Food webs describe most ecosystems more accurately than a single food chain does, because most organisms eat, and are eaten by, more than one species.
Correct Answer
True
True. A food chain follows one straight path of feeding, which oversimplifies real ecosystems. A food web shows the many interconnected feeding relationships across trophic levels.
Category: Energy Flow
Question 2
Gross primary productivity is the energy that remains after producers have used some for their own respiration.
Correct Answer
False
False. Gross primary productivity is the total rate at which producers capture energy. The energy left after producers use some for respiration is net primary productivity, which is what primary consumers can access.
Category: Productivity
Question 3
Decomposers such as bacteria and fungi return nutrients from dead organisms to the ecosystem.
Correct Answer
True
True. Decomposers break down dead organisms and wastes, releasing nutrients that producers can take up again. Without them, nutrients would stay locked in dead material.
Category: Energy Flow
Question 4
Herbivores are secondary consumers because they feed directly on producers.
Correct Answer
False
False. Herbivores feed directly on producers, which makes them primary consumers. Secondary consumers are carnivores that eat primary consumers.
Category: Energy Flow
Question 5
DDT built up in bald eagles and caused them to lay eggs with thin shells, contributing to sharp population declines.
Correct Answer
True
True. DDT became concentrated at the top of aquatic food chains, and in eagles and other predatory birds it thinned eggshells so that many eggs broke before hatching. The United States banned DDT in the 1970s.
Category: Ecosystem Dynamics
Question 6
Biomagnification involves mainly water-soluble substances that organisms excrete quickly.
Correct Answer
False
False. Biomagnification involves persistent, fat-soluble substances such as DDT, PCBs and mercury compounds, which are stored in tissues rather than excreted, so they build up at each higher trophic level.
Category: Ecosystem Dynamics
Question 7
Most of Earth's fresh water is locked in ice or held underground rather than found in lakes and rivers.
Correct Answer
True
True. Ice caps, glaciers and groundwater hold most fresh water. Lakes and rivers contain less than 1 percent of it, which is why accessible fresh water is a limited resource.
Category: Water and Carbon Cycles
Question 8
Evapotranspiration is the movement of water from the atmosphere into the soil as rain.
Correct Answer
False
False. Evapotranspiration is water vapor rising into the atmosphere from evaporation off surfaces plus transpiration from plants. Water falling from the atmosphere as rain or snow is precipitation.
Category: Water and Carbon Cycles
Question 9
Burning fossil fuels moves carbon that was stored underground for millions of years into the atmosphere as carbon dioxide.
Correct Answer
True
True. Coal, oil and natural gas formed from ancient organisms, locking their carbon away for very long periods. Combustion releases that carbon rapidly as carbon dioxide, raising atmospheric levels.
Category: Water and Carbon Cycles
Question 10
Most organisms can use atmospheric nitrogen gas directly to build proteins and nucleic acids.
Correct Answer
False
False. Nitrogen gas makes up about 78 percent of the air, but most organisms cannot use it. It must first be fixed into ammonia or ammonium by certain bacteria, such as cyanobacteria and Rhizobium, before it enters food webs.
Category: Nutrient Cycles
Question 11
Denitrifying bacteria convert nitrate back into nitrogen gas, which returns to the atmosphere.
Correct Answer
True
True. Denitrification, carried out by bacteria such as Pseudomonas and Clostridium, completes the nitrogen cycle by returning nitrogen to the atmosphere as nitrogen gas.
Category: Nutrient Cycles
Question 12
Phosphorus is often a limiting nutrient for growth in freshwater ecosystems.
Correct Answer
True
True. Phosphorus is needed for nucleic acids, phospholipids and ATP but is often scarce in water, so it limits the growth of algae and plants. Adding phosphorus from runoff or sewage can trigger algal blooms.
Category: Nutrient Cycles
Question 13
Tropical rainforest soils are typically rich in nutrients because so much plant material falls on them.
Correct Answer
False
False. Tropical rainforest soils are typically nutrient poor, because heavy rainfall leaches nutrients out and the dense vegetation takes up the rest quickly. Most of the ecosystem's nutrients are held in living plants.
Category: Terrestrial Biomes
Question 14
Temperate grassland soils are deep and fertile because dense grass roots add large amounts of organic matter.
Correct Answer
True
True. The thick network of grass roots and rhizomes builds organic-rich soil, which is why prairies and steppes became some of the world's most productive farmland.
Category: Terrestrial Biomes
Question 15
The boreal forest is dominated by broad-leaved deciduous trees such as oaks and maples.
Correct Answer
False
False. The boreal forest, or taiga, is dominated by cold-tolerant evergreen conifers such as pine, spruce and fir. Oaks and maples are typical of temperate forests.
Category: Terrestrial Biomes
Question 16
Savanna plants have well-developed root systems that let them resprout quickly after fire.
Correct Answer
True
True. Fire is a common disturbance on the savanna, and grasses and other plants survive it because their roots remain alive underground and send up new growth soon afterward.
Category: Terrestrial Biomes
Question 17
Desert biomes typically receive more than 100 cm of precipitation per year.
Correct Answer
False
False. Deserts generally receive less than 30 cm of precipitation a year, and the rain that does fall is unpredictable. Some deserts receive only a few centimeters.
Category: Terrestrial Biomes
Question 18
During coral bleaching, corals expel the photosynthetic protists that live in their tissues, often because the water has become too warm.
Correct Answer
True
True. Corals depend on mutualistic photosynthetic protists for much of their nutrition. When water grows too warm, corals expel them and turn white, and they can starve if the stress continues.
Category: Aquatic Biomes
Question 19
The photic zone of the ocean extends to a depth of about 2,000 meters.
Correct Answer
False
False. The photic zone, where enough light penetrates for photosynthesis, reaches only to about 200 meters. Below that lies the aphotic zone, which makes up most of the ocean's volume.
Category: Aquatic Biomes
Question 20
The stagnant water of a bog is typically rich in dissolved oxygen.
Correct Answer
False
False. Bogs have low water flow, so their water is oxygen depleted and acidic, conditions that make nitrogen hard for plants to obtain. Carnivorous plants such as sundews survive there by capturing insects for nitrogen.
Category: Aquatic Biomes