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A Steaming Leaf Pile: Cellular Respiration in a City Park

Grade 7 life science: analyze a park compost pile's temperatures, a carbon dioxide jar test and a year's mass data to model how decomposers break down and rebuild food.

Grade 7ScienceInteractive · Printable

Aligned toMS-LS1-7

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What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
10 questions
Classroom-ready

Details

Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Short answer

About this worksheet

What students practice

Students use temperature and carbon dioxide data to show that decomposers release energy from food molecules.
Students explain where the mass of rotting leaves goes using a respiration model.
Students identify evidence that decomposers also build new molecules as they grow.

How to use

Read the model in paragraph 2 aloud and connect it to a time students saw steam rising from a leaf or mulch pile, then let students work through the three data sets.

Curriculum

NGSS standard covered

MS-LS1-7

Model how food is broken down and rearranged in cellular respiration to release energy and build new molecules.

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A Steaming Leaf Pile: Cellular Respiration in a City Park

Follow fall leaves through a year in a park compost pile.

Fall and winter: the pile heats up

Read the passage and study Table 1. Then answer the questions.

Steam on a Frosty Morning

1Every November, the crew at Bramblewood Park rakes the fallen leaves from its lawns and paths. Behind the maintenance yard, they mix the leaves with grass clippings from the last mowing of the year and pile them in a long row about 2 meters high, called a windrow. Seventh grader Ruth Abebe volunteers with the park ecologist, Mr. Callum Fitzgerald. On a frosty January morning, she was surprised to see steam rising from the top of the windrow while the lawns around it were white with frost. By spring the windrow is much lower, and by the next fall it has become dark, crumbly compost.

2Mr. Fitzgerald explained that the pile is full of decomposers: huge numbers of bacteria and fungi, plus worms and insects near its edges. Decomposers break large molecules in the leaves, such as cellulose, which is made of many linked sugar units, into small sugar molecules. In their cells, cellular respiration combines the sugars with oxygen, and the atoms are rearranged into carbon dioxide and water. This releases energy. The decomposers use some of the energy and some of the small molecules to build new cell parts as they grow and divide, and much of the energy is given off as thermal energy.

3Ruth and Mr. Fitzgerald pushed a thermometer with a 1-meter metal stem into the center, or core, of the pile once a week and also recorded the air temperature (Table 1). Right after the week 4 reading, a crew member turned the pile with a small loader, breaking it apart and piling it up again so that fresh air filled the spaces between the leaves. In week 0, a drop of water squeezed from the pile held only a few bacteria under the school microscope. In week 2, a drop held about 50 times as many. By week 3, white threads of fungi had spread through many of the leaves.