Adapting to the Environment, Using Leaves to Introduce Students to Ecophysiology

Contributor
Type Category
Instructional Materials
Types
Lesson/Lesson Plan
Note
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be “fully aligned,” the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.

Reviews

Description

This article is in the October 2014 edition of The Science Teacher. The author engages students by posing the question of whether the leaves at the top of a tree are different from the leaves at the bottom of the tree. The students discuss what environmental differences might be at the top versus the bottom of a tree. The teacher is encouraged to assist the students in thinking about light availability, temperature and water loss. The students are then asked to formulate a hypothesis relating to differences between the groups of leaves using the “if- then” format and to provide an explanation as part of the hypothesis. The lesson engages students as they collect leaves, use measuring tools and proper units, work with microscopes, collect data, analyze their data, and share their data with classmates as they work to evaluate their hypothesis. The students use all of these skills to analyze characteristics of tree leaves and compare their data to the leaves ecological performance. Students have an opportunity to conduct an investigation in the same manner that scientists do. The students and the teacher go outside to cut and collect leaves and make other observations of the trees in the area.  After returning to the classroom students examine leaves for differences in leaf surface area, thickness and stomata density and are challenged to construct a data table to organize the various characteristics observed.  Students are encouraged to work in small groups to record weights, trace their leaves, make a cut out model and learn to use a modified formula for leaf density. This formula that relates the surface area, weight and thickness of leaves is used by botanists to compare their leaves.  Students make molds of their leaves using clear nail polish and tape to help in determining stomata density. Using microscopes, students examine their leaf molds and count the number of stomata within the field of view. Class data are collected and compared. Additional supporting resources for this article are provided at https://www.nsta.org/highschool/connections/201410Instructions.pdf. This lesson is intended and appropriate for high school students. 

Intended Audience

Educator and learner
Educational Level
  • High School
Language
English
Access Restrictions

Available by subscription - The right to view and/or download material, often for a set period of time, by way of a financial agreement between rights holders and authorized users.

Performance Expectations

HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.

Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.

This resource appears to be designed to build towards this performance expectation, though the resource developer has not explicitly stated so.

Comments about Including the Performance Expectation
The author states that this activity is aligned to the performance expectation HS-LS1-5 directly relating to photosynthesis. While the function of leaves and stomata is directly related to photosynthesis, the emphasis of this article is more on the structure of the leaves relating to placement on the tree and the number of stomata per leaf than the specialized cells and photosynthesis. Leaf placement is dependent on the geographical region, temperature and humidity. Teachers will need to be proactive to be sure students are fully engaged with the disciplinary core ideas found within the life science performance expectations. Student will draw on data evidence collected during their analysis of the leaves and teachers may need to present additional learning experiences such as determining surface area and reviewing density prior to or within this lesson.

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
This lesson is centered on collecting and analyzing data from a living organism as evidence for the relationship of the location of leaves and structural characteristics of the leaves. This provides students with an authentic task and students are challenged to decide what data they need to collect. The connections to collecting and analyzing data could be strengthened by providing students the opportunity to share their initial calculations of leaf density and/or data from microscopic observations with their peers and discuss any difficulties or discrepancies they may be seeing. Making their thinking explicit and sharing their thinking with others will help to deepen student understanding and engagement. Students enjoy going outside, and this lesson should peak their natural curiosity. The author cites four scientific and engineering practices 1) developing and using models 2) using mathematical and computational thinking 3) analyzing and interpreting data and 4) planning and carrying out investigations that this lesson addresses. All four of these practices are part of this lesson. While all of these practices are definitely included, students constructing explanations based upon the evidence collected and analyzed stands out, and it is important for teachers to emphasize this practice.

Disciplinary Core Ideas

This resource is explicitly designed to build towards this disciplinary core idea.

Comments about Including the Disciplinary Core Idea
Teachers will need to be sure students have background understanding of the role of stomata in gas exchange in leaves and explicitly CO2 used in photosynthesis. Students must also be able to manipulate measurements into a formula for comparison of leaf surface area and weight and the number of stomata per field of view in their mold samples viewed with the microscope and may need special assistance here depending on comfort with mathematics and microscopes. A fairly easy video clip of photosynthesis is found at https://www.youtube.com/watch?v=uixA8ZXx0KU , the Amoeba Sisters Photosynthesis and may be appropriate for an introduction to this lesson or as a short review of photosynthesis. This lesson has strong emphasis on data collection and analysis. The author provides background information and encourages teachers to provide an opportunity for students to do some research relating leaf location and size and provides some references as well. The article does provide details of student data collections and manipulation and teachers will want to pay special attention to where students may have difficulty and monitor group progress throughout the lesson.

Crosscutting Concepts

This resource is explicitly designed to build towards this crosscutting concept.

Comments about Including the Crosscutting Concept
Understanding and application of structure, in this case surface area and depth of leaves and the number of stomata/field of view to determine density of stomata and the function of gas exchange as related to light capture and overall leaf function can be a difficult concept for students. Teachers will need to help students make connections of each concept as related to photosynthesis This includes making connections between light capture, CO2 collections, water loss and leaf placement in trees. A handout that helps students build understanding of these connections is included in the On the Web link. Additional resources for teacher background are provided by the author and teachers are encouraged to utilize these resources. Focusing on the connections to the crosscutting concept will maximize student learning in relation to the targeted Disciplinary Core Idea and Performance Expectation. Teachers should also consistently challenge students to use concepts of structure and function as the students make conclusions based on their experimental data.

Resource Quality

  • Alignment to the Dimensions of the NGSS: This lesson is grade appropriate for high school and may be used effectively to engage students in exploring the relationship between the structure of the leaf—in this case specifically the number of stomata and their density—to the phenomena of photosynthesis. This lesson incorporates the three dimensions of the Next Generation Science Standards by combining the Disciplinary Core Idea with the Crosscutting Concepts and the Performance Expectations. The lesson resources do include instructional materials that directly relate to the NGSS practices. However, explicit connections between the Crosscutting Concepts, Performance Expectation and Disciplinary Core Ideas are not given so teachers will need to emphasize each of those in their own lesson. Asking generative questions to make those connections is encouraged.

  • Instructional Supports: Some teachers may not have adequate background or familiarity with this specific topic to implement this lesson. Guidance is provided throughout the article as well as references cited at the end of the article for the teacher to utilize to increase their comfort with this lesson. The connections to the living organisms in the students' own environment and the connection to the process of the concepts involving photosynthesis at the high school level make the extra time and effort investment by the teacher worthwhile because students have an opportunity to do an investigation in the same manner that scientists do and student enthusiasm will be evident. The author encourages the teacher to begin this lesson with a challenge question that will also engage students. Cautions and possible student misconceptions are addressed and ideas for different levels of assessment are included in the lesson. The on-line resources provided in the aforementioned On the Web link provided in the article are well done and helpful. Included are pre-lab questions, background information, directions for collecting leaves and necessary calculations, a data sheet, and analysis and conclusion questions. The second resource outlines the ecophysiology of the leaves. Another resource specifically provides questions relating to photosynthesis and leaf placement. The students are asked to contemplate how plants manage the trade-offs between light capture, CO2 collection and water loss, which helps students to contemplate leaf placement and size. In the additional resources, the author makes suggestions of how to collect and store leaves, provides a possible data collection page and questions for analysis and conclusions are included. Throughout this lesson students will need support as they measure and weigh their leaves and as they manipulate their data into a usable form with the provided equation. Teachers will need to be astute in their questioning to help students be successful. The author mentions that students often want to use surface area instead of using density of stomata. Students made need assistance to successfully measure leaves to determine leaf thickness. The correct way to solve the problem using the formula for leaf density may prove challenging to some students and teachers will need to assist any students having difficulty. A lesson on measuring leaf external dimensions and weight as well as determining answers using the formula maybe helpful before students work with the leaves they collect. The author also mentions that this work provides an opportunity to discuss outliers in data collection. Unless the students have an extended lab period the day their leaves are collected it is likely the lab portion will carry over into more than one class period. Having the students make outlines and card stock cutouts of their leave will help, but students will need the leaves for the molds to determine stomata density. The author suggests leaves may be stored in Ziploc bags from one class period to the next. It may be a good idea to place the bags in newspapers with weights to keep the leaves flat. Teachers will want to explore what works best without damaging leaves. The term ecophysiology is emphasized in one of the additional online resources and appropriateness of the term should definitely be discussed with students. This is not a “cookbook” laboratory activity, and teachers will need to support students as they use techniques for their data collection and appropriate units, etc. If this activity is done fairly early in the fall before leaves have fallen off trees, students may need a refresher on microscope use or a full lesson on microscope use depending on proficiency. The author suggests using heterogeneous grouping as a means of differentiating instruction. If teachers know their students well enough, groups may be made with the more proficient math students and the more artistic in each group. The author also suggests extensions such as using leaves of different species or shaded areas of a tree vs. nonshaded areas.

  • Monitoring Student Progress: Constant monitoring and feedback by the teacher for each group of students will be required. No specific assessments are given but several suggestions for varied forms of assessment are provided in the article and analysis and conclusion questions are included in additional resources. Teachers should monitor and provide feedback to students as they construct their leaf card stocks, view stomata molds, and collect and analyze their data. Supportive questioning is critical to student success in this and similar lessons.

  • Quality of Technological Interactivity: This is not a technology-based lesson. Technology may be incorporated in supporting instruction.