Aqa A-Level Biology Paper 1 Questions And Answers 100% Verified A+ Guaranteed

red blood cells are biconcave discs. Explain one advantage of a biconcave disc over a spherical cell of the same volume in transporting oxygen. {Ans: Large (surface) area; For diffusion;}H bonds {Ans: Cellulose molecules are crosslinked by}what is a 'sink' cell? {Ans: cells that use/store organic solutes}why do veins have thinner walls than arteries? {Ans: thinner walls because blood is at lower pressure, and so less stretch and recoil with each contraction of ventricles.}How is cellulose adapted to its function? {Ans: Straight chains. Form fibrils. Cross linked. Provides strengths.}why is DNA stable? {Ans: 1. the phosphodiester backbone protects the more chemically reactive organic bases inside the double helix 2. many hydrogen bonds link the base pairs together, so it adds strength overall.}explain cohesion-tension theory {Ans: water is drawn from cell to cell by osmosis. it moves across the root cortex to keep a constant column of water. this creates 'tension' on the column of water in the xylem. water shows cohesion due to its H bonding. this makes the column very strong. so, water is pulled up the xylem to replace the water lost by evaporation. water moves between the cells of a