Question 22N.2.SL.TZ0.1
| Date | November 2022 | Marks available | [Maximum mark: 13] | Reference code | 22N.2.SL.TZ0.1 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Compare and contrast, Discuss, Identify, State, Suggest | Question number | 1 | Adapted from | N/A |
The biodiversity of insects worldwide is in decline. Destruction of habitats, pollution and climate change have contributed to the decline in global insect populations and to the extinction of insect species. A comprehensive literature review was carried out to determine the annual global rate of decline in insect species. The graph shows the results for three major orders of terrestrial insects and the total decline in insect biomass worldwide.
State the mean annual decline in insect biomass.
[1]
2.5%;
% required
In general, the Data based question was well answered. In (a) all but a handful of candidates failed to state 2.5, but unfortunately many failed to also include the unit. In (b) Most gave a difference, but similarities were rarer. The statement that both show a decline would have earned the mark. A surprising number were confused by the arithmetic involved in (c), with most calculating that the decrease was 8000, but either forgetting to subtract this from the 400,000, or doing it incorrectly. In (d) almost everyone counted 5 correctly and in (e) a large proportion gained both marks for a comparison and a contrast. The calculation in (f) involved the use of ratios. There was a G2 comment that this was not common knowledge. However, as all IB students continue to study mathematics at some level, it was not considered beyond their capabilities. 40% of the students gained the mark. A similar number gained the mark in (g), usually for an correct answer, but many answered in terms of the actual ratios, which did not gain the mark. In (h) 80% were able to spot that there was an inverse relationship between high lipid content and survivability, but in (i) fewer were able to cite the 10:1 diet as closest to the normal diet, some failing to state the reason. The answers t (j) were very varied, with most gaining marks for the possible loss of natural food sources or
the bees having to look for others. Better candidates noted that there was no control where the bees were fed their normal diet as it was a simulation, not using pollen. There was a G2 comment that the graph was somewhat crowded and should have been bigger. This is perhaps true.
Compare and contrast the results for Hymenoptera and Lepidoptera.
[2]
- both show a decline in number;
- the mean decline for Hymenoptera is less than the mean for Lepidoptera
OR
there is a wider range of decline among the species of Lepidoptera;
Calculate the number of Coleoptera species that would be expected to exist after one year from a starting number of 400000 species, assuming the mean rate of decline.
[1]
392000 (species);
One species of the order Hymenoptera is the buff-tailed bumblebee (Bombus terrestris), which feeds on pollen and nectar obtained from specific plants.
Destruction of preferred habitats has affected the size of bumblebee populations and for survival, bumblebees have to feed on pollen from other available plant habitats. To simulate different pollens, researchers fed bumblebees on eight diets consisting of a mixture of proteins and lipids in different ratios (P:L). The bumblebees also had access to sucrose. There was no restriction on the amount of each food the bumblebees could consume. The chart shows the mean daily mass of food eaten for eight diets with different P:L ratios.
[Source: Buhl, V., 2010. Bombus terrestris. [image online] Available at: https://commons.wikimedia.org/wiki/File:2010-04-
28_(35)_Erdhummel,_Buff-tailed_bumblebee,_Bombus_terrestris.jpg [Accessed 6 December 2021].
[chart] Adapted from Vaudo, A.D., Stabler, D., Patch, H.M., Tooker, J.F., Grozinger, C.M and Wright, G.A., 2016.
Bumble bees regulate their intake of essential protein and lipid pollen macronutrients. Journal of Experimental
Biology 219, pp. 3962–3970.]
Identify in how many of the diets sucrose was the greatest mass of food consumed.
[1]
5;
Compare and contrast the results for the 1:1 and the 1:10 P:L diets.
[2]
- in both a greater mass of sucrose was eaten (than of the P:L mixture)
OR
the total mass eaten by both groups is the same/very similar; - the mass of sucrose eaten in the 1:10 mixture diet is greater than in the 1:1 diet
OR
the mass of the P:L mixture eaten in the 1:10 is less than in the 1:1;
Accept vice versa for all answers.
Calculate the mass of lipid eaten when the bumblebees were presented with the 5:1 diet.
[1]
0.025g;
Unit needed
Suggest a reason that the mass of protein and lipid mixture eaten at 25:1 is lower than at 50:1.
[1]
- the mixture was closer to what the bees ate naturally;
- the bees like the taste better/prefer sucrose;
- there was more lipid in the 25:1 mixture so they achieved their daily lipid/energy requirement with less mass of food;
- the bees eating 50:1 diet ate more to reach their daily lipid requirement;
- prefer the higher proportion of protein (in the 50:1)
The graph shows the percentage of bumblebees that survived each day while being fed on different P:L diets. For each trial, n = 15.
[Source: adapted from Vaudo, A.D., Stabler, D., Patch, H.M., Tooker, J.F., Grozinger, C.M and Wright, G.A., 2016. Bumble bees
regulate their intake of essential protein and lipid pollen macronutrients. Journal of Experimental Biology 219, pp. 3962–3970.]
State the relationship between high lipid content and survivability on day 7.
[1]
the higher the lipid content, the fewer bees survived/negative correlation;
Suggest with a reason which P:L diet is closest to the normal diet of these bumblebees.
[1]
10:1 diet as this has the highest survival rate (after 7 days);
Reason must be given.
Discuss whether these studies show that habitat destruction can affect global bumblebee numbers.
[2]
- habitat destruction removes the plants/flowers/natural food source of the bees;
- bees have to look for other food sources;
- many of these alternative sources of food are not suitable for bee survival
OR
pollen with a different proportion of protein to lipid would reduce survival; - no control where bees are fed their normal diet is included;
- simulation is not using natural pollen / habitat;
OR
sample size is too small to make conclusions;
Accept other reasonable discussion using the data.