.
Major Organic Molecules (The Big Four)
These four types of organic molecules are very important and make up about 93% of the dry mass (excluding water) of living organisms:
- Carbohydrates – Give us energy
🥖 Found in: bread, rice, fruits - Proteins – Build our muscles and tissues
🍳 Found in: eggs, meat, beans - Lipids (Fats) – Store energy and help form cell membranes
🧈 Found in: oils, butter, nuts - Nucleic Acids – Carry genetic information
📘 Found in: every cell (DNA and RNA)
🧠 Mnemonic to Remember Them: “CPLN” (Carbohydrates, Proteins, Lipids, Nucleic acids)
Think: “Cool People Love Nature“
Minor Components (The Small Helpers)
Only about 7% of a living thing’s dry mass is made of other small organic or inorganic molecules, but they are still very important!
🔸 Small Organic Molecules:
- Vitamins – Help with body functions and immunity
🔹 Inorganic Molecules:
- Carbon dioxide – Used by plants in photosynthesis
- Salts and acids – Help in digestion, maintaining pH
Macromolecules and Polymers
➤ Macromolecules:
These are very large molecules made up of smaller building blocks. The word “macro” means big.
- Examples: Carbohydrates, proteins, nucleic acids
➤ Polymers:
Many macromolecules are polymers. A polymer is made by joining together many small repeating units called monomers.
Think of a polymer like a train, where:
- Each train compartment = a monomer
- The whole train = a polymer