Students identify the process used by plants make their own food and discover how photosynthesis provides the food they eat. Grades K-2

photosynthesis: the process by which plants convert carbon dioxide, water, and light energy into sugars and oxygen in order to store energy; the opposite of cell respiration

This lesson is part of the Fun with the Plant Nutrient Team series which were written to help children better understand what the soil needs to be healthy in order to provide us with healthy foods. The lessons encourage students to think for themselves, ask questions, and learn problem-solving skills while learning the specific content needed to better understand the world in which they live. The lessons include:

• People and Plants Need Nutrients
• The Soil We Grow In
• Photosynthesis and You
• Weather on the Farm
• Where Did Your Hamburger Come From?

Photosynthesis is the process by which plants and some algae and bacteria capture sunlight energy to make their own food.

The inputs for photosynthesis are sunlight, carbon dioxide, and water. The outputs are oxygen and carbohydrates in the form of sugars or starch.

People would not have food to eat if it weren’t for photosynthesis. Plants need the process to make their food, and people and other organisms depend on consuming plants or other organisms that eat plants. Plants and animals are interdependent; plants need the carbon dioxide that animals release during respiration and animals need the oxygen released by plants during the process of photosynthesis.

Plant leaves are the main site of photosynthesis. The chemical chlorophyll allows special cell structures called chloroplasts to absorb light energy. Carbon dioxide passes through the stomata on the underside of the leaves and moves to the cells where energy from the sun has been trapped and stored. Water is absorbed by the root hairs and transported up the stem. Through a chemical reaction, water and carbon dioxide are converted into carbohydrates that are used by the plant for energy and growth. Oxygen is then released from the plant into the atmosphere.

1. Ask students what benefits we receive from the sun. Allow time for students to offer their ideas. Recognize that sun provides light and warmth to the earth. Point out that the sun is necessary for plants to grow.
2. Ask students why plants are important. Allow students to answer the question and provide further guiding questions to help them realize that some of the food we eat comes from plants. For older students, point out that meat and milk (provided by animals) is also dependent on plants because the animals eat plants to grow and be healthy. Plants such as cotton provide fabric for clothing and trees provide lumber to build houses and other buildings.
3. Inform students that they will be learning about photosynthesis, a process plants use to gain energy from the sun. This process is important because it is necessary to grow the food we eat.

Have students turn to page sixteen in their Fun With the Plant Nutrient Team Student Activity Book. Explain that they will be carrying out this experiment as a class.

Explain that plants A, B, and C are all the same types of plants and are the same age. Note: tomato seedlings work well for this experiment. The class will note their observations of the three plants on days 1, 4, 7, 11, and 14 on page sixteen.

1. Show students that Plant A is planted in sand and will be watered with distilled water. Explain that distilled water has been filtered so it does not contain any minerals or nutrients. Plant A will be set in a place where it receives sunlight for most of the day.
2. Show students that Plant B is planted in potting soil that contains the important nutrients for plant growth. Plant B will be watered with tap water and will be set in a place where it receives sunlight for most of the day. Explain that tap water has been treated so it is safe for people to drink and may also contain some minerals.
3. Show students that Plant C is planted in sand and will be watered with tap water. Place Plant C inside a heavy brown paper bag so it does not receive sunlight.
4. Ask students to predict which plant will be the healthiest at the end of the experiment and why. Tally votes on the board and make a bar graph of class predictions.
5. Give all three plants the same amount of water on the same days as needed.
6. Allow students 5-10 minutes to observe the plants and write down their observations on days 1, 4, 7, 11, and 14. Older students can write down notes with descriptive observations while younger students can use the smiley faces on page sixteen.
7. On day 14 of the experiment, compare the results with the class predictions. What plant is the healthiest and why? What plant did not do well and why? Discuss these questions and answers as a class.
8. Explain that Plant C did not get sunlight and therefore, was not able to carry out photosynthesis to make its own food. When a plant cannot make its own food, it doesn’t have energy to carry out life processes and it will become sick or die. Plant C was also planted in sand, which does not contain the nutrients that are important for plants to survive.
9. Explain that Plant A was planted in sand, which does not contain the nutrients that are important for plants to survive. It was also watered with distilled water, which doesn’t have any nutrients. For these reasons, plant A didn’t grow much and wasn’t very healthy at the end of the experiment.
10. Explain that Plant B is likely the healthiest because during the experiment it received everything a plant needs to grow and be healthy. Plant B received sunlight, water, and potting soil that contained important nutrients for plant growth.
11. Ask students why it is important to have healthy plants that can carry out the process of photosynthesis. Explain that we depend on photosynthesis for plants to make the food that we eat. Use a bowl of cereal and milk as an example. Where did the wheat, rice, or corn in the cereal come from? (plants) Where did the milk come from? (a cow) What do cows eat? (plants/grass)

Worksheet Procedure

1. Provide the student handout, Photosynthesis and You, to older students and read aloud as a class. For younger students, summarize the main points of the reading to provide background information for the drawing activity.
2. Lead students through the photosynthesis drawing activity step by step.

After conducting these activities, review and summarize the following key concepts:

• Plants provide food for us to eat.
• Plants rely on the sun to obtain energy to grow. The process is called photosynthesis.
• The sun is a natural resource that farmers use to grow and produce the food we eat.

The Educator’s Guide was funded by California Department of Food and Agriculture’s Fertilizer, Research, and Education Program (FREP) and developed by California Foundation for Agriculture in the Classroom.

Executive Director: Judy Culbertson
Illustrator: Erik Davison
Layout and Design: Nina Danner and Renee Thompson
Copy Editor: Leah Rosasco
Special Thanks to: Nutrients for Life Foundation, International Plant Nutrition Institute, Fertilizer Research and Education Program, and California Department of Food and Agriculture.

• Desktop Greenhouses Kit
• Fun With the Plant Nutrient Team Student Activity Book
• Sun in My Tummy
• The Magic School Bus Gets Planted: A Book About Photosynthesis
• Timelapse: Photosynthesis Seen from Space
• You're Aboard Spaceship Earth