SRI LANKAN SCHOOL MUSCAT

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1 Withdrawal Examination 2015/2016 SRI LANKAN SCHOOL MUSCAT CLASSES SUBJECT PAPER DURATION 13 SCIENCE Biology WBI04/01 Unit 4B: The Natural Environment and Species Survival 1 hour and 30 minutes % Grade Candidate Name Index Number Marks Allocated Obtained Q.No Total 90 INSTRUCTIONS TO CANDIDATES Answer all questions in the space provided Candidates may use a calculator Paper is set by THAMODINI KARUNASINGHE Sri Lankan School 1

2 Answer ALL questions. 1. The process of photosynthesis has two main stages. The first of these involves the light-dependent reactions. (a) The statements below describe important parts of the light-dependent reactions of photosynthesis. Place a cross in the box next to the term that completes each statement correctly. (i) When light is absorbed by chlorophyll, it excites A B C D electrons neutrons photons protons (1) (ii) Oxygen is produced when water molecules are split in the process of A B C D analysis autolysis hydrolysis photolysis (1) (iii) The products of the light-dependent reactions that are used in the light-independent reactions are reduced NADP and A B C D ATP GALP DNA RuBP (1) Sri Lankan School 2

3 (b) Describe the structures in a chloroplast that are involved in the light-dependent reactions of photosynthesis. (3) (c) In an investigation, wheat plants were grown using artificial lighting. Three different types of lighting were used. When the wheat plants were mature, the total biomass of the plants and the mass of the grain (seeds) they produced were measured for each type of lighting. The table below shows the results of this investigation. Type of lighting Low pressure sodium lamps High pressure sodium lamps Total biomass / kg Mass of grain / kg Grain yield as a percentage of total biomass (%) Metal halide lamps (i) Calculate the grain yield, as a percentage of total biomass, for the wheat grown under metal halide lamps. Show your working. Answer...% Sri Lankan School 3

4 (ii) With reference to the data in the table, suggest the conclusions the investigators may have made about the effect of using different types of lighting on grain yield. (3) (iii) Suggest two advantages of growing crops of wheat in glasshouses with artificial lighting rather than growing them in open fields. (Total 13 marks) Sri Lankan School 4

5 2. Protein synthesis in cells involves molecules of DNA and RNA. (a) The table below describes some features of the molecular structure of DNA and RNA. Place a tick ( ) in the box next to each statement to show whether it applies to DNA only, RNA only or to both DNA and RNA. Description DNA only RNA only Both DNA and RNA Polymer formed from a single strand of nucleotides Pentose present in the nucleotides Adenine, cytosine, guanine and thymine present Nucleotides linked by phosphodiester bonds (b) The diagram below shows the sequence of the last six amino acids in a protein molecule. The trna anticodon that corresponds to each amino acid is also shown. amino acids Alanine Glutamine Glycine Asparagine Proline Valine trna anticodon CGA GUU CCA UUA GGA CAA Using this information, explain how each of the following processes leads to the synthesis of this sequence of amino acids. (i) The formation of mrna during transcription in the nucleus (3) Sri Lankan School 5

6 (ii) The translation of mrna into the sequence of amino acids in a ribosome (3) (c) Suggest why the final triplet of nucleotides, on the strand of mrna involved in the synthesis of this sequence of amino acids, did not correspond with any anticodon on trna. (Total 10 marks) Sri Lankan School 6

7 3. A study of tree pollen grains in a peat bog in Finland was carried out. The number of pollen grains of different tree species was recorded at different depths in the peat. The data for four of these trees are given as a percentage of the total tree pollen sample, in the table below. An estimate of the age of the sample at each depth was also made. Depth of Age / Tree pollen grain / % sample years Spruc / m Larch Pine Beech e The diagram below shows the present-day distribution of the four tree species found in the main climatic zones of the northern hemisphere. Climatic zone Distribution of trees Arctic Boreal Larch Spruce Temperate Pine Beech Sub-tropical Sri Lankan School 7

8 (a) Suggest how pollen grains can provide evidence about which species of tree were growing successfully in Finland as the peat bog was forming. (b) (i) Put a cross in the box next to the species of tree that does not provide evidence about the changes in climate in Finland during the last years. A B C D Larch Spruce Pine Beech (1) (ii) Explain your answer to (b)(i). Sri Lankan School 8

9 (c) With reference to the present-day distribution of the four tree species and the results of the pollen grain study, suggest in what way the climate in Finland has changed during the last years. Give reasons for your answer. (5) (d) Describe how dendrochronology can be used to provide evidence for climate change. (Total 12 marks) Sri Lankan School 9

10 4. (a) Forensic entomology can be used to estimate the time of death of a mammal. Adult female blowflies soon arrive to lay their eggs on the body and the blowfly life cycle follows a precise sequence. The diagram below shows the sequence and times (in hours) for each stage when the surrounding temperature is 21 C. (i) Using information in the diagram, calculate the total percentage of the life cycle that a blowfly spends as a larva when the surrounding temperature is 21 C. Answer... % (ii) Temperature has an effect on the length of the blowfly lifecycle. Suggest an explanation for the effect of temperature on the length of the blowfly lifecycle. Sri Lankan School 10

11 (iii) Suggest two factors, other than temperature, that may affect the timing of the blowfly lifecycle and lead to an incorrect estimate of the time of death. (3) (b) Time of death can also be estimated by studying the degree of rigor mortis in muscles. Describe how rigor mortis in muscles occurs. (3) Sri Lankan School 11

12 (c) The process of succession occurs in plant communities as well as in a dead body. Compare these two forms of succession. (3) (Total 13 marks) 5. Tuberculosis (TB) is caused by the bacterium, Mycobacterium tuberculosis. (a) The table below lists five structural features that may be found in bacteria and viruses. Put a cross in the box if the structural feature is present. Structural feature Bacteria Viruses Mesosome Capsid Nucleic acid Cytoplasm Ribosome (5) (b) The table below shows the number of new TB cases recorded in 1994 and in 2004 from four different geographical regions. These data exclude people who are HIV positive. Sri Lankan School 12

13 Year Number of new TB cases per of the population Africa Asia South America Europe (i) Describe the trends shown by the data. (ii) HIV positive people were excluded from the data. If they had been included suggest how the data would differ. Give an explanation for your answer. (3) Sri Lankan School 13

14 (c) TB is increasing in some countries which have well-funded health services. Suggest two reasons for this. (Total 12 marks) 6. The flow diagram below summarises some of the stages used to copy DNA in the polymerase chain reaction (PCR). Sri Lankan School 14

15 (a) Explain why the DNA is heated during Stage 1. (b) Describe the structure of the primers used in Stage 2 and explain why they are used. (3) (c) Another method of producing many copies of a DNA sample is to introduce the DNA into bacteria and allow them to reproduce. Suggest one disadvantage of this technique compared with PCR. (1) (Total 6 marks) Sri Lankan School 15

16 7. A new technique for vaccinating people involves injecting them with DNA. Viruses have proteins on their coats that are coded for by their DNA. The genes for producing viral proteins can be isolated and inserted into loops of DNA (plasmids). Plasmids can enter human cells which will then produce the viral proteins. The proteins will become part of the surface membrane of the human cell. The immune system will recognise these proteins as foreign and respond by producing antibodies and T killer cells. The process is summarised for one protein in the following diagram. Plasmid including gene from viral DNA Protein synthesis Cell in human body Viral protein present on cell surface membrane Nucleus Production of antibodies and T killer cells by immune system Sri Lankan School 16

17 (a) Explain why the response of the immune system to the viral proteins is an example of active immunity. (b) Explain how active immunity provides immunity against future infections by the virus. Sri Lankan School 17

18 (c) The table below compares the production and distribution of vaccines made using traditional methods with those made using DNA. Time to develop vaccine against new strain of virus Time to produce enough doses for effective protection of population Treatment during distribution DNA vaccine Traditional vaccine 2 3 weeks 4 6 months 2 3 months 2 3 years No special treatment Constant refrigeration Use the information in the table to suggest why the DNA vaccine is likely to be more effective at preventing the spread of a new strain of virus. (3) (Total 07 marks) Sri Lankan School 18

19 8. A new species of large cat, the clouded leopard (Neofelis diardi) has been identified on the island of Borneo. Neofelis diardi on Borneo is distinct from Neofelis nebulosa on the mainland. (a) Explain why the clouded leopard and the mainland leopard share the name Neofelis. (1) (b) There are 46 genetic differences between the two species of leopard. Explain how these differences may have arisen, assuming that the two species share a common ancestor. (3) Sri Lankan School 19

20 (c) The clouded leopards are found in regions of the island of Borneo that are governed by three different countries, Brunei, Indonesia and Malaysia. Suggest reasons why this may make the conservation of leopard habitats difficult. (Total 6 marks) Sri Lankan School 20

21 Mass of leaves / g 9. In an investigation, several leaves were removed from a Magnolia tree. These leaves were weighed and then placed on the surface of some moist compost in an incubator set at 25 C. At two-day intervals for a period of 4 weeks, the leaves were weighed and then replaced on to the surface of the compost. Figure 1 Graph of mass of leaves against time after removal from the Magnolia tree Time after removal from tree / days Figure 2 Photograph of a freshly-picked Magnolia leaf compared with a Magnolia leaf that has been on the surface of the compost for 28 days Freshly-picked leaf Leaf after 28 days on compost Sri Lankan School 21

22 (a) (i) Describe the changes in the mass of the leaves during the first 14 days of the investigation. (ii) Suggest why it is unlikely that the activity of saprobiontic microorganisms in the compost caused these changes in mass during the first 14 days. (iii) Suggest a possible reason for the changes in mass in the first four days. (1) Sri Lankan School 22

23 (b) State one difference in appearance of the two leaves in Figure 2, and suggest how saprobiontic microorganisms brought about this change. (4) (c) When leaves are added to compost heaps, explain why it is important that the compost is not allowed to become waterlogged or compacted. (Total 11 marks) Total for the Paper =90 Sri Lankan School 23