Deck 18: Biogeochemical Cycles

Question 1

In the systems approach to biogeochemical cycles,

A) nutrients are found in sinks.
B) fluxes are the pathways of net gain or loss of nutrients.
C) the cycle must be in equilibrium.
D) the boundaries of the ecosystem are not defined.
E) none of the above

Answer 1

A

Question 2

In the carbon cycle,

A) photosynthesis always balances respiration.
B) CO₂ enters the ocean primarily by photosynthesis.
C) CO₂ in the ocean forms a weak acid.
D) carbon enters the food chain in the form of CO₃^-2.
E) none of the above

Answer 2

C

Question 3

Nitrogen fixation

A) is the product of respiration and photosynthesis.
B) can be accomplished by most plants.
C) requires energy to break the triple bond in N₂.
D) occurs when nitrate is converted to nitrite.
E) none of the above

Answer 3

C

Question 4

Mutualistic bacteria in legumes

A) include the cyanobacteria.
B) provide fixed nitrogen in exchange for carbon.
C) provide carbon in exchange for fixed nitrogen.
D) release nitrogen to the atmosphere.
E) none of the above

Question 5

Eutrophication occurs when

A) trophic levels change.
B) nitrogen is no longer limiting.
C) algal blooms die off.
D) nitrogen fixation releases N₂.
E) none of the above

Question 6

The phosphorus cycle differs from the nitrogen cycle in that

A) the phosphorus cycle has a short residence time.
B) there is no limiting step in the phosphorus cycle.
C) there is a large sedimentary pool of nitrogen.
D) there is a large sedimentary pool of phosphorus.
E) none of the above.

Question 7

The carbon cycle differs from the nitrogen cycle in that

A) there is a large atmospheric pool of carbon.
B) the residence time of carbon is longer.
C) the nitrogen cycle requires specialized organisms.
D) the carbon cycle is in equilibrium.
E) none of the above

Question 8

The increase in oxygen in the atmosphere

A) led to the replacement of eukaryotes by prokaryotes.
B) is associated with changes in the size and diversity of organisms.
C) required new forms of electron donors.
D) was due to the increase in respiration during the Devonian.
E) none of the above

Question 9

Which of the following is not a source of inorganic nutrients in ecosystems?

A) aerosols
B) alluvial deposition
C) weathering
D) loess
E) none of the above

Question 10

Which of the following is not a mechanism of nutrient input to soil?

A) mineralization
B) decomposition
C) photosynthesis
D) humification
E) none of the above

Question 11

Human agriculture is threatened by

A) humus in the A horizon.
B) excess phosphorus and nitrogen in soil.
C) loss of the A horizon.
D) increases in mycorrhizal fungi.
E) none of the above

Question 12

In a nutrient spiral,

A) nutrients are transported downstream.
B) nutrients are transported to deeper waters.
C) salmon move nutrients to terrestrial systems.
D) nutrient cycles occur in discrete segments of the stream.
E) none of the above

Question 13

The two main limiting processes in nutrient cycles are

A) decomposition and nutrient spiraling.
B) decomposition and input of inorganic nutrients.
C) photosynthesis and respiration.
D) deposition of loess and nitrogen fixation.
E) none of the above

Question 14

Studies of nutrient cycles at Hubbard Brook show that

A) nitrogen is continually lost from undisturbed forest.
B) nutrient cycles resist disturbance.
C) disturbance increases stream flow and nutrient loss.
D) disturbance increases the rate of nitrogen cycling.
E) none of the above

Question 15

When organic phosphorus is added to streams

A) the nutrient spiral removes most of it.
B) it is converted into an inorganic form.
C) retention of phosphorus depends on the age of the surrounding forest.
D) retention of phosphorus requires a disturbance.
E) none of the above

Question 16

During the Cambrian explosion,

A) photosynthesis evolved.
B) all organisms were heterotrophs.
C) the atmosphere was anoxic.
D) many novel organisms appeared.
E) none of the above

Question 17

At the Hubbard Brook Experimental Forest stream nitrogen has decreased because of

A) decreased atmospheric nitrogen.
B) disturbance of the vegetation by a hurricane.
C) increased microbial denitrification.
D) increased immobilization of nitrogen in soil.
E) none of the above

Question 18

The phosphorus cycle is driven by the fundamental processes of photosynthesis and respiration.

Question 19

Photosynthetic plants are not usually limited by CO₂.

Question 20

The variance in the pools and fluxes of the carbon cycle is very small.

Question 21

The movement of nutrients in ecosystems is linear.

Question 22

Nutrient fluxes occur by physical and biological processes.

Question 23

N₂ cannot be absorbed by plants.

Question 24

Algal blooms are indicators of healthy nutrient cycles.

Question 25

Glacial till is a significant threat to agriculture.

Question 26

Humus consists of the stable breakdown products of carbohydrates, lipids, and proteins.

Question 27

Phosphorus has a short residence time in parent material.

Question 28

What is the effect of spatial scale on nutrient budgets?

Question 29

Why is nitrogen fixation the limiting step in the nitrogen cycle?

Question 30

What are the key similarities and differences between the nitrogen and carbon cycles?

Question 31

Why was it important that eukaryotes use oxygen as a final electron receptor in respiration?

Question 32

Why are leaf cutter ants important to the function of tropical rain forests?

Question 33

What factors affect the length of nutrient spirals?