Worksheet

No Plants in the Dark: Matter and Energy in a Bat Cave

Grade 7 life science: use cave floor surveys and an energy model to show how matter cycles and energy flows through a bat cave's guano community.

Grade 7ScienceInteractive · Printable

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1 NGSS standard
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11 questions
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Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Sorting, Short answer

About this worksheet

What students practice

Students use survey data to trace where the matter and energy in a cave community come from.
Students calculate how much energy passes from one level of a food web to the next.
Students explain why matter can cycle back to producers while energy must keep entering an ecosystem.

How to use

Read paragraph 2 together and draw the model on the board, starting outside the cave. Students then use both tables on their own and compare their open responses with a partner.

Curriculum

NGSS standard covered

MS-LS2-3

Model how matter cycles and energy flows among producers, consumers and decomposers in an ecosystem.

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Name Date

No Plants in the Dark: Matter and Energy in a Bat Cave

Model how matter and energy reach a cave community that has no producers of its own.

Summer and winter under the roost

Read the passage and Table 1, then answer the questions.

Life Under the Roost

1Every spring and summer, about 20,000 gray bats live in Hollow Rock Cave in the Ozark hills of Missouri. Most are females that raise one pup each in a large roost on the ceiling of a dark chamber. Each evening the bats fly out to hunt mayflies, moths, beetles and other night-flying insects over the river and the forest, and they return before dawn. In the fall, the colony leaves to hibernate in a colder cave many kilometers away, and the chamber stays empty until spring. The chamber stays near 13 °C all year. Seventh grader Theo Lindahl joined state cave biologist Dr. Marguerite Esposito on two survey trips, one in May, before the pups were born, and one in January. The team stayed only a short time, kept quiet and used dim red lights so they would not disturb the bats.

2No green plants grow in the dark chamber, so there are no producers there. Dr. Esposito's model starts outside the cave: plants use energy from sunlight to make sugars from carbon dioxide and water, insects eat the plants, and bats eat the insects. Under the roost, the bats' droppings, called guano, pile up on the floor. Fungi and bacteria break down the guano, and tiny mites, springtails and guano beetles eat the guano and the fungi growing on it. Cave spiders and centipedes hunt these small animals. Every living thing in the model uses some of the energy in its food for its life processes, and that energy ends up as heat.

3On each trip, the team took measurements under the roost and at a spot on the same chamber floor 50 m away, where no guano falls. They measured the dry mass of guano added each week, counted the small animals in floor samples and measured the carbon dioxide in the air just above the floor (Table 1). Air moves slowly through the cave and out of its entrance.

4Dr. Esposito also used measurements from other studies of gray bats to build an energy model for one May night (Table 2).

Table 1. Hollow Rock Cave Floor Surveys (guano as dry mass)
Place and month	Guano added (kg/week)	Mites, beetles/100 cm²	Spiders/centipedes/10 m²	CO₂ above floor (ppm)
Under roost, May	30	85	12	2,400
Under roost, January	0	17	4	900
No-guano spot, May	0	2	1	600
No-guano spot, January	0	2	1	600

Under the roost, there were times as many mites and beetles per 100 cm² in May as in January.

Use paragraph 2. Where did the energy in the guano beetles' food first come from?

A. Minerals in dripping water, which guano beetles turn into food energy
B. Carbon dioxide in the cave air, which fungi use the way plants use it
C. Sunlight captured by plants outside, passed through insects and bats
D. Heat flowing up from deep rock, which cave fungi capture to make food

Under the roost, the small animals and their predators were much fewer in January than in May. Which explanation fits the passage and Table 1 best?

A. With the bats gone, no new guano arrived, so there was less food for the small animals and their predators.
B. The chamber got much colder in winter, which killed most of the small animals on the floor.
C. The small animals dropped at the no-guano spot too, so the whole chamber changed in the same way.
D. The spiders and centipedes ate most of the mites and beetles, so the predators grew in number by January.

The carbon dioxide just above the floor was highest under the roost in May. Which explanation fits the model and Table 1 best?

A. The guano gave off carbon dioxide on its own as it dried, without any living things involved.
B. Carbon dioxide blew in through the entrance on warm May nights and settled under the roost.
C. Guano beetles took in carbon dioxide from the air to build their bodies, so it built up around them.
D. Fungi, bacteria and small animals broke down guano in respiration, which released carbon dioxide.

Which path could a carbon atom in the guano follow to end up inside a bat again?

A. Guano → CO₂ from decomposers → leaf sugar in a tree → moth → bat
B. Guano → heat from decomposers → leaf sugar in a tree → moth → bat
C. Guano → minerals in cave water → guano beetle → cave spider → bat
D. Guano → CO₂ from decomposers → bat breathes it in → bat muscle

The energy model

Use Table 2 and paragraph 2.

Table 2. Energy Model for One May Night
Where the energy goes	Energy (kJ per night)
Insects eaten by the colony	480,000
Used by bats' cells; leaves as heat	384,000
Built into the bats' bodies	19,200
Left in the guano	76,800
Eaten by mites, springtails, beetles	7,680
Eaten by spiders and centipedes	768

What percent of the energy in the insects the colony ate was left in the guano? %

The mites, springtails and beetles took in times as much energy as the spiders and centipedes that eat them.

Under the roost in May, there were far fewer spiders and centipedes than mites and beetles. Which explanation fits Table 2 best?

A. Most of the energy in the mites and beetles passes on to the predators, so a few predators get all they need.
B. Only a small part of the energy in the prey reaches the predators, because most is used and lost as heat.
C. The spiders and centipedes eat the guano too, so they compete with the beetles and lose.
D. The predators get their energy from the cave air, so they do not need many prey animals.

Sort each event by what it does to matter in the cave.

Bats return before dawn with insects in their stomachs.Guano falls from the roost onto the chamber floor.Carbon dioxide from the guano pile drifts out of the entrance.A guano beetle eats fungi growing on the guano.Rainwater seeping through the ceiling carries bits of dead leaves from the forest above.A cave spider catches and eats a springtail.

Brings matter into the cave	Moves matter around inside the cave	Carries matter out of the cave

10.

Suppose the gray bats stopped using Hollow Rock Cave. Based on the data, what would most likely happen under the old roost over the next few years?

A. The small animals would increase, because no bats would be roosting above them.
B. The guano pile would stay the same size, because no decomposers live in the dark.
C. Plants would start to grow on the guano and become the new producers of the cave.
D. The guano would run out, and the floor animals would drop toward the no-guano spot's counts.

11.

A cave visitor says, “The guano community recycles everything it needs. Even if the bats never came back, it could keep going forever.” Do you agree? Write a claim, use evidence from Tables 1 and 2, and use the model in paragraph 2 to explain what happens to matter and to energy in the cave.