Data-Based Questions (DP IB Biology: HL): Exam Questions

Different ecosystems have different levels of productivity due to differences in the abiotic and biotic factors in the environment.

The cycling of nutrients in an ecosystem determines the nutrients available to plants for growth and therefore has a direct impact on the net primary productivity (NPP) of that ecosystem.

The table shows the decomposition cycles of 6 different vital nutrients across three different biomes, as well as the NPP for each biome.

Note that a decomposition cycle is the number of years it takes for a nutrient in dead organic matter to be made available again to plants

Identify the biome that shows the slowest rate of decomposition.

Suggest a biotic factor which may impact decomposition rates in an ecosystem.

List two carbon-containing compounds found in plants.

Describe the relationship between net primary productivity (NPP) and decomposition rate for the three biomes.

A study was conducted to establish the relationship between different abiotic factors and the rate of decomposition in a Mediterranean Forest ecosystem.

The data can be seen in the graph below.

Identify the abiotic factor that produced the biggest change in the rate of decomposition. 

Describe the effects of the different abiotic factors on decomposition.

Explain the effect of temperature on decomposition rate.

Using the data provided, deduce why tropical forests have the highest rate of productivity of the 3 biomes studied.

EDTA is a chemical that reacts with metal ions to form a stable, harmless compound. It is commonly used to reduce levels of calcium in many medical procedures, e.g. during dental work. EDTA has also been shown to have antimicrobial properties that are effective in the treatment of Staphylococcus aureus infections. 

Scientists wanted to establish how effective EDTA could be in the treatment of infection with Escherichia coli bacteria. The growth of E.coli bacteria was monitored in response to treatment with EDTA over a period of 5 days.

The chart below shows the results.

Explain why a group with no EDTA treatment has been included in the study.

Calculate the percentage difference between the number of bacteria in the sample treated with EDTA and the number of bacteria in the untreated sample after 5 days.

Outline the effect of EDTA on the growth of E. coli populations.

The presence of antibiotic resistance within E.coli populations was studied and the results are presented in the graph below.

Which antibiotic has been shown to be the least effective against E.coli?

Describe the levels of antibiotic resistance in E. coli across the antibiotics studied.

Note that no additional marks will be awarded for naming the least effective antibiotic, as this was addressed in part (d).

The table below shows some of the side effects associated with the antibiotics studied.

Using all the information provided, evaluate whether EDTA is the best antibiotic to treat E.coli.

Suggest 2 different methods that could be used to help reduce the development of antibiotic resistance.

Agriculturalists in Mozambique investigated how planting density and nitrogen fertiliser affected yield in sweet potato plants (Ipomoea batatas).

Nitrogen was supplied, in the form of urea (CH₄N₂O), at three application rates (30, 35 and 40 g m⁻²). This was tested in combination with three plant spacings (16, 20 and 25 cm).

The mean underground dry mass per plant, and mean crop yield, were recorded after 175 days of growth. All other growing conditions were kept constant.

(1 hectare = 10 000 m²)

Describe the overall effect of nitrogen addition on yield of sweet potato plants.

(i) Identify the conditions that produced the highest yield.

[1]

(ii) Calculate the percentage difference in yield for the highest yield compared to the lowest yield.

[2]

The agriculturalists also investigated the mass of plant matter above ground (both fresh mass and dry mass). This was measured against leaf length and crop yield at the three levels of urea previously tested. All these data were gathered from sweet potato plants spaced at 20 cm distance. The results are shown in the graph below.

The scientists concluded that the following planting regime should be recommended to farmers:

• plants spaced 20 cm apart

• more than 35 g m^-2 urea

Evaluate the scientists' conclusion, using the data above and from part a).

Explain how the use of nitrogen fertiliser can lead to eutrophication in nearby aquatic ecosystems.

Discuss how increasing agricultural productivity can affect biodiversity in surrounding ecosystems.

Bananas with less starch and more sugar are sweeter and ripen faster. Scientists identified a bacterial enzyme that decreases starch production and transferred its gene into bananas to create transgenic lines with lower starch content.

The table below shows the mean starch and sugar content of three control banana lines and three transgenic lines.

(i) Identify the line of transgenic bananas that has the highest sugar content.

[1]

(ii) Calculate the difference in the mean percentage of starch in control and transgenic bananas.

[1]

(i) Compare the mean starch and mean sugar content of the control and transgenic banana lines.

[1]

(ii) Explain how transferring the bacterial gene changes carbohydrate composition in transgenic bananas.

[3]

Bananas were harvested from trees and stored. Sample bananas were removed from storage after 2, 4, 6 or 8 days. The colour of the bananas was then measured and the value reported using a 0-8 rating (0 = pale yellow through to 8 = dark green), where a score of 4 or lower indicates acceptable ripeness for selling. The results are shown in the bar chart.

Describe the effect of transferring the bacterial gene on the suitability of the transgenic bananas for selling, compared to control bananas.

Calculate how many days earlier the transgenic bananas reached a colour score of 4 (acceptable ripeness) compared with the control bananas.

An important part of storage management is to delay the formation of brown or black spots on the skin of bananas. A second sample of bananas was harvested and stored. Bananas were removed from storage on day 8. They were then examined, and the number of brown or black spots present was recorded. The mean number of spots is indicated in the graph for control lines (C1, C2 and C3) and transgenic lines (T1, T2 and T3) of bananas.

Determine how the bacterial gene affects the storage time of bananas.

Artificial floating islands are man-made rafts or platforms that can be introduced to bodies of water to increase existing habitat for a variety of organisms, including invertebrates, amphibians and birds.

As artificial floating islands have been increasingly introduced to ponds and lakes in parks in London, UK, ecologists have studied the number of rafts available and how many of these are being used as nesting sites by birds. In particular, they have monitored the proportion of rafts used by common moorhens (Gallinula chloropus). Data was collected halfway through each year.

Estimate the number of rafts that were introduced to ponds and lakes between mid-2011 and mid-2012.

Describe the data for the number of rafts available and the number of rafts being used.

Foxes, badgers and cats are all known to predate on G. chloropus chicks. An ecologist conducted an investigation to see whether using ultrasonic repellers (usually used to deter and repel cats in domestic gardens) could reduce the numbers of these predators visiting a pond where G. chloropus were known to be nesting.

Contrast the number of visits to ponds with and without ultrasonic repellers for the three different predators.

Suggest an explanation for the difference in visits to ponds with and without ultrasonic repellers seen in badgers.

Over the same time period and for the same ponds and lakes in London that were studied in part (a), the ecologists monitored G. chloropus nests located on the banks of the ponds and lakes and on floating rafts in the centre of those ponds or lakes.

Many of the ponds and lakes had ultrasonic repellers placed on their banks over the study period. Every two years, the ecologists measured the average number of chicks that survived per nest.

A student looked at the graph and concluded that providing rafts was a more effective way of increasing chick survival than the use of ultrasonic repellers.

Evaluate the student's conclusion.

Suggest how scientists could estimate the size of a local G. chloropus population.

Helicoverpa punctigera (native budworm) is a species of moth that is a major pest of chickpea crops. Yield and seed quality decline when larval density reaches 10–20 per m². Larvae are classified into four instars (sizes):

• very small (VS): 1–2 mm

• small (S): 4–7 mm

• medium (M): 8–23 mm

• large (L): 24–30+ mm

Farmers regularly monitor chickpea crops to decide the point at which insecticides are needed to control H. punctigera populations.

Distinguish between the feeding preferences of larval instars that are <8 mm with instars that are >8 mm.

Suggest why the feeding behaviour of H. punctigera shown in (a) causes a decline in chickpea yield.

Pest management is economically and environmentally important to farmers.

To manage pests of chickpea crops, scientists assessed two approaches:

• Genetically engineered chickpea plants expressing Bacillus thuringiensis (Bt), which produce a toxin lethal to herbivorous insects

• The synthetic pyrethroid α-Cypermethrin, to which H. punctigera currently shows low resistance.

The graphs below represent data from the experiments undertaken.

Identify the pest control management method that was most successful in controlling larvae that are <8 mm in length, prior to pod development.

State the conclusions that can be drawn about the effectiveness of the pest management techniques when applied during pod development.

A team of scientists seeking solutions for South Australian chickpea farmers proposed importing an egg-parasitoid wasp (Trichogramma pretiosum) that is native to the Americas. Female T. pretiosum lay their eggs inside moth eggs (including the eggs of H. punctigera). The wasp larva develops inside the moth egg, so the pest egg does not hatch and no caterpillar emerges.

Explain why introducing this biological control agent could cause problems for the local ecosystem.

Australia’s wildlife is unusually distinctive and fragile, with many endemic species.

Outline why the researchers are very unlikely to be granted permission to release T. pretiosum in South Australia.

Grey seals (Halichoerus grypus) are large seals found in coastal waters around northern Europe and North America. Their diet consists of a variety of fish species, crustaceans and molluscs, and they are known to dive for periods of up to 45 minutes while searching for food. 

The graph shows blood flow to various organs in the body of a grey seal while they are searching for and actively chasing food at or near to the water’s surface (i.e. not during a dive).

Estimate the difference in blood flow to the heart when the seal is searching for food compared to when it is actively chasing prey.

Compare and contrast the difference in blood flow when the seal is searching for food and when it is actively chasing prey between the kidneys, flipper muscles, and brain.

Suggest why blood flow to the seal’s organs is different when the seal is searching for food compared to when it is actively chasing prey.

Another grey seal’s heart rate was measured before, during, and after a feeding dive. The results are shown in the graph.

Describe the changes in heart rate throughout the monitoring period.

Suggest how the heart rate changes shown in the graph above might affect the seal’s body during a dive.

Plant species living in dry climates need to preserve water and often have adaptations that helps them to do this. 

Scientists are interested in discovering crop varieties that have water-saving adaptations; one study looked at the effect of dry conditions on several varieties of wheat.

The researchers measured the water content of four varieties of wheat (V1, V2, V3, and V4) at the end of a 10-day period without water; their results are shown in the graph below.

Calculate the difference in water content between the control and dry conditions for variety 2.

Compare and contrast the effect of water availability on plant water content for the different varieties of wheat shown in part (a).

The image below shows the effect of 10 days without water on the four varieties of wheat.

Describe the effect of 10 days without water on wheat varieties 1-4

Suggest why dry conditions caused the impacts seen in part (c).

The scientists also analysed the potassium ion (K⁺) content of the tissues of each variety after the 10 day experiment period. The results of this analysis are shown in the graph below.

Describe the impact of dry conditions on the potassium ion content of the different varieties.

With reference to the results shown in parts (a), (c) and (e):

(i) deduce the effect of potassium ion content on the response of wheat to dry conditions

[1]

(ii) suggest how some wheat varieties are able to minimise the impact of dry conditions

[2]

After reading the results shown in parts (a), (c) and (e), a farming organisation recommended that variety 4 should be planted by farmers in parts of the world where drought is common. 

Evaluate this recommendation.