Active Transport Essay

887 WordsAug 15, 20154 Pages
Previous IB Exam Essay Questions: Unit 2 Biology IB HL 1 Previous IB Exam Essay Questions: Unit 2 Use these model essay question responses to prepare for essay questions on your in class tests, as well as the IB Examination, Paper 2. These questions have appeared on recent IB examinations, exactly as shown below. Following each question is the markscheme answer which was used to evaluate student answers on the examination paper. 1. Draw a diagram to show the structure of a cell membrane 5 marks phospholipids labelled with hydrophillic (heads) and hydrophobic (tails) phospholipid bilayer clearly shown and labelled proteins shown in the bilayer and labelled transmembrane and peripheral/extrinsic proteins shown and labelled glycoproteins shown and labelled cholesterol shown and labelled glycolipids shown and labelled thickness shown as 10 nm/ + or - 2 nm 2. Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes. 9 marks phospholipid structure hydrophobic tail/hydrophilic head head made from glycerol and phosphate tail made from two fatty acids saturated/ unsaturated fatty acid (in tail) arrangement in membrane phospholipids form a bilayer heads face outside the membrane/ tails face inside the membrane/ hydrophic interior/ hydrophilic exterior of membrane A suitable annotated diagram may incorporate all or many of the above points. Award 5 marks maximum for a suitable diagram that is labelled correctly. phospholipids held together by hydrophobic interactions phospholipid layers are stabilized by interaction of hydrophilic heads and surrounding water phospholipids allow for membrane fluidity/ flexibility fluidity/ flexibility helps membranes to be (functionally) stable phospholipids with short fatty acids/ unsaturated fatty acids are more fluid fluidity is important in breaking and

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