5 Steps to a 5 AP Biology, 2014-2015 Edition

232 ❯ STEP 4. Review the Knowledge You Need to Score High

by plants and then eventually by animals to complete the nitrogen cycle. Denitrificationis the

process by which bacteria themselves use nitrates and release N 2 as a product.

Water cycle.The earth is covered in water. A considerable amount of this water evapo-

rates each day and returns to the clouds. Eventually, this water is returned to the earth in

the form of precipitation. This process is termed the water cycle.

Review Questions

Nitrogen fixation by bacteria Nitrification

N 2 NH 4 (ammonium) NO 2 – (nitrites)

Decomposers Denitrification

Dead animals

Animals Plants NO 3 (nitrates)

Animals die Snack time for animal Absorption

Figure 18.9 The nitrogen cycle.

1. How would you describe the population
   depicted in the age structure graph shown here?
   A. Growing rapidly
   B. Growing slowly
   C. Not growing at all
   D. Experiencing slow negative growth
   E. Experiencing rapid negative growth
   2. Carbon is most commonly present in the atmos-
   phere in what form?
   A. CCl 4
   B. CO
   C. CO 2
   D. CH 2
   E. C 6 H 12 O 6
   3. Which of the following is a density-dependent
   limiting factor?
   A. Flood
   B. Drought
   C. Earthquake
   D. Famine
   E. Tornado

Age % Males % Females

80+
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
5 4 3 2 1 0 1 2 3 4 5