During fertilisation, the acrosome of a mature sperm cell releases enzymes. These enzymes digest a path through the glycoprotein in the layer surrounding the secondary oocyte. Explain how the glycoprotein is broken down by these enzymes. Addition of water molecules / hydrolysis; Protein to amino acids / break peptide bonds; Carbohydrate to monosaccharides / break gycosidic bonds; Glycoprotein attaches to active site / forms E-S complex; Because it has complementary/matching shape; [reject same shape] max 2 [allow 1 mark for glycoprotein broken down to amino acids/monosaccharides]
Past exam question Describe a blastocyst. The markscheme Hollow balls of cells; Cells at one end form embryo; Accept points from a labelled diagram / diagram accompanying explanation. blastocyst
Only a small amount of blood passes through the lungs of a fetus. Draw arrows on the Figure to show one pathway which transports carbon dioxide from the body tissues to the placenta and which does not pass through the lungs.
<ul><li>(Arrows) from body tissues up to and into right atrium; [Reject: If arrow points down umbilical vein to placenta] </li></ul><ul><li>Into right ventricle and ductus arteriosus, then to umbilical artery and placenta/ into left atrium and left ventricle, then to umbilical artery and placenta; 2 </li></ul><ul><ul><ul><li>[Reject: [1f arrow passes from lungs] [Accept: Arrows alongside structures] </li></ul></ul></ul>