Skip to main content
Biology LibreTexts

46.E: Ecosystems (Exercises)

  • Page ID
    72590
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)

    46.1: Ecology of Ecosystems

    Review Questions

    The ability of an ecosystem to return to its equilibrium state after an environmental disturbance is called ________.

    1. resistance
    2. restoration
    3. reformation
    4. resilience
    Answer

    D

    A re-created ecosystem in a laboratory environment is known as a ________.

    1. mesocosm
    2. simulation
    3. microcosm
    4. reproduction
    Answer

    C

    Decomposers are associated with which class of food web?

    1. grazing
    2. detrital
    3. inverted
    4. aquatic
    Answer

    B

    The primary producers in an ocean grazing food web are usually ________.

    1. plants
    2. animals
    3. fungi
    4. phytoplankton
    Answer

    D

    What term describes the use of mathematical equations in the modeling of linear aspects of ecosystems?

    1. analytical modeling
    2. simulation modeling
    3. conceptual modeling
    4. individual-based modeling
    Answer

    A

    The position of an organism along a food chain is known as its ________.

    1. locus
    2. location
    3. trophic level
    4. microcosm
    Answer

    C

    Free Response

    Compare and contrast food chains and food webs. What are the strengths of each concept in describing ecosystems?

    Answer

    Food webs show interacting groups of different species and their many interconnections with each other and the environment. Food chains are linear aspects of food webs that describe the succession of organisms consuming one another at defined trophic levels. Food webs are a more accurate representation of the structure and dynamics of an ecosystem. Food chains are easier to model and use for experimental studies.

    Describe freshwater, ocean, and terrestrial ecosystems.

    Answer

    Freshwater ecosystems are the rarest, but have great diversity of freshwater fish and other aquatic life. Ocean ecosystems are the most common and are responsible for much of the photosynthesis that occurs on Earth. Terrestrial ecosystems are very diverse; they are grouped based on their species and environment (biome), which includes forests, deserts, and tundras.

    Compare grazing and detrital food webs. Why would they both be present in the same ecosystem?

    Answer

    Grazing food webs have a primary producer at their base, which is either a plant for terrestrial ecosystems or a phytoplankton for aquatic ecosystems. The producers pass their energy to the various trophic levels of consumers. At the base of detrital food webs are the decomposers, which pass this energy to a variety of other consumers. Detrital food webs are important for the health of many grazing food webs because they eliminate dead and decaying organic material, thus, clearing space for new organisms and removing potential causes of disease. By breaking down dead organic matter, decomposers also make mineral nutrients available to primary producers; this process is a vital link in nutrient cycling.

    46.2: Energy Flow through Ecosystems

    Review Questions

    The weight of living organisms in an ecosystem at a particular point in time is called:

    1. energy
    2. production
    3. entropy
    4. biomass
    Answer

    D

    Which term describes the process whereby toxic substances increase along trophic levels of an ecosystem?

    1. biomassification
    2. biomagnification
    3. bioentropy
    4. heterotrophy
    Answer

    B

    Organisms that can make their own food using inorganic molecules are called:

    1. autotrophs
    2. heterotrophs
    3. photoautotrophs
    4. chemoautotrophs
    Answer

    D

    In the English Channel ecosystem, the number of primary producers is smaller than the number of primary consumers because________.

    1. the apex consumers have a low turnover rate
    2. the primary producers have a low turnover rate
    3. the primary producers have a high turnover rate
    4. the primary consumers have a high turnover rate
    Answer

    C

    What law of chemistry determines how much energy can be transferred when it is converted from one form to another?

    1. the first law of thermodynamics
    2. the second law of thermodynamics
    3. the conservation of matter
    4. the conservation of energy
    Answer

    B

    Free Response

    Compare the three types of ecological pyramids and how well they describe ecosystem structure. Identify which ones can be inverted and give an example of an inverted pyramid for each.

    Answer

    Pyramids of numbers display the number of individual organisms on each trophic level. These pyramids can be either upright or inverted, depending on the number of the organisms. Pyramids of biomass display the weight of organisms at each level. Inverted pyramids of biomass can occur when the primary producer has a high turnover rate. Pyramids of energy are usually upright and are the best representation of energy flow and ecosystem structure.

    How does the amount of food a warm blooded-animal (endotherm) eats relate to its net production efficiency (NPE)?

    Answer

    NPE measures the rate at which one trophic level can use and make biomass from what it attained in the previous level, taking into account respiration, defecation, and heat loss. Endotherms have high metabolism and generate a lot of body heat. Although this gives them advantages in their activity level in colder temperatures, these organisms are 10 times less efficient at harnessing the energy from the food they eat compared with cold-blooded animals, and thus have to eat more and more often.

    46.3: Biogeochemical Cycles

    Review Questions

    The movement of mineral nutrients through organisms and their environment is called a ________ cycle.

    1. biological
    2. bioaccumulation
    3. biogeochemical
    4. biochemical
    Answer

    C

    Carbon is present in the atmosphere as ________.

    1. carbon dioxide
    2. carbonate ion
    3. carbon dust
    4. carbon monoxide
    Answer

    A

    The majority of water found on Earth is:

    1. ice
    2. water vapor
    3. fresh water
    4. salt water
    Answer

    D

    The average time a molecule spends in its reservoir is known as ________.

    1. residence time
    2. restriction time
    3. resilience time
    4. storage time
    Answer

    A

    The process whereby oxygen is depleted by the growth of microorganisms due to excess nutrients in aquatic systems is called ________.

    1. dead zoning
    2. eutrophication
    3. retrofication
    4. depletion
    Answer

    B

    The process whereby nitrogen is brought into organic molecules is called ________.

    1. nitrification
    2. denitrification
    3. nitrogen fixation
    4. nitrogen cycling
    Answer

    C

    Free Response

    Describe nitrogen fixation and why it is important to agriculture.

    Answer

    Nitrogen fixation is the process of bringing nitrogen gas from the atmosphere and incorporating it into organic molecules. Most plants do not have this capability and must rely on free-living or symbiotic bacteria to do this. As nitrogen is often the limiting nutrient in the growth of crops, farmers make use of artificial fertilizers to provide a nitrogen source to the plants as they grow.

    What are the factors that cause dead zones? Describe eutrophication, in particular, as a cause.

    Answer

    Many factors can kill life in a lake or ocean, such as eutrophication by nutrient-rich surface runoff, oil spills, toxic waste spills, changes in climate, and the dumping of garbage into the ocean. Eutrophication is a result of nutrient-rich runoff from land using artificial fertilizers high in nitrogen and phosphorus. These nutrients cause the rapid and excessive growth of microorganisms, which deplete local dissolved oxygen and kill many fish and other aquatic organisms.

    Why are drinking water supplies still a major concern for many countries?

    Answer

    Most of the water on Earth is salt water, which humans cannot drink unless the salt is removed. Some fresh water is locked in glaciers and polar ice caps, or is present in the atmosphere. The Earth’s water supplies are threatened by pollution and exhaustion. The effort to supply fresh drinking water to the planet’s ever-expanding human population is seen as a major challenge in this century.


    46.E: Ecosystems (Exercises) is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by OpenStax.

    • Was this article helpful?