AQA A-Level Biology - Topic 3 (2022/2023) with Verified Answers

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AQA A-Level Biology - Topic 3 (2022/2023) 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 and water flows over them in the other direction. Water with Hugh oxygen concentration flows over blood with low concentration maintaining a high concentration gradient over the whole length of the gill The main gas exchange surface in plants is the surface of the ............1......... cells in the leaf. Gases move in and out through special pores in the epidermis called ..........2........... the ........2........... can open to allow exchange of gases and close if the plant is losing too much water. ..............3............ control the opening and closing. ✔✔1. Mesophyll. 2. Stomata. 3. Guard cells Insects have microscopic air filled pipes called .........1......... which they use for gas exchange. Air moves into these through pores on the surface called ..........2............ oxygen travels down the concentration gradient towards the cells. The ......1........... branch off into smaller .........3............. which have thin permeable walls and go to i [Show More]

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