Shining light on photosynthesis

This exercise is a part of Educator Guide: AI Technology and Photosynthesis / View Guide
photo of large leaves from a tropical plant taken from below the forest canopy
When leaves get too hot, the proteins that convert light energy into sugars stop working.Buena Vista Images/Photodisc/Getty Images Plus

Directions for teachers:

For homework, or if you have time in class, have students read the Science News Explores article “Explainer: How photosynthesis works.” Suggest that students perform a close reading exercise, such as highlighting or notetaking, to gather details from the articles.

Ask students to work with a partner to answer the first five questions in the “Breaking down photosynthesis” section. Divide the class into groups that will each create a comic or graphic tale depicting one of the chemical reactions in the process. Group topics can include: the overall chemical reaction of photosynthesis, the light reactions, and the steps of the Calvin cycle. Use this lesson plan to download the storyboard template. Have students present their comics in the order in which the chemical reactions generally occur. Make sure each group points out how their reaction or step is dependent on the reactants or energy produced by preceding reactions (or the incident sunlight). Display the comics in your classroom in a way that depicts the correct order.

To explore how changes in certain conditions can impact plants’ ability to photosynthesize and how plants can adapt to such changes, ask students to read the Science News article“Some leaves in tropical forests may be getting too hot for photosynthesis” and discuss the second set of questions.

Directions for students:

After reading the Science News Explores article “Explainer: How photosynthesis works,” work with a partner to complete the first section of questions as instructed by your teacher.

Breaking down photosynthesis

1. Based on what you read, write an overall chemical reaction for photosynthesis. If you have learned how to balance chemical reactions, balance it.

2. As the article indicates, photosynthesis is the result of multiple chemical reactions that are often described as two separate processes. What reactions do the “photo” in “photosynthesis” refer to? What reactions are classified by the “synthesis” in “photosynthesis”? Where do each of the processes occur?

“Photo” refers to the reactions that are triggered by light, as they require photons’ energy to be absorbed by chlorophyll. This occurs in the thylakoid membranes, which are located inside the chloroplast, an organelle in plant cells. The “synthesis” reactions also take place inside the chloroplast, but they take place outside the thylakoid, in the stroma. This series of reactions makes up the process called the Calvin cycle, which produces glucose, a sugar that plants use to produce other carbohydrates such as cellulose, starch or fructose.  

3. Working with a partner, use the article to diagram all the major chemical reactions in the “photo” and “synthesis” processes. Discuss the purpose or function of a single reaction in terms of how it fits into the overall cycle. Where are the reactions taking place? Are they consuming or producing energy? How is the energy used in subsequent steps?

Chlorophyll absorbs light and uses the light’s energy to initiate the process of splitting oxygen off water molecules. Free oxygen atoms immediately pair up to create oxygen gas (a biproduct of the overall photosynthesis reaction). The reaction also produces NADPH and ATP, molecules that store energy and that are consumed during the Calvin cycle. The four major steps of the Calvin cycle are carbon fixation, reduction, carbohydrate formation and regeneration. Plants bring in CO2 from the air for carbon fixation. Rubisco, a plant enzyme, attaches the carbon atom in CO2 to ribulose 1,5-bisphosphase (RuBP) to form a six-member ring. That ring immediately breaks into two molecules that each contain three carbons. In reduction, the ATP and NADPH produced from the light reactions are used to change the three-carbon molecules into a small sugar, glyceraldehyde 3-phosphate (G3P). In carbohydrate formation, some G3P leaves the cycle to be converted into larger sugar molecules, such as glucose. During regeneration, the remaining G3P gains two more carbons to produce RuBP, and the Calvin cycle can continue. Each of the reactions helps to create products that are used in a subsequent step.

4. After reviewing all the steps of the photosynthesis, does the overall reaction capture everything that occurs during photosynthesis? What does the overall reaction tell you? What does it leave out?

The overall reaction does not indicate the pathway or chain of reactions that ultimately create the plant’s glucose and the oxygen byproduct. It only gives an overview of what the reactants and products are. 

5. Why might it be important to understand all the steps and details of photosynthesis and not just memorize the overall reaction?

Answers will vary. Photosynthesis is a complex series of reactions that isn’t fully described by the overall reaction. Understanding the steps can help us appreciate how plants have adapted to use carbon dioxide, water and sunlight to grow. This also reveals the process by which plants get the materials and energy to produce carbohydrates that are key parts of the foods that we eat.  

6. Create a comic or graphic tale that explains one of the chemical reactions in the process of photosynthesis. Make sure you highlight the reactants and products and point out how your reaction plays an important role in the overall process of photosynthesis. What preceding reaction is your reaction dependent on, and why is your reaction critical to the overall process? Is your reaction producing or consuming energy? Use additional resources to look up more information about the reaction or part of the process that is assigned to you.  

Can plants adapt?

To investigate how certain conditions can impact plants’ ability to photosynthesize and how plants can adapt to such conditions, read the Science News article“Some leaves in tropical forests may be getting too hot for photosynthesis” and discuss the second set of questions with a partner.

1. Almost all plants undergo photosynthesis. What are some environmental factors that can affect the process of photosynthesis and therefore the health of plants? Explain using an example from the Science News article.

Temperature, amount of sunlight, precipitation, soil nutrient level. In the article, scientists determined that some plant leaves in tropical forests were getting too hot for photosynthesis to occur. High temperatures can break down the proteins that are needed to convert light energy into sugar. 

2. In the study referenced in the Science News article, what data did scientists collect to learn that leaf temperatures may be getting too hot for photosynthesis?

The researchers used data from ECOSTRESS, a thermal sensor on board the International Space Station, combined with temperature data from sensors taped to leaves and in a tower in the Amazon.

3. Describe your neighborhood’s environmental conditions. What conditions are your local plants exposed to throughout the year?

Students should describe the environmental conditions, such as precipitation, sun, temperature and humidity, that their region experiences during the seasons of the year. Students can also describe attributes of the seasons, such as mild winters, stormy summers, rainy autumns, etc.

4. Given your area’s environmental conditions, what adaptations do your local plants need to survive? Think beyond photosynthesis. For example, if you live in an area with high levels of erosion, plants need strong roots.

Answers will vary. For example, if students reported that their area receives a lot of rain, plants should have strong roots. If they mentioned that their area is very dry, plants should have high water-retention abilities.

The care and keeping of plants

Choose a native plant that grows in your local area. Do some research and fill in the information below to create a “care card” for your plant. Include a description of the adaptations your plant needs to survive in your local area in the “Additional notes” portion. What makes the plant grow well in your local area?

Plant’s Common Name:

Plant’s Scientific Name:

Average size:

Water requirements:

Sun tolerance:

Cold hardiness:

Common pests:

Additional notes:

A sample answer is given below.

Plant’s Common Name: Goldenrod

Plant’s Scientific Name: Solidago

Average size: 1.5–5 ft. tall, 1-3 ft. wide

Water requirements: Mature plants are drought tolerant, so they don’t typically need watering. Newly planted goldenrod needs damp but not soggy soil.

Sun tolerance: Full sun

Temperature: Thrives in temperatures 65-80 degrees Fahrenheit

Common pests: Beetles, aphids

Additional notes: Goldenrod grows well in my local area because the temperatures in summer are mild and we don’t get a lot of rain.