2021 Bio H2 MCQ Explanations

1. N21Q1 B chloroplast mitochondrion ribosome phosphorylation ✓ oxidation ✓ translation ✓ polymerisation ✓ transcription ✓ replication  transcription ✓ reduction ✓ polymerisation ✓ translation ✓ phosphorylation ✓ transcription  Chloroplast – it contains circular DNA and 70S ribosomes: transcription and translation can occur. The synthesis of mRNA and polypeptides are also polymerisation reactions. In photosynthesis, ATP is synthesised in the light - dependent reactions. This involves phosphorylation of ADP to form ATP. Mitochondrion – it contains circular DNA and 70S ribosomes: transcription and translation (good to note this even though it is not in the question) can occur. Aerobic respiration involves the mitochondrion where glucose is oxidised. There are also several reactions that are oxidation by dehydrogenation in the Krebs cycle. Passing of electrons down the electron transport chain involves a series of redox reactions: the electron donor is oxidised, whereas the electron acceptor is reduced. (Note that electron transport chains are also in the chloroplast even though this is not in the question.) Ribosome – it is the site of translation and the process involves the polymerisation of amino acids to form polypeptides; 2. N21Q2 D According to endosymbiosis, mitochondrion was once a bacterial-like single cell organism. Thus it shows similarity with bacteria such as circular DNA, 70S ribosomes and reproduction by binary fission. The ability to synthesise proteins is not unique to bacteria / prokaryotes. 3. N21Q3 D Consider the features and select those that are unique to viruses: 1: genome of circular double -stranded DNA – this is a feature of some (not all) viruses and is also a feature of bacteria 2: enclosed within a protein coat – this describes non-enveloped viruses 3: layer of lipids – this describes the viral envelope, but is also true of any other cell that has a phospholipid bilayer as its cell surface membrane. 4: replicates only in the cytoplasm of a eukaryotic cell – this describes an obligate parasite which is a feature of viruses 4. N21Q4 A Only bacteriophage has no phospholipid while influenza virus and HIV are enveloped virus and Mycobacterium tuberculosis is a bacteria with plasma membrane. 5. N21Q5 D The difference between -glucose and - glucose is the position of the OH group attached to carbon -1. For -glucose, the OH group is below the plane of the ring (on the opposite side of the ring as carbon -6), while for -glucose, the OH group is above the plane of the ring (on the same side of the ring as carbon-6). GCE A Level H2 Biology 9744 Biology November 2021

Options A and B are incorrect as the OH groups cannot be replaced. Option D describes carbon -1 correctly as carbon -1 is attached to O in the ring and the O of the OH group, so it is the carbon that forms bonds with 2 oxygen atoms. 6. N21Q6 D For this type of questions, look for things that are inconsis