Activity 3.3: Observing Plants in the Light and Dark (60 min over 2 days)

Target Student Performance

Students observe how plants affect BTB in the light and dark, identify patterns in data, and reach consensus with other groups about their results.

Resources You Provide

Radish plants (either in tubes (GL) or containers (PT) from the Pre-Lesson. Note: 3-4 tubes or 1-2 containers will be plenty for each experiment replicate.
Dark box, thick black trash bag, or very dark closet (1 per class)
Fluorescent grow light or sunny windowsill (1 per class)
Label (1 per group student group)
Petri dish with blue BTB (1 per container/student group)
Petri dish with yellow BTB (1 per container/student group)
Sealable 6.8 liter (or 29 cup) container (1 per group)
(From previous lesson) 3.1 Predictions and Planning Tool for Plant Investigations with student answers

Resources Provided

Recurring Resources

BTB Color Handout

Setup

Assign each group of students a treatment (light or dark). For each group, select growing radishes (3-4 GL tubes or 1-2 PT containers) that were planted in the Plants Unit Pre-Lesson. For each group, provide 1 sealable 6.8-liter (29 cup) container, one Petri dish of blue BTB, one Petri dish of yellow BTB, and a label. Prepare enough space under a grow light or in a sunny windowsill for the “plants in the light” containers, and enough room in a dark closet for the “plants in the dark” containers. Optionally, print a few copies of the BTB Color Handout for students to use as a color reference.

Refer to the BTB Information and Instructions Handout for information about preparing BTB.
Prepare your computer and projector for the 3.3 Observing Plants in the Light and Dark PPT.
Print one copy per student of the 3.3 Observing Plants in the Light and Dark Worksheet.
Print one copy of the 3.3 Plants in the Light and Dark Class Results 11 x 17 Poster.

Directions

1. Use the instructional model to show students where they are in the course of the unit.

Show slide 2 of the 3.3 Observing Plants in the Light and Dark PPT.

2. (Day 1) Have students prepare for the plants in the light and dark investigation.

Follow the instructions in Part A of the 3.3 Observing Plants in the Light and Dark Worksheet.

Slide 3 of the 3.3 Observing Plants in the Light and Dark PPT has pictures of the setup for the investigation.
Let students re-watch the first three minutes of the Carbon TIME Growing Plants Video. This part discusses the questions and shows the setup for the investigation.
If you have multiple classes, each class can set up one or two 6.8 liter sealable plastic containers in the light and one or two 6.8 liter sealable plastic containers in the dark. Note: large sealable containers with room for the BTB and plants will do; the container does not need to be this exact size.
If you have a single class, then each group of four students can set up one 6.8 liter sealable plastic container, with half the 6.8 liter sealable plastic containers going into the light and half going into the dark.

3. (Day 1) Leave the containers overnight.

Leave the lights on for the 6.8 liter sealable plastic containers in the light.

4. (Day 2) Have students observe and record results.

Each student should be responsible for observing one 6.8 liter sealable plastic container in the light and one 6.8 liter sealable plastic container in the dark and recording their observations in Part B of the 3.3 Observing Plants in the Light and Dark Worksheet.

Show slide 4 to allow students to see the possible colors of BTB.

Record results for all the containers on the 3.3 Observing Plants in the Light and Dark Class Results 11 x 17 Poster.

5. Have students compare data between groups and look for patterns.

Show slide 5. Discuss the general patterns the class sees for all the containers, and have students record summaries of those patterns in Part C of the 3.3 Observing Plants in the Light and Dark Worksheet. (In the light, yellow BTB turns blue. In the dark, blue BTB turns yellow.)

Show the second part of the Carbon TIME Growing Plants Video, after the first intermission where Darryl and Nina discuss the results of the Plants in the Light and Dark investigation (begin at about 2:30).
Ask the class to compare their results to Darryl and Nina’s results, pausing the video when the data are shown. Ask students if they see the same patterns, any similarities and/or differences. Ask them why there may be similarities and/or differences.
If your students’ plants in the light dark investigation fails to provide the expected BTB color changes (which could happen for a variety of reasons, including too much NaOH in the BTB or too high concentration of BTB), use the Carbon TIME Growing Plants Video to help them compare their results with the desired results. Use this as a starting point for a conversation and ask the students why the results are different.

6. Revisit predictions from the previous activity.

Show slide 6. Ask students to retrieve their completed tools from the previous activity: 3.1 Predictions and Planning Tool for Plant Investigations. Have them compare the predictions they made with the results of the investigation. Which predictions were correct? Which predictions were incorrect? What questions do they still need to answer?

Remind students that food is necessary for plants to be able to grow and move. Tell students that they will use the data that they collected here to help them to be able to explain two processes that relate to plants growing: photosynthesis and cellular respiration.

7. (Optional) Partially complete the Evidence-Based Argument tool.

If you plan on teaching Lesson 4 while waiting for students’ radish plants to dry (see the Plants Unit Front Matter file for more information on making this choice), be sure to have students partially complete the 3.5 Evidence-Based Arguments Tool for Plants first. See Activity 3.5 for more guidance on completing this step.

8. Have students complete an exit ticket.

Show slide 7 of the 3.3 Observing Plants in the Light and Dark PPT.

Conclusions: What did you observe during the investigation?
Predictions: What do you think happened to the CO₂ that the plants absorbed in the light?
On a sheet of paper or a sticky note, have students individually answer the exit ticket questions. Depending on time, you may have students answer both questions, assign students to answer a particular question, or let students choose one question to answer. Collect and review the answers.
The conclusions question will provide you with information about what your students are taking away from the activity. Student answers to the conclusions question can be used on the Driving Questions Board (if you are using one). The predictions question allows students to begin thinking about the next activity and allows you to assess their current ideas as you prepare for the next activity. Student answers to the predictions question can be used as a lead into the next activity.

Assessment

Use the class discussion to interpret how successful your students are at identifying patterns in the class data. Use the 3.3 Grading the Observing Plants in the Light and Dark Worksheet to determine if your students had any trouble with data collection.
During this activity, note students’ success in observing changes in BTB. Also note students’ ability to reach a consensus about patterns in data and how they interpret results.
The discussion in step 5 can be helpful for informal assessment in two ways: 1) it can help you assess your students’ skills in identifying sources of error and finding patterns in data, and 2) it can help you assess how well students identify the limits of the evidence. Do they recognize that the investigation does not fully answer the Three Questions?

Tips

Discuss threats to accuracy of measurement.
Check to see if students can identify unanswered questions from the investigation.

Differentiation

Strategic grouping with strong speakers
Have students explain aloud the observation plan after reading it
Compare class data orally and on the spreadsheet

Modifications

Conduct the investigation as a demonstration if you are short on time or resources.
Parts 1 and 2 of the Carbon TIME Growing Plants Video show the investigation and patterns of results. While we do not recommend this, if time is not available, students can watch the video instead of doing the investigation.
Have students develop the experimental design on their own using the tools provided. For example, students may choose to set up a control treatment as a container with BTB and no plants.
Put the “plants in the dark” container inside an opaque plastic bag instead of in a dark closet.

Extending the Learning

Have students compare photosynthesis rates between plants in the sun and plants under a grow light.