PCB 3043 Chapter 21

Suppose scientists place 100g of leaves in a leaf decomposition bag. The rate of decomposition for these leaves is 0.1g per day. Calculate the remaining mass of leaves after 10 days and 50 days. -37g, 1g -0.0005g, 0.0023g -50g, 3.1g -272g, 1484g

-37g, 1g

Suppose scientists place 100g of leaves in a leaf decomposition bag. The rate of decay for these leaves is 0.05g per day. Calculate the remaining mass of leaves after 10 days and 50 days. -165g, 1218g -32g, 0.3g -61g, 8g -0.07g, 0.34g

-61g, 8g

Why is methane gas commonly produced in swamps? -Cyanobacteria in bottom sediments break down into methane whenever oxygen is present. -Decomposers respire anaerobically and release methane when bottom sediments dry out. -Carbon dioxide and water combine to form methane in the oxygen-poor bottom sediments. -Archaea that decompose bottom sediments produce methane during anaerobic respiration.

-Archaea that decompose bottom sediments produce methane during anaerobic respiration.

Ecologists studied the decomposition of three species of leaves. Ones species' leaves had a rate of decomposition, k, of 0.01g per day, the second species had a k of 0.05g per day, and the third species had a k of 0.10g per day. Leaf mass in grams at 10, 50, and 100 days is provided in the table. k/10 days/50days/100 days 0.01/90/61/37 0.05/61/8/1 0.10/37/1/0 How does the value of k affect leaf mass over time? -The remaining leaf mass is unaffected by the value of k. -Small values of k result in an initial increase in leaf mass and then a decline in leaf mass. -As k increases, the mass of the remaining leaves at time t increases. -As k increases, the mass of the remaining leaves at time t decreases.

-As k increases, the mass of the remaining leaves at time t decreases.

The ocean absorbs about one-third of the carbon dioxide released into the atmosphere from fossil fuel combustion and other human activities. Some of the carbon dioxide that dissolves in ocean water returns to the atmosphere, and some of it remains sequestered in the ocean. How does the ocean sequester carbon from the carbon dioxide that dissolves in the water? -Calcium carbonate precipitates out of the water and sinks into the deep ocean. -Dead organisms settle to the ocean floor where they are sometimes buried for many years. -Organic carbon compounds get used up when living aquatic organisms respire. -Bicarbonate ions that combine with hydrogen ions remain dissolved in ocean water.

-Calcium carbonate precipitates out of the water and sinks into the deep ocean. -Dead organisms settle to the ocean floor where they are sometimes buried for many years.

Where does the majority of biomass in terrestrial plants come from? -Carbon dioxide in the air. -Carbon in the soil. -Nutrients in the soil. -Oxygen in the air.

-Carbon dioxide in the air.

What is the source of fossil fuels? -Carbon from dinosaurs trapped in the soil for millions of years. -Carbon that precipitates in the ocean and becomes locked in the sediments. -Weathering of rocks and soil. -Carbon from plants that was trapped in soil millions of years ago.

-Carbon from plants that was trapped in soil millions of years ago.

The ocean bottom is an anaerobic environment. However, some of the biological processes that take place there require oxygen. Which process in the nitrogen cycle releases oxygen that organisms at the ocean floor can use? -Nitrification releases oxygen when bacteria convert ammonium into nitrite and nitrate. -Nitrogen fixation releases oxygen when organisms or abiotic processes convert atmospheric nitrogen to nitrate or ammonium. -Mineralization releases oxygen when decomposers convert biological nitrogen compounds into ammonium. -Denitrification releases oxygen when bacteria convert nitrate into nitrite, nitric oxide, and nitrogen gas. -Assimilation releases oxygen when producers take up ammonium and construct amino acids.

-Denitrification releases oxygen when bacteria convert nitrate into nitrite, nitric oxide, and nitrogen gas.

What type of equation is used to model leaf decomposition? -Positive and linear. -Negative and linear. -Logistic. -Natural exponential.

-Natural exponential.

Why is the weathering of bedrock in a New Hampshire forest responsible for such a small fraction of the nutrients available to plants? -Most nutrients from the bedrock are absorbed by consumers before plant roots can access them. -Plants do not absorb nutrients from bedrock as easily as they do from organic matter. -Nutrients from organic matter do not leach from soil as quickly as they do from bedrock. -Nutrients from organic sources are released much faster than nutrients from inorganic sources.

-Nutrients from organic sources are released much faster than nutrients from inorganic sources.

How might global warming cause the release of greenhouse gasses from boreal forest soils? -The amount of precipitation increases and causes CO2 to leach from the soil. -Ozone O3 spontaneously combines with decomposing organic matter to produce CO2. -The rate of photosynthesis increases and causes release of methane from plant roots. -Organic matter in the soil thaws and begins to decompose, releasing methane.

-Organic matter in the soil thaws and begins to decompose, releasing methane.

How might the introduction of a symbiotic, nitrogen-fixing bacteria, to an ecosystem affect the environment of the host plants? -The number of species per unit area would increase overall. -Plant competition for resources would increase overall. -Nitrogen availability for producers would decrease overall. -Producers' abilities to sustain consumers would decrease overall.

-Plant competition for resources would increase overall.

Why do agricultural soils in boreal Canada retain nutrients for years longer than agricultural soils in tropical South America? -Soil nutrients in boreal Canada are rapidly replenished through cooler temperatures that allow a rapid rate of decomposition. -Soil nutrients in tropical South America are absorbed by excess metals in the soil and become unusable by plants. -Soil nutrients in tropical South America are rapidly assimilated into living biomass and are removed when vegetation is harvested. -Soil nutrients in boreal Canada are rapidly replenished through high rates of weathering and nutrient release from bedrock.

-Soil nutrients in tropical South America are rapidly assimilated into living biomass and are removed when vegetation is harvested.

Select the definition of leaf decomposition. -The death and loss of leaves from stems. -The uptake of carbon by leaves. -The breakdown of insects by carnivorous plant leaves. -The breakdown of organic compounds within a leaf.

-The breakdown of organic compounds within a leaf.

Why do tropical and temperate soils have different rates of nutrient regeneration? -The climate causes faster rates of nutrient cycling in tropical regions. -The bedrock has been completely weathered in tropical regions. -Organisms have shorter life spans in temperate regions. -Organic matter does not fully decompose in temperate regions.

-The climate causes faster rates of nutrient cycling in tropical regions.

What does the variable, k, represent in the equation for leaf decomposition? -The amount of potassium in the leaves. -The mass of leaves at time t. -Temperature measured in Kelvin. -The loss of leaf mass per day.

-The loss of leaf mass per day.

How does the sun drive the movement of water from the oceans to the continents? -The sun provides light to phytoplankton for photosynthesis and evapotranspiration. -The sun heats ocean water, which flows directly into groundwater reservoirs. -The sun's energy heats the oceans and causes the evaporation of water molecules. -The warmth of the sun causes the ocean's clouds to condense and precipitate over land.

-The sun's energy heats the oceans and causes the evaporation of water molecules.

How can scientists study historical atmospheric CO2 levels? -Measuring the carbon dioxide in the air on mountains. -Measuring the carbon that is locked in oceanic floors. -Measuring how much carbon plants take up each year. -Using ice cores from glaciers that contain small amounts of air trapped for hundreds of thousands of years.

-Using ice cores from glaciers that contain small amounts of air trapped for hundreds of thousands of years.

Arrange the events in the order that they would most likely lead to a fish kill in the Gulf of Mexico.

1. Raw sewage is dumped into the Mississippi River. 2. Excess nutrients arrive in the Gulf of Mexico. 3. Phytoplankton undergo explosive growth. 4. Phytoplankton release oxygen and toxins into the water. 5. Zooplankton and bacteria undergo explosive growth. 6. Oxygen in the water is depleted. 7. Massive numbers of fish die in the Gulf of Mexico.

Label the arrows that indicate where processes of the nitrogen cycle take place.

Atmospheric nitrogen --> Nitrogen fixation, abiotic or biotic --> Assimilation --> Mineralization --> Nitrification by bacteria --> Denitrification by bacteria --> Atmospheric nitrogen

Label the processes involved in the hydrologic cycle.

Condensation --> Precipitation --> Infiltration. --> Groundwater flow --> Evaporation --> Condensation Surface flow in the center