Biological Molecules

What Biological Molecules covers

Biological molecules is the second section of Module 2. It covers the properties that make water suitable for life, the structure and function of carbohydrates, lipids and proteins, the inorganic ions cells depend on, and the biochemical tests and separation techniques used to identify each group.

The 10 subtopics

Each one has its own page.

• The properties of waterWhy water is polar, the hydrogen bonds that follow from it, and how solvent action, high specific heat capacity, evaporative cooling and floating ice support life.Open →
• Monomers, polymers and the elements of lifeMonomers and polymers, the condensation and hydrolysis reactions that join and break them, and the elements found in carbohydrates, lipids, proteins and nucleic acids.Open →
• Monosaccharides and disaccharidesHexose and pentose sugars, the difference between alpha and beta glucose, glycosidic bonds, and the monosaccharides that make up sucrose, lactose and maltose.Open →
• Polysaccharides and their functionsAmylose, amylopectin, glycogen and cellulose, and how the shape of each one suits it to energy storage in plants and animals or to structural support.Open →
• LipidsTriglycerides and phospholipids and what they are built from, saturated and unsaturated fatty acids, why fat stores so much energy per unit mass, and the role of cholesterol.Open →
• Amino acids and protein structureThe general structure of an amino acid, peptide bond formation, and the primary, secondary, tertiary and quaternary levels with the bonds holding each one together.Open →
• Globular and fibrous proteinsGlobular proteins such as insulin and enzymes alongside fibrous proteins such as collagen, keratin and elastin, and how shape and solubility follow function.Open →
• Inorganic ionsThe biological roles of calcium, sodium, potassium, hydrogen, ammonium, nitrate, hydrogencarbonate, chloride, phosphate and hydroxide ions.Open →
• The biochemical testsBiuret for protein, Benedict's for reducing and non-reducing sugars, iodine for starch and the emulsion test for lipids, with the colour change each one gives.Open →
• Colorimetry and chromatographyUsing a calibration curve to find an unknown concentration, and separating molecules by paper and thin layer chromatography with the Rf calculation.Open →

What you need to know

Answer each one before you reveal it.

Take Biological Molecules further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Condensation vs Hydrolysis

  Condensation: joining molecules while releasing water. Hydrolysis: splitting molecules through the addition of water.

Questions from this topic

Each one with the model answer underneath.

1. 1

   Why is water described as a polar molecule?

   Model answer

   Water is polar because the oxygen atom has a slight negative charge and the hydrogen atoms have slight positive charges, creating an uneven distribution of charge across the molecule.

2. 2

   What charge does the oxygen atom carry in a water molecule?

   Model answer

   A slight negative charge.

3. 3

   What charge do the hydrogen atoms carry in a water molecule?

   Model answer

   Slight positive charges.

4. 4

   How do hydrogen bonds form between water molecules?

   Model answer

   Electrostatic attraction occurs between the slightly positive hydrogen atoms of one water molecule and the slightly negative oxygen atom of another water molecule, forming hydrogen bonds.

5. 5

   Explain how water acts as a solvent for ionic compounds.

   Model answer

   Water's polarity allows it to surround ions with hydration shells, separating and dissolving ionic compounds and other polar molecules.

6. 6

   What is a hydration shell?

   Model answer

   A layer of water molecules that surrounds an ion due to the attraction between the polar water molecules and the charged ion.

What is inside Levo

Six ways to work the same material.

Biological Molecules revision questions

What does Biological Molecules cover in OCR A-Level Biology?

10 subtopics: the properties of water, monomers, polymers and the elements of life, monosaccharides and disaccharides, polysaccharides and their functions, lipids, amino acids and protein structure, globular and fibrous proteins, inorganic ions, the biochemical tests and colorimetry and chromatography. Each one has its own page with questions and model answers.

How is Biological Molecules organised?

By the OCR H420 specification, subtopic by subtopic, so it matches the order you are taught it in.