At deep-sea hydrothermal vents, where no sunlight reaches, which organisms form the base of the food web by drawing energy from inorganic chemicals such as hydrogen sulfide?
Chemoautotrophs
✓
Photoautotrophs
Detritivores
Herbivores
Correct Answer
Chemoautotrophs
Chemoautotrophs, mostly bacteria and archaea, capture energy from inorganic chemicals and use it to make organic molecules, so they can support ecosystems in total darkness. Photoautotrophs such as plants and algae need sunlight, which does not reach the vents. Detritivores feed on dead organic matter rather than producing it. Herbivores are consumers that eat producers, so they cannot be the base of a food web.
Category: Energy Flow
Question 2
In the food chain grass, grasshopper, frog, snake, which trophic level does the frog occupy?
Primary consumer
Secondary consumer
✓
Tertiary consumer
Producer
Correct Answer
Secondary consumer
The frog eats the grasshopper, which is a primary consumer, so the frog is a secondary consumer. The primary consumer is the grasshopper, an herbivore that eats the grass. The tertiary consumer is the snake, which eats the frog. The producer is the grass, which captures energy from sunlight.
Category: Energy Flow
Question 3
Producers in a marsh capture 25,000 kcal/m2/year of energy (gross primary productivity) and use 15,000 kcal/m2/year for their own respiration. What is their net primary productivity?
40,000 kcal/m2/year
15,000 kcal/m2/year
10,000 kcal/m2/year
✓
25,000 kcal/m2/year
Correct Answer
10,000 kcal/m2/year
Net primary productivity is gross primary productivity minus the energy producers use in respiration: 25,000 - 15,000 = 10,000 kcal/m2/year, and this is the energy available to primary consumers. 40,000 comes from adding the two values instead of subtracting. 15,000 is the energy spent on respiration, not the energy left over. 25,000 is the gross figure before respiration is subtracted.
Category: Productivity
Question 4
Producers in an ecosystem store 10,000 kcal of energy, and the primary consumers that eat them store 1,000 kcal. What percentage of the energy was transferred to the primary consumers?
1%
90%
0.1%
10%
✓
Correct Answer
10%
Transfer efficiency is the energy at the higher level divided by the energy at the level below, times 100: 1,000 / 10,000 x 100 = 10%. 1% results from misplacing the decimal point. 90% is the share of energy that was not passed on, lost mostly as heat and to decomposers. 0.1% is off by a factor of one hundred.
Category: Productivity
Question 5
Why do food chains rarely include more than four or five trophic levels?
Energy is lost at each transfer, much of it as heat
✓
Matter cannot be recycled between trophic levels
Top predators cannot find enough drinking water
Producers capture too little carbon dioxide
Correct Answer
Energy is lost at each transfer, much of it as heat
At each step up a food chain, most energy is used for metabolism and lost as heat or passes to decomposers, so too little remains to support many additional levels. Matter is recycled, which is what decomposers and nutrient cycles do. Water availability is not what caps food chain length. Carbon dioxide supply does not explain the shrinking energy at each level.
Category: Energy Flow
Question 6
Which organism would be found at the base of a detrital food web?
A deer browsing on shrubs
A fungus breaking down leaf litter
✓
A grass plant capturing sunlight
A hawk hunting mice
Correct Answer
A fungus breaking down leaf litter
A detrital food web starts with organisms that consume dead organic matter, such as fungi, bacteria and detritivores feeding on fallen leaves. A grass plant capturing sunlight is the base of a grazing food web. A deer browsing on shrubs is a primary consumer in a grazing food web. A hawk hunting mice is a higher-level consumer in a grazing food web.
Category: Energy Flow
Question 7
A lake is contaminated with PCBs, which are persistent and fat soluble. Which organism in the lake food web would most likely carry the highest PCB concentration in its tissues?
Phytoplankton
Zooplankton
Fish-eating birds
✓
Small minnows
Correct Answer
Fish-eating birds
Persistent, fat-soluble toxins become more concentrated at each higher trophic level, so fish-eating birds at the top of the food web carry the most. Phytoplankton, at the base, hold the lowest concentration. Zooplankton eat phytoplankton and hold more, but still far less than top predators. Small minnows are intermediate consumers and are themselves eaten by the birds that concentrate the toxin further.
Category: Ecosystem Dynamics
Question 8
Which term describes how quickly an ecosystem returns to equilibrium after a disturbance?
Resistance
Productivity
Biomagnification
Resilience
✓
Correct Answer
Resilience
Resilience is the speed with which an ecosystem recovers its equilibrium after a disturbance such as a fire or storm. Resistance is the ability to stay at equilibrium in the first place despite the disturbance. Productivity is the rate at which producers capture and store energy. Biomagnification is the buildup of toxins at higher trophic levels.
Category: Ecosystem Dynamics
Question 9
Which reservoir holds the largest share of Earth's water?
Oceans
✓
Glaciers and ice caps
Groundwater
Lakes and rivers
Correct Answer
Oceans
The oceans hold about 97 percent of all water on Earth, almost all of it salt water. Glaciers and ice caps hold most of the fresh water, but fresh water is only a small fraction of the total. Groundwater is a large freshwater store that is still far smaller than the oceans. Lakes and rivers hold less than 1 percent of fresh water.
Category: Water and Carbon Cycles
Question 10
Which process moves carbon from atmospheric carbon dioxide into organic molecules?
Cellular respiration
Photosynthesis
✓
Fossil fuel combustion
Volcanic eruption
Correct Answer
Photosynthesis
Photosynthesis uses light energy to combine carbon dioxide with water to build sugars, transferring carbon from the air into living matter. Cellular respiration does the reverse, releasing carbon dioxide from organic molecules. Fossil fuel combustion releases stored carbon into the atmosphere. Volcanic eruptions also add carbon dioxide to the atmosphere rather than removing it.
Category: Water and Carbon Cycles
Question 11
Rhizobium bacteria living in the root nodules of legumes convert nitrogen gas from the air into ammonia that the plant can use. What is this process called?
Nitrification
Denitrification
Nitrogen fixation
✓
Ammonification
Correct Answer
Nitrogen fixation
Nitrogen fixation converts atmospheric nitrogen gas into ammonia or ammonium, a form living things can use; Rhizobium, cyanobacteria and free-living Azotobacter all do this. Nitrification converts ammonium into nitrite and then nitrate. Denitrification converts nitrate back into nitrogen gas. Ammonification releases ammonium from wastes and dead organisms.
Category: Nutrient Cycles
Question 12
Soil bacteria such as Nitrosomonas convert ammonium into nitrite, a step that leads to the formation of nitrate. What is this part of the nitrogen cycle called?
Denitrification
Nitrogen fixation
Assimilation
Nitrification
✓
Correct Answer
Nitrification
Nitrification is the conversion of ammonium to nitrite and then to nitrate by soil bacteria, producing a form many plants absorb readily. Denitrification turns nitrate back into nitrogen gas. Nitrogen fixation converts nitrogen gas into ammonia. Assimilation is the uptake of nitrogen compounds by plants and their use in building molecules.
Category: Nutrient Cycles
Question 13
How does phosphate mainly enter terrestrial ecosystems?
Weathering of rocks
✓
Fixation of phosphorus gas by soil bacteria
Uptake of phosphorus gas through leaves
Conversion of nitrogen into phosphate by bacteria
Correct Answer
Weathering of rocks
Phosphate is released when rocks weather, and it then dissolves into soil and water where plants can take it up. Fixation of phosphorus gas by soil bacteria does not happen, because the phosphorus cycle has no significant gas phase; bacteria fix nitrogen, not phosphorus. Uptake of phosphorus gas through leaves is impossible for the same reason. Conversion of nitrogen into phosphate cannot occur, because one element cannot be turned into another by living things.
Category: Nutrient Cycles
Question 14
Fertilizer runoff causes a large algal bloom in a bay, and soon fish begin dying. What directly kills the fish in such a dead zone?
Too much sunlight reaching the deep water
Oxygen depletion as bacteria decompose dead algae
✓
A sharp rise in salinity from fertilizer salts
Freezing of the surface water
Correct Answer
Oxygen depletion as bacteria decompose dead algae
When the algae die, bacteria decomposing them use up dissolved oxygen, leaving too little for fish and other animals. Excess sunlight is not the problem; the dense algae actually block light. Fertilizer does not raise salinity enough to cause the die-off. Freezing has nothing to do with nutrient runoff and dead zones.
Category: Nutrient Cycles
Question 15
Burning coal releases which gas that is a major cause of acid rain?
Methane
Water vapor
Sulfur dioxide
✓
Hydrogen gas
Correct Answer
Sulfur dioxide
Sulfur dioxide released by fossil fuel burning and volcanoes reacts with water in the atmosphere to form acids that fall as acid rain, lowering the pH of lakes and damaging marble and limestone buildings. Methane is a greenhouse gas that does not form acid in rain. Water vapor is the carrier of the acid, not its source. Hydrogen gas is not a significant product of burning coal and does not acidify rain.
Category: Nutrient Cycles
Question 16
Which two climate factors largely determine which terrestrial biome develops in a region?
Soil color and elevation
Wind speed and day length
Predation and competition
Temperature and precipitation
✓
Correct Answer
Temperature and precipitation
Temperature and precipitation set the conditions plants can tolerate, so they determine the dominant vegetation and therefore the biome; similar climates far apart produce the same biome. Soil color and elevation are not the factors used to classify biomes. Wind speed and day length can matter locally but do not define biomes. Predation and competition are biological interactions, not climate factors.
Category: Terrestrial Biomes
Question 17
Which terrestrial biome has the greatest species diversity?
Tropical rainforest
✓
Temperate forest
Savanna
Boreal forest
Correct Answer
Tropical rainforest
Tropical rainforests have the highest biodiversity of any terrestrial biome, supported by warm, stable temperatures and abundant rain year-round. Temperate forests have cold winters and fewer species. Savannas are grasslands with scattered trees and a long dry season. Boreal forests are cold and dominated by a few kinds of conifers.
Category: Terrestrial Biomes
Question 18
Which biome is dominated by shrubs, receives most of its rain in mild winters, has hot, dry summers and contains seeds that germinate only after a hot fire?
Savanna
Chaparral
✓
Desert
Temperate grassland
Correct Answer
Chaparral
Chaparral, found in California and around the Mediterranean, is shrubland with wet winters and dry summers, and fire is a natural part of its cycle. Savanna is grassland with scattered trees in a warm climate with a long dry season. Desert receives too little rain to support dense shrub cover. Temperate grassland is dominated by grasses, with hot summers and cold winters.
Category: Terrestrial Biomes
Question 19
In which biome do many perennial plants have deep roots, small leaves and stems that store water?
Arctic tundra
Chaparral
Desert
✓
Temperate forest
Correct Answer
Desert
Deserts receive little and unpredictable rain, so their perennial plants reduce water loss with small leaves, reach deep water with long roots and store water in their stems. Arctic tundra plants are low-growing and limited by cold and frozen soil, not water storage. Chaparral shrubs are adapted mainly to dry summers and fire. Temperate forests receive steady rain and are dominated by broad-leaved trees.
Category: Terrestrial Biomes
Question 20
Which ocean zone, extending from the low-tide line to the edge of the continental shelf, has the highest productivity and supports most of the world's fisheries?
Oceanic zone
Abyssal zone
Intertidal zone
Neritic zone
✓
Correct Answer
Neritic zone
The neritic zone lies over the continental shelf, where sunlight and nutrients are plentiful, so it is the most productive and diverse ocean zone. The oceanic zone is open water beyond the shelf, where nutrients are scarce. The abyssal zone is deep, dark, cold and under high pressure. The intertidal zone is the narrow strip between high and low tide.
Category: Aquatic Biomes