IB Biology Scientific inquiry worked solutions

B earns [1]. The dependent variable is the quantity measured in response to the change. Light intensity is the independent variable; temperature and species are controlled variables.

Any two of: the independent variable and its range are not stated [1]; the organism is not named by species [1]; the dependent variable and how it is measured are not stated [1]. Maximum [2].

B earns [1]. A replicate is a separate biological unit given the same treatment. A and C are repeated measurements of one unit; D adds no data.

Any two of: participants agree freely after being told what will happen, and may stop at any time [1]; data are anonymised and stored safely [1]; the exercise is mild, with no risk to health or anyone with a medical condition excluded [1]. Maximum [2].

Half the smallest division is 0.5\,\mathrm{cm^3} [1]. Percentage uncertainty =0.5/20\times100=2.5\% [1].

A earns [1]. A standard-deviation bar shows the spread of the replicates. Overlap leaves a difference uncertain, and instrument uncertainty is a separate quantity.

Degrees of freedom =4-1=3 [1]. The calculated value is below the critical value, so the counts are consistent with 9:3:3:1 and the null hypothesis is not rejected [1].

This is a systematic error [1]. Each reading is displaced in the same direction by the same amount, so the mean carries the same offset however many readings are taken [1].

B earns [1]. The reader can only trust processed values and graphs if the readings behind them can be inspected. The other options describe no benefit.

Raw readings keep the instrument's decimal places, so every entry has two [1]: 2.40, 2.35 and 2.35\,\mathrm{g} [1].

(a) Independent variable: pH; dependent variable: time for the blue-black colour to disappear [1] (both needed). (b) Any two, each with a method [1 each]: temperature held in a water bath and checked; same volume and concentration of enzyme measured with a graduated pipette; same starch volume; same iodine drop and the same end-point rule. (c) A boiled-enzyme or no-enzyme tube shows no reaction, which confirms the enzyme causes the change [1].

(a) Null: no significant effect of concentration on germination percentage [1]; alternative: a significant effect [1]. (b) A decreasing trend [1]. Higher salt concentration lowers the water potential of the surroundings, so seeds take up water more slowly or lose it, which delays or prevents germination [1].

Lay out a grid with tapes along two sides [1]. Generate 20 pairs of random numbers within 0 to 40\,\mathrm{m} and 0 to 20\,\mathrm{m} [1]. Place the quadrat at each coordinate and count or estimate cover the same way each time [1]. Record two abiotic factors, such as soil moisture, light intensity, soil pH or temperature [1].

(a) (41+44+39+42+44)/5=42.0\,\mathrm{s} [1]. (b) Deviations -1,2,-3,0,2; squares sum to 18 [1]; s=\sqrt{18/4}=2.1\,\mathrm{s} [1]. (c) The replicate spread is about ten times the timer uncertainty, so biological or procedural variation, not the stopwatch, dominates [1].

(a) A: 11.3 to 13.5; B: 13.6 to 16.2; C: 13.9 to 16.7 [1]. B and C overlap; A and B do not, and A and C do not [1]. (b) ANOVA [1] compares three or more means in one test, avoiding the false positives of repeated t-tests [1]. (c) A statement of what the bars show, or the sample size, for example n=6 [1].

(a) 120\times3/4=90 tall and 30 short [1]. (b) \chi^2=(84-90)^2/90+(36-30)^2/30=0.40+1.20=1.6 [2]. (c) Degrees of freedom =2-1=1, critical value 3.84 [1]. Since 1.6<3.84 the null hypothesis is not rejected, so the results are consistent with a 3:1 ratio [1].

(a) \sqrt{0.55^2/10+0.48^2/10}=\sqrt{0.03025+0.02304}=0.2308; t=0.51/0.2308=2.21 [2]. (b) 2.21>2.10, so reject the null hypothesis [1]; sun-grown seeds have a significantly greater mean mass [1]. (c) Unless other variables were controlled, light may not be the only difference between the plants, so the test shows a difference but not its cause [1].

(a) Any two hazards with a matching precaution, [1] for each hazard-and-precaution pair, up to [2]: falling in or slippery banks, work in pairs and keep back from the edge; infection from pond water, cover cuts and wash hands; sun or heat, hats and water. (b) Return organisms promptly to where they were found, or limit damage to the bank and vegetation [1]. (c) Agree the net size, sampling time and counting method so that results are comparable [1].

Any two faults, each with its correction, [2] each: a straight line is forced through a curved trend, so draw a smooth curve through the points [1+1]; the line starts at the origin without evidence, so fit the data rather than the origin [1+1]; no error bars, so add bars for the standard deviation and state what they show [1+1]; the axis lacks a unit, so label it with the quantity and the unit [1+1]. Maximum [4].

Any two weaknesses [1] each: “prove'' is too strong for one investigation; the claim has no numbers and states no range; the bubble count is only a stand-in for the rate and assumes equal bubbles of oxygen. A rewrite that quotes the data, for example bubble counts rose from 6 to 19 per minute as the lamp moved from 50 to 10\,\mathrm{cm}, that uses “supports'' and limits the claim to that range [2].

(a) Systematic error [1]: the real temperature in each run was lower than the set value by up to 4\,{}^\circ\mathrm{C}, so rates are shifted and the apparent optimum may be displaced [1]. (b) Half the smallest division, \pm0.5\,{}^\circ\mathrm{C} [1]. The drift of about 4\,{}^\circ\mathrm{C} is eight times larger, so it, not the thermometer, limits the accuracy of the set temperatures [1]. (c) Any two: an insulated, lidded or thermostatically controlled bath [1]; a temperature probe that logs the actual temperature during runs [1]; smaller temperature steps around 40\,{}^\circ\mathrm{C} [1]. Maximum [2].

(a) A scatter graph with distance on the x axis and cover on the y axis [1]. (b) |r|=0.99>0.707, so there is a significant, strong positive correlation between distance and cover [1]. Also r^2\approx0.99, so about 99\% of the variation in cover is shared with distance [1]. (c) Light, soil compaction and moisture may also change with distance, so a correlation in a survey does not show cause [1]. (d) Assign matched plots to set trampling intensities, including an untrampled control [1], and compare cover after a fixed time, with replicates in each treatment [1].

Marks, one each: a focused question naming the variables and the organism, for example, how does \mathrm{NaCl} concentration (0.0 to 0.5\,\mathrm{mol\,dm^{-3}}) affect the percentage mass change of cylinders from one Solanum tuberosum tuber [1]; at least five evenly spaced concentrations including 0.0 as a control [1]; dependent variable as percentage change in mass, from initial and final masses on the same balance [1]; two controls with methods, such as cylinders cut with a cork borer to one length from one tuber, fixed solution volume and soaking time, same blotting routine, constant temperature [1]; at least three replicate cylinders per concentration, with mean and spread [1]; one safety or ethical point, such as using a cork borer on a tile, or disposing of the solutions and plant waste as directed [1].

(a) Any two: the sampling sites and times [1]; units and a shared spreadsheet format [1]; roles and deadlines [1]. Maximum [2]. (b) The member must pose an individual research question [1] and process and interpret the data personally, with the source acknowledged [1]. (c) A review of the process, such as which delays occurred, how decisions were made and what would change next time [1].

(a) \mathrm{SE}=s/\sqrt{n}: 8.5/5=1.70 and 9.2/5=1.84\,\mathrm{mm} [1 each]. (b) \sqrt{8.5^2/25+9.2^2/25}=\sqrt{2.89+3.386}=2.505; t=9.5/2.505=3.79 [2]. (c) 3.79>2.01, so reject the null hypothesis: shade leaves are significantly longer [1]. (d) Any one: light may not be the only difference between the plants; plants came from one site; no information on how plants were chosen [1].