Lesson 4 of 12
Objective: SWBAT define and measure transpiration of a plant over a given time.
This activity works best on a sunny day, and you might want to try it yourself on a few plants so you know what to expect.
I ask my class to discuss how they know plants are living things. This activates their prior knowledge as well as gives them an opportunity to hear a variety of viewpoints. Then they share out and they record it on the board. If they don't mention it, I ask them if plants breathe. Whatever their response, I ask how they know, and ask them to tell a partner. This gives practice supporting claims with evidence.
I then have them write the focus question "How can we measure the respiration of plants?" on the board, and have them write it in their science notebooks. Right away, I also have them write down respirate with a definition in their science notebooks so that they can refer back to it when needed. From this point on, I consistently use the word "respirate" instead of "breathe" to help my students build a precise scientific vocabulary.
Then I ask them where they think the water goes in a plant. I show them a short video on transpiration. I then tell them we will be attempting to measure how much water plants transpire over a given period by capturing the water that travels through the leaves in special transpiration collection containers (plastic bags), and demonstrate how to seal the bag around the leaf, and seal it up tightly with tape on My Volunteer Plant.
Engagement Part 1
I give each pair a gallon size plastic bag, and remind them of expectations for outside science. I have my students work in pairs because it's good to have extra hands when sealing bags on. I take them out, and tell them to bag some leaves, and seal them up tightly. You could have them do all different types of plants and compare, or all do the same plants and compare results. I left it open, and most of my class chose the same plant, because that's what they could reach. After about 5 minutes, I take them back in and have them write a prediction in mL for how much water they will find in the bag.
Engagement Part 2
Later that afternoon, I take my class out to collect their bags. They can see right away that some bags have considerably more water than others, and they start coming up with explanations right away, such as being in the sun, or not having it taped tightly.
After they collect their bags, I have them bring them back to the classroom.
My plan was for them to measure the volume of water with graduated cylinders, but there was less that 5 mL of water in each cylinders, so there were a lot of 0's recorded. If you have digital scales available (I didn't), finding the mass is a much more accurate way because you don't have to pour the water out.
After they recorded their results, I have a few share their results, then independently write down as many ideas as possible that might explain why the results varied so much. When I checked science notebooks, I looked for at least 3 possibilities (i.e. not taping correctly, being in the sun or shade, different plants). While there are some other concerns with this student's entry, I was pleased to see on the Student Notebook Sample that the student wrote down "fog on the bag" because it is evidence that they are recognizing all of their observations as valuable data.