Let's break down lipids and carbohydrates for AP Biology. Both are essential biomolecules, but they serve different roles in living organisms.
Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen, usually in a ratio of 1:2:1. Their primary function is to provide energy to cells. Simple carbohydrates, like glucose and fructose, are quickly used for energy, while complex carbohydrates, like starch and cellulose, provide longer-term energy storage and structural support.
Lipids are a diverse group of hydrophobic (water-insoluble) molecules, also composed of carbon, hydrogen, and oxygen, but with a much higher proportion of carbon and hydrogen than carbohydrates. Lipids include fats, oils, phospholipids, and steroids. Their main functions include energy storage, insulation, and forming structural components of cell membranes.
| Feature | Lipids | Carbohydrates |
|---|---|---|
| Elements | Carbon, Hydrogen, Oxygen (higher C:O ratio) | Carbon, Hydrogen, Oxygen (1:2:1 ratio) |
| Monomers | Glycerol and Fatty Acids (for triglycerides) | Monosaccharides (e.g., glucose, fructose) |
| Polymers | Triglycerides, Phospholipids | Polysaccharides (e.g., starch, cellulose, glycogen) |
| Primary Function | Long-term energy storage, insulation, cell membrane structure | Short-term energy, structural components in plants (cellulose) |
| Energy Content | Higher (approx. 9 kcal/gram) | Lower (approx. 4 kcal/gram) |
| Solubility in Water | Insoluble (hydrophobic) | Soluble (hydrophilic), especially monosaccharides |
| Examples | Fats, oils, waxes, steroids (e.g., cholesterol) | Sugars, starches, cellulose |
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