What is Ecology & energy flow on the Living Environment Regents?

Ecology & energy flow is a Ecology topic on the Living Environment Regents. RegentsLab has 23 practice questions on it, each with a full worked solution.

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Ecology & energy flow: Living Environment Regents Practice

Practice Ecology & energy flow for the Living Environment Regents with real-style questions and full worked solutions. Miss one? Read the solution — the exam reuses the same ideas every year.

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Question 16 · 1 pt

In a food chain, the organisms that capture energy from sunlight and make their own food are the

(A) decomposers
(B) producers ✓
(C) herbivores
(D) top predators

Worked solution

$\text{sunlight} \to \text{producers}$ Autotrophs convert light energy to chemical energy.

Answer: \text{producers}

Producers (autotrophs, like plants) use photosynthesis to make food, forming the base of the energy pyramid.

Question 49 · 2 pts

In nearly all ecosystems on Earth, what is the original source of the energy that flows through a food web?

(A) The Sun ✓
(B) Herbivores
(C) Decomposers in the soil
(D) Minerals dissolved in the soil

Worked solution

$\text{Energy must enter the living world through producers (autotrophs).}$ Producers are the entry point of energy into a food web.

$\text{light energy} \xrightarrow{\text{photosynthesis}} \text{chemical energy in glucose}$ Producers capture sunlight and store it as chemical energy.

$\text{Therefore the Sun is the original energy source.}$

Answer: The Sun

Producers convert light energy from the Sun into chemical energy during photosynthesis, and almost every other organism ultimately depends on this captured solar energy.

Question 50 · 2 pts

In the food chain grass $\rightarrow$ grasshopper $\rightarrow$ frog $\rightarrow$ snake, what does each arrow represent?

(A) The recycling of nutrients back from the snake to the grass
(B) The movement of organisms as they migrate to new habitats
(C) The direction in which each predator searches for prey
(D) The flow of energy from one organism to the organism that eats it ✓

Worked solution

$\text{An arrow points from the food (eaten) to the consumer (eater).}$ Grass is eaten by the grasshopper, so the arrow points toward the grasshopper.

$\text{grass} \rightarrow \text{grasshopper means energy passes from grass into grasshopper}$

$\text{Each arrow therefore shows energy flow from prey to predator.}$

Answer: The flow of energy from one organism to the organism that eats it

In a food chain, each arrow indicates the direction in which energy is transferred, always pointing from the organism being eaten to the organism doing the eating.

Question 61 · 2 pts

A tick attaches to a deer and feeds on the deer's blood. The tick benefits while the deer is harmed. This relationship is best classified as...

(A) mutualism
(B) parasitism ✓
(C) commensalism
(D) predation

Worked solution

$\text{The tick benefits because it gains food.}$

$\text{The deer is harmed because it loses blood but is not immediately killed.}$

$\text{One organism benefits while the other is harmed, which defines parasitism.}$

Answer: parasitism

Parasitism is a relationship in which one organism (the parasite) benefits at the expense of another (the host), which is harmed but usually not killed right away.

Question 8 · 2 pts

In a food chain consisting of grass, grasshoppers, frogs, and snakes, most of the energy available at the grass level is lost as heat at each step. This best explains why

(A) population size increases at each higher feeding level
(B) matter is destroyed as it passes through the food chain
(C) there is usually less available energy at each higher feeding level ✓
(D) energy is created at each higher feeding level

Worked solution

$Organisms use much of the energy they consume for life processes such as respiration, movement, and maintaining body temperature, releasing it as heat.$ energy loss

$Only a small fraction (about 10%) of energy is stored in body tissue and available to the next feeding level.$

$As a result, the amount of available energy decreases at each successive feeding level in a food chain.$

Answer: there is usually less available energy at each higher feeding level

Because organisms use most consumed energy for their own life processes and release it as heat, only a small percentage is passed on to the next feeding level, so available energy decreases moving up a food chain.

Question 17 · 2 pts

In a food chain consisting of grass, grasshoppers, frogs, and snakes, only about 10% of the energy at each level is transferred to the next level. Which statement best explains why so little energy is transferred?

(A) Decomposers immediately return all energy to the grass before it can be used
(B) Energy is destroyed as it moves from one organism to another
(C) Producers absorb all of the energy and none is available to consumers
(D) Most energy is lost as heat through life processes such as respiration at each level ✓

Worked solution

$Organisms at each feeding level use most of the energy they take in for life processes like movement, growth, and cellular respiration.$ Energy use

$During cellular respiration and other metabolic activities, a large portion of energy is released as heat and is no longer available to the next level.$ Heat loss

$Only the energy stored in body tissue that is actually eaten can be passed to the next consumer.$ Energy pyramid rule

$This is why roughly 10% of energy is transferred between feeding levels while the rest is lost, mostly as heat.$ Conclusion

Answer: Most energy is lost as heat through life processes such as respiration at each level

Energy is not destroyed, but at each feeding level most of it is used for life processes and released as heat, so only about 10% remains available to be passed on to the next level, which is why energy pyramids narrow sharply at higher levels.

Question 54 · 4 pts · constructed response

In a food chain, grass is eaten by a grasshopper, the grasshopper is eaten by a frog, and the frog is eaten by a snake. Describe the original source of energy for this food chain and explain why the amount of available energy decreases at each successive feeding level.

Model answer: The original source of energy is the sun, which is captured by grass during photosynthesis. At each feeding level, most of the energy consumed (about 90%) is used for life processes such as movement, growth, and reproduction, or is lost as heat, so only about 10% of the energy is stored in body tissue and available to the next consumer.

Worked solution

$\text{Sun} \rightarrow \text{grass (producer, photosynthesis)}$ Original energy source

$\text{Grass} \rightarrow \text{grasshopper} \rightarrow \text{frog} \rightarrow \text{snake}$ Energy passes along the food chain

$\text{At each level, roughly } 90\% \text{ of energy is used or lost as heat}$ Energy is used for metabolism and lost as heat

$\text{Only about } 10\% \text{ passes to the next level}$ Explains the energy decrease

Answer: The original source of energy is the sun, which is captured by grass during photosynthesis. At each feeding level, most of the energy consumed (about 90%) is used for life processes such as movement, growth, and reproduction, or is lost as heat, so only about 10% of the energy is stored in body tissue and available to the next consumer.

Energy flows from the sun through producers to consumers, but only a small fraction (about 10%) of energy is transferred to the next trophic level because most is used for life processes or lost as heat, which is why food chains are limited in length.

Question 51 · 2 pts

An energy pyramid shows that the producers in a meadow store about $20{,}000$ kcal of energy. Approximately how much of this energy is available to the primary consumers (herbivores) that feed on them?

(A) About 20,000 kcal
(B) About 18,000 kcal
(C) About 2,000 kcal ✓
(D) About 200 kcal

Worked solution

$\text{About 10\% of energy is passed to the next trophic level.}$ The rest is used for life processes or lost as heat.

$0.10 \times 20{,}000 = 2{,}000$

$\text{So roughly 2{,}000 kcal reaches the herbivores.}$

Answer: About 2,000 kcal

Only about 10% of the energy stored at one trophic level is transferred to the next, because most energy is used by the organisms or released as heat.

Question 52 · 2 pts

Why can a stable ecosystem usually support a much greater mass of producers than of top-level predators?

(A) Energy is lost as heat at each transfer, so less energy is available at higher trophic levels ✓
(B) Top predators reproduce too slowly to ever become numerous
(C) Predators require less energy than producers do
(D) Producers are always physically larger than predators

Worked solution

$\text{At each level, energy is used for life processes and much is released as heat.}$ Only about 10% moves to the next level.

$\text{producers} > \text{primary consumers} > \text{secondary consumers} > \text{top predators}$

$\text{Less energy at higher levels supports less living mass (biomass).}$

Answer: Energy is lost as heat at each transfer, so less energy is available at higher trophic levels

Because usable energy decreases at every transfer, higher trophic levels have less energy available and can support a smaller total mass of organisms, producing the pyramid shape.

Question 53 · 2 pts

What is the primary role of decomposers, such as bacteria and fungi, in an ecosystem?

(A) They break down dead organisms and wastes, returning nutrients to the environment ✓
(B) They serve as the main food source for top predators
(C) They convert nitrogen gas directly into proteins for plants
(D) They capture energy from sunlight to begin the food web

Worked solution

$\text{Decomposers feed on dead organisms and waste material.}$ They are heterotrophs, not producers.

$\text{dead matter} \xrightarrow{\text{decomposers}} \text{nutrients returned to soil and water}$

$\text{These recycled nutrients can then be reused by producers.}$

Answer: They break down dead organisms and wastes, returning nutrients to the environment

Decomposers recycle matter by breaking down dead organisms and wastes into simpler nutrients, which producers can then reuse to keep the ecosystem's materials cycling.

Question 55 · 2 pts

Which statement best describes how energy is first captured and then made available to other organisms in an ecosystem?

(A) Energy is recycled endlessly through the ecosystem, so no new input of energy is ever needed
(B) Both autotrophs and heterotrophs make their own food directly from sunlight
(C) Heterotrophs capture light energy and pass the food they make to autotrophs
(D) Autotrophs convert light energy into chemical energy stored in organic molecules, which heterotrophs later use ✓

Worked solution

$\text{Autotrophs (producers): light energy} \rightarrow \text{chemical energy in organic molecules}$ This is photosynthesis.

$\text{Heterotrophs (consumers): obtain energy by eating other organisms}$

$\text{So autotrophs capture energy and heterotrophs use it.}$

Answer: Autotrophs convert light energy into chemical energy stored in organic molecules, which heterotrophs later use

Autotrophs capture light energy and store it as chemical energy in organic molecules, and heterotrophs obtain that energy by consuming other organisms, so energy flows one way through the ecosystem.

Question 57 · 2 pts

Decomposers such as bacteria and fungi play a key role in ecosystems. If nearly all of the decomposers in a forest ecosystem were suddenly removed, which outcome would be most likely over time?

(A) The amount of sunlight reaching the ecosystem would increase.
(B) Dead organic matter would accumulate and the recycling of nutrients back to producers would slow. ✓
(C) Producers would receive more nutrients and grow faster than before.
(D) Energy would be recycled more efficiently through the food web.

Worked solution

$\text{Decomposers break down dead organisms and wastes.}$

$\text{This returns nutrients to the soil and water so producers can reuse them.}$ This is the recycling of matter.

$\text{Remove decomposers, so dead matter builds up and nutrient recycling slows.}$

Answer: Dead organic matter would accumulate and the recycling of nutrients back to producers would slow.

Decomposers break down dead organisms and wastes, returning nutrients to the environment so producers can reuse them; without them, matter is not recycled and dead material accumulates.

Question 58 · 2 pts

Which statement best describes how energy and matter move through an ecosystem?

(A) Both energy and matter flow in one direction and cannot be reused.
(B) Energy flows in one direction and is eventually lost as heat, while matter is cycled and reused. ✓
(C) Energy is recycled, while matter flows in one direction and is lost.
(D) Both energy and matter are continuously recycled and reused by organisms.

Worked solution

$\text{Energy enters as sunlight and moves through the trophic levels.}$

$\text{At each transfer much energy is lost as heat, so energy flow is one way.}$ Energy is not recycled.

$\text{Atoms of matter such as carbon, nitrogen, and water are reused and cycled repeatedly.}$

Answer: Energy flows in one direction and is eventually lost as heat, while matter is cycled and reused.

Energy moves one way through an ecosystem and is steadily lost as heat, but the atoms that make up matter are recycled again and again among organisms and the environment.

Question 60 · 2 pts

A mature forest is completely burned in a wildfire, but the soil along with many buried seeds and roots remains intact. The gradual regrowth of the plant community in this area is best described as...

(A) secondary succession ✓
(B) a climax community
(C) primary succession
(D) ecological equilibrium

Worked solution

$\text{Soil and seeds remain, so the area is not lifeless or bare rock.}$

$\text{Succession that begins where soil already exists is secondary succession.}$ Primary succession starts on bare rock with no soil.

$\text{Therefore the regrowth here is secondary succession.}$

Answer: secondary succession

Secondary succession occurs when a community regrows in an area where soil and some life still remain after a disturbance, such as the regrowth after a forest fire.

Question 62 · 2 pts

A small group of deer is introduced to an island. The deer population grows rapidly at first, then levels off and fluctuates around $500$ individuals for many years. The value of about $500$ deer best represents the...

(A) biotic potential of the deer population
(B) carrying capacity of the island for deer ✓
(C) rate of exponential growth
(D) limiting factor acting on the population

Worked solution

$\text{Rapid early growth slows as resources become limited.}$

$\text{The population then levels off and fluctuates around a stable size.}$ Limiting factors hold it near this level.

$\text{This stable maximum the environment can support is the carrying capacity.}$

Answer: carrying capacity of the island for deer

Carrying capacity is the maximum population size an environment can support over time given its limiting factors, shown when the population levels off and fluctuates around a stable value.

Question 9 · 2 pts

The large-scale burning of fossil fuels by humans has increased the concentration of carbon dioxide in the atmosphere. This human activity most directly disrupts which natural process?

(A) the process of meiosis in reproductive cells
(B) the replication of DNA in dividing cells
(C) the flow of energy from producers to consumers
(D) the cycling of carbon between the atmosphere and living organisms ✓

Worked solution

$Carbon normally cycles between the atmosphere, organisms, and long-term storage such as fossil fuels through processes like photosynthesis, respiration, and decomposition.$ carbon cycle

$Burning fossil fuels releases carbon that had been stored for millions of years back into the atmosphere much faster than it can be removed.$

$This disrupts the natural balance of the carbon cycle, increasing atmospheric carbon dioxide levels.$

Answer: the cycling of carbon between the atmosphere and living organisms

Burning fossil fuels rapidly releases stored carbon into the atmosphere, overwhelming natural carbon cycle processes like photosynthesis and contributing to rising atmospheric carbon dioxide levels.

Question 23 · 2 pts

The large-scale burning of fossil fuels by humans has increased the amount of carbon dioxide in the atmosphere. This increase is most directly linked to which environmental effect?

(A) A decrease in the ozone layer caused directly by carbon dioxide molecules
(B) An increase in the amount of oxygen available for cellular respiration
(C) A permanent decrease in global biodiversity within one year
(D) An enhanced greenhouse effect leading to global warming ✓

Worked solution

$Burning fossil fuels releases stored carbon as carbon dioxide gas into the atmosphere.$ Source of CO2

$Carbon dioxide is a greenhouse gas that traps heat energy radiating from Earth's surface.$ Greenhouse gas property

$Higher concentrations of CO2 trap more heat, intensifying the natural greenhouse effect.$ Enhanced effect

$This enhanced greenhouse effect raises average global temperatures, known as global warming.$ Result

Answer: An enhanced greenhouse effect leading to global warming

Fossil fuel combustion adds large amounts of carbon dioxide, a greenhouse gas, to the atmosphere; this enhances the natural greenhouse effect by trapping more heat and is a major contributor to global warming, distinct from ozone depletion, which is caused by different chemicals.

Question 53 · 4 pts · constructed response

A population of deer lives in a forest where the amount of available food is limited. Explain how food availability, as a limiting factor, affects the carrying capacity of the deer population and describe what would happen to the population if the deer number exceeded the carrying capacity.

Model answer: Food availability sets an upper limit on how many deer the environment can support, since not enough food is present to sustain a larger population; this maximum sustainable population size is the carrying capacity. If the deer population exceeds carrying capacity, food will become scarce, leading to increased starvation and competition, which will cause the death rate to rise and the population to decrease back toward the carrying capacity.

Worked solution

$\text{Limiting factor: food supply}$ Identify the limiting resource

$\text{Carrying capacity = max population a limiting factor can sustain}$ Define carrying capacity

$\text{Population > carrying capacity} \Rightarrow \text{food shortage}$ Consequence of exceeding limit

$\text{Increased starvation/competition} \Rightarrow \text{death rate rises} \Rightarrow \text{population declines}$ Population self-regulates back toward carrying capacity

Answer: Food availability sets an upper limit on how many deer the environment can support, since not enough food is present to sustain a larger population; this maximum sustainable population size is the carrying capacity. If the deer population exceeds carrying capacity, food will become scarce, leading to increased starvation and competition, which will cause the death rate to rise and the population to decrease back toward the carrying capacity.

Limiting factors such as food restrict population growth; when a population exceeds the carrying capacity set by that resource, increased death rates from starvation and competition bring the population back down.

Question 31 · 1 pt

In an energy pyramid, only about $10\%$ of the energy at one level is available to the next. This is mainly because most energy is

(A) recycled directly back to producers
(B) converted into new sunlight
(C) stored permanently in the top predator
(D) lost as heat during life processes ✓

Worked solution

$\text{metabolism} \Rightarrow \text{heat loss}$ Respiration releases energy as heat.

$\Rightarrow \sim 10\% \text{ passes up}$

Answer: \text{lost as heat}

Each level uses most of its energy for life processes, releasing it as heat, so only ~10% is stored and available to the next level.

Question 54 · 2 pts

In a food web, hawks eat both snakes and rabbits, snakes eat rabbits, and rabbits eat grass. If a disease suddenly eliminated all of the snakes, what is the most likely immediate effect on the rabbit population?

(A) The rabbit population would immediately become extinct
(B) The hawks would die out because snakes were their only food source
(C) The rabbit population would likely increase at first, because one of its predators has been removed ✓
(D) The grass population would increase because the rabbits would disappear

Worked solution

$\text{Identify the rabbit's predators: snakes and hawks.}$ Removing snakes removes one of two predators.

$\text{Fewer predators on rabbits} \Rightarrow \text{lower predation pressure}$

$\text{Therefore the rabbit population tends to rise, at least initially.}$ Hawks still eat rabbits, so the rise may be limited over time.

Answer: The rabbit population would likely increase at first, because one of its predators has been removed

Removing one predator reduces the predation pressure on its prey, so the rabbit population is most likely to increase at first; food webs show how changes in one population ripple through connected organisms.

Question 56 · 2 pts

In a pond, algae (producers) capture about $100{,}000$ kcal of energy. Zooplankton eat the algae, and small fish eat the zooplankton. Approximately how much of the original energy is available to the small fish (the secondary consumers)?

(A) About 90,000 kcal
(B) About 1,000 kcal ✓
(C) About 10,000 kcal
(D) About 100 kcal

Worked solution

$\text{Transfer 1 (algae to zooplankton): } 0.10 \times 100{,}000 = 10{,}000$ About 10% reaches the primary consumers.

$\text{Transfer 2 (zooplankton to small fish): } 0.10 \times 10{,}000 = 1{,}000$ Another 10% reaches the secondary consumers.

$\text{So about 1{,}000 kcal is available to the small fish.}$

Answer: About 1,000 kcal

Roughly 10% of energy passes to each successive trophic level, so two transfers from the producers leave only about 1% (about 1,000 kcal) for the secondary consumers.

Question 59 · 2 pts

In an energy pyramid, only about $10\%$ of the energy at one trophic level is passed to the next. If the producers in a meadow capture $20{,}000$ kcal of energy, about how much of this energy is available to the secondary consumers?

(A) $18{,}000$ kcal
(B) $200$ kcal ✓
(C) $2{,}000$ kcal
(D) $20$ kcal

Worked solution

$\text{Producers (level 1): } 20{,}000 \text{ kcal}$

$\text{Primary consumers (level 2): } 20{,}000 \times 0.10 = 2{,}000 \text{ kcal}$

$\text{Secondary consumers (level 3): } 2{,}000 \times 0.10 = 200 \text{ kcal}$ Two transfers are needed to reach the secondary consumers.

Answer: $200$ kcal

Each step up an energy pyramid passes only about 10% of the energy to the next level, so reaching the secondary consumers (third trophic level) requires applying the 10% rule twice.

Question 64 · 2 pts

Suppose that nearly all of the green plants in a large region suddenly died, while other organisms continued to carry out cellular respiration. Over the following weeks, what would most likely happen to the atmospheric levels of carbon dioxide and oxygen in that region?

(A) Carbon dioxide would decrease and oxygen would increase.
(B) Both carbon dioxide and oxygen would increase.
(C) Both gases would stay the same because they are unrelated to plants.
(D) Carbon dioxide would increase and oxygen would decrease. ✓

Worked solution

$\text{Photosynthesis removes } CO_2 \text{ and releases } O_2.$

$\text{Cellular respiration releases } CO_2 \text{ and uses } O_2.$

$\text{With plants gone, photosynthesis stops but respiration continues.}$ CO2 is added and not removed; O2 is used and not replaced.

$\text{So } CO_2 \text{ rises and } O_2 \text{ falls.}$

Answer: Carbon dioxide would increase and oxygen would decrease.

Photosynthesis removes carbon dioxide and releases oxygen, balancing respiration; if the producers die, respiration alone raises carbon dioxide and lowers oxygen.

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