Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
Marking schemes for Advanced Level Biology
AS Biology with Stafford Unit Three: Practical Workbook
Paper reference: 6BIO7
The book is available at the following link http://www.amazon.com/gp/aw/s/ref=is_s_?k=AS+A2+Biology+with+stafford
A copy of this marking scheme and many other resources can be downloaded from the following link http://www.facebook.com/groups/biologywithstafford/ and www.staffordeducationalservices.com
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
Copyright © Stafford Valentine Redden Unauthorized duplication contravenes applicable laws. Typeset & layouts by : Mohamed Sobir Cover designed by : Mohamed Sobir Printed in Maldives by : Copier Repair Published by : Author publisher All rights reserved. No part of this publication may be Reproduced, stored in a database or retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the author
ISBN: 978-81-910705-2-1
Note: A few graphs have been drawn to give students an idea on how to find the scale and plot range or variability. Other graphs have not been drawn as students need to practice the graph drawing. Do post your graphs on my FB group and I can give a feedback on the graphs. Any other queries on any aspect of the practical paper can be clarified on my FB group http://www.facebook.com/groups/biologywithstafford/ I have also included additional notes on referencing, citation or bibliography at the end of the document. Evaluation of references is also dealt with in detail. Cheers and all the best…. Stafford Valentine Redden (M.A; M.Sc.; M.Ed.; (Ph.D)) Head of Departm ent (Biology) Villa International School, Male’, Republic of Maldives Em ail:
[email protected] Mobile: +960 7765507
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
SAQ1. a. (i) Correct mean calculation; consistency with decimal places; Relative Caffeine Heartbeat rate of daphnia in beats per minute concentration (%) Daphnia 1 Daphnia 2 Daphnia 3 Mean 0 (pond water) 82 90 87 86.3 1.56 83 87 89 86.3 3.12 88 91 94 91.0 6.25 96 97 102 98.3 12.5 97 98 106 100.3 25 140 142 146 142.7 50 150 156 154 153.3 100 (pure Red Bull) 181 184 183 182.7 (ii) Relative caffeine concentration; (1) (iii) Heartbeat rate of daphnia; (1) (iv) Use Daphnia of the same size, as size or surface area to volume ratio could influence the rate of absorption of caffeine into the body; it is not possible to measure the size or surface area of Daphnia, but Daphnia of similar size can be selected for the experiment by simple observation and judgement; Do not keep the Daphnia on the cavity slide for too long after removing it from the water bath, as the temperature could change and thereby influence the heartbeat rate; This can be controlled by counting the heartbeat rate 30 seconds as soon as the Daphnia is transferred to the cavity slide; The concentration of dissolved oxygen in each caffeine soultion; this can be controlled by aerating the solutions by passing air through it to saturate the solution with oxygen; (b) Refer to graph 1, on page 2. Axes labelled and correctly oriented with units; scale more than 50% of graph covered; points clearly indicated with a cross or dot and circle at the accurate position on the graph; single neat line drawn either with a ruler from point to point or freehand curve / no extrapolation; range bars plotted accurately; (c)Tap water contains chlorine, which could be toxic to daphnia. A beaker containing tap water can be left open overnight to allow chlorine to evaporate. (d) Metabolic activity is slowed down at low temperatures due to lack energy as respiratory enzymes have low kinetic energy. The aeration ensures that the water gets saturated with oxygen and metabolic activity is not limited by lack of oxygen for respiration. (e) As the caffeine concentration increases there is a corresponding increase in the mean heartbeat rate of daphnia. The increase is not linear. (f) Blind counting means that the person who is counting the heartbeat rate is not aware of the caffeine concentration that the daphnia has been exposed to. This can help to reduce bias while counting. (Total 20 marks)
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
Graph 1 (Total 20 marks) SAQ 2 a. Duration since exposure to caffeine / time; b. mean heartbeat rate of daphnia; c. i. This is a random error. All other readings lies close to the expected values and follow a trend. Only this value lies away from the trend and is unexpected. A systematic error will lead to the entire set of data devaiting from the actual trend. ii. Duration since exposure Heartbeat / beats per minute to caffeine / minutes Flea 1 Flea 2 Flea 3 Mean 0 184 180 185 183 2 220 222 224 222 4 232 234 230 232 6 246 240 120 243 8 242 240 238 240 10 230 232 234 232 iii. Axes labelled and correctly oriented with units; scale more than 50% of graph covered; points clearly indicated with a cross or dot and circle at the accurate position on the graph; single neat line drawn either with a ruler from point to point or freehand curve / no extrapolation; AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
d. The heartbeat rate of 182 beats per minute without caffeine is the control. All result s from caffeine treatment must be compared with the control to make any conclusions about caffeine exposure and heartbeat rate. The mean heartbeat rate increases with time as more caffeine is absorbed into the body from the solution as time increases. So t he greater caffeine concentration in tissues increases the heartbeat rate. However, after 8 minutes the heartbeat rate begins to decerase, maybe because diffusion stops or caffeine begins to be excreted from the tissues. e.
f. Use a microscope fitted with a video camera and integrate timer to record the heartbeat rate. Then replay the video in slow motion and count the number of heartbeats in one minute as shown on the integrated timer. g. Daphnia has reduced awareness of pain because of the lack of a well developed nervous system. It is transparent and its heart is visible without the need for dissection. Daphnia is abundant in nature and there is no threat to it or its dependent species (food chains). Some people also feel that it is bred for fish food and will thus die anyway. Daphnia can reproduce asexually and may be clones, therefore there is no loss of genetic variation. (Total 20 marks) SAQ3 a. i. Concentration of nitrogenous fertilizer used ii.) Vitamin C concentration of the oranges iii.) concentration of other fertilizers in the soil; Volume of water provided to each plant; Edaphic factors / Soil type / Humus content of soil; Pest control strategy and application; b. i.) Blue ii.) Colourless iii.) Risk: The DCPIP solution could stain clothes and skin. This could be minimized by using rubber gloves / wearing a laboratory coat / using a pipette to transfer DCPIP; c. i. And ii. CB = (VA x CA) / VB = (8 x 0.1) / mean volume First example (8 x 0.1) / 28 = 0.029
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
Plot Number
Mass of fertilizer used / kg
1 2 3 4 5 6 7 8 9 10
0 2 4 6 8 10 12 14 16 18
Volume of orange juice needed Concentration of -3 to reach the end point / cm Vitamin C in the oranges / mg cm-3 Orange 1 Orange 2 Mean 29 27 28.0 0.029 27 30 28.5 0.028 25 23 24.0 0.033 23 21 22.0 0.036 20 19 19.5 0.041 17 17 17.0 0.047 16 17 16.5 0.048 17 18 17.5 0.045 15 16 15.5 0.052 12 18 15.0 0.053
c. iii. Due to the orange colour of the juice, it is difficult to accurately observe the point at which the DCPIP becomes colourless; d. Axes labelled and correctly oriented with units; scale more than 50% of graph covered; points clearly indicated with a cross or dot and circle at the accurate position on the graph; single neat line drawn either with a ruler from point to point or freehand curve / no extrapolation; e. As the mass of fertilizer used increases there is a general increase in the vitamin C concentration of the oranges; Suitable manipulation; SAQ 4. (a) Fruit
Grapefuit juice Pineapple juice Orange juice Fresh lemon juice Black currant juice
Volume of juice needed to decolourise DCPIP / cm-3 Trial 1 Trial 2 Trial 3 1.50 1.70 1.65 12 11.20 11.50 2.00 2.25 2.10 1.90 1.70 1.60 24.0 23.5 24.5
Mean 1.62 11.57 2.17 1.73 24.0
Vitamin C concentration / mg cm-3 (VAxCA)/VB=CB (0.6x10)/1.62= 3.75 (0.6x10)/11.57=0.52 (0.6x10)/2.17=2.76 (0.6x10)/1.73=3.46 (0.6x10)/24.0=0.25
(b) Axes labelled and correctly oriented with units; scale more than 50% of graph covered; Bar graph with space between the bars; Range bars to show range of data for each fruit juice;concentration plotted as range bars; Refer to graph 2 on next page.. (c) Fresh lime juice shows the highest variability, as the data is spread far away from the mean. The range bar is the longest. This indicates that the results are less reliable than the others. The black currant juice shows the least variability in the results. (d) The dark colour of the juice makes it difficult to observe the exact point at which the DCPIP changes colour. So, the accuracy of the readings is likely tobe low and hence the validity of the results will be low. (e) Weigh 6mg of vitamin C powder by using an electronic balance; add distilled water into a volumetric flask of 100cm-3 and dissolve the powder into the distilled water to prepare 100 cm-3 of the vitamin C solution;; (f) The vitamin C reduces the DCPIP.
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
Graph 2
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
SAQ 5. (a)(i) different beetroots may have different concentration of pigment / the stability of eell membrane may vary due to different storage conditions or age of the samples; (b) (i) IV: Ethanol concentration; (ii) DV: absorbance or permeability of the membrane (iii) The filter used in the colorimeter must be the same for all samples. Set the colorimeter filter knob to blue. Or Use discs cut from the same beetroot, so that genetic variation, storage conditions, growth conditions will not influence the results. (iv) Ethanol Concentration (%) 0 0.2 0.4 0.6 0.8 1.1 1.3 1.5
Absorbance / arbitrary units Sample 1 Sample 2 Sample 3 0 0 0 0.4 0.3 0.2 0.8 0.7 0.9 1.2 1.2 1.2 1.4 1.6 1.7 1.6 1.7 1.8 1.8 1.9 2.0 2.0 2.1 2.2
Mean 0 0.3 0.8 1.2 1.6 1.7 1.9 2.1
(v) Axes labelled and correctly oriented with units; scale more than 50% of graph covered; points clearly indicated with a cross or dot and circle at the accurate position on the graph; single neat line drawn either with a ruler from point to point or freehand curve / no extrapolation; range bars plotted accurately; (c) To remove cell debris and red pigment from the disc surface; (d) As the ethanol concentration increases there is an increase in the absorbance of red colouration in the solution. This increase in absorbance is not linear. (e) Ethanol dissolves the phospholipids in the cell membrane and disrupts the phospholipid bilayer. This makes the membrane freely permeable to the red pigment which can rapidly diffuse out of the cells.
SAQ6 (a) (i) Independent Variable: Enzyme concentration; (ii) Surface area to volume ratio of the meat; cut meat into cubes of equal length breath and height by using a very sharp scalpel and ruler; Protein content if meat; use Meat from the same source or animal; Temperature; by using a thermostatic water bath; pH of the solution should be 2 or 3 as it is a stomach enzyme; use a buffer solution of pH 3 to maintain a constant pH; AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
(b) The student recorded the data in a table: Concentration Time taken for the meat of enzyme (%) completely/ sec 1 ∞
2 ∞
812
820 811 800 805 817 800 805 808.8
1.24
2
624
612 607 635 620 621 614 606 617.3
1.62
3
586
568 575 564 580 582 584 580 577.4
1.73
4
409
400 404 415 412 416 406 410 409
2.44
5
305
310 309 315 300 302 306 301 306.1
3.27
Distilled water 1
3 ∞
4 ∞
5 ∞
6 ∞
∞ means infinity (no reaction) dissolve Mean Rate = (1 / mean time) x 1000
to 7 ∞
8 ∞
∞
0
c. Time taken to dissolve the meat is inversely proportional to the rate and would be difficult to interpret. I/mean time is directly proportionate to the rate and is easy to interpret. However, 1/mean time gives very small numerical values which are difficult to work with and plot on a graph. Multiplying by 1000 gives more convenient numbers. d. Protease enzymes are proteins and could cause allergic reactions. So, avoid direct contact with the enzyme by wearing gloves and using pipettes; The meat pieces or broth produced can be a good nutrient medium for harmful pathogenic bacteria to grow. So thoroughly clean all spills by wiping with bleach or 70% ethanol. A buffer solution of pH 3 could cause skin damage; avoid contact with skin; (e) Axes labelled and correctly oriented with units; scale more than 50% of graph covered; points clearly indicated with a cross or dot and circle at the accurate position on the graph; single neat line drawn either with a ruler from point to point or freehand curve / no extrapolation; (f) As enzyme concentration increases, there is a non linear increase in the rate of enzyme action. (g) an enzyme concentration of 5% causes the fastest digestion of meat; SAQ7 a) Concentration of catalase / mmol dm-3 0 20 45 95 155 180
Rate of reaction / S-1 0 0.05 0.10 0.15 0.17 0.17
b) Axes labelled and correctly oriented with units; scale more than 50% of graph covered; points clearly indicated with a cross or dot and circle at the accurate position on the graph; single neat line drawn either with a ruler from point to point or freehand curve / no extrapol ation; (3) AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
c) a buffer solution maintains a constant and optimum pH.
(1)
d) (i) As enzyme concentration increases from 0 to 95 mmol dm-3 there is a general increase in the rate of enzyme action; the increase is non linear; beyond 155 mmol dm-3 enzyme concentration the rate of enzyme action remains constant and maximum; (3) (ii) As the enzyme concentration increases the rate of reaction increases with a decreasing gradient. This is because there will be a greater concentration of free active sites, at any given time. So the rate of enzyme substrate complex formation increases. Thus rate of reaction increases. The rate of reaction doesn’t increase beyond the V m ax because the substrate concentration becomes a limiting factor. Even though there will be many free active sites, there will not be enough substrate molecules to bind with them. So, rate of enzyme substrate complex formation remains constant at V m ax. (3) (c) Repeating the experiment gives us a means of checking the reliability of the results; if the data shows a lot of variability then it indicates that the results may not be reliable; if the experiment is not repeated then we cannot check the reliability; (2) d) This instrument makes a more relevant and accurate measurement of the dependent variable;; so the reliablity and validity of the results will improve; (3) e. i. Concentration of catalase (%) 0.5 2.5 5.5 7.5 9.5 11.5 13.5
Rate of reaction / S-1 0.05 0.11 0.16 0.20 0.23 0.24 0.24
(ii) Each disc may not absorb the same volume of enzyme solution; There will be reaction time errors when measuring time taken for discs to rise / low accuracy of measurement; (Total 25 marks) SAQ 8. (a) Treat the root tissue with dilute Hydrochloric acid for 4 to 5 minutes. This softens the tissue and allows easy squashing. Avoid contact with the acid by using a teat pipette to transfer the acid into a watch glass. Stain the tissue with acetocarmine or acetoorcein (reddish or pink dye). Chop or macerate into tiny pieces to mix the tissue with the dye. Place a cover slip slowly and ensure no bubbles are produced. Squash the tissue by applying gentle pressure and a slight sideways movement on the top of the cover slip. Squashing opens up cells so that chromosomes become visible. Heat the slide gently. Heating makes the stain darker so that chromosomes are more visible. Observe under high power magnification to observe the chromosomes and cells in different stages of the cell cycle. (4)
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
(b)
(c) In all stages the range bars overlap, so the colchicine does not have any significant effect in changing the number of cells in each stage of division;;;; d. i. Treatment with colchicine ii. Percentage of cells in a stage of cell division; iii. Duration of exposure to colchicine; All tissues exposed to same concentration of colchicine; Temperature of growth and other nutrients available to the root during growth of roots; (Total 18 marks) SAQ9. a.i. Percentage success rate (%) Source of Petri Petri explants dish dish 1 2 Leaf discs 40 50 Root discs 60 50
Petri dish 3 60 70
Petri dish 4 40 80
Petri dish 5 30 40
Petri dish 6 50 50
Petri dish 7 40 80
Petri dish 8 50 90
Petri dish 9 60 70
ii. Type of marigold plant tissue used as explant
Petri Mean dish 10 50 47.0 90 68.0 (2) (1)
iii. percentage success of callus formation
(1)
iv. Size of explants: as the surface area could influence the rate at which nutrients are absorbed from the medium; temperature: as it could influence the rate of metabolism in the explants tissues and influence growth; AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
concentration of nutrients in each dish: as this could influence the rate of nutrient absorption into each explants and influence growth; type of nutrients in each dish: the type of nutrients can influence development. Forexample auxins in the medium stimulate root formation in the callus and cytokinins can stimulate shoot formation. It also can influence growth of the explants; type of tissue in the explants: lots of cambium can stimulate rapid growth and lots of xylem will slow growth as xylem consists of dead cells; (4) b. Bar Graph with range bars.(4) c.i. Follow aseptic techniques to prevent the growth of harmful bacteria in the nutrient medium; Bleach could decolourise clothing and may also release chlorine; so avoid direct contact with the bleach and do not inhale fumes from the bleach: (2) ii. The plant tissue (explants and callus) may be directly destroyed by the bacteria that may enter the dish; the bacteria may absorb nutrients from the agar medium and compete with the palnt tissue for nutrients; (2) d. Since the range bars overlap, it means that the mean values are not significantly different. So, both root discs and leaf discs are equally effective for use as explants; (2) [Total marks 18] SAQ10. a) Sucrose concentration / Mass of callus / g Percentage change mmol dm-3 in mass (%) Initial Final 0.1 0.2 0.3 0.4 0.5
2.1 2.6 2.3 2.1 2.7
2.6 3.8 4.6 4.2 5.4
23.8 46.2 100 100 100
(4) b) Line graph (4) c.i. Sucrose concentration of the medium (1) ii. growth rate of the callus (1) iii) Size of explants; temperature; concentration of nutrients other than sucrose; type of nutrients in each dish; type of tissue in the explants; (4) (d) vegetative propagation / asexual reproduction; (1) (e) Grow more rapidly; No genetic variation, so desirable characters can preserved; (2) (f) no genetic variation in plants produced by tissue culture so if virus destroys one plant all others will be destroyed; in plants produced by seeds there will be genetic variation so some plants may have features that help it to resist the viral attack; (2) (g) Auxins in high concentration will switch on the genes needed for root development and cytokinins will switch on the genes for shoot formation; (1) [Total marks 20] SAQ11. a. i. Add weights to the weight holder; Increase the weight in suitable increments; Keep adding weights till fibres snaps / breaks; Take care to add the weights gently / do not drop the weights on to the holder; Intially add larger increments and as the fibre begins to stretch then add smaller weights to get a more accurate measurement; Standardise the length and diameter of the fibres; (4) AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
ii. Source of coconut Fibre Leaf Fruit
Tensile strengt h /N Trial 1 Trial 2 Trial 7 Mea mm-2 n 12.3 11.2 13.2 12.8 13.6 14.4 13.7 13.0 25.9 18.5 17.3 16.7 17.9 19.5 16.8 19.5 18.0 28.9 (4) iii. Paired bar graph with range bars for breaking force. (3) iv. The breaking force for leaf fibres has a range of 3.2N, where as the breaking force for fruit fibres has a range of 2.8N. A higher range indicates lower reliability; (2) b. Source of plant fibre within the plant; (1) c. Breaking force or tensile strength; (1) d. Variable 1 cross sectional area or diameter of the fibres; How the variable can be controlled: measure the diameter of many fibres and select the fibres of the same diameter. Very thick fibres can be split and torn apart to reduce the diameter; Variable 2 length of the fibres; How the variable can be controlled: Cut all fibres to the same length; Moisture content in the fibres: dry all fibres in an oven at 90 0C ttill the mass is constant, so that all fibres have no moisture; (4) e. The mean tensile strength of fruit fibres is higher than leaf fibres; (1) [Total 20 marks] Breaking force of fibre / N Trial 3 Trial 4 Trial 5 Trial 6
SAQ12 (a) line graph with two curves. Range bars plotted for each.
(4)
b) i. in both fibers the tensile strength decreases as the duration of retting increases; at the end of 13 days of retting there is a decrease of 34% in the breaking force of hemp fibers and 16% in breaking force for jute fibers. (3) ii. the standard deviation for hemp fibers is higher for jute fibers. This indicates a high variability in the breaking force for hemp fibers and is suggestive of low reliability. This could limit the validity of the results. (3) d) Temperature during the retting process; As it could influence the rate of enzyme activity by decomposers; Aeration; as aeration is necessary for decomposition of soft tissue by aerobic bacteria; (4) e) Micrometer screw gauge (1) f) Add weights in small increments; Place weights gently on to the weight holder;
(2)
g) Wear eye protection to prevent the fibre from lashing you in the eye when the fibre snaps; Place a tray with cotton wool padding to hold the weights when the fibers break; (2) h) Validity can be checked by comparing the results with identical studies which are valid and have adopted a thorough scientific review; (1) (Total 20 marks)
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
SAQ13. a. Nitrate Flask concentration / Arbitrary units A 0.0 B 0.2 C 0.4 D 0.6 E 0.8 F 1.0
Mass of algae at end of two days /g Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Mean 2.4 3.2 4.4 6.4 7.5 7.3
3.2 3.4 4.5 6.0 7.8 7.4
2.3 3.6 4.4 6.3 7.9 7.2
2.4 3.2 4.3 6.8 7.2 7.8
1.9 3.0 4.6 6.2 7.4 7.3
2.4 3.3 4.4 6.3 7.6 7.4
(3) b. i. Nitrate concentration in the growth medium; (1) ii. Growth rate of algal culture; (1) iii. Temperature of incubation: incubate the flasks in an incubator at a fixed temperature; volume of nutrient solution in each flask: use a measuring cylinder to accurately measure the nutrient solution before adding it into the conical flasks; light intensity: use a light bulb of fixed wattage and focus it from a fixed distance into the incubator on to the flask, through the transparent glass door of the incubator; carbon dioxide availability: dissolve a fixed mass of sodium hydrogen carbonate into each flask to provide carbon dioxide; (8) c. Line graph with range bars for each concentration of nitrate. (5) d. as concentration of nitrates increases there is a non linear increase in the growth rate of the algae; this is because nitrates are used for making proteins and nucleic acids which promote the growth of the culture by enhancing rate of cell division;; (3) e. increasing the nitrate concentration up to 0.8 arbitrary units increases the growth rate of algae; beyond this concentration there is no further increase in growth of algae;(2) [Total 23 marks] SAQ14. a) Plant Diameter of clear zone / mm Area of clear zone / mm2 extract Vertical Horizontal Diagonal Diagonal 2 Mean 1 Garlic 10.0 10.0 9.0 10.0 9.75 Πr2 = (4.8752)x3.14 = 74.6 Onion 7.5 7.5 7.0 6.0 7.00 Πr2 = (3.52)x3.14 =38.5 Mint 10.0 12.5 12.0 12.5 11.75 Πr2 = (5.8752)x3.14 =108.4 Control 2.0 2.0 2.0 2.0 2.0 Πr2 = (12)x3.14 =3.14 b. Graph c. i. count the number of squares covered by the clear zone; the number of squares is equal to the area of the clear zone in mm2; count only squares that are covered more than half; ii. Plant extract Area of clear zone / mm2 Garlic 63 Onion 36 Mint 85 Control 4 iii. The photograph method is more accurate, as the direct measurement method assumes that the clear zone is a circle (which is not the case); the photograph method gives a more accurate means of counting the actual area of the clear zone;
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
d. i. This gives enough time for the antibiotics to diffuse into the agar and inhibit the growth of bacteria or kill bacteria; it also allows enough time for the colonies to grow in areas where the antibiotic does not reach; e) the mint extract is the most effective antibiotic against this bacteria; the area of the clear zone is more than all other discs; this implies that the mint extract has a greater antibacterial effect than other extracts; f.i. Type of plant extract; ii. antibacterial effect / diameter of clear zone; iii. 1. standard procedure for preparation of extract – same mass of plant tissue in the same volume of distilled water or ethanol for each extract; 2. concentration / volume of extract in each disc; 3. size of each disc; 4. aseptic techniques followed in placing the discs on the agar / use sterile forceps to place each disc on to the agar surface to prevent contamination of the culture; 5. bacteria must be spread evenly throughout the surface of the agar; 6. some form of standardisation of tissue from which the extract is prepared, for example tissues from similar parts of each plant – leaf extracts, root extracts, peeled tissue, etc.; g. aseptic techniques prevent the culture from being contaminated by other bacteria from the surroundings; this could allow pathogenic bacteria into the dish and prove unsafe; aseptic procedures also prevent bacteria from the Petri dish from contaminating the surroundings; h. if the extract is prepared by using distilled water, then the filter paper disc should be soaked in distilled water; if the extract is prepared by using ethanol, then the filter paper disc should be soaked in ethanol of the same concentration; i. 37oC is a suitable temperature for growth of pathogenic bacteria that grow in the human body; A temperature of 25oC will prevent the growth of pathogenic bacteria; [Total marks: 40]
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
Articles marking schemes Model article One a. Somatic cell gene therapy inserts normal genes into somatic cells, where as, Germ line gene therapy inserts normal genes into gametes or embryonic cells. Somatic cell gene therapy is temporary and permitted, where as, Germ line gene therapy is permanent by prohibited. (2) b.i.
Functions of the CFTR protein The CFTR acts as a channel to transport negatively charged chloride ions out of the epithelial cells. The CFTR protein also regulates the function of sodium ion channels. 1. CFTR channel is absent or dysfunctional and is not able to regulate the sodium channel. 2. Na+ channel is permanently open and Na+ ions continue to enter the cell at the apical end, through the open Na+ channels. 3. No Clˉ secretion takes place. 4. Water is continually removed from mucus by osmosis. Mucus is always thick and sticky.
(3) ii.
Normal (Carrier) Father x Dd
Normal (Carrier) Parent Phenotype Mother Dd Parent Genotype Meiosis
D
d
D
d Gametes Fertilization
DD
Dd
Dd
dd
Offspring Genotype Phenotype
Normal Normal Normal Cystic (carrier) (carrier) Fibrosis Offspring
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
c. i. Line 69 to 70 Because it explains how a foreign gene can get inserted into another gene sequence, which is undesirable in gene therapy. It caused leukemia in this case. Ideally the gene should be inserted into the ‘junk’. Both diagrams illustrate this idea. ii. The student will have to cite the source of information in the following format in the bibliography. Author/editor, initials. (Year) Title [online]. Place of publication: Publisher. Available from: URL [Accessed date]. (2) d. Environmental issue: Genetically Modified plants may out-compete native plant species and reduce biodiversity; Social issue: Genetically Modified plants can increase food production and reduce food shortage in many societies; (2) e. i. Line graph with axes appropriately labelled; scale (more than 50% covered); plotting accurately and clearly indicated; neat single line;
(4) [Total 20 marks]
Model article Two a. Benefits Line 10 - 11 Cell cultures can be used to study the effect of drugs. line 44 Stem cells may provide a cure for people with serious physical injury Risk Line 16 - 17 Complications may arise from stem cell transplants Line 22 May prompt people to use embryonic stem cells, which is unethical b. Cystic fibrosis / Thalassaemia / eq.; c.i. Transcription The gene is unzipped by RNA Polymerase and antisense strand acts as a template for mRNA formation. Line 30 ii. Sequence of bases on mRNA act as a template for tRNA anticodons and specific amino acids are joined by peptide bonds i. Should not be considered as the sample size is too small to represent the views of the entire population. ii. (38 /100) x 50 = 19
(3)
c) From 1995 to 2010, there is a general increase in the success of embryonic stem cell use, tissue stem cell use and induced pluripotent stem cells used in research; AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
From 1995 to 2010, the percentage success of embryonic stem cells used in research increases by 57% (87 – 30);; In all the years, the success percentage of embryonic stem cells is greater than the other types of stem cells; (4) d) I would insert the graph in the report at line 43 Reason: the section describes federal funding for stem cell research. So the graph would provide a more easily understood record of funding at a glance; (2) e) UK stem cell bank can be cited; Human Fertilisation and Embryology Authority can be cited; Warnock report 1984 can be referred to; Federal funding agency could be cited; Evaluation can be done by directly looking into the information from the official websites of these organizations and maybe even send an email of phone call to verify the authenticity of the information cited; can even enquire about the vetting process followed by these organizations; (3) [Total 20 marks] Model article Three a.) Ethical implication: embryos are destroyed during the process. Explanation: Many people consider this as murder as the embryos are potential human lives; Economic implication: Federal funding is not distributed in favour of adult stem cells; Explanation: more funds are allocated for treatment of other diseases and embryonic stem cell research; (4) b.) The student found the following data for the distribution of US Government federal funds for different fields of stem cell research. Type of disease Cardiovascular diseases Neural Diabetes Liver Kidney Cancer
Distribution of funds 15 35 10 25 10 15
i) Line number 10
(1)
ii) The information can be verified by checking with the relevant official website or organisation that distributes federal funds for research. (2) iii) Bar graph; type of disease on x axis; distribution of funds on Y axis;
(3)
c.) Advantage: Gives an indication about the toxicity or side effects and effectiveness of the drug; Disadvantage: The treatment may be effective in animals but may play out differently in humans, so makes the animal trials futile. A lot of time and money is usually spent on preclinical (animal trials). (2)
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
d.) i) When two studies on the same issue come up with different or conflicting results then it is called as conflicting evidence. For example the two opinion polls show conflicting views. (3) ii) The study that gave adequate information about the current status of stem cells research and the different types of stem cell research, followed by a questionnaire will be more reliable as people make well informed choices while polling. (2) iii) Total Number of people in each poll / neutrality or bias of people with regard to stem cell research; (1) e.) If you are given a choice to obtain information about stem cells from bibliography reference 1 and bibliography reference 2, which would you choose. Give reason for your choice. (2) Source: reference 2 (more reliable) Reason: scientific journals follow a thorough vetting and review before publishing information / no reason for bias as the work is academic with no vested interests; Private companies could be biased as they have vested interests and commercial incentives by promoting the use of stem cells; so information could be biased; [Total 20 mark]
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
Notes on bibliography or referencing and evaluation of references 3.1. Use information or arguments obtained from three or more sources (including at least one web based and one non web based) when researching the visit or issue. Clearly identify any quotes from sources. Plagiarism Many people think of plagiarism as copying another's work, or borrowing someone else's original ideas. But terms like "copying" and "borrowing" can disguise the seriousness of the offense: According to the Merriam-Webster Online Dictionary, to "plagiarize" means to steal and pass off (the ideas or words of another) as one's own to use (another's production) without crediting the source to commit literary theft to present as new and original an idea or product derived from an existing source. In other words, plagiarism is an act of fraud. It involves both stealing someone else's work and lying about it afterward. Most cases of plagiarism can be avoided, however, by citing sources. Simply acknowledging that certain material has been borrowed, and providing your audience with the information necessary to find that source, is usually enough to prevent plagiarism. Citing References in Text Cite the work of those individuals whose ideas, theories, or findings have directly influenced your work, even if you are paraphrasing or describing someone else's idea. To avoid plagiarism, take careful notes as you research to keep track of all sources and collect the information you need to cite them properly. Author-date citation technique According to Jones (1998), "Students often had difficulty using references, especially when it was their first time" (p. 199). Jones (1998) found "students often had difficulty using references" (p. 199); what implications does this have for teachers? She stated, "Students often had difficulty using references" (Jones, 1998, p. 199), but she did not offer an explanation as to why. 3.2. Provide information about the source, author and date of three or more references used in the visit or issue report. Link references to the appropriate text in the visit or issue report. A reference list consists of all sources cited in the text of a paper, listed alphabetically by author’s surname. A bibliography, however, may include resources that were consulted but not cited in the text as well as an annotated description of each one. Bibliographies may be organized chronologically, or by subject, rather than alphabetically. Points to remember List all references in alphabetical order. Each reference is listed only once.
AS Biology with Stafford. Unit Three: Practical Workbook answers / Unit three paper BIO7
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Marking scheme for AS Biology with Stafford, Unit Three Practical Workbook. Book available at http://www.amazon.com/gp/aw/s/ref=is _s_?k=AS+A2 +Bi ology +with+ stafford
Format for a reference from a Book Redden, S.V. (2002). AS Biology with Stafford, Stafford Publications, Orissa, India, pp103106. 3.3. Evaluate at least two references used in the report Remember that there is an ocean of information available today and it is often all too easy to get lost and choose inaccurate or less reliable information. It is therefore important to evaluate the sources from which we obtain information, lest we end up with information that is misleading and inaccurate. Some factors that we may consider are: An article on space science would be reliable if written by a NASA scientist, rather than by a college student. Likewise, you would not want to trust an article on acupuncture written by a NASA scientist. It would be better to look for information provided by an acupuncture specialist. Remember: Use information from sources prepared by experts in their relevant field of expertise. Authors may have vested interests and may write article to promote their point of view, often in a very convincing manner. These authors usually have affiliations to institutions with vested interests. For example, a scientist employed by a fossil fuel company may write articles that play down the effects of global warming and scientists who work for companies that sell solar cells may magnify the effects of global warming. Remember: Information from independent organisations with no vested interests will be more valid and reliable than information from individuals working for organisations with vested interests or individuals with their own biased views. Scientific journals publish research finding from various individuals or organisations. The methods of research, data procurement, data analysis and data interpretation can also influence the validity of information. Renowned scientific journals publish work which has been through a rigorous vetting process. Remember: Work which has been reviewed by peers and other independent sources is more valid and reliable.
Refer to more than one source while researching for information. If many source say the same thing about the topic then it is likely to be more reliable. If many sources give conflicting information, then further referencing or research is needed. Remember: Cross referencing does not make the information more reliable, it simply is a means to verify or assess the reliability of information in a source.
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