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Sea Lettuce in the Light: Photosynthesis in a Marine Lab

Grade 7 life science: analyze sealed-jar oxygen data and growth data for sea lettuce to explain how photosynthesis cycles matter and moves energy.

Grade 7ScienceInteractive · Printable

Aligned toMS-LS1-6

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What’s included

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

Details

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

About this worksheet

What students practice

Students analyze jar data to explain the role of light, carbon dioxide and oxygen in photosynthesis.
Students trace how matter cycles and energy flows from light into sugar and on to a consumer.

How to use

Use after introducing the photosynthesis word model; have students predict the oxygen change in each jar before they read Table 1.

Curriculum

NGSS standard covered

MS-LS1-6

Explain how photosynthesis cycles matter and moves energy into and out of organisms.

Preview

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Name Date

Sea Lettuce in the Light: Photosynthesis in a Marine Lab

Use jar and growth data to trace matter and energy through a green alga.

The jar investigation

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

From the Rocky Shore to the Lab Bench

1In October, the marine biology elective at Harborview Middle School took a field trip to a rocky beach at low tide. On the wet rocks, the students found bright green, paper-thin sheets of sea lettuce, a kind of green alga. Sea lettuce often grows where the rocks are covered by water at high tide and exposed at low tide. Like plants, algae have chloroplasts and carry out photosynthesis. With a park ranger's permission, their teacher, Ms. Delgado, collected a small amount for the school's marine lab.

2Back in the lab, the class set up three clear jars, each filled with 500 mL of seawater from the same tank. Jar 1 held 5 g of sea lettuce and sat under a lamp. Jar 2 held 5 g of sea lettuce and was covered with a dark box. Jar 3 held no sea lettuce and sat under the lamp. The jars were sealed and kept in a water bath at 15 °C. Students measured the dissolved oxygen in each jar with a probe at the start and after 4 hours, and used a second probe to compare the carbon dioxide. Their results are in Table 1.

3The rest of the sea lettuce went into a lab tank with a lamp that was on 12 hours a day. The tank held seawater with a small amount of dissolved nutrients but no sand or soil. Each week, students lifted out the sea lettuce, blotted it dry and weighed it (Table 2 in Section 2). They also checked that the water stayed near 15 °C. A periwinkle snail that lived in the tank grazed on the sea lettuce.

4Scientists often summarize photosynthesis with a word model: carbon dioxide + water → sugar + oxygen, using light energy. Algae and plants use the sugar they make as food. Snails and many other animals that graze on algae get their food from the algae they eat.