AQA A-Level Biology - Topic 3 (2023/2024) with Verified Answers

Smaller organisms have a ........... surface area to volume ratio Higher How do single called organisms exchange substances? Diffuse directly into or out of the cell across the cell surface membrane Give 2 reasons why in multicellular organisms, diffusion across outer membrane would be too slow? 1. Some cells deep within body- big distance between them and outside 2. Larger animals have low surface area to volume ratio- difficult to exchange enough substances to supply large volume What 2 things do most gas exchange surfaces have in common that increases the rate of diffusion? 1. They have large surface area 2. They're thin- short diffusion pathway Each gill is made of lots of thin plates called .....................which give a large surface area Gill filaments Gill filaments are covered in lots of tiny structures called............. which increase surface area Lamellae Explain the counter current system in fish? Blood flows through the lamellae in one direction