Unit 1: The Living World: Ecosystems
Env. Science · Unit 1 · Paper 2

The Living World: Ecosystems unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1Paper 2Paper 3
Each paper is built from this unit’s 31 terms and is the same for everyone, so a teacher can assign “Unit 1, Paper 2” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.
Suggested time 37 min 34 points0/17 attempted
1

Trophic levels and the 10% rule

2

Why the 10% rule is only a rule of thumb

3

Calculating net primary productivity

4

Ammonification

5

Fast carbon pool vs slow carbon pool

6

Predation, competition and resource partitioning

7

Producer and primary productivity

8

Detritivores vs decomposers

9

Ecosystem

10

Terrestrial biomes

11

Symbiosis types

12

Food chain vs food web

Short answer 1. Define or explain: Hydrologic cycle

3 pts

Short answer 2. Define or explain: Carbon cycle reservoirs

3 pts

Short answer 3. Define or explain: Lake zones

3 pts

Short answer 4. Define or explain: Nitrogen fixation

3 pts

Free response

10 pts

ANALYZE AN ENVIRONMENTAL PROBLEM USING MODELS. Examine the model, described below. THE NITROGEN CYCLE. A diagram shows the following pools and processes. Atmospheric N₂ makes up about 78 percent of the atmosphere. An arrow labeled "nitrogen fixation" runs from atmospheric N₂ to ammonium (NH₄⁺) in soil, carried out by bacteria in soil and in the root nodules of legumes, and also by lightning and by the industrial Haber-Bosch process. An arrow labeled "nitrification" runs from ammonium to nitrite (NO₂⁻) and then to nitrate (NO₃⁻), carried out by soil bacteria. An arrow labeled "assimilation" runs from nitrate and ammonium into plant tissue, and from plants into consumers. An arrow labeled "ammonification" runs from dead organic matter and waste back to ammonium, carried out by decomposers. An arrow labeled "denitrification" runs from nitrate back to atmospheric N₂, carried out by bacteria under anaerobic conditions. A dashed arrow labeled "leaching" runs from nitrate in soil to groundwater and surface water.

A(i). Identify the process in the model by which atmospheric nitrogen becomes available to plants. A(ii). Identify the process that returns nitrogen from soil to the atmosphere.

B. Explain why nitrogen gas cannot be used directly by most plants despite being abundant in the atmosphere.

C. Explain why nitrate leaches from soil more readily than ammonium does.

D. Describe one way human activity has increased the amount of fixed nitrogen entering ecosystems, and explain the consequence for a downstream aquatic ecosystem.

E. Explain how the conversion of a wetland to cropland would affect the rate of denitrification in that area.

F. Describe one management practice that would reduce nitrate leaching from agricultural soil, and explain the mechanism by which it works.