RI N19 H2 P2 ans

2019 H2 A level Paper 2 2019 H2 Biology A Level Paper 3 [Turn over Section A Answer all the questions in this section. 1 (a) List three structural features of E. coli that are visible in Fig. 1.1 [3] 1. Ribosomes 2. Circular DNA 3. (Peptidoglycan) Cell wall 4. Cell surface membrane (b) For one of the structural features listed in (a), state a detail of this feature that is characteristic of a bacterial cell. [1] 1. Ribosomes – 70s ribosomes in bacteria 2. DNA - circular DNA that is double stranded OR DNA molecule is not associated with histone but other histone-like protein molecules. 3. Cell wall – Made up of peptidoglycan* polymers 4. Cell surface membrane - Phospholipid bilayer with electron transport chains and ATP synthase are embedded to produce ATP (c) Describe what happens to the genome of bacteria during binary fission. [2] 1. Bacterial genome which is made of DNA replicates by semi-conservative replication* 2. DNA is unzipped by breaking hydrogen bonds between bases of the 2 strands 3. each parental strand serves as a template for synthesis of daughter strands 4. free deoxyribonucleotides complementary base pair with bases on the parental /template strand 5. DNA polymerase* forms phosphodiester bonds* between adjacent deoxyribonucleotides (d) Describe how the generation time and mean mass of an individual bacterial cell changes with nutrient availability, as shown in Table 1.1. [2] 1. As nutrient availability increased from low to high, the generation time decreased from 100 to 24 minutes (quote data); 2. And mean mass of individual bacterial cells increased from 150 x 10-15 g to 870 x 10- 15 g (quote data). (e) Suggest an explanation for the effect of decreasing nutrient availability on the generation time of these bacteria, as shown in Table 1.1. [2] Name nutrient + Effect of a lack of these nutrients on named cell processes 1. With low or no glucose, the bacteria will be unable to carry out aerobic respiration to generate sufficient levels of ATP 2. Hence the bacterial cells will have insufficient energy required for cell division/binary fission and hence take a longer generation time OR 1. Certain essential amino acids, which cannot be produced by the bacterial cells, need to be taken up from the environment 2. Without which the bacterial cells will be unable to synthesize important bacterial proteins for growth, and hence require a longer generation time AVP [Total: 10]

2 2019 H2 Biology A Level Paper 3 2 (a) Name the monomers that join to form a cellulose molecule. [1] β-glucose monomers (b) Name the covalent bond between two of these monomers in a cellulose molecule and describe how this bond is formed. [3] 1. (1-4) glycosidic bond* 2. The glycosidic bond forms between C1 of one β glucose* monomer and C4 of another β glucose* monomer; 3. Condensat