13.2. Investigation of limiting factors
A subsection of Biology, 9700, through 13. Photosynthesis
Listing 10 of 75 questions
Sentences and are extracted from longer definitions of ecological terms. Each has one or more missing words. Complete and using the correct terms chosen from the list below. a population a community an ecosystem a niche a habitat trophic level producers organisms consumers ………………………………………………… is the particular location and type of local environment occupied by ………………………………………………… or organism, characterised by its physical features or by its dominant ………………………………………………… . ………………………………………………… is the functional role or place of a species of organism within ………………………………………………… . Only a small proportion of the light energy striking the leaves of producers becomes converted to chemical energy. The proportion that is converted is known as the photosynthetic efficiency (PE). Outline the possible reasons why a large proportion of light energy striking the leaves of plants is not converted into chemical energy. Most crops have a PE of 1% to 4%. Sugar cane, an important crop plant for food production and for the production of biofuel, has a PE of 7% to 8%. Suggest the advantages of growing crops with high PE for food production or for biofuel. Fertilisers containing nitrate are added to improve or maintain yield of crops such as sugar cane. Name two organic compounds containing nitrogen that are made by plants and state one function of each in plant growth. organic compound 1 function organic compound 2 function
9700_s15_qp_22
THEORY
2015
Paper 2, Variant 2
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Use In Queensland, Australia, the effect of the water-holding capacity of soil on the yield of sorghum and wheat was investigated. • Four test plots were prepared, two with high water-holding capacity (HWC) soil and two with low water-holding capacity (LWC) soil. • Sorghum seeds were sown on one plot with HWC soil and one plot with LWC soil. • Wheat seeds were sown on the second plot with HWC soil and the second plot with LWC soil. • The plots were regularly watered or irrigated throughout the growing season. • The yield of sorghum and wheat from all four plots was measured at the end of the growing season. shows the results of this investigation. sorghum LWC yield / kg per hectare sorghum HWC wheat LWC wheat HWC Examiner’s Use Describe and explain the results shown in . State two factors, other than water, light and temperature that would have to be controlled during this investigation to ensure that the results were valid. Sorghum is able to carry out photosynthesis at high temperatures by preventing photorespiration. Explain how sorghum is able to prevent photorespiration.
9700_w09_qp_42
THEORY
2009
Paper 4, Variant 2
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The light dependent stage of photosynthesis in a suspension of isolated chloroplasts can be investigated using the Hill reaction. Dichlorophenolindophenol (DCPIP) can be used to follow the process. DCPIP is a blue dye which turns colourless when it is reduced by accepting hydrogen and electrons. oxidised DCPIP reduced DCPIP blue colourless DCPIP is an artificial hydrogen acceptor that can be used in the Hill reaction. Name the natural hydrogen acceptor found in chloroplasts that is replaced by DCPIP in the Hill reaction. Outline the way in which hydrogen is made available to reduce the hydrogen acceptor in the light dependent stage of photosynthesis. A suspension of isolated chloroplasts for measuring the rate of the Hill reaction can be prepared by carrying out the following steps: • prepare buffer solution with the same water potential as the stroma of chloroplasts • liquidise spinach leaves in ice cold buffer solution • filter the liquid and obtain the filtrate • centrifuge the filtrate to obtain a pellet of chloroplasts • add the chloroplast pellet to fresh buffer solution in a beaker and mix to obtain a suspension. Explain the reason for: keeping the temperature very low using a buffer solution using a solution of the same water potential as the stroma of chloroplasts. An experiment was carried out to measure the time taken for decolourisation of DCPIP mixed with a suspension of chloroplasts. The results are shown in Table 2.1. Table 2.1 replicate time taken for DCPIP to decolourise / s rate / s–1 mean Complete Table 2.1 by calculating: for the three replicates, the mean time taken for the DCPIP to decolourise the mean rate using the formula: rate = 1000 t where t = time in seconds. The time taken to decolourise DCPIP was measured at a range of light intensities. State and explain the expected relationship between light intensity and time taken to decolourise DCPIP. expected relationship explanation
9700_w17_qp_42
THEORY
2017
Paper 4, Variant 2
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Azolla filiculoides is an aquatic fern that floats on the surface of lakes. The nitrogen-fixing microorganism, Anabaena azollae, lives within the leaves of the fern. The beetle, Stenopelmus rufinasus, feeds on A.filiculoides. State the ecological terms applied to each of the following descriptions of these species. description ecological term all the members of the species A. filiculoides floating on a lake all the organisms, including A. filiculoides, A. azollae and S. rufinasus, found living in and on the lake organisms, such as A. filiculoides, that absorb light energy, fix carbon dioxide and make organic compounds available to animals that eat them the role of species, such as A. filiculoides, A. azollae and S. rufinasus, in the lake ecosystem Explain the importance of nitrogen-fixing organisms, such as A. azollae, in ecosystems.
9700_s14_qp_21
THEORY
2014
Paper 2, Variant 1
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Questions Discovered
75