Reach For the Sun Teacher Guide - Photosynthesis

Photosynthesis

Time Required

2 CLASS PERIODS

Objectives

Students will discuss the process of photosynthesis and its importance in Reach for the Sun.
Students will complete a hands on activity and observe a demonstration.

Materials

FOR THE STUDENT

FOR THE CLASS

Large green leaf that has been exposed to sunlightLarge variegated leaf that has been exposed to sunlight250-ml beakerEthyl alcoholTweezersIodine in dropper bottleWaterHot plateSaucepanOven mittStopwatch or timer

FOR EACH GROUP OR PAIR

Computer and Internet accessLarge-leaved plantClear plastic wrap or baggieTape

Preparation

Purchase a large-leaved plant for each student pair ahead of time.
Prepare for Lesson 3 by soaking lima beans (4–5 for each student pair) in water for at least 24 hours.

Plant Growth Observations

Have students make observations of their plants from the lab in Lesson 1 and record their observations on the Lab Sheet from the Appendix.

Warm Up: Think-Pair-Share: What Do You Know about Photosynthesis?

Distribute colored pencils and have students complete the Think-Pair-Share activity in the Student Guide. Have students complete part A individually, and divide them into pairs to answer part B. Finally, ask a student to come forward and draw a diagram of photosynthesis on the board.

Review the reactants and products of photosynthesis and discuss how energy is cycled during this process. Plants convert light energy from the sun into chemical energy. This chemical energy is stored in plants as sugars, also know as carbohydrates. The carbohydrates act as a food source for the plants, enabling them to grow, reproduce, and make seeds. Explain that sugars (glucose) are a product of photosynthesis, and plants use these sugars as fuel and to build larger starch molecules, which are stored throughout the plant.

Photosynthesis occurs in the chloroplasts of leaves. Chloroplasts contain the green pigment chlorophyll, which absorbs light energy.

Draw the diagram below on the board or project the Photosynthesis Diagram in the Appendix on a whiteboard.

Game Play!

Have students play Reach for the Sun with their partners for approximately 30 minutes. Students should continue where they left off with the previous game by clicking the Resume button in Classic mode.

Pause and Think

Ask students to pause the game after about 15 minutes and ask them to share how the experience is different from the first game play session. Ask the following questions related to photosynthesis:

  • Where in the plants would you find chlorophyll?
    Chlorophyll is found inside the chloroplasts, which are in the leaves.
  • Why is photosynthesis important in the game?
    It provides the energy source that the plants need in order to grow and reproduce.
  • Which resource builds in the game when your plant undergoes photosynthesis? How does building this resource help you play the game successfully?
    Photosynthesis builds starch, which enable the plant to grow new plant parts. This leads to the plant’s ability to grow fruits and seeds.
  • Why is it important to grow many roots before growing leaves?
    Photosynthesis uses nutrients and water, which are both absorbed by the plant’s roots; therefore, students should grow as many roots as possible before they begin growing leaves.

Game Discusson

Discuss students’ responses to question B in the Student Guide as a class:

  • How did your success compare to the success of your first game? Why do you think this is so?
    Sample answer: I was able to grow my plants faster and produce seeds before the growing season ended. I was more used to the pace of the game and was better able to balance the resources.
  • How did your plants in Reach for the Sun undergo photosynthesis? Were your plants always able to complete this process? Why or why not?
    Sample answer: The plants completed photosynthesis when I clicked on the leaves as they turned color. Sometimes I wasn’t fast enough or didn’t have enough water.
  • What were the costs and benefits of undergoing photosynthesis in the game? How does this relate to plants in real life?
    Photosynthesis uses up water and nutrients, but makes sugars [starches] that are used by the plant to grow. This is similar to the process in real life, since plants take in water and nutrients from the environment and produce sugars.

Hands-On Activity: Transpiration

Explain to students that they will be completing an activity that will help them observe another plant process called transpiration. During transpiration, tiny openings in leaves called stomata open and allow for the release of water. This helps keep plants cool and regulates internal pressure, maximizing the flow of nutrients and water through the roots.

Instruct students to complete steps 2 and 3, and have them place their plants in a sunny spot or under a lamp. Students will observe the plants after the demonstration.

Demonstration: Testing for Starch

Have students read the information in the Student Guide about the demonstration. Discuss the questions below, accepting all reasonable responses. Show students both of the leaves that you are going to use for the demonstration. Have students consider and discuss the following questions:

  • How does an iodine test relate to photosynthesis?
  • What do you think will happen to a green leaf when it is exposed to iodine? Why?
  • How will the results be different for a variegated leaf? Why?
  • How does this demonstration apply to what you are learning in Reach for the Sun?

Complete the demonstration as follows:

  • Place about 50 ml of ethyl alcohol in the beaker. Place the beaker in a saucepan filled with water. As the water and alcohol are heating up, explain to students that the alcohol breaks down chlorophyll, taking out the green pigmentation from leaves.
  • Once the alcohol boils, use oven mitts to remove the beaker from the heat. Use the tweezers to submerge each leaf in the hot water for 60 seconds.
  • Next, place the leaves in the beaker of ethyl alcohol for about two minutes, or until they turn white.
  • Set the leaves in a shallow tray or pan and add several drops of iodine to each leaf so that all areas of the leaves have been exposed to the iodine.
  • Have students observe the results and discuss what happened. The green leaf should have turned a blue-black color. The variegated leaf should have blue-black color in the areas that were originally green. Ask students to explain how this relates to photosynthesis.

It should be time for students to check their plants for evidence of transpiration. Instruct students to answer question 4 in the Hands-On Activity: Transpiration section of the Student Guide. Discuss their responses as a class. Most students should have observed water collecting on the plastic wrap, which indicates that the leaf released water through its stomata.

Exit Slip

Have students complete the Exit Slip activity in the Student Guide and submit the activity before leaving the classroom. Review the student responses before the next lesson.