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Snails in the Dark: Following Food Through Pond Animals

Grade 7 life science: use pond-jar oxygen data, a tadpole tail under the microscope and a feeding study to model how food is used by cells.

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
12 questions
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Details

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

About this worksheet

What students practice

Students use dissolved oxygen data to show that animal and plant cells use oxygen in cellular respiration.
Students use a food mass budget to model how food is rearranged into body molecules or broken down for energy.

How to use

Read the passage together and trace the two paths in the model (build new molecules or release energy) before students work on the tables on their own.

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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Name Date

Snails in the Dark: Following Food Through Pond Animals

Use dark-jar oxygen data and a tadpole feeding study to model what cells do with food.

The dark jars

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

The Mill Pond Study

1Every fall, Ms. Wren Halvorsen's seventh-grade class at Lakeview Middle School studies Mill Pond, a small pond at the edge of the school grounds. This year the class asked a question about the pond's animals: what happens to their food after they take it in?

2The study began at the microscope. Students placed a young tadpole in a shallow dish of pond water for one minute, looked at its thin, see-through tail under low power and then returned it to its tank. They watched red blood cells squeeze, one at a time, through tiny blood vessels that run right beside the tail's muscle cells.

3Ms. Halvorsen shared a model of how an animal uses food. In digestion, large food molecules are broken down into smaller ones, such as sugars and amino acids. The blood carries these small molecules, along with oxygen taken in at the gills, to cells all over the body. Inside a cell, the small molecules can go two ways. Some are rearranged and joined into new large molecules, such as proteins and fats, that become part of the growing body. Others react with oxygen in cellular respiration, which releases energy the cell can use and produces carbon dioxide and water.

4Next, the class set up four sealed 500 mL jars of pond water, as shown in Table 1. Jars 1 and 2 each held six pond snails of about the same size, Jar 3 held 5 g of a pond plant called elodea, and Jar 4 held only pond water. Jar 2 sat in a cooler with ice packs to keep it at 10 °C, while the others stayed at 20 °C. All four jars were kept in complete darkness for 3 hours, and a dissolved oxygen probe measured the oxygen in the water at the start and at the end.

5Finally, the class raised 20 tadpoles in an aquarium for 14 days and fed them dried algae pellets. They weighed the pellets before each feeding and removed and weighed any pellets the tadpoles did not eat. Twice a week they siphoned out the droppings, which Ms. Halvorsen dried and weighed. At the start and the end, the class weighed the group and used a chart from a university lab to estimate its dry mass, the mass left when water is not counted. Table 2 shows the results.