A-level Biology Paper 1 Specimen Set 2, Exams of Biology

Download A-level Biology Paper 1 Specimen Set 2 and more Exams Biology in PDF only on Docsity! A-level Biology Paper 1 Specimen Set 2 No organelles are visible in the cytoplasm of this red blood cell. Suggest why. (1) - Cytoplasm of red blood cells filled with haemoglobin Before the cell was examined using the electron microscope, it was stained. This stain caused parts of the structure of the cell-surface membrane to appear as two dark lines. Suggest an explanation for the appearance of the cell-surface membrane as two dark lines. (3) - - membrane has phospholipid bilayer - stain binds to phosphate - on inside and outside of membrane Figure 4 shows that Rhizopus is able to reproduce both asexually and sexually. Suggest and explain one advantage of asexual reproduction and one advantage of sexual reproduction in this life cycle. (2) - asexual: fewer stages so quicker sexual: increases genetic diversity so greater chance of survival A scientist wanted to calculate the mean volume of Rhizopus spores. Describe how she could use Figure 5 do this. You may assume the spores are perfectly spherical. - - measure diameter of large number of spores - divide measured values by 700 - correct reference to 4/3 pi r3 as volume Explain the results without inhibitor (curve A) shown in Figure 6. (2) (Graph is "Initial rate of reaction" against "Substrate concentration" - - increases because more enzyme-substrate complexes formed - levels off because all enzyme molecules involved in enzyme-substrate complexes Figure 6 shows that the maximum initial rate of reaction (Vmax) when a competitive inhibitor was present (curve B) is different from that when a non-competitive inhibitor was present. (curve C) Explain this difference (4) - - competitive inhibitor binds to active site of enzyme but non-competitive inhibitor binds at allosteric site - binding of competitive inhibitor does not cause change in shape of active site but binding of non- competitive does - so with competitive inhibitor, at high substrate concentrations enzymes are still available but with non- competitive inhibitor enzymes aren't available - at higher substrate concentrations likelihood of enzyme-substrate collisions increases with competitive inhibitor but this isn't possible with non-competitive The Michaelis constant (Km) is the substrate concentration at which the initial rate of reaction is half its maximum value (Vmax). How could you use the Michaelis constant to determine the type of inhibition occurring in an enzyme- catalysed reaction? Use information from Figure 6 to support your answer (1) - - reaction with non-competitive inhibitor has the same value Km as with no inhibitor The UK government pays farmers to leave grassy strips around the edges of fields of crops. These grassy strips contain a variety of plant species. Leaving the strips is an attempt to encourage biodiversity of animals A group of scientists investigated the effect of grassy strips on the biodiversity of soil animals. • They divided a field into plots measuring 25 m × 5 m, with a 5-metre-wide grassy strip of land between each plot. • Each year, they planted wheat in each of the plots. - Concentration of haemoglobin in blood = 150 g dm-3 . - Volume of oxygen carried by fully saturated haemoglobin = 1.35 cm3 g-1 . - Resting heart rate = 60 beats minute-1 . - Volume of blood pumped out of left ventricle each beat = 60 cm3 . Use these data and information from Figure 8 to calculate the volume of oxygen released to the man's tissues per minute whilst he was at rest. Show your working. (3) - - correct answer 280-367 cm3 minute-1 - vol of oxyen released to tissues = 150 * 1.35 - blood flow = 60 * 60 = 3.6 dm3 minute-1 Boron is an element that is needed in very small amounts for normal plant growth. One group of scientists tested a hypothesis that boron combines with sucrose to produce a sucrose- borate complex that is translocated more effectively than sucrose molecules. They grew tomato plants in nutrient-poor sand. Prior to starting their experiment, they left the mature plants in a dark room for 48 hours. For each plant, the scientists put one of its leaves into a solution of sucrose that was radioactively labelled. These leaves were left attached to the plants. They used two radioactively labelled sucrose solutions: - solution A contained boron at a concentration of 10 parts per million. - solution B contained no boron. After a period of time, the scientists removed samples from parts of the plants, dried them in an oven and ground each into a powder. They then measured the radioactivity in each powdered sample. The s - - sand: to ensure no boron provided - dark: to ensure no sucrose produced in photosynthesis The scientist dried the plant samples in an oven at 100*c. Give two reasons why they used this temperature. (2) - - evaporates all water - but does not burn organic compounds Do the scientists results support their hypothesis? (4) (Hypothesis: One group of scientists tested a hypothesis that boron combines with sucrose to produce a sucrose-borate complex that is translocated more effectively than sucrose molecules.) Mean radioactivity with boron vs no boron: Stem tip: 14.2 / 1.7 First leaf above treated: 3.3 / 0 Upper stem 31.2 / 8.3 Lower stem: 28.3 / 13.3 First leaf below treated: 21.7 / 0 Roots: 3.5 / 1.7 - YES: - uptake of sucrose greater - transport to other parts of plant greater - use correct data NO: - no evidence that sucrose-borate complex is formed Suggest how the scientists could adapt their method to determine which tissue carried the radioactively labelled sucrose. (2) - - take thin sections of plant tissue - place against photographic film in dark for several hours Bacterial meningitis is a potentially fatal disease affecting the membranes around the brain. Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis. In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis. (6) - - antigen on the surface of bacterium binds to surface receptor on a specific B cell - activated B cell divides by mitosis - division simulated by cytokines - B cells release antibodies - some B cells forms memory cells - memory cells produce antibodies faster Penicillin has been the antibiotic of choice for the treatment of bacterial meningitis. Since the year 2000, strains of Neisseria meningitidis that are resistant to penicillin, sulfonamides and rifampin have been discovered in the UK. Describe how a population of Neisseria meningitidis (Nm) can become resistant to these antibiotics (4) - - mutation - results in Nm cell with allele for resistance to one antibiotic - this cell survives and passes the allele for resistance to offspring - process repeated with different genes conferring resistance to each of the other two antibiotics Contrast the structure of a bacterial cell and the structure of a human cell (5) - - bacterial cell is much smaller than a human cell - bacterial cell has a cell wall but human cell does not - bacterial cells lacks a nucleus but human cell has a nucleus - bacterial cells lacks membrane-bound organelles but human cell has membrane-bound organelles - bacterial DNA is circular but human DNA is linear