14.10.2 Ecosystems and Material Cycles: Nitrogen and Phosphorus Cycles

Question 1

Ecosystems and Material Cycles: Nitrogen and Phosphorus Cycles

Answer 1

• Review: Six major elements cycled through organisms are sulfur, phosphorus, oxygen, nitrogen, carbon, and hydrogen.
• In the phosphorus cycle, inorganic phosphorus enters ecosystems from the weathering of rocks. Plants take it up and convert it to an organic form.
• In the nitrogen cycle, nitrogen-fixing bacteria convert N2 into ammonium (NH4+), which plants use.

Question 2

note

Answer 2

• Review: The mnemonic “SPONCH” refers to six major elements that cycle through living organisms. The elements are sulfur, phosphorus, oxygen, nitrogen, carbon, and hydrogen.
• In living organisms, phosphorus is an essential component of ATP, DNA, and phosphorylated intermediates. Phosphorus enters ecosystems from the weathering of rocks in soil and water. Phosphorus is taken up by plants, and thereby enters the food chain. The processes of detritivores recycle the phosphates.

Question 3

nitrogen cycle

Answer 3

• Seventy-five percent of the earth’s atmosphere is gaseous nitrogen (N2). Though the majority of our atmosphere is nitrogen, our bodies cannot absorb nitrogen gas.
• Nitrogen-fixing bacteria convert atmospheric nitrogen (N2) into ammonium (NH4+), a compound that is usable by plants. Nitrogen-fixing bacteria of the genus Rhizobium live as symbionts in nodules on the roots of legumes.
• Nitrifying bacteria convert NH4+ to nitrites (NO2–) and nitrates (NO3–), which are forms of nitrogen that are usableby plants.
• Denitrifying bacteria convert nitrates into atmospheric N2.

Question 4

Which group of bacteria belongs in circle 4?

Answer 4

• decomposing bacteria

Question 5

The ultimate source of phosphorus for the phosphorus cycle is

Answer 5

• rocks

Question 6

Which of the following biological components do not contain phosphorus?

Answer 6

• protein

Question 7

Nitrogen gas comprises __________ of the Earth’s atmosphere.

Answer 7

• 78%

Question 8

Which of the following does not have a gaseous component in its biogeochemical cycle?

Answer 8

• phosphorus

Question 9

All of the following processes occur in the nitrogen cycle except which of the following?

Answer 9

• deamination

Question 10

Which type of bacteria are represented by circle 3?

Answer 10

• nitrifying bacteria

Question 11

Gaseous nitrogen is converted to ammonium by

Answer 11

• nitrogen fixation

Question 12

Which group of bacteria belong in circle two?

Answer 12

• nitrifying bacteria