Biological Molecules | OCR A-Level Biology A (H420)

Biological Molecules

113 questions
10 subtopics
Module 2: Foundations in biology
Component 01, Component 02 and Component 03

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.

Sample questions from Biological Molecules

Answer each one closed book first, then open the answer.

The properties of water

Explain how water acts as a solvent for ionic compounds.

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Water's polarity allows it to surround ions with hydration shells, separating and dissolving ionic compounds and other polar molecules.
Monomers, polymers and the elements of life

What happens during a condensation reaction?

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A molecule of water is removed and a covalent bond is formed between two monomers, joining them together.
Monosaccharides and disaccharides

What is the structural difference between α-glucose and β-glucose?

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The position of the hydroxyl group on carbon 1: in α-glucose it is below the plane of the ring, in β-glucose it is above the plane.
Polysaccharides and their functions

Describe the structure of glycogen.

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A highly branched polysaccharide of α-glucose molecules with 1,4-glycosidic bonds in chains and 1,6-glycosidic bonds at frequent branch points.
Lipids

What is an unsaturated fatty acid?

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A fatty acid with one or more carbon-carbon double bonds in its hydrocarbon chain, causing kinks that prevent close packing.
Amino acids and protein structure

How are dipeptides and polypeptides broken down?

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By hydrolysis reactions that break peptide bonds.
Globular and fibrous proteins

What type of protein are enzymes and what determines their function?

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Enzymes are globular proteins that act as biological catalysts, with a specific active site shape determined by their tertiary structure.
Inorganic ions

State two biological processes involving hydrogen ions.

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Determining pH and the electron transport chain.

The 10 subtopics

One subtopic is one session. Work down the list.

Subtopic	What it covers	Questions
The properties of water	Why 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.	12
Monomers, polymers and the elements of life	Monomers and polymers, the condensation and hydrolysis reactions that join and break them, and the elements found in carbohydrates, lipids, proteins and nucleic acids.	8
Monosaccharides and disaccharides	Hexose and pentose sugars, the difference between alpha and beta glucose, glycosidic bonds, and the monosaccharides that make up sucrose, lactose and maltose.	12
Polysaccharides and their functions	Amylose, amylopectin, glycogen and cellulose, and how the shape of each one suits it to energy storage in plants and animals or to structural support.	11
Lipids	Triglycerides 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.	11
Amino acids and protein structure	The general structure of an amino acid, peptide bond formation, and the primary, secondary, tertiary and quaternary levels with the bonds holding each one together.	15
Globular and fibrous proteins	Globular proteins such as insulin and enzymes alongside fibrous proteins such as collagen, keratin and elastin, and how shape and solubility follow function.	8
Inorganic ions	The biological roles of calcium, sodium, potassium, hydrogen, ammonium, nitrate, hydrogencarbonate, chloride, phosphate and hydroxide ions.	10
The biochemical tests	Biuret 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.	16
Colorimetry and chromatography	Using a calibration curve to find an unknown concentration, and separating molecules by paper and thin layer chromatography with the Rf calculation.	10

Biological Molecules is 113 of the 1,833 questions in the guide.Get the guide, £8

How the guide is worked

Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.

Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.

Read the full method, the return schedule and the research behind it.