AP Biology : Understanding Ecosystems

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Understanding Ecosystems

A certain grassland ecosystem consists of grasses that grow on the plains, mice that eat the grains the grasses produce, weasels that eat both the grass and the mice, and hawks that eat the weasels.

Which of these species will account for the smallest proportion of the biomass of this ecosystem?

Possible Answers:

The bacteria in the soil

The mice

The weasels

The hawks

The grass

Correct answer:

The hawks

Explanation:

Trophic energy levels show reduced biomass as you go up a food chain from producer, to consumer, to secondary consumer, and so on due to the loss of energy as heat. The hawks, as a secondary consumer, will have the smallest amount of proportional biomass compared to the other species.

Example Question #2 : Ecology

Which of the following terms describes a relationship between two different species, in which both species benefit?

Possible Answers:

Parasitism

Amensalism

Synnecrosis

Commensalism

Symbiosis

Correct answer:

Symbiosis

Explanation:

Symbiosis describes a relationship in which both parties benefit. It has been theorized that eukaryotic cells evolved from a symbiotic relationship in which one prokaryote engulfed another. The engulfed cell gained protection from the environment, while the engulfing cell gained an energy source from the engulfed cell.

Commensalism describes a relationship in which one party benefits and the other is neither helped, nor harmed. Parasitism describes a relationship in which one party benefits, while the other is harmed. Amensalism describes a relationship in which one party is unaffected, while the other party is obliterated. Synnecrosis is a relationship that is deadly to both parties involved.

Example Question #2 : Understanding Ecosystems

An ecologist is surveying a portion of land that is believed to contain a specific animal species of interest. If the ecologist is measuring the number of this animal species per square meter, what is she measuring?

Possible Answers:

Carrying capacity

Dispersion

Population range

Competition

Population density

Correct answer:

Population density

Explanation:

The population density is the measure of the population per unit area or volume, and may be measured over land or water.

The carrying capacity refers to the maximum number of organisms that can be sustained by the resources of an environment. The range of a population is simply the area over which the population can be found. Dispersion refers to the different regions where a species is found within a given area. Competition is the use of limited resources between multiple members of a population, or multiple species within a niche.

Example Question #4 : Ecology

Of the following, which is the most likely to affect the population growth of species in a density-dependent manner?

Possible Answers:

Disease

Floods

Hurricanes

Frost

Earthquakes

Correct answer:

Disease

Explanation:

Disease is a biotic factor, while the other choices are abiotic factors. Density-dependent factors are biotic in nature, and may involve things such as mating, food, competition, and disease. Density dependent factors will affect different populations differently depending on how many organisms are present in a given area. In the case of disease, consider that the flu will spread more easily in a densely-populated city than it will in a loosely-populated desert.

The other answer options will affect a population the same, regardless of density, because they affect large areas with the same magnitude.

Example Question #5 : Understanding Ecosystems

Which of the given choices is an example of a mutualistic relationship?

Possible Answers:

Plant roots and fungi

Human blood vessels and S. mansoni (worm)

Cat and mouse

Barnacle and a mollusk shell

Correct answer:

Plant roots and fungi

Explanation:

Mutualistic relationships exist when both organisms benefit from a shared relationship. In the correct answer choice, plants provide energy to the fungi through carbohydrates and the fungi provides nitrogenous compounds to the plant.

Human blood vessel and S. mansoni is a parasitic relationship, as the worm is actually damaging to the host. Cat and mouse is a predatory relationship. The barnacle and mollusk shell is commensalism, with the barnacle benefitting and no effect occurring on the mollusk shell.

Example Question #3 : Understanding Ecosystems

Which of the given options represents the highest level of biological organization?

Possible Answers:

Earth

Ecosystem

Atmosphere

Biome

Biosphere

Correct answer:

Biosphere

Explanation:

Biological organization extends from the level of subatomic particles all the way up to the biosphere. Within the fields of molecular and cell biology, the atomic, molecular, and cellular levels of biology are most important. In the fields of physiology and anatomy, organs, organ systems, and organisms feature prominently.

Within ecology and population genetics, the higher levels of organization are most pertinent. Several organisms make up a population, which in turn makes up a community, and then an ecosystem. A group of ecosystems make up a biome, and the sum of all the biomes is a biosphere. 

Atmosphere and Earth are not considered levels of biological organization.

Example Question #4 : Ecology

Of the following, which refers to the most inclusive level of ecology?

Possible Answers:

Population ecology

Community ecology

Ecosystem ecology

Organismal ecology

Landscape ecology

Correct answer:

Landscape ecology

Explanation:

Global ecology refers to large-scale interactions between the earth’s ecosystems, atmosphere, landscapes, and seascapes. Landscape ecology refers to the spatial orientation and patterns within specific landscapes or seascapes. Ecosystem ecology observes the interactions, both biotic and abiotic, within a given landscape area. Community ecology is like ecosystem ecology, but applies to communities of organisms. It observes the spatial distribution, abundance, relationships, and interactions between organisms of different species in a given ecosystem. Population ecology refers to the spatial distribution, abundance, relationships, and interactions within the same species in a given community. Organismal ecology studies each organism’s behavior, anatomy, evolution, adaptation, and relative fitness in a given environment. 

Example Question #5 : Ecology

A lizard warms himself up on a rock that has been out in the sun. When the sun sets, his body temperature drops back down. Is the lizard endothermic or exothermic?

Possible Answers:

Exothermic; the lizard's body temperature is governed by external, environmental factors

Exothermic; the lizard regulates his own body temperature 

Exothermic; the lizard can regulate his own body temperature with help from external environmental factors

Endothermic; the lizard's body temperature is governed by external, environmental factors

Endothermic; the lizard regulates his own body temperature

Correct answer:

Exothermic; the lizard's body temperature is governed by external, environmental factors

Explanation:

Endothermic organisms can regulate their own body temperature via internal regulation mechanisms independent of environmental factors. For example, a dog is able to cool itself down in the heat of day by panting. Exothermic organisms cannot internally regulate their own body temperature. Rather, they have external regulation, and they depend on environmental factors. The lizard mentioned cannot regulate his own body temperature. In order to warm up, he must find sunlight and heat to increase his body temperature; in order to cool down he may find shade or seek refuge underground. Exothermic organisms are extremely dependent on climate to carry out life functions. 

Example Question #4 : Understanding Ecosystems

Which of the following best explains the principle of allocation with regards to energy?

Possible Answers:

Organisms can access stored energy for life functions even after they have expended significant energy when chasing prey 

Energy is equally distributed between daily life functions

When an organism expends energy catching prey, it does not have energy for other functions

If large amounts of energy are spent catching prey, organisms must spend time recovering the lost energy 

Energy is saved for internal or external regulation of the organism 

Correct answer:

When an organism expends energy catching prey, it does not have energy for other functions

Explanation:

The principle of allocation, in regards to energy, states that energy spent doing one activity takes away the energy that could be spent doing other activities. For example, if an organism expends energy chasing prey, the organism will be tired and will have less energy to carry out other functions. 

Example Question #5 : Understanding Ecosystems

An organism’s measure of success is dependent on various environmental variables. Algae will increase growth and reproduction as their light supply increases. However, there is a point where adding more light no longer increases growth and reproduction, and the algae begin to die due to increased temperature. In this scenario, light is an example of __________

Possible Answers:

variable optimum 

both variable optimum and variable stimulating 

variable stimulating 

variable limiting

variable inhibiting 

Correct answer:

variable inhibiting 

Explanation:

Variable limiting refers to when an environmental variable that is lacking. If light is lacking, the algae will not grow and reproduce; the environmental variable, light, is limiting the algae’s success. The variable optimum is when the variables are perfectly balanced. Variable inhibiting refers to when when an environmental variable is in abundance, to the point where it is harmful. If there is too much light, the algae will no longer continue growing and reproducing, but will begin too die off.  In this situation, light is variable inhibiting. 

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