Case studies in photosynthesis

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Students will explore several case studies to determine how photosynthesis benefits humans.

Big Idea

Everything we eat is processed sunshine.

What Students will Learn in this Lesson

1 minutes

In this lesson students will explore several case studies to help them better understand the process of photosynthesis. These case studies will also help them understand the relationship between cellular respiration and photosynthesis. Finally, at the end of the lesson, students consider what might happen to the world if all the plants were to disappear or die. Here is an overview of what students will learn today.

Hook/Check for Understanding

3 minutes

As a class, students should watch the Science Up Close tutorial.  Using the following student handout, they should consider the answer to following questions:

  • Plants use photosynthesis to make __________________ for the plant.

Possible student answer:  food

  • What do plants need in order to perform photosynthesis?

Possible student answer:    light

  • How is the plant able to obtain each “ingredient?”

Possible student answer:   Light comes from the sun or some other light source. Carbon dioxide comes from the air into the leaves through the stomata in leaves.  Water comes from the soil through the roots into the veins. 

  • Identify the plant cell organelle in which photosynthesis takes place. 

Possible student answer:   The cell organelle is the chloroplast.

  • Summarize the process of photosynthesis--Water and carbon dioxide enter the chloroplast…..

 Possible student answer:   A chemical reaction occurs that changes the water and carbon dioxide into sugar.  Energy to make this chemical reaction happen comes from the sun.

  • What happens to the oxygen that is produced as a result of photosynthesis?

Possible student answer:  The oxygen is not needed for photosynthesis so it is released into the air.

  • Why is photosynthesis also important for people and animals?

Possible student answer:  Sugar is stored in plants which can serve as a food source for animals and people. 

Student Activity: Analysis of Two Case Studies

20 minutes

Students will look at two cases studies involving photosynthesis experiments.  (See attached handout). 

The first Virtual Lab is Measuring the Rate of Photosynthesis of Elodea from the University of Reading.  In this lab, students calculate the rate of photosynthesis in an Elodea plant by changing the intensity of the light source.  Students count the number of bubbles produced in a minute, then they graph the results and depend the rate of photosynthesis by calculating the slope of the line.   Students then compare the findings of this simulation with what they have learned in previous labs.

The second Virtual Lab allows students to manipulate many variables. They have already observed how light colors will affect the growth of a plant in previous lessons. In the last simulation they also directly measured the rate of photosynthesis by counting the number of bubbles of oxygen that are released. There are 3 other potential variables they will test with this simulation: amount of carbon dioxide, light intensity, and temperature. Students should keep the light settings at white light since you have already tested colored light in a previous experiment. First, they should set the thermometer at room temperature and the light intensity at 20.  Students should make observations about what has happened.  Students should then manipulate the temperature and determine how that affects the rate of photosynthesis. Students should also manipulate the light and carbon dioxide settings to determine the conditions for highest rate of photosynthesis.

Class Discussion: Comparing Our Data with Others

15 minutes

Bring the class back together.  During this class discussion, walk students through each of the parts of the photosynthesis equation and show the supporting evidence from the labs that have been performed in this unit.  

Have students synthesize their data by drawing a picture which shows the overall process of photosynthesis.  

Putting It All Together: Why Photosynthesis is Important to Humans

15 minutes

Outline the role of photosynthesis in maintaining a healthy ecosystem by having students consider the following questions:  

  • What is the importance of photosynthesis to living things other than plants?
  • What would happen in a world without plants?
  • Imagine the sun stopped producing light, but didn't consume the Earth.  What would happen to life on Earth after 20 minutes? 20 hours? 20 days? 20 years?

Students should write their response in their lab notebook or on the provided handout.