1. Fruits remain alive for a period of time after harvesting. Cellular respiration continues and it can greatly influence the maturation (ripening) process in the fruits. The rate of respiration depends on many factors such as the type, quality, degree of ripeness and water content of the fruits, temperature and air composition. Respiration that continues after harvesting may sometimes lead to the over-ripening and eventual loss of an entire cargo of fruit during transport. Studies of the maturation process in bananas are summarized in the following graph. Relative rate green green/yellow yellow Time/arbitrary units (showing colour changes in bananas) Key: chlorophyll breakdown starch breakdown water release CO 2 formation Sugar formation [Source: www.containerhandbuch.de/chb_e/scha/index.html?/chb_e/scha/scha_15_02_03_02.html] (a) (i) State two chemical products released as gases during cellular respiration. 1 ........................................................................................................................ 2 ........................................................................................................................ (1) (ii) State one non-chemical product of respiration. ........................................................................................................................... (1) 1 (b) Using the data, analyse the events that occur when maturation begins in bananas. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (c) Suggest, giving reasons, two ways in which transport conditions can be controlled to minimize over-ripening. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 6 marks) 2. At the start of glycolysis, glucose is phosphorylated to produce glucose 6-phosphate, which is converted into fructose 6-phosphate. A second phosphorylation reaction is then carried out, in which fructose 6-phosphate is converted into fructose 1,6-bisphosphate. This reaction is catalyzed by the enzyme phosphofructokinase. Biochemists measured the enzyme activity of phosphofructokinase (the rate at which it catalyzed the reaction) at different concentrations of fructose 6-phosphate. The enzyme activity was measured with a low concentration of ATP and a high concentration of ATP in the reaction mixture. The graph below shows the results. Low ATP concentration Enzyme activity High ATP concentration Fructose 6-phosphate concentration 2 (a) (i) Using only the data in the above graph, outline the effect of increasing fructose 6-phosphate concentration on the activity of phosphofructokinase, at a low ATP concentration. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Explain how increases in fructose 6-phosphate concentration affect the activity of the enzyme. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (b) (i) Outline the effect of increasing the ATP concentration on the activity of phosphofructokinase. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (ii) Suggest an advantage to living organisms of the effect of ATP on phosphofructokinase. ........................................................................................................................... ........................................................................................................................... (1) (Total 7 marks) 3 3. Biosphere 2, an enormous greenhouse built in the Arizona desert in the USA, has been used to study five different ecosystems. It is a closed system so measurements can be made under controlled conditions. The effects of different factors, including changes in carbon dioxide concentration in the greenhouse, were studied. The data shown below were collected over the course of one day in January 1996. 1200 1600 1400 1000 1200 CO 2 / 800 ppm light / 1000 mol m–2 s –1 600 800 600 400 400 Key: 200 0 CO 2 Light 200 0 0 1.5 3 4.5 6 7.5 9 10.5 12 13.5 15 16.5 18 19.5 21 22.5 24 Time / hours [Source: http://www.Ideo.columbia.edu/martins/climate_water/labs/lab6/labinstr6/html] (a) (i) Identify the time of day when the sun rose. ........................................................................................................................... (1) (ii) Identify the time of minimal CO2 concentration. ........................................................................................................................... (1) (b) Determine the maximum difference in the concentration of CO2 over the 24-hour period. ..................................................................................................................................... ..................................................................................................................................... (1) 4 (c) Suggest reasons for changes in CO2 concentration during the 24-hour period. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 5 marks) 4. Plants that grow in the desert have many adaptations that enable them to cope with full sunlight and low water availability, such as thicker leaves with reduced surface area. Researchers have also observed that leaf pubescence (presence of white leaf surface hairs) may be another adaptation to dry environments. A study was done to evaluate the effects of leaf pubescence on two species of Californian plants, Encelia farinosa, a desert species with pubescent leaves and Encelia californica, a native of the moist coast with non-pubescent leaves. The graph below shows the absorption spectrum of intact leaves of both species in the photosynthetically active spectrum between the wavelengths 400 nm (blue light) and 800 nm (red light) of light. 100 Key: 90 E. californica 80 E. farinosa 70 60 Absorption 50 /% 40 30 20 10 0 400 450 Blue 500 550 Green 600 650 Yellow 700 Orange 750 800 Red Wavelength / nm [Source: From J. Ehleringer et al., “Leaf Pubescence: Effects on Absorptance and Photosynthesis in a Desert Shrub”, Science (23 April 1976), vol. 192, issue 4237, pp. 376-377. Reprinted with permission from AAAS] 5 (a) Calculate the difference in absorption between E. farinosa and E. californica at 600 nm. .................................................................................................................................... .................................................................................................................................... (1) (b) Suggest a possible explanation for the decrease in absorption at 550 nm for E. californica. .................................................................................................................................... .................................................................................................................................... (1) The following graph shows the rate of CO2 uptake of three leaves of Encelia farinosa with different absorbance coefficients (x) (proportion of light absorbed) which is related to the degree of pubescence of the leaf. The higher the coefficient the more light is absorbed. x = 0.82 4.0 3.5 x = 0.65 3.0 2.5 x = 0.53 Rate of CO 2 uptake / 2.0 n mol CO 2 cm–2 sec–1 1.5 1.0 0.5 0.0 0 50 100 150 200 250 Light intensity / mol cm–2 sec–1 [Source: From J. Ehleringer et al., “Leaf Pubescence: Effects on Absorptance and Photosynthesis in a Desert Shrub”, Science (23 April 1976), vol. 192, issue 4237, pp. 376-377. Reprinted with permission from AAAS] 6 (c) Using the graph above, compare the maximum CO2 uptake of E. farinosa at absorbance coefficients 0.82 and 0.53. .................................................................................................................................... .................................................................................................................................... (1) (d) (i) Using the data, deduce the relationship between pubescence and light absorption. .......................................................................................................................... .......................................................................................................................... (1) (ii) Evaluate the relationship of leaf pubescence and CO2 uptake. .......................................................................................................................... .......................................................................................................................... (1) (e) Suggest how natural selection may have caused the difference in leaf pubescence between E. farinosa and E. californica. .................................................................................................................................... .................................................................................................................................... (1) 7 6 0.35 5 0.30 0.25 4 0.20 3 0.15 2 0.10 1 0 Key: Water use effciency Pubescence Thickness /mm Water use effciency / arbitrary units Further research was carried out to evaluate the relationship between leaf pubescence during the growing season of E. farinosa and its water use efficiency. Water use efficiency is defined as the amount of CO2 uptake divided by the amount of water lost by transpiration from the leaf. The graph below shows the seasonal change in leaf pubescence and water use efficiency of E. farinosa. The period of maximum growth is indicated on the graph. During the course of the year the optimum temperature for photosynthesis remains at 30C while the air temperature fluctuates from a high of 38C in the summer months (May–September) to a low of 8C during the winter months (December–February). Pubescence thickness 0.05 M J J A S O N D J Time of the year / month F M A M 0.00 maximum growth period new leaves emerge [Source: Ecology by William K. Smith and Park S. Nobel. Copyright 1977 by Ecological Society of America. Reproduced with permission of Ecological Society of America in the format of CD-Rom via Copyright Clearance Center.] (f) State the month with the highest water use efficiency. .................................................................................................................................... (1) (g) Outline the changes in leaf pubescence of E. farinosa during the year. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2) 8 (h) Analyse the change in the level of water use efficiency between July and December for E. farinosa. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... (2) (Total 11 marks) 9
