A-Level Biology - Gas Exchange in Fish | Countercurrent Exchange System (2026/27 exams)

⭐️ Check out our website https://www.cognito.org/ ⭐️ ** WHAT'S COVERED ** 1. Why Fish Need Specialised Gas Exchange Surfaces The challenges of being a large, multicellular organism with a high oxygen demand. The specific difficulties of gas exchange in water compared to air. 2. The Structure and Adaptations of Fish Gills The role of gill filaments and gill lamellae. Key adaptations for efficient gas exchange, including a large surface area, short diffusion pathway, and rich blood supply. 3. The Countercurrent Exchange System How countercurrent flow (where blood and water flow in opposite directions) works. A comparison between countercurrent flow and parallel flow, explaining why the countercurrent system is more efficient at absorbing oxygen. 4. How Fish Ventilate Their Gills The process of ventilation involving the buccal cavity and operculum. How pressure changes create a continuous, unidirectional flow of water over the gills. ** EXAM BOARD SPECIFIC INFO ** AQA - You don't need to know about how fish ventilate their gills OCR - Everything is relevant to your course! CIE - This video isn't on your course ** CHAPTERS ** 0:00 Introduction to Gas Exchange in Fish 0:27 Why Fish Need Specialised Gas Exchange Surfaces 1:27 Structure and Adaptations of Fish Gills 2:50 The Countercurrent Exchange System 5:25 How Fish Ventilate Their Gills ** PLAYLISTS **    • KS3 Biology      • KS3 Chemistry      • KS3 Physics      • GCSE Maths (9-1)      • GCSE Biology (9-1)      • GCSE Chemistry (9-1)      • GCSE Physics (9-1)      • A-Level Biology   #ALevel #Biology #study #revision #school #exam #AQA #OCR #Edexcel