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Light at Every Depth: Photosynthesis in a Quarry Pond

Grade 7 life science: analyze pond oxygen and algae counts at four depths and a waterweed bubble test to explain how photosynthesis moves matter and 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
12 questions
Classroom-ready

Details

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

About this worksheet

What students practice

Students analyze depth data to link light, algae and dissolved oxygen in a pond.
Students interpret a bubble test to explain how light affects the rate of photosynthesis.
Students explain how light energy is stored in sugar and passed to consumers.

How to use

Read the passage together and make sure students can read both tables before they start. Section 3 works well as a pair discussion before students write the claim on their own.

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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Light at Every Depth: Photosynthesis in a Quarry Pond

Use pond samples, microscope counts and a bubble test to explain where the pond's oxygen and food come from.

The pond at four depths

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

The Quarry Pond Study

1Stonecrest Botanical Garden has a pond that fills an old stone quarry. It is small, but it is about 4 m deep in the middle, and on calm summer days its water forms layers: warmer water near the top and colder water near the bottom. Henrik Lindqvist's seventh-grade class, taught by Mr. Tomasz Kowalczyk, visits the pond each fall to study the living things in it.

2On a sunny September afternoon, a garden staff member rowed to the middle of the pond with a water sampler and filled one bottle at each of four depths. At each depth she also lowered a light meter in a waterproof case and recorded the light as a percent of the light at the surface. A probe measured the water temperature and the dissolved oxygen. Cold water can hold more dissolved oxygen than warm water, so the class predicted that the deep water would have the most oxygen.

3Back in the classroom, students placed one drop from each bottle on a slide and counted the green algae cells in the field of view at the same magnification. Each count in Table 1 is the average of five drops. Under high power, every algae cell held green chloroplasts. A few water fleas, tiny animals that eat algae, swam through some of the drops.

4Next, the class tested a sprig of waterweed, a common pond plant, in a tube of pond water. The tube stood in a water bath that kept it at 20 °C, and the same sprig was used for every trial. A student placed an LED lamp, which stays cool, at different distances from the tube and counted the tiny bubbles rising from the cut end of the stem for one minute. Each count in Table 2 is the average of three trials. Last, the lamp was switched off and the tube was covered.

5Scientists often summarize photosynthesis as carbon dioxide + water → sugar + oxygen, using light energy that chloroplasts capture. Algae and plants use the sugar as food and build it into their bodies. Like animals, they also carry out cellular respiration day and night, using oxygen to break down sugar and release the energy stored in it.