*Biology Paper 5 tips*

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Please someone tell me and explain
When is difference significant in chi squared test and when is it not significant?
 
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Organism Growth:
  • source: corn syrup, glucose, protein, low grade NH3
  • never write nutrient broth
  • mention 2 examples at least
  • same amount or conc of nutrient broth to the two sets of specimen
  • the nutrient supply must be kept constant
  • mention flow rate through fermenter
  • For batch culture: note the amount of time the organism is left in the fermenter
  • keep in mind the O2 supply, temperature, pH
  • sterility of the fermenter is very important [so that no other organism grows and acts as a competitor]
  • sterility is important in both batch and continous culture- in fact, every time you set up a batch culture, sterility must be mainatained
Planning Questions:
  • decide what the experiment is on (like diffusion, osmosis, photosynthesis)
  • use the same apparatus; describe what you're going to vary and what must be kept constant- decide which is the dependant and independant variable (eg light intensity? CO2 conc? or gas produced?)
  • how will you vary (count bubbles? use gas syringe?)---always ask yourself: is it a comparison
  • units--same volume, same mass, same concentration
  • What are the constants? How will you keep them constant?
  • give brief discription of the steps; if time is required, BE SPECIFIC.
  • inference: in some exps you need a control, but don't write anything which isn't required otherwise
  • precautions (FREE MARK!!!)
Reliability:
> give time for caliberation
(Calibration time is adjusting time)
>Repeat 3 times to be certain that the results are consistent-do not change the parameter
>large sample size

Why repeat?
  • increases the certainty that the results are consistent
  • so that anomalous results can be removed
  • permit variance from mean
  • to take an average
Accuracy:
  • means measuring in a reliable manner. Eg
  1. weighing scale
  2. thermometer
  3. verneir caliper
  4. measuring cylindrer
  5. gas syringe
  • use of a buffer solution to maintain pH
  • using sol of known conc (by serial dilution)
  • comparing colors of sol by a colorimeter
  • larger number of known conc
  • washing syringes and pipettes
  • mixing and stirring for uniformity to prevent settling of suspension
  • in microscopy: eye-piece graticule
  • to measure the surface area, the specimen is placed on a grid, where the full squares, half or more than half are taken into consideration
  • FILTERING AND CENTRIFUGING: the suspension spins and the more dense sinks at the bottom
Control:
  • in an exp with living organisms, the control must be a dead organism
  • whatever factor is being used in the question is emitted from the control
  • For counting chromosomes and making them visible, the growing regions of the plant are cut
  • cut surface of the specimen
  • chromosomes are counted by placing cut surface under a high power light microscope(with high magnification)
  • How to make chromosomes visible?
  • > add dye/stain them
  • > Examples of dyes:
  1. methylene blue
  2. aceto-carmine
  3. aceto-orcein
So that's all that was dictated to me, I hope it is helpful inshAllah! :)
thanks a lot! may God bless u and u get straight A*s! but what was the thread method of measuring the length of the plant?
 
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Can you please send me the notes too and any tips if you have im really scared about p5 :(
When my light comes on I will send you them from my desktop. I complied the frequently asked questions and the experiments. Although they don't give the same experiments, you will get a general idea of how to approach them and what to mention even if you have zero idea how to write now. Don't worry :) aim for ATLEAST a B in paper 5 insh Allah
 
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Can someone please help me with this?
I think if it's exposed to light meaning the light dependant reaction will increase so the electron acceptor will turn colourless of course. On the X axis I think it will be light intensity and on the Y axis I think colour change of electron acceptor. So with increasing light intensity the electron acceptor will change to colourless more quickly. So a straight line I'm guessing
 
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I think if it's exposed to light meaning the light dependant reaction will increase so the electron acceptor will turn colourless of course. On the X axis I think it will be light intensity and on the Y axis I think colour change of electron acceptor. So with increasing light intensity the electron acceptor will change to colourless more quickly. So a straight line I'm guessing
This is the answer. But I need to know how did to deduce that.
 

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Can someone please help me with this?
think of it like this:
*as temperature increases, the electron acceptor changes to colorless more quickly; more electron uptake per unit time; rate of light-dependent reaction increases (enzyme activity)
*until it reaches a maximum, where the enzymes are denatured; less electrons accepted per unit time; electron acceptors take more time to change color; rate of light-dependent stage decreases
 
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Can you please send me the notes too and any tips if you have im really scared about p5 :(

Q. Plan an investigation to compare the respiration rate of small invertebrates & germinating seeds.


1. known mass of invertebrate/invertebrate weighed; allow a reasonable value; (5g)

2. same mass of germinating seedlings; reject number

3. use seedlings before plumule emerged/if green, cover to keep out the light;

4. dye at end of capillary tube furthest from tube; allow ref. to moves to the left

5. must be airtight;

6. temperature constant;

7. ref. to safety of carbon dioxide absorbent and suitable method of protection;

8. ref. to time for organism to adjust

; 9. ref. to closing clip before taking measurements;

10. measure distance moved by dye for standard time/measure time taken to move standard distance; 11. repeat (at least 3 times);

12. ref. to the idea of reset by releasing clip;

13. replace carbon dioxide absorbent between measurements;

14. calculate volume by measuring diameter capillary and multiplying by the length/distance moved; 15. named carbon dioxide absorbent used; hydrogen carbonate.



Q. Plan an investigation to show the effect of carbon dioxide concentration on the rate of photosynthesis




ref. to varying the independent variable:

1. suitable method of providing different concentrations of carbon dioxide; (e.g.(sodium) hydrogen carbonate/calcium carbonate/baking powder/ gas cylinder/bubbler) allow HO3 – 2. at least 5 concentrations of carbon dioxide; 3. ref. to measuring/maintaining each carbon dioxide concentration with the probe; ref. to measuring dependent variable: 4. amount of gas produced in known time/time to collect a known amount of gas; ref. to controlling any 2 of the key variables: 5. method of standardising pond weed; (e.g. mass/length/same piece/same number of leaves/same species) 6. method of maintaining constant light intensity; (e.g. light fixed distance from plant) – no fixed time limit on light exposure 7. method of maintaining temperature; (e.g. water bath/insulator) allow – air conditioned room 8. method of standardising water; (e.g. same volume/removing gases by boiling) ref. to any 2 procedures of using apparatus: 9. use of pond weed and syringe; (e.g. cutting pond weed and inserting into syringe under water/solution) 10. time for equilibration of pond weed in different carbon dioxide concentrations; 11. working in a dark room/green illumination/enclosing apparatus in a box to eliminate any other light sources; 12. ref. to 3 sets of measurements and a mean/average ref. to any 1 safety issue and precaution: 13. idea of a low risk experiment; 14. ref. to potential risks; (e.g. electric shocks faulty equipment/wet wiring/handling chemicals/cutting pond weed and sensible precautions)


Q. How to find number of stomata in a leaf


ref. to varying the independent variable: 1. (strip from) upper and lower epidermis; 2. (strips from 5) different leaves of same type of plant; ref. to measuring the independent variable: 3. use of microscope and graticule; 4. counting number of stomata visible e.g. in field of view; 5. counting/using 4 strips of epidermis from each side of the leaves; ref. to arrangement and steps in procedure: 6. mount epidermis in water/glycerol/( suitable) stain; 7. measuring diameter field of view using graticule; 8. calculating area field of view using formula π r2; 9. converting from area measured to mm2 ;




Q. Outline how electerophroesis is used to obtain a genetic fingerprint


samples (in wells) in agarose gel/support medium; buffer solution; potential difference applied (to buffer); DNA (fragments) move to positive electrode/anode/DNA is negatively charged; fragments of different sizes move different distances/ smaller fragments move further (in given time)/faster




Q. Why can probes be used to locate specific alleles of genes?

They have complementary base sequences, that bind to (specific parts) of the gene;



Q. Why gas collected from an oxygen absorbant may not be pure oxygen


water used to make solutions contains air; allow nitrogen unused carbon dioxide gas from the solution; plant contains air which may be given off with oxygen; allow nitrogen air may remain in syringe when setting up the apparatus; allow respiration of microorganisms produces carbon dioxide;



Q. How to measure and calculate the actual diameters of anything (e.g. tubules)


ref. to measuring (tubules/lumens/sections) with eyepiece graticules; ref. to using stage micrometer and eyepiece graticule; e.g.; calculating the number of eyepiece graticule units per stage micrometer unit allow formula:

Number of stage micrometer didvions DIVIDED BY number of eyepeiece gratuculeunits MULTIPLIED BY value of 1 micrometer divison



Q. how to control light intensity


1. lamp with variable intensity/different wattage; 2. filters of different density; allow paper/fabric correctly described 3. lamp with same intensity, moved different distances; 4. different number of lamps at the same distance; colour filters/different locations/foil, muslin, light combinations



Q. Varibales to be controlled in immbolised enzyme experiment



quantity of substrate – same concentration/same volume; temperature – use water bath; allow other methods of maintaining temperature e.g. incubator enzyme – same volume/number of immobilised balls; flow rate through column – add at constant speed; time – substrate in contact with enzyme same time; pH – use a buffer



Q. How to control varaiblrs between indivisuals and ethinic groups?


1. very large sample

2. take sample(s) from as many races/ethnic groups/as many countries as possible



Q. Variables to be contolled in a experiment to test antibiotic on a range of different bacteria:


ref. to volume/concentration of bacteria culture (added to plates); ref. to dimensions of well e.g. diameter/depth/area/volume; ref. to volume of antibiotic added; ref. to volume of agar (in each plate); Sterile technique aw; pH;



Q. Varibales that should be controlled during fermentation


temperature; nutrient concentration; flow rate through fermenter; oxygen/air supply;



Q. What does Standard devation tell you about results?

to spread of data around the mean; ref. to difference between the data and reliability



Q. Describe a method by wich the tissue which conducts water up the stem can be identified


ref. to cutting sections of the stem; ref. to use of microscope and to find the location of the dye


Q. Descibe how an apparatus with only a testube of dye solution and a layer of oil with a part of a plant i.e. stem and leaves, can be set up and used to find the rate of movement of water up the stem




Method of measuring independent variable 1. ref. to suitable method of measuring time and distance; e.g. cut sections/observing dye through stem, at known time interval and known distances / known distance and record time for dye to reach it. 2. ref. to accuracy measuring distance; e.g. using thread to measure stem and ruler in cm/mm, vernier callipers Procedure: 3. ref. to using several shoots/sequential measurements on the same shoot; 4. ref. to cutting under water/dye (to avoid air entering); Method for controlling external variables: max 2 examples 5. ref. to number/surface area of leaves; 6. temperature and suitable method e.g. temperature controlled room; 7. (light and) suitable method e.g. dark room with light of fixed illumination/ light at fixed distance; 8. (air flow and) suitable method e.g. fan set at constant speed; 9. ref to volume/concentration (dye) solution: Reliability: 10. ref. to making at least 3 measurements and taking a mean; Safety: 11. ref. to a low risk investigation



Q. Why do we choose/use a chi square test?


When the data is being categoric / discrete;


Q. Outline a procudre using a pollen trap that can test the hypothesis that as the light increases the number of pollen grains present I the atmosphere will increase & then decrease as the light decreases.


independent variable 1. ref. to exposing slide / apparatus for period of time in different light intensities to include dark (zero intensity) / to light and dark conditions; dependent variable 2. ref. to counting pollen in field of view; 3. ref. to counting at least 3 areas of the slide; 4. ref. measuring diameter of field of view using graticule; 5. ref. to calculating area of field of view (using formula πr 2 ) ; control variables – max 4 6. ref. time of exposure constant; 7. ref. same location for all readings; 8. ref. to removing any pollen on opening between each slide ; 9. ref. to outside location; 10. detail of location; e.g. no walls/hedges/trees in the way / facing wind; 11. ref. to an attempt to control environmental factors / some environmental variable cannot be controlled ; reliability 12. ref. to repeating the whole investigation on 3 different days and taking mean; safety: max 1 13. low risk investigation ; pollen allergy and use of mask; electrical safety and ref. to water



Q. State the data needed to calculate the standard deviation


number of samples (for each condition tested);

mean value (for each condition tested);



Q. Why do we use t tests?


data is a continuous / shows a normal distribution / comparing differences in means;


Q. How could you estimate the relative size of a testois of a fish


ref. to weighing / finding mass of the fish; ref. to suitable method of measuring testis e.g. mass / volume / length; ref to suitable units for chosen method e.g. g / kg / cm3 / cm; ref. to a sample of 3 or more and taking a mean; ref. to proportion calculated by, mass / volume / length testis divided by mass of body;
 
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Q. Suggest how a microscope slid and a grid can be used to estimate the number of cells per mm3 of a culture?


1. ref. to adding sample to slide; 2. ref. to idea the sample is uniform; 3. ref. counting cells; 4. ref. to any detail of counting e.g. exclusions / number of squares; 2 of: 5. ref. to grid volume 0.2 mm × 0.2 mm × 0.1 mm = 0.004 mm3; 6. ref. to factor × 250 to estimate number of cells per mm3 / dividing by the grid volume (0.004 mm3); 7. ref. to counting min.3 areas / slides and taking mean;


Q. Using a potometer outine a procdure that one can use to test the hyppthesis that a mesophyte plant loses more water then a xerophytes plant


1. ref. to shoots / leaves of different types of plant / xerophyte and mesophyte / type of plant used; 2. ref. to similar surface area; dependent variable 3. ref. to measuring / recording the movement (of water) along the capillary; 4. ref. to time (of water movement) / description of measuring time; control variables (max 3) 5. ref. to same (environmental) conditions; 6. ref. to inserting / cutting shoot under water / cutting shoot at an angle; 7. ref. to drying leaves before measuring; 8. ref. to airtight seal (around shoot) / airtight apparatus / no air locks; procedure 9. ref. to using syringe to set (water level) in capillary; 10. ref. to leaving until steady rate / equilibrate; reliability 11. ref. to repeats / replicates – min 3 and mean value; safety: 12. ref. to a low risk experiment( care in cutting)



Q. explain how the actual volume of water lost can be calculated using a capillary tube


ref. to finding surface area of the capillary; ref. to multiplying (surface area (πr2)) by distance moved;



Q. How is increase calculates/


Increase DIVIDED BY orginal


Q. Explain why leaf discs rise to the surface in light


oxygen / gas / air, produced (by photosynthesis);



Q. Using a syringe with leaf discs and hydrogen carbonate solution held upritght outline how one can test the hypothesis that leaf discs from shade leaves will photosytheisis r a higer rate in low light intensity than leaf discs from sun leaves?


independent variable 1. a method of varying light intensity or use low light intensity; 2. ref. to a method of measuring light intensity; 3. ref. to a method of eliminating other light sources; 4. ref. to testing leaf discs for the two locations separately; dependent variable 5. ref. to a method of measuring photosynthesis by rising of discs; 6. ref to time taken; standardising variables (max 3) 7. ref. to discs from more than one leaf (from each location); 8. ref. leaf discs all being same diameter / size / number / mass. 9. ref. to same volume of hydrogen carbonate solution (in syringe); 10. ref. to using fresh hydrogen carbonate solution for each measurement / same concentration of H carbonate; 1. e.g. lamp (with standard bulb) and vary distance / lamp at same distance and vary wattage / lamp at same distance and use filters of different thickness /11. ref. to method of standardising temperature; 12. ref. to acclimatising before measuring; Reliability 13. ref. to repeating at least three times and taking mean; safety: 14. ref. to low risk investigation / AW or any suitable safety concern + precaution;



AW 2. e.g. (light) meter / photodiode / light dependent resistor / photometer / low wattage / 60 or below Allow ref. to using a camera meter 3. e.g. dark room or box for measurement 4. often implied 5. Do not allow: counting bubbles / leaves rising 6. e.g. time for (all or a specified number of) discs to rise / specified time and count the number of discs floating / distance risen in stated time Allow: ecf time for bubble counting 8. Allow: use same straw for cutting 9/10 Watch for confusion with hydrogen carbonate indicator 11. water bath / incubator / controlled room Do not allow: room temp Do not allow: pH for standardising variables 13. Allow: several or many Allow: to remove anomalies / outliers 14. e.g. hydrogen carbonate + gloves / eye protection dry hands to prevent electrical shock / AW Do not allow: be careful unqualified Do not allow: care with cutting



Q. Why is a layer of oil needed in some expierments?


to prevent oxygen entering



Q. Outline how one can use a testube filled with active yeast suspension and methylene blue solution with a layer of oil on top, to fund the optimum temperature for the respiration of yeast?



independent variable: 1. ref. to water-baths at different temperatures ; 2. at least 5 different temperatures ; 3. ref. to suitable range ; 4. ref. to retesting within the approximate optimum zone ; dependent variable 5. ref. to fastest time until blue disappears is optimum ; 6. ref. to colour comparison / control without methylene blue added ; control variables 7. ref. to standard volume of yeast / suspension (in tube) ; 8. ref. to adding standard volume methylene blue ; procedure 9. ref. inverting / stirring (to mix indicator and yeast) ; 10. ref. to repeats / replicates – min 3 and mean value to remove anomalies ; safety: 11. ref. to a low risk experiment ;


1. allow other suitable means of maintaining constant temperature 3. e.g. 0°C – 70°C. Any range in this but at least one below 30°C and one above 5. A ...becomes colourless 7. R amount unqualified A known mass / weight for (dried) yeast provided some water added Ignore glucose 8. R amount /drop(s) A inject known volume of methylene blue through the oil layer 11. A ref. to possible toxicity of methylene blue / allergy to yeast / hot water and tongs, etc.
 
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Q. Why is raw data converted to percentage?



allows for different starting points between individuals / can see the changes more clearly;


Q. Outline a procure whereby one can obtain results of a leaves internode lengh, Surface area, mass, rate of water loss and mean leaf surface area: leaf mass ratio


independent variable: 1. ref. to a systematic way of obtaining leaves; dependent variables: 2. ref. to a method of measuring surface area; 3. ref. to how surface area is calculated; 4. ref. to idea of both sides needed to get total surface area; 5. ref. to a method of measuring mass; 6. ref. to finding dry mass; 7. ref. to a method of measuring internode length either on the plant or a cut section from a plant; 8. ref. to a method of measuring water loss; 9. ref. method of using the transpiration apparatus; 10. ref. to keeping constant environment when measuring water loss; (max. 6) safety: 11. ref. to low risk investigation; reliability 12. ref. to mean values of the whole sample; 13. ref. to method of working out SA : mass ratio; 14. ref. to calculating standard deviation;


1. e.g. 3rd leaf from the apex / different heights / all from the same height / equal light exposure 2. e.g. draw round each leaf on grid or use transparent grid over leaf / measure diameter(s) of leaf 3. count squares / use formula πr2 5. e.g. digital balance / scales 6. e.g. sample leaves dried in oven until mass constant 7. by holding against a ruler / use string or cotton to mark distance measure with ruler 8. e.g. use a potometer / weigh leaf / place leaf inside a plastic bag (to collect water) 9. measure distance moved by water / weigh at hourly intervals / weigh bag or leaf after a stated time 11. e.g. ref. heat and suitable precaution if use dry mass / leaf allergy 12. do not allow ‘mean of three idea’



Q. Descibe how one could use a procudre to find the water potential of the plant storsage tissue that has coloured cell sap (52/M/J/11)


independent variable: 1. ref. to making a range of 0.2, 0.4, 0.6, 0.8, 1.0 mol dm-3 sucrose solution / making separate solutions of 0.2, 0.4, 0.6, 0.8, 1.0 mol dm-3 from sucrose and water ; 2. ref. to using distilled / deionised water (for making dilutions); 3. ref. to leaving plant tissue for suitable time – minimum of 20 min dependent variable: 4. ref. to a suitable method of timing the movement of the drop ; 5. ref. to marking the centre / start point of the solution (to measure drop) ; 6. ref. to how the drop is released ; standardising variables (max 3): 7. ref. to using same volume of each solution for soaking ; 8. ref. to same volume of each solution used for timing the drop ; 9. ref. to using same number / mass / volume of tissue ; 10. ref. to suitable method of keeping constant temperature ; 11. ref. to same time for soaking tissue discs ; safety: 12. ref. to low risk investigation / any suitable safety precaution ; reliability: 13. ref. to at least 2 / several / many replicates and a mean / average ; 14. ref. to increasing number of intermediates / repeating with more values close to water potential ; 12. e.g. cutting away from hands / cutting on a tile, allergy to plants and wearing gloves



Q. How to find the water potential of diffdrent parts of a tuber using discs of poatoto tissure and securose solution of different tissues? (51/M/J/11)


A. independent variable 1. ref. to making a range of 0.2, 0.4, 0.6, 0.8, 1.0 mol dm-3 sucrose solution / making separate solutions from sucrose and water ; 2. ref. to using distilled / deionised water (for making dilutions) ; 3. ref. to leaving plant tissue for suitable time – minimum of 20 min ; dependent variable 4. ref. to using tuber from each region in separate containers of each molar solution ; 5. ref. to weighing before and after immersion in sucrose solutions ; standardising variables (max 3): 6 ref. to using same, number / mass / weight /volume, of potato ; 7. ref. to known / same volume of each molar solution ; 8. ref. to same time in solutions ; 9. ref. to blotting tissue dry before reweighing ; 10. ref. to suitable method of keeping temperature constant ; 11. ref to standardising the source of material ; safety: 12. ref. to low risk investigation / any suitable safety precaution; reliability 13. ref. to minimum of three repeats and a mean ;


allow a general statement of making 5 (min) solutions from 0-1 mol dm-3 allow any volumes in correct proportions for making sucrose solutions do not allow if refer to serial dilutions unless it would give the concs. stated by the candidate ignore ref. to 0.0 as a sucrose solution 3. allow in terms of ‘long enough for osmotic changes to occur’ ignore keeping in water/solution before using 4. look for containers. But give if done for one set 6. ‘same size’. Ignore amount. Allow (surface) area / description 7. allow idea of tissue totally immersed 8. can be awarded in the context of mp3 10. e.g. water bath, incubator, temperature controlled room. allow room temperature. ignore air conditioning 11. e.g. same species/variety or clearly same tuber 12. e.g. cutting away from hands / using tile for cutting. e.g. plant allergy gloves or mask etc. ignore gloves for cutting. ignore water and electricity 13. allow reference to 3 repeats in terms of spotting anomalous results


Q. Suggest another way one can do to provide support for the conclusion that starch and sugar are In the storage tissue


iodine test - idea of using colour intensity to find concentration for sugar: allow Benedict’s test to estimate precipitate or colour change to find concentration.



Q. Why do we keep a plant etc in an extract of ice cold

In order for the ezymes to slow down


Q. Why do we use a fine mesh to filter the extract?


So that cell debris is trapped.

Q. How to count choromosomes in the ells of an embroyo plant and make them visible



1. ref. germinating / growing seeds (to cause cell division) ; 2. ref. to using a region, showing cell division / mitosis / named example ; 3. ref. to a means of separating the cells / cutting sections / squashing; 4. ref. to staining / dying / (correct) named stain; 5. ref. to using microscope at high power / high magnification / × 400; 6. idea of: (counting) chromosomes at a named suitable stage of mitosis ; 7. ref. to (counting) several different embryos;


1. allow ref. to removing (whole or part of the) embryo 2. e.g. root tips / shoot tips / meristem / radicle / plumule do not allow: fruit 3. allow ref. of maceration / heating do not allow: centrifuging / grinding / scraping cells from an embryo 4. e.g. aceto-orcein, aceto-carmine, methylene blue do not allow iodine / ink / food dye / ninhydrin ignore glycerol; 5. allow any magnification from ×250 to ×1000 do not allow electron microscopes 6. e.g. anaphase or metaphase, allow prophase do not allow stages of meiosis
 
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Q. How can one meaure the length of the pollen tubes using a microscope?




1. ref. to suitable magnification X400 (in context of looking at pollen) ; 2. ref. to use of, an eye-piece graticule / AW (to measure the length of the pollen tubes) ; 3. ref. to calibrating eye-piece with stage, micrometer / graticule / AW ; 4. to find the value in mm of an eyepiece unit ; 5. ref. to conversion of, mm / eye-piece units




Q. A student used solid sodium nitrate to prepare the highest concentration of sodium nitrate solution (25 mmol dm–3). This concentration was then used to prepare all the other concentrations. Describe the procedure that the student used to prepare the concentrations, 25,20,15,10,5. Your description should be sufficiently detailed so that another person can easily follow your procedure. The molar mass of sodium nitrate is 85 g mol–1.


1 ref. to (weighing), 0.025 of molecular mass in g / 2.125g ; 2 ref. to adding 1dm3 (deionised) water ; 3 ref. to using deionised / distilled water ; 4 ref. to adding different proportions of nitrate solution and water ; 5 ref. making suitable dilutions to give range of dilutions in Fig. 1.2; (allow in a table) 6 ref. to stirring / swirling /


1 A if weigh 85g and make 1 M solution then must dilute by factor of 0.025 or 25 × 10–3 A rounding of decimal places 3 A pure / sterile, water. 4 A formula c1 / m1 . v1 = c2 / m2 . v2 Ignore serial dilution 5 look for a description of measuring known volumes of 25mmoldm-3 and adding water to make a dilution. (4:1, 3:2, 2:3, 1:4 ratio for the sequence in Fig. 1.2). All must be correct 6 A mix, thoroughly / with a glass rod



Q. How can a number of cells be estimated?


ref. using a counting grid / haemocytometer; ref. to counting cells in sample of known volume; ref. to using a microscope and suitable magnification; ref. to multiplication of the cell count to find the actual / original number of cells ;



Q. How to fine the optimum rate of something when concerations are involved?


using concentrations with smaller intervals



Q. A student used the highest concentration (4000 mg dm–3) to prepare the other concentrations of sodium nitrate. Describe a procedure that the student used to prepare the other concentrations 2000 mg dm-3, 1000 mg dm-3, 500 mg dm-3, 250 mg dm-3. Your description should be sufficiently detailed so that another person can easily follow your procedure.



1 ref. to using (sterile) pond water to make dilutions ; 2 ref. to sterile conditions to make dilutions; 3 ref. to serial dilution ; 4 ref. to 50 : 50 dilution (each time); 5 detail in order to make all of the solutions ; 6 ref. to stirring / swirling solutions (between dilutions);



Q. How to test the hypothesis : As the concentration of GA increases to an optimum the rate of germination of barley grains and the early growth of the young plants increases. ( M/J/13/52)



independent variable: 1. ref. to a method of diluting the (3 mmol dm-3) GA to give a minimum of (any) five dilutions ; 2. ref.to concentrations (other than 0) that fall in the range 3mmoldm–3 to any value above 0 with units (µmoldm–3 / mmoldm–3 / gdm–3) 3. ref. to soaking grains (in GA solutions) for min 24 hours / max 72 hours ; 4. ref. to (removing from GA and) growing in soil / suitable containers on paper /cotton wool and kept dark ; 5. ref. to one stated (germination) temperature ; 6. ref. to a control using seeds soaked in water ; dependent variable 7. ref. to a suitable method of measuring young plant ; standardising variables (max 3, mp 8–12): 8. ref. to using same / stated number of barley grains for each concentration ; 9. ref. to suitable stated / same volume of each soaking solution / GA ; 10. ref. to method of maintaining the germination temperature ; 11. ref. to leaving for stated number of days (for germination / growth) ; 12. ref. to (regularly) adding stated / same volume of water ; safety: 13. ref. to low risk investigation / hazard and suitable safety precaution ; reliability 14. ref. to replicates and mean / to identify or eliminate anomalies ;



Q. How can a counting grid for a light microscope be used to estimate the number of cells per cm3 of a culture?


1. ref. to diluting the sample ; 2. ref. to a uniform sample i.e. shaking and stiring ; 3. ref. counting cells ; 4. ref. to any systematic counting process ; 2 of: 5. ref. to grid volume 0.2mm × 0.2mm × 0.1mm / 0.004mm3 / 4 × 10-3mm3 ; 6. ref. to dividing the number of cells by the grid volume ; 7. × 1000 (and dilution factor ) or multiply number of cells by 250 000 or by 0.0004

Q. What do error bars show about the reliability of data?


If the error bars are wide i.e overlap, they show that the data is NOT reliable.



Q. How to find out if value of t is significant


Calculate degrees of freedom, use 0.05 probabilty to find critical value, compare the calulcated t with crictical value. If t is higher than crictical value it is signigicane and not due to chance.


Q. How to find optimum temperatures of range more precisleyy?


Find the range of optuimum activy and divide these into smaller intervals



Q. A student calculate the rate of respiration of oxygen as pxygen used PER UNIT MASS of the organisms. Explain how this rate of respiration was calculated?


Volume of oxygen DIVDED BY time X mass



Q. How can one use a respirometer to find rate of co2 production?


Remove co2 aborbant and weigh them at srat and end of experiment. Find difference in measurement in mass.


Q. Why is detergent used?

To destroy the phospholipd membrane


Q. Varibles that students should standaridse to endure that thie results from gel eceltrophorsis can be compared


1. volume of DNA

2. Consistensy of agar rose gel



Q. Exaplin how RNA pribes are used to select fragmebnts of DNA

A. RNA probe is single stranded and has exposed bases. It bases paiors via complentmnarty base pairing. Different RNA probes base pair with different/ speiocifc sticky ends of DNA.


Q. What does p<0.05 mean?


Idea that 0.05 means that there is less than 5% chance of obatning oberseved results by chance



Q. Outline a procedure the student could use to compare the activity of lactase that has been

immobilised in different ways.

Your method should be detailed enough for another person to use


independent variable:

1. ref. to using, the same (equivalent) / fixed, concentration of,

enzyme / lactase ;

dependent variable:

2. ref. to, measuring with biosensor AW / comparing dip sticks or

clinistix to colour chart ;

control variables :

3. ref. to, same / fixed, volume of lactose solution

4. ref. to method of keeping same temperature (for each

enzyme) ;

5. ref. to buffer to control pH (at same level for each enzyme) ;

6. standardising time (for lactose to be in contact with enzyme) /

AW ;

7. ref. to method of timing (in context of mp6) ;

Procedure

8. ref. to suitable apparatus to set up columns for immobilised

enzyme ;

1. 9. ref. to (method of) controlling flow rate through enzyme

2. 10. ref. to method of collecting product ;

3. reliability

4. 11. repeat at least 3 times and find mean / identify anomalies ;

5. safety:

6. 12. ref. to named hazard and suitable precaution



Q. Outline how the student could immobilise the enzyme ethanol dehydrogenase


ref. to first mixing the enzyme / it with (any) alginate ;

ref. to then adding (alginate and enzyme) to calcium

chloride ;

ref. to method of dropping mixture (to form beads) ;
 
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