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Science · Drill 15

Science practice 15

15 questions ~9 min recommended
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Weed Combination E. crassipes E. crassipes + Commelina sp. E. crassipes + Justicia sp. E. crassipes + V. cupsidata E. crassipes + Commelina sp. + Justicia sp. + V. cupsidata Fresh Weight (g) 652.7 452.2 320.2 332.7 342 Plant Height (cm) 38.4 33.7 26.5 21.8 29.2 Leaves per Plant 9.3 9 8.6 8.6 Plant Density (per m?) 51.7 38.9 37.9 26 28.3 Total Biomass (per m?) 30.98 16.09 12.3 7.77 9.50

Weed Combination E. crassipes E. crassipes + Commelina sp. E. crassipes + Justicia sp. E. crassipes + V. cupsidata Fresh Weight (g) 180.80 129.08 151.66 Plant Height (cm) 8.69 8.80 8.88 8.24 Leaves per Plant 10.54 10.70 9.90 9.75

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

An invasive species is a species that is not native to an ecosystem and whose introduction has harmful environmental, economic, and/or human health effects.

Eichhornia crassipes (water hyacinth) is an invasive species of floating aquatic weed found in freshwater waterways in tropical and temperate regions worldwide. It is highly tolerant of fluctuations in water level, nutrient availability, pH, and temperature. This allows it to grow rapidly and outcompete native aquatic plant species for resources. Dense floating mats of E. crassipes further alter aquatic communities by reducing dissolved oxygen levels and access to light. Decomposing matter from E. crassipes mats increases sediment deposition in waterways.

Ecological studies have shown that the growth of a plant can be influenced by competition with different species of neighboring plants. A group of scientists carried out the following studies to determine the effects on the growth of E. crassipes when paired with three other, more benign, aquatic weed species.

Study 1

Scientists collected growth data on E. crassipes mats in the Kagera River in Tanzania. Scientists marked off 1 square meter (m2) sample areas containing E. crassipes alone and in combination with three other aquatic weeds common to the Kagera River.

To determine the effects of the other three weed species on E. crassipes growth, scientists analyzed five growth parameters. Fresh weight was determined by removing and immediately weighing 10 E. crassipes plants from each area. Plant height was measured from the base of the plant to the tip of the tallest leaf. The total number of E. crassipes plants within a sample area was recorded as plant density, which was then multiplied by fresh weight to determine total biomass. The number of leaves per plant was also recorded. Table 5.1 lists the averages for each growth parameter for E. crassipes growing alone and in combination with the three other aquatic weed species.

TABLE 5.1 Kagera River Data

Source: http://www.academicjournals.org/ijbc/fulltext/2011/August/Katagira%20et%20al.htm.

Study 2

Scientists transplanted young E. crassipes, Commelina sp., Justicia sp., and V. cupsidata plants from the Kagera River to a greenhouse. In the greenhouse, E. crassipes potted alone and in combination with the other three weed species were allowed to grow in water from the Kagera River for four months. At the end of the four-month growth period, the parameters of fresh weight, plant height, and leaves per plant were all determined by the same methods used in Study 1.

Table 5.2 lists the averages for each growth parameter for E. crassipes growing in the greenhouse alone and in combination with the other aquatic weed species.

TABLE 5.2 Greenhouse Experiment Data

Source: http://www.academicjournals.org/ijbc/fulltext/2011/August/Katagira%20et%20al.htm.

1. According to the passage, species identified as invasive are always:

2. According to the passage, water hyacinths upset freshwater ecosystems by doing all of the following except:

3. Which weed combination was tested in Study 1 but not Study 2?

4. In Study 1, plant density was measured as:

5. Which weed combination serves as the control group in Study 1?

6. In Study 1, V. cupsidata caused the greatest reduction in:

7. Based on the data in Table 5.1, which weed exerts the least competitive pressure on E. crassipes?

8. In Table 5.2, Commelina sp. and Justicia sp. are both shown to have:

9. In Study 2, the water hyacinths grown alone exhibited a greater average:

10. Total biomass was not included as a growth parameter in Table 5.2 because:

11. Which of the following statements is supported by the data collected in both studies?

12. Based on the data in Table 5.2, the most significant impact of growing E. crassipes in combination with other weeds in a greenhouse environment appears to be the production of:

13. The greatest advantage of the experimental design in Study 2 is that scientists were able to:

14. According to Table 5.1, the presence of all three competitor weeds within the same square meter appears to have:

15. Ecologists have found that introducing a competitor to an ecosystem is sometimes more effective in reducing an unwanted population than introducing a predator. Based on the results of this pair of studies, increasing the presence of which of the following species can be predicted to best reduce the water hyacinth population?

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