Exam wrong answers - jan 2025

Question 1

Explain two ways in which the structure of fish gills is adapted for efficient gas exchange (2)

Answer 1

Many lamellae so large surface area
Thin surface so short diffusion pathway

Question 2

Explain how the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills (3)

Answer 2

Water and blood flow in opposite directions
Blood always passing water with a higher oxygen concentration
Diffusion gradient maintained throughout length of gill