Chapter 46

Which of the statements is true regarding atmospheric CO2 levels during the last 400,000 years?

Atmospheric CO2 levels fluctuate periodically, with the highest levels occurring during interglacial periods.

Imagine that a researcher has discovered a leaf fossil from the Cambrian Period that is 500 million years old. He notices that the leaf had very few stomata compared to present-day leaves. What does this tell the researcher about atmospheric CO2 levels during the Cambrian Period?

Atmospheric CO2 levels were higher during the Cambrian Period than today.

A researcher is measuring Earth's atmospheric CO2 levels, gathering data on CO2 levels in northern and then southern hemispheres. What do you expect that she will find?

Because atmospheric CO2 measurements represent global amounts, measurements in the Northern Hemisphere and Southern Hemisphere will be approximately the same.

Which of the statements is true regarding CO2?

CO2 is a greenhouse gas, CO2 plays a vital role in maintaining Earth's temperature, CO2 is released as a product of respiration, CO2 can be produced by natural and man-made processes.

The majority of carbon stored in abiotic reservoirs is in the form of:

CaCO3

An increased rate of photosynthesis is the most likely explanation as to why atmospheric CO2 levels appear lowest during glacial periods of Earth's history.

False

Scientists can gain information about ancient atmospheric CO2 levels through ice core data. CO2 in ice cores is primarily the result of sediments being trapped in glaciers, which scientists can subsequently assess for different carbon isotopes 13C, 12C, and 14C.

False

A _____ takes into account the diverse interactions between primary producers, consumers, and decomposers. It depicts the flow of carbon through an environment as interdependent of primary producers, consumers, and decomposers.

Food web

Which of the statements is true regarding the carbon cycle?

It cycles both carbon and H2O, It involves both long- and short-term processes, It evolved before plants appeared on Earth, It was based on microbes during the early stages of Earth's history.

Which biogeochemical cycle does not include oxidation and reduction reactions that provide energy to microorganisms?

Phosphorus

Imagine that scientists have discovered a new planet that is apparently devoid of life but has ice caps located at the poles. These ice caps reveal that the planet's atmospheric O2 levels sharply increased about 1,000,000 years ago but then quickly dropped 50,000 years ago. What could account for these changes in atmospheric O2 levels?

Photosynthetic organisms evolved on the planet 100,000 years ago but went extinct 50,000 years ago.

Recall that during the Paleozoic Era, atmospheric CO2 levels decreased. Why?

Photosynthetic, woody plants first appeared during this period.

Which of the statements explains how an oxygen-rich atmosphere became possible on Earth?

Rates of oxygen consumption are lower than rates of photosynthesis.

Which of the answer choices are reservoirs of carbon?

Soil, oceans, organisms, and the atmosphere

Which of the answer choices is a reservoir of carbon?

Soil, oceans, the atmosphere, and organisms

How can scientists distinguish among different sources of CO2 in the atmosphere?

The amount of different carbon isotopes in the CO2 differs based on the source.

Which of the statements is true regarding subduction?

The carbon it removes is eventually returned to the atmosphere by volcanism

Trout and amoebas are both heterotrophs and can inhabit similar environments, such as a freshwater pond. However, these organisms are very different when it comes to their shape and size. Why?

Trout and amoebas evolved to utilize different sources of C6H12O6 (or other organic compounds

Phosphorus released from sedimentary rocks through chemical weathering can be immediately assimilated by primary producers and contributes to the biomass of primary producers in an ecosystem.

True

Primary consumers obtain carbon, nitrogen, and phosphorus through ingestion of primary producers.

True

A scientist studying a material has determined that 12C, 13C, and 14C occur in the material in a ratio of 1000:10:1. How did he most likely differentiate between these forms of carbon?

by the number of neutrons in 12C, 13C, and 14C

The observation that atmospheric CO2 levels were typically low during glacial periods in Earth's history is an example of:

correlation

A community of organisms and the physical environment it occupies are known together as a(n):

ecosystem

A(n) _____ is a community of organisms and the physical environment it occupies.

ecosystem

Examining the relationship between primary producers, primary consumers, and secondary consumers is one way to track the flow of _____ through a system.

energy contained in organic compounds

A _____ depicts the flow of carbon through an ecosystem, whereas a _____ depicts the transfer of energy.

food web; trophic pyramid

To some extent, Earth's surface reflects solar radiation (in the form of heat), which is subsequently absorbed by certain _____ gases in the atmosphere, such as methane and CO2.

greenhouse

Which of these relationships best depicts the amount of carbon stored in the atmosphere, sedimentary rocks, living organisms, and soil?

living organisms < the atmosphere < soil < sedimentary rocks

The _____ cycle deals with geological processes and carbon reservoirs, some of which have been built up or take place over a period of millennia. In contrast, the _____ cycle involves biological processes that are carried out on a daily and/or seasonal basis.

long-term carbon; short-term carbon

Recall that in the northern hemisphere, atmospheric CO2 levels are highest in early spring and lowest in early fall. What accounts for this seasonal fluctuation in atmospheric CO2 levels?

photosynthesis

The movement of Earth's crust, plate tectonics, contributes to the long-term carbon cycle through all of the answer choices except:

photosynthesis

Cyanobacteria, milkweed plants, and oak trees are all considered:

primary producers

Which of these organisms can incorporate atmospheric carbon directly into C6H12O6, thereby playing a major role in a food web?

primary producers

Decomposers are vital components of a food web because they:

return carbon (as CO2) to the atmosphere.

Photosynthesis and respiration both play a major role in the _____ carbon cycle and can affect atmospheric CO2 levels on a seasonal or annual basis.

short term

Which of the processes is responsible for the change scientists observed in atmospheric concentrations of 12C, 13C, and 14C over the last 200 years?

the burning of fossil fuels

Over the last several decades, what have researchers discovered about atmospheric CO2 levels?

they have increased

Energy flow through ecosystems can be depicted using a(n):

trophic pyramid

Because energy transfer is not 100% efficient across trophic levels, an average of about _____ of energy and biomass available at one trophic level is available at the next.

10%

Which of these organisms is considered a primary consumer?

A grasshopper

Which of the statements is an accurate reflection of photosynthesis and chemical weathering?

Both processes use CO2 as a reactant; that is, they decrease atmospheric CO2 levels.

Which of the equations is the chemical reaction for cellular respiration?

C6H12O6 + 6O2 → 6CO2 + 6H2O

What can Antarctic ice core samples tell us about atmospheric CO2 levels? Select all that apply.

CO2 ice core data confirm CO2 measurements taken directly from the atmosphere. Ice cores can help scientists estimate atmospheric CO2 levels from centuries ago.

The equation CaSiO3 + CO2 → CaCO3 + SiO2 takes into account which of these processes associated with the long-term carbon cycle?

Chemical weathering

The long-term and short-term carbon cycles are connected by the fact that some of the carbon contained in C6H12O6 (or other organic molecules) in plants is incorporated into sedimentary rocks or oil; carbon in sedimentary rock and oil is not immediately cycled back to the atmosphere.

True