Prentice Hall Biology (California)
1st Edition
ISBN: 9780132013529
Textbook solutions
All Solutions
Section 4.2: What Shapes and Ecosystem?
Exercise 1
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A biotic factor is a biological influence on organisms within an ecosystem, while an abiotic factor is a physical (nonliving) factor.
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aboitic factors are the physical non-living factors that affects the ecosystem
biotic factors are biological factors that affects the ecosystem
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see explanation for solution
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**Biotic** factors include living organisms that live in a particular area. Some examples of biotic factors include plants, animals, fungi, and microorganisms such as bacteria and protozoans.
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**Abiotic** factors include the nonliving components and conditions of the physical environment. Some examples of abiotic factors include sunlight, water, soil, climate, and temperature.
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The interaction between the biotic factors and the abiotic factors is what characterizes an ecosystem. Living organisms may affect the physical environment around them and vice versa.
Exercise 2
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Three types of community interactions are competition, predation, and symbiosis. (Other acceptable answers include: mutualism, commensalism, parasitism.)
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There are many types of community interactions that can affect an ecosystem. These include *mutualism*, *commensalism*, *parasitism*, *predation*, and *competition*.
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Mutualism occurs when both organisms benefit from the interaction. Commensalism occurs when one organism benefits, while the other organism is not affected by the interaction.
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Parasitism occurs when one organism benefits at the cost of the other organism which is harmed. Predation occurs when a predator organism hunts and consumes a prey organism.
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Lastly, competition occurs when organisms or species compete for the same resources or niche. In many cases, the superior species or organisms will eventually outcompete the others.
Exercise 3
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Primary succession occurs where no soil exists. Restoration of a disturbance without damaging the soil is referred to as secondary succession.
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primary succession occurs on surfaces where no soil previously existed while secondary succession occurs after land has been impacted by natural disasters or human activity
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see explanation for solution
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After a major disturbance such as a devastating wildfire, primary or secondary succession may occur. **Primary succession** would occur when the disturbance had left barren rock, which is then colonized by pioneer species such as mosses and lichens.
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On the other hand, **secondary succession** would occur when the disturbance did not leave barren rock and the soil (and some organisms) may be intact. This allows the surviving organisms to re-grow and colonize the area rather than the pioneer species.
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Therefore, we would expect primary succession to take more time as compared to secondary succession. This is because primary succession has to start from barren land, whereas secondary succession can begin from pre-existing soil and survived organisms.
Exercise 4
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An organism’s niche is determined by its food, how the food is obtained, its required physical conditions, and its reproductive method.
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An organisms niche is determined by the biological and physical conditions it lives in and interacts with.
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see explanation for solution
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The **niche** of an organism can be described as the ecological role of the organism in a given ecosystem. To illustrate, a niche may be compared to the occupation of a person in a society.
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An organism’s niche can be determined by looking how it interacts with the environment. The niche would involve an organism’s food preferences, where it lives, and where it reproduces.
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The niche of an organism can also be described by looking how it interacts with other organisms. They may exhibit certain forms of interactions such as mutualism and commensalism.
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As an example, the niche of a species of birds can be described based on what it eats (nuts, fruits, etc.) or where it lives (on top of trees or along the ground), and how it interacts with other species in the ecosystem (mutualism, competition, predation, etc.)
Exercise 5
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The three symbiotic relationships are all similar because they involve two living organisms within the same ecosystem. Mutalism is when both living organisms benefit, commensalism is when one benefits while the other remains neither harmed nor helped. The last form is parasitism where one benefits while the other is harmed (this organism is called the host).
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See solution explanation.
Exercise 6
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Microorganisms on the sea floor would aid in maintaining equilibrium because as the whale decays these microorganisms would consume the by-products of the decay process so that there would not be too many chemicals within the sea floor to harm the other living things nearby.
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See solution explanation.
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One of the major ways by which organisms maintain the equilibrium of their ecosystem is by recycling matter. In the case of a decaying dead whale, microorganisms play an important role.
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Microorganisms and other decomposers help maintain equilibrium by breaking down the decaying matter into usable nutrients. These can then be taken up by other organisms such as scavengers and other deep-ocean creatures near the decaying dead whale.
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Nutrients from the decaying whale may also be carried upwards the water column by ocean currents. In this case, nutrients may then be taken up by autotrophic organisms found at the surface. This allows them to recycle the nutrients to produce more food.
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Without the help of microorganisms as well as other deep-ocean creatures, dead whales would probably accumulate at the bottom of the ocean. Not only that the materials would not be recycled, but the bottom of the ocean would also be littered by these large masses.
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