2023 Bio H2 Biology Paper 1 Explanations

1. N23Q1 B Option A is wrong since the cell theory does not make reference to high temperature denaturing enzymes or killing cells. Option C is factually correct. The curvature of the swan neck indeed prevents air currents carrying any cells from passing into the nutrient media. However, this has no connection to cell theory. Option D statement is also factually accurate. However, you do not need to do this swan neck experiment to know that the statement in Option D is correct. Only Option B shows that all cells come from pre-existing cells, which is part of cell theory. The swan-neck experiment proved this, because as long as the swan neck is present, there is no way air current can introduce bacterial cells or spores from the external to the broth. There is no cell in the broth since it was previously heated, so no cells wi ll grow. The top diagram contrasts with the bottom diagram, where once the swam neck “seal” is broken, pre -existing bacteria cells from outside can enter the broth and bacteria can divide to give even more bacteria – one central tenet of cell theory. 2. N23Q2 A Only statements 1 and 2 are correct, and the explanations are given below: 1: 70S ribosomes are found only in bacteria, mitochondria, and chloroplasts. 2: Prokaryotic DNA is not coiled around histone proteins, unlike eukaryotic DNA. 3: Cell wall is peptidoglycan, so it contains peptides, hence in addition to those named, there is also nitrogen. 4: Prokaryotes have free ribosomes, which are not attached to any membrane (phospholipids) in cytoplasm. 3. N23Q3 D Option A: Statement would have been correct if the second statement is “Binding of one oxygen molecules to a haemoglobin molecule causes a conformational change that makes binding of additional oxygen molecules easier.” Option B: Statement would have been correct if the first statement is “Up to four molecules of oxygen can bind to four haem groups in a haemoglobin molecule.” Option C incorrectly stated that there were four haem groups per subunit of haemoglobin. 4. N23Q4 D Statement 1 is wrong as for myeloid blood stem cells, genes that cause the cells to differentiate into cells other than certain blood cells cannot be switched on since myeloid blood stem cells are multipotent. Similarly, embryonic stem cells are pluripoten t, so the genes that cause the cell to turn into cells of the placenta cannot be switched on. It is likely that some of their DNA is methylated to silence those genes, hence statement 4 is false. Statement 2 is wrong. Embryonic stem cell is pluripotent. 5. N23Q5 D Statement 4 is wrong so Option C is wrong. Students should note that radioactive threonine will only account for a small proportion of amino acids in each glycoprotein molecule. Students must also realise that radioactive glucose will account for a very large proportion of the monosaccharides that are incorporated into glycoproteins. Statement 1 is wrong because the peptide b