2020 Bio H2 MCQ Explanations

1. N20Q1 C The three tenets of cell theory are: 1. Cells are the smallest unit of life. 2. All cells come from pre-existing cells. 3. Living organisms are composed of cells. 2. N20Q2 A A centriole is indeed a hollow cylinder formed by a ring of microtubules. A lysosome is a spherical sac surrounded by a single membrane, not a double membrane. A mitochondrion is a double membrane organelle with the inner membrane folded, rather than enclosing a folded membrane. A ribosome is made up of two different sized subunits (one large and one small). It can be attached to the rER membrane or it can be free. 3. N20Q3 C Statement 1 is wrong because amylopectin, just like glycogen, is branched. Since we are told that due to the branching enzyme action, the amylopectin is made more soluble than amylose (unbranched), this mean that, equally, the glycogen is also made more soluble. Soluble molecules will always have an osmotic effect in the cell, so statement 3 is wrong. Statement 2 about the molecule being more compact and hence occupies less space and statement 4 about the branching helping the molecule to have more free ends for hydrolysis to break down into glucose faster, are both good properties of glycogen being a suitable storage molecule 4. N20Q4 D Follow the sequence given in the question, asp-ala-gly-lys Synthesis of polypeptide always occur in the N to C terminus, and NH3+ will form peptide bond with COO- thus it starts with 9 bonded to 7, 6 bonded to 2, 1 bonded to 5 5. N20Q5 B Haemoglobin Statement 1 is wrong, because Haemoglobin has haem group that contain iron and porphyrin ring Statemnt 4 is wrong, because repeating pattern of 3 type of amino acids is referring glycine X Y of collagen and not Haemoglobin Collagen Statement 3 is wrong, because it is insoluble. It does not have hydrophilic amino acid on it is surface. The R of it amino acids project into the core of it is triple helical structures. 6. N20Q6 C 2,3-BPG functions similar to inhibitor of an allosteric enzyme (note that haemoglobin is not an enzyme). At low concentrations of oxygen, 2,3-BPG has a higher affinity and will bind to haemoglobin, stabilizing it in inactive conformation, oxygen is unable to compete with it for oxygen binding sites. A and B incorrect – carbon dioxide and oxygen do not bind to the same binding site in haemoglobin, in any case it should not cause pH in red blood cell to fall (as stated in statement A). D – statements provide no evidence of any interaction between carbon dioxide and 2,3-BPG 7. N20Q7 D Enzyme Z is an allosteric enzyme and graph shape should be sigmoidal. In the presence of an inhibitor, the graph should shift to the right, meaning a higher concentration of substrate is required to reach the same rate of reaction compared to when the inhibitor is absent. GCE A Level H2 Biology 9744 Biology November 2020

8. N20Q8 A A person with Tay-Sachs cannot break down the gangliosides and th