WJEC A Level Biology Unit 1: Basic Biochemistry and Cell Organisation Exam Questions

About WJEC A Level Biology Unit 1: Basic Biochemistry and Cell Organisation

Unit 1 of WJEC A Level Biology, Basic Biochemistry and Cell Organisation, is the first AS unit and introduces the molecules and cells that the rest of the course depends on. It covers carbohydrates, lipids, proteins, water and inorganic ions, cell ultrastructure, membrane structure and transport, enzyme action, nucleic acids and protein synthesis, and cell division. Later units such as respiration, photosynthesis and inheritance assume this knowledge. Examiners frequently ask for drawn or completed molecular structures, explanations of how structure suits function, calculations using an eyepiece graticule, water potential problems and comparisons of mitosis and meiosis.

What you need to know

• 1.1 Roles of inorganic ions such as iron, calcium and phosphate; properties of water; alpha and beta glucose, disaccharides and polysaccharides including starch, glycogen, cellulose and chitin; triglycerides and phospholipids; amino acids and the four levels of protein structure; and biochemical tests.
• 1.2 Ultrastructure of eukaryotic and prokaryotic cells, the functions of organelles, the structure of viruses, and the organisation of cells into tissues, organs and systems.
• 1.3 The fluid mosaic model, factors affecting membrane permeability, diffusion, facilitated diffusion, osmosis and water potential, active transport, and endocytosis and exocytosis.
• 1.4 Enzymes as globular proteins, induced fit, the effects of temperature, pH and concentration, competitive and non-competitive inhibition, and immobilised enzymes and biosensors.
• 1.5 Structure of nucleotides, ATP, DNA and RNA, semi-conservative replication and the Meselson and Stahl experiment, the triplet code, transcription, and translation at ribosomes.
• 1.6 The cell cycle, the stages and significance of mitosis and meiosis, and how errors in cell cycle control can lead to cancer.

Common mistakes in Unit 1: Basic Biochemistry and Cell Organisation

• Saying chitin is a protein. Chitin is a structural polysaccharide made of beta glucose units with nitrogen-containing groups, found in fungal cell walls and arthropod exoskeletons.
• Writing that ATP is used for long-term energy storage. ATP is an immediate energy source; storage molecules include starch, glycogen and triglycerides.
• Describing non-competitive inhibitors as binding to the active site. They bind to an allosteric site, changing the shape of the active site.
• Thinking that viruses are prokaryotic cells. Viruses are acellular, with a nucleic acid core and a protein capsid, and can only replicate inside host cells.
• Mixing up cholesterol's role. Cholesterol regulates membrane fluidity and stability; it does not act as a channel protein.

Try three Unit 1: Basic Biochemistry and Cell Organisation exam-style questions