Lab22 Elodea & Snails 0910 - Orange County Public Schools

OCPS Essential Labs
Grade 6 Life Science

Elodea & Snails

Big Idea 18: Matter and Energy Transformations
Benchmarks: SC.8.L.18.1 and SC.8.L.18.3
Objective: Conduct an experiment that demonstrates the need for carbon dioxide in the process of
photosynthesis and describe and investigate how cellular respiration breaks down food to provide energy
and then releases carbon dioxide.

Key Question: How is carbon dioxide balanced by the chemical reactions of photosynthesis and cellular
respiration?

Background Information:
Elodea is a genus of aquatic plants often called the waterweeds. Elodea, also known as Anacharis, is
native to North America. It is also widely used as aquarium vegetation. It can be used for science
experiments in classrooms as it can show how plants use carbon dioxide with the usage of bromothymol
blue (BTB). Pond snails are commonly used by aquarium enthusiasts to maintain a clean habitat for their
plants and fish. The prolific breeding habits of most fresh water snails generally keep the purchase price
reasonable. Expect to only pay a few dollars for yours.

Preparing for the Lesson Teaching Tips: Timeframe:

• Both the aquatic snails and the Elodea (also known as Anacharis) are available at • Safety
local pet stores. Call your nearest Petco or PetsMart to inquire about availability Review and
and freshness of both. Setup will
take ONE
• For the jars, you can check with your local grocery store or big box store (e.g., 50-minute
Wal-Mart for canning jars with lids. You will only need small, wide-mouth jars, class period.
approx. 4 to 8 ounces).
• Data
• If you have limited funds, you can do this lab as a demonstration with just 8 jars, 8 collection will
snails, and 8 sprigs of Elodea and still have students collect data and respond to be “bell work”
the questions. for the next 4
to 5 class
• You can dispose of the BTB and water solution from the jars by pouring them days.
down a drain and running the water for approximately 3 to 5 minutes.

Safety Precautions:

• Review general lab safety precautions with emphasis on glassware safety. Read and review the
MSDS for bromothymol blue with your students.

STEP 1 - ENGAGE: Materials

1. Demonstrate how the bromothymol blue solution is a pH indicator by • See student lab sheet
adding drops of dilute acid or base to a dilute solution of bromothymol for detailed materials
blue. list.

2. Demonstrate how carbon dioxide is an acid by inserting a straw into a
beaker/flask of the Bromothymol blue solution and blowing until the
solution changes color from blue to green.

3. In order to show how the solution will return to normal color (blue) after
the carbon dioxide has left, you can put a lid on the beaker/flask and
shake it to release the gas.

OCPS Essential Labs
Grade 6 Life Science

STEP 2 - EXPLORE:

See student lab sheet for step-by-step procedure

STEP 3 - EXPLAIN:

See student lab sheet

STEP 4 - ELABORATE:

See student lab sheet

STEP 5 - EVALUATE:

1. What do living things need to survive?
2. Why are photosynthesis and cellular respiration essential processes for

living organisms?
3. How is carbon recycled through the environment?

ENGAGE Name____________________________________
Date_____________________________________
Class Period______________________________

Elodea & Snails

Key Question:
How is carbon dioxide balanced by the chemical reactions of photosynthesis and cellular respiration?

Student Predictions/Ideas: Record your initial ideas about the answer to the key question.

EXPLORE Safety Precautions:
• Make sure to use caution when handling glassware.
• Make sure to report any accidents quickly to your teacher.
• Make sure to review safety information on bromothymol blue (BTB); the chemical you will be using in

this lab.

Materials:
• Lab sheet (per student)
Per Table:
• Aquatic Snails, need 8
• Elodea Sprigs (approximately 2 inches long), need 8
• bromothymol blue (BTB) 0.04% Aqueous Solution
• Glass Jars with lids, need 8
• Medicine Dropper
• Spring Water
• Sharpie Permanent Marker
Per Class:
• Grow Light set to run for 24 hours

Procedure:

1. Using the marker to number your jars from 1 to 8 and to put the first names of your lab partners on
the jar and then fill each of the jars about 4/5 full of spring water.

2. Use the medicine dropper to add enough of the BTB solution to each jar to obtain a green color
(about 2-3 mL).

NOTE: The snails and the Elodea will not be harmed by the BTB solution and can be reused or kept in a
classroom aquarium for future usage.
3. Add the following items to each indicated bottle and screw the lid on tightly.

Bottle # Contents
1 and 5
2 and 6 2 Sprigs of Elodea
2 Snails
3 and 7 2 Sprigs of Elodea AND 2
Snails
4 and 8 Nothing - this is the control

4. Place bottles 1 – 4 in the light station your teacher has designated for your class and place bottles
5 – 8 in the dark (inside a cabinet or a drawer for example).

5. Record your observations in the next section.

Name____________________________________
Date_____________________________________
Class Period______________________________

Observations & Data:

Your bell work for the next 4 to 5 days is to make observations about the color and contents in all 8 of
your jars. One person from each group should do this quickly at the beginning of each class.

Day # Observations

0 (Setup Day)

1

2

3

4

5 (Optional)

Data Analysis:

Which jar(s) had the most drastic changes over the course of the experiment? Explain your answer(s) in
detail.

EXPLAIN

ELABORATE Name____________________________________
Date_____________________________________
Class Period______________________________
Explanation of Key Question Based on Evidence:
How is carbon dioxide balanced by the chemical reactions of photosynthesis and cellular respiration?

Reflection:
1. How are the chemicals necessary for photosynthesis related to the chemicals necessary for cellular

respiration?

2. After analyzing the results of this lab, what do you think would be the effect on the Earth if all the
producers were to suddenly disappear?