Ch. 37 Communities and Ecosystems

Taylor - Campbell Biology: Concepts & Connections 10th Edition

Taylor, Simon, Dickey, Hogan10th EditionCampbell Biology: Concepts & ConnectionsISBN: 9780136538783Not the one you use?Change textbook

Taylor, Simon, Dickey, Hogan 10th Edition

Ch. 37 Communities and Ecosystems

Problem 12

Chapter 37, Problem 12

What roles do bacteria play in the nitrogen cycle?

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Identify the different forms of nitrogen in the environment and understand that nitrogen must be converted into different forms to be usable by plants and animals. Nitrogen exists in the atmosphere primarily as inert N2 gas.

Recognize the role of nitrogen-fixing bacteria, which convert atmospheric nitrogen (N2) into ammonia (NH3) or related compounds. These bacteria often live in the root nodules of leguminous plants and are crucial for providing nitrogen to the plant in a usable form.

Understand the process of nitrification, where nitrifying bacteria convert ammonia into nitrites (NO2-) and then into nitrates (NO3-), which are forms of nitrogen that plants can readily absorb and use for growth.

Learn about denitrifying bacteria, which convert nitrates back into nitrogen gas (N2), releasing it into the atmosphere. This step is essential in balancing the nitrogen cycle by removing excess nitrates from the soil and water.

Explore the role of decomposing bacteria that break down organic matter, including plant and animal proteins, releasing ammonia back into the soil, thus making nitrogen available again for nitrification.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nitrogen Fixation

Nitrogen fixation is the process by which certain bacteria convert atmospheric nitrogen (N2) into ammonia (NH3), a form that plants can utilize. This process is crucial because most organisms cannot use atmospheric nitrogen directly. Bacteria such as Rhizobium, which form symbiotic relationships with leguminous plants, are key players in this process, enriching the soil with nitrogen compounds.

Nitrification

Nitrification is a two-step process carried out by specific bacteria that convert ammonia into nitrites (NO2-) and then into nitrates (NO3-). Nitrates are a vital nutrient for plants, making this process essential for soil fertility. Bacteria such as Nitrosomonas and Nitrobacter are involved in these transformations, facilitating the availability of nitrogen in a form that plants can absorb.

Denitrification

Denitrification is the process by which bacteria convert nitrates back into nitrogen gas (N2), returning it to the atmosphere. This process is important for maintaining the nitrogen balance in ecosystems and preventing the accumulation of excess nitrates in the soil, which can lead to environmental issues like water pollution. Bacteria such as Pseudomonas and Paracoccus are commonly involved in denitrification.

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Nitrogen Cycle

Related Practice

Textbook Question

What is rapid eutrophication? What steps might be taken to slow this process?

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Textbook Question

In Southeast Asia, there's an old saying: 'There is only one tiger to a hill.' In terms of energy flow in ecosystems, explain why big predatory animals such as tigers and sharks are relatively rare.

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Textbook Question

For which chemicals are biogeochemical cycles global? Explain.

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Textbook Question

An ecologist studying plants in the desert performed the following experiment. She staked out two identical plots, which included a few sagebrush plants and numerous small, annual wildflowers. She found the same five wildflower species in roughly equal numbers on both plots. She then enclosed one of the plots with a fence to keep out kangaroo rats, the most common grain-eaters of the area. After two years, to her surprise, four of the wildflower species were no longer present in the fenced plot, but one species had increased dramatically. The control plot had not changed. Using the principles of ecology, propose a hypothesis to explain her results. What additional evidence would support your hypothesis?

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Textbook Question

"In a classic study, John Teal measured energy flow in a salt marsh ecosystem. The table below shows some of his results.

a. What percentage of the energy in sunlight was converted into chemical energy and incorporated into plant biomass? What term describes this new biomass?

b. What percentage of the energy in plant biomass was incorporated into the bodies of the primary consumers? What became of the rest of the energy (see Figure 37.16A)?

c. How much energy is available for secondary consumers?

Based on the efficiency of energy transfer by primary consumers, estimate how much energy will be available to tertiary consumers."

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