Biology Practice Test: Ecology and Energy Flow
- Ecology and Energy Flow
- 10 questions
- 13 minutes
This test focuses on how energy enters an ecosystem and moves through food chains and food webs. Tip: at each step up a food chain, most energy is used for life processes and lost as heat, so only about 10% is passed on.
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Question 1
At deep-sea hydrothermal vents, no sunlight reaches the sea floor, yet tube worms, clams and crabs live there. The producers are bacteria. Where do these bacteria get their energy?
Correct answer: C
Vent bacteria use chemical energy from compounds such as hydrogen sulfide to make food, a process called chemosynthesis. They are the producers that support the rest of the vent community.
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Question 2
Only about 10% of the energy at one trophic level is passed on to the next level. What happens to most of the rest?
Correct answer: D
Organisms use most of the energy they take in for movement, growth and keeping cells alive, and cellular respiration releases much of it as heat. Heat cannot be used by the next level.
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Question 3
Primary consumers in a meadow take in 5,000 kilocalories of energy. Assume 10% passes from one trophic level to the next. About how much energy reaches the tertiary consumers?
Correct answer: A
Secondary consumers get 10% of 5,000, which is 500 kcal, and tertiary consumers get 10% of 500, which is 50 kcal. The answer 500 stops one level too early.
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Question 4
If all the decomposers were removed from a forest, what would most likely happen over time?
Correct answer: B
Decomposers such as fungi and bacteria break down dead organisms and wastes and release their nutrients into the soil. Without them, plants would soon run short of nutrients.
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Question 5
A bear eats berries. It also eats fish that eat insect larvae, and those larvae eat algae. At which trophic levels does the bear feed?
Correct answer: B
Eating berries makes the bear a primary consumer. In the chain algae → larvae → fish → bear, the bear is the fourth level, a tertiary consumer. Omnivores often feed at more than one level.
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Question 6
Which type of ecological pyramid can never be upside down?
Correct answer: D
Each level always has less energy than the level below it, because energy is lost at every step. A pyramid of numbers can be inverted, for example when thousands of caterpillars feed on one tree.
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Question 7
Why do food chains rarely have more than four or five trophic levels?
Correct answer: A
Because about 90% of the energy is lost at each step, the energy left after four or five steps is too small to support a population at a higher level.
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Question 8
The plants in a grassland capture 10,000 kcal of energy per square meter per year (gross primary productivity) and use 4,000 kcal of it for their own cellular respiration. What is the net primary productivity?
Correct answer: B
Net primary productivity is the energy left for growth after the plants' own respiration: 10,000 − 4,000 = 6,000 kcal. This is the energy available to herbivores.
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Question 9
In a meadow food web: grasshoppers and rabbits eat grass; frogs eat only grasshoppers; songbirds eat grasshoppers and seeds; snakes eat frogs and rabbits; hawks eat rabbits, songbirds and snakes.
If a disease wiped out the grasshoppers, which animal would lose its only food source?
Correct answer: A
Frogs eat only grasshoppers, so they would lose all their food. Songbirds could still eat seeds, and snakes and hawks have other prey.
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Question 10
A field of grain can feed more people if the grain is eaten directly than if it is fed to cattle and people eat the beef. What explains this?
Correct answer: C
Adding a trophic level means about 90% of the grain's energy is used by the cattle for their own life processes. Eating lower on the food chain makes more of the original energy available.
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