The Building Blocks of Life

Your body is essentially a walking chemistry set! Organic molecules make up about 93% of your dry body mass, and they fall into four main groups: carbohydrates, proteins, lipids, and nucleic acids. The remaining 7% consists of small inorganic molecules and ions.

But here's the amazing bit - nearly all the chemical reactions that keep you alive happen in water. Water isn't just there for the ride; it's actively involved as a solvent where reactions occur and often as a product of these reactions.

Water molecules are special because they form hydrogen bonds with each other. The hydrogen atoms carry a slight positive charge whilst the oxygen carries a slight negative charge, creating an attraction between different water molecules.

Quick Fact: Each water molecule can form hydrogen bonds with up to 4 other water molecules, creating a network that gives water its unique properties!

Water as Nature's Ultimate Solvent

Water's polarity (uneven distribution of charges) makes it brilliant at dissolving other substances. When you add charged molecules like ions or amino acids to water, the polar water molecules cluster around them like a protective shield.

Hydrogen bonds in water have four key features: they form between adjacent water molecules (specifically between oxygen and hydrogen atoms), each water molecule can bond with up to four others, and they're relatively weak so they break and reform easily.

This makes water an exceptional solvent because most cellular reactions need to happen in aqueous solution. Water also acts as a transparent medium in living organisms, which is pretty handy for things like your eyeballs!

Hydrophilic substances (like salts) love water and dissolve easily, whilst hydrophobic substances (like oils) hate water and won't dissolve.

Remember: If it dissolves in water, it's hydrophilic. If it repels water, it's hydrophobic!

Water's Superpowers

Water's hydrogen bonding gives it some incredible properties that make life possible. Although individual hydrogen bonds are weak, collectively they make water remarkably stable.

Water has an unusually high specific heat capacity - it takes loads of energy to heat up just 1kg of water by 1°C. This helps regulate your body temperature and keeps Earth's climate stable.

The weakness of individual bonds means water molecules constantly jostle each other in the liquid phase, giving water its molecular mobility. Here's something weird though - water actually expands when it freezes! As it gets colder, molecules slow down and need more space to form the maximum number of hydrogen bonds.

This is why ice floats and why frozen pipes burst. Without this property, lakes would freeze from the bottom up, killing all aquatic life.

Cool Fact: Water's expansion when freezing is why ice floats - if it didn't, entire ecosystems would collapse!

Buffers and pH Control

Your body needs to maintain a stable pH, and that's where buffers come in. A buffer is a substance that resists pH changes when acids or bases are added to it. Think of buffers as pH bodyguards!

Hydrogen carbonate ions and blood proteins like albumin act as natural buffers in your body. This is absolutely crucial because enzymes (which are proteins) need their specific 3D shape to work properly.

If the pH changes too much, enzymes become denatured - they lose their shape and stop working. That's why buffers are essential in enzyme practicals and why your body works so hard to maintain pH balance.

Inorganic ions are equally important for structure and metabolism. These charged particles have lost or gained electrons, and many dissolve easily in water where they can do their jobs.

Key Point: Without buffers, even small pH changes would denature your enzymes and stop vital reactions!