AQA A - Level BIOLOGY Paper 3 June 2026 TOPIC 1 8 EXAM GUIDE QNS & ANS Complete And Study material 15pages LEARNEXAMS

TOPIC 1 – 8 EXAM GUIDE QNS & ANS 1. Describe the structure of a water molecule and explain how its properties are conducive to its role in biological organisms. Answer: A water molecule has a bent shape with one oxygen atom covalently bonded to two hydrogen atoms. The oxygen atom is more electronegative, creating a polar molecule with a partial negative charge near the oxygen and a partial positive charge near the hydrogens. This polarity allows water to form hydrogen bonds, making it an excellent solvent for ionic and other polar molecules. It also contributes to water's high specific heat, surface tension, and cohesion, all of which are essential for life. 2. Explain the fluid mosaic model of cell membranes and its significance in the transport of substances. Answer: The fluid mosaic model describes the cell membrane as a fluid, dynamic structure with various proteins embedded in or attached to a bilayer of phospholipids. The phospholipids have hydrophilic heads and hydrophobic tails, creating a semipermeable barrier. Proteins serve functions such as transport, signal transduction, and cell recognition, allowing cells to exchange substances with their environment selectively.