National Agricultural Literacy Curriculum Matrix


A "Sour" Subject

Grade Level(s)

3 - 5

Estimated Time

75 minutes


In this lesson students will learn about the growth and production of citrus fruits and participate in an activity where they use skills of observation and mathematical computation to compare and contrast grapefruits and lemons.


Interest Approach – Engagement:

  • Grapefruit
  • Lemon
  • Lemon & Grapefruit Venn Diagram

Activity 1:

  • Citrus Fruits Commodity Fact Sheet
  • Lemon & Grapefruit Venn Diagram

Activity 2:

  • Grapefruit, one-half per group
  • Lemon, one-half per group
  • A "Sour" Subject student lab report
  • Balance
  • Calculators
  • Hand lens, minimum 1 per group
  • Small paper cups, 2 per group
  • Paper towels


Essential Files (maps, charts, pictures, or documents)

Essential Links


citrus: a tree of a genus that includes citron, lemon, lime, orange, and grapefruit; cultivated in warm countries for their fruit, which has juicy flesh and a pulpy rind

evergreen: a classification of plant that has leaves throughout the year that are always green

pest: a destructive insect or other animal that attacks crops, food, or livestock

Did you know? (Ag Facts)

  • Citrus fruits are available yearly from the states of California, Arizona, and Florida. Florida ranks as the number one producer of citrus fruits and California is second.
  • The nectar from oranges and lemons was used as a drink and as a medicine in the ancient days of the Middle East.
  • California has approximately 271,000 acres of citrus trees.
  • One orange alone can provide a full day's requirement of Vitamin C.

Background Agricultural Connections

Grapefruit, lemons, oranges, and limes are citrus fruits that are grown in warm climates including California, Arizona, and Florida. Florida is the top producing citrus state. Florida and Arizona most often produce oranges that are processed into juices. Most California oranges are of the navel variety, which is a seedless fruit.

Grapefruit, as do lemons, grow on evergreen trees whose leaves have a waxy cuticle covering. Grapefruit were given their name when people noticed that they grow in clusters, just like grapes grow in clusters. Grapefruit trees produce best when they are grown in places that have hot summers and winters that never get colder than 20°F (-6.66° C).

Lemons are a popular ingredient in many dessert dishes, but are most often recognized as the main ingredient in lemonade. Ventura County in California is the leading producer of lemons in the United States. Because of its unique coastal location, some lemon trees in this region can produce fruit three to four times per year.

Over the past several decades, more citrus varieties have been developed and commercialized. For example, the Pixie mandarin, a small, sweet, orange-colored fruit was developed by the University of California in Riverside. It is now a popular citrus fruit in stores today.

Farmers must protect their trees from winter frost and summer "sunburn." Perhaps you have seen some trees painted with white paint to protect the trunks from the sun. During the winter, growers must protect their trees from too much water. If this is a challenge, tree trunks are painted with a substance that is greenish-blue. This chemical prevents wet trees from getting diseases that are caused by bacteria and fungi that grow on wet citrus roots.

All citrus farmers must protect their trees from insects and other pests. The most common pest is the common garden snail. Copper rings are placed around citrus trunks. This produces a physical barrier that, if crossed by the snails, will emit an electric shock. Garden snails are also controlled by the release of special types of carnivorous snails. These special snails eat the harmful snails and do not eat any plants. You may also research other citrus pests, such as the "citrus bud mite."

Lemons are usually smaller than grapefruit and are generally more sour than grapefruit. There is one exception to this, however. The Ponderosa lemon tree produces lemons that weigh approximately two pounds each! They have a very mild lemon flavor similar to the taste of the lemon flavor in lemonade.

Interest Approach – Engagement

  1. Show the students a grapefruit and lemon. Pass the fruit around and have the students examine the shape, size, color, and smell of each fruit.
  2. Tell the students they will be comparing and contrasting these two types of citrus fruits grown in California, Arizona, and Florida.
  3. Pass out the Lemon & Grapefruit Venn Diagram found in the Essential Files and have students fill this out by comparing and contrasting what they notice while observing each fruit.


Activity One

  1. Project the Citrus Fruits Commodity Fact Sheet onto a large screen. Arrange the students so they can see and participate in a shared reading of the fact sheet.
    • Shared reading is an instructional strategy used by teachers as an interactive reading experience. Students join in or share the reading responsibilities on an enlarged text while guided and supported by an experienced reader or teacher.
  2. After reading about citrus fruits, organize the students into small groups and have the groups work cooperatively to add more information to the Venn diagrams they began in the Interest Approach – Engagement.
  3. Bring the students back together as a whole group and have them sit in a circle to participate in a Text, Talk, and Time discussion using their Venn diagrams and the Citrus Fruits Commodity Fact Sheet. To see a demonstration of this teaching strategy, watch the video, Analyzing Texts: Text, Talk, and Time. Refer to the reminders below to emphasize the rules of this strategy:
    • Thumbs up: Share new information
    • Two fingers: Add to an answer
    • Teacher's hand up: Students are quiet, the next question is asked.
  4. Have the students add additional the information gained from the class Text, Talk, and Time discussion to their Venn diagrams  

Activity Two

  1. Show the students grapefruit and lemons. Discuss what a cross-section is and cut the fruit in half.
  2. Ask the students what they already know about these fruits: 
    • "What are the names of the fruit?" (grapefruit and lemons)
    • "What kind of fruit are they?" (citrus)
    • "What nutrients are they high in?" (Vitamin C and Olic Acid)
  3. Have students individually complete the "Predictions" section on page one of their A "Sour" Subject lab report.
  4. As a class, read and discuss the "Introduction" section of the lab report.
  5. Organize students into groups of three to four students. 
  6. Have students complete the remainder of the lab report following your instructions, which should include:
    • Set-up and clean-up procedures
    • Special hints on how to complete the worksheet
    • Other appropriate information

Concept Elaboration and Evaluation

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

  • Grapefruit, lemons, oranges, and limes are citrus fruits. They grow on trees in warm climates such as California, Arizona, and Florida.
  • Scientists help citrus farmers develop new and improved varieties of citrus fruits.
  • Citrus fruits provide an abundant source of vitamin C.


  • Compare a non-citrus fruit, such as a banana, to a citrus fruit.
  • Have students design their own problems related to their data.

We welcome your feedback! Please take a minute to tell us how to make this lesson better or to give us a few gold stars!


Enriching Activities

  • Compliment this lesson with reading, writing, and economics activities that incorporate research on the citrus industry in California, Arizona, or Florida.

  • Have students research how naval oranges, which do not have seeds, are cultivated.

  • Discuss how increase in trade agreements and technology have enabled countries around the world to grow citrus much cheaper. The importing of such goods affects the American growers and the economy of the United States. Discuss the benefits and risks of international trade.

  • Invite a citrus grower to your classroom to discuss their operation.

  • Using grocery ads, have students write and solve citrus math word problems.

  • Using a "standard" set of data available to all students, have them answer questions such as the following:

    • If a grapefruit's total mass is 98 grams and the peel, juice, and pulp have a total mass of 96.9 grams, what is the total mass of the seeds?
    • If the pulp of a lemon is 42 grams and the total lemon had a mass of 202 grams, what percent of the fruit is pulp?

Suggested Companion Resources

Agricultural Literacy Outcomes

Culture, Society, Economy & Geography

  • Provide examples of agricultural products available, but not produced in their local area and state (T5.3-5.e)

Food, Health, and Lifestyle

  • Identify food sources of required food nutrients (T3.3-5.g)

Education Content Standards


Health Standard 5: Demonstrate the ability to use decision-making skills to enhance health.

  • 5.5.5
    Choose a healthy option when making a decision.


5-PS1: Matter and Its Interactions

  • 5-PS1-3
    Make observations and measurements to identify materials based on their properties.

Common Core Connections

Reading: Anchor Standards

    Read closely to determine what the text says explicitly and to make logical inferences from it; cite specific textual evidence when writing or speaking to support conclusions drawn from the text.
    Read and comprehend complex literary and informational texts independently and proficiently.
    Determine central ideas or themes of a text and analyze their development; summarize the key supporting details and ideas.

Speaking and Listening: Anchor Standards

    Prepare for and participate effectively in a range of conversations and collaborations with diverse partners, building on others’ ideas and expressing their own clearly and persuasively.
    Evaluate a speaker’s point of view, reasoning, and use of evidence and rhetoric.
    Present information, findings, and supporting evidence such that listeners can follow the line of reasoning and the organization, development, and style are appropriate to task, purpose, and audience.

Language: Anchor Standards

    Demonstrate command of the conventions of standard English grammar and usage when writing or speaking.
    Demonstrate command of the conventions of standard English capitalization, punctuation, and spelling when writing.

Writing: Anchor Standards

    Write routinely over extended time frames (time for research, reflection, and revision) and shorter time frames (a single sitting or a day or two) for a range of tasks, purposes, and audiences.
    Write informative/explanatory texts to examine and convey complex ideas and information clearly and accurately through the effective selection, organization, and analysis of content.
    Produce clear and coherent writing in which the development, organization, and style are appropriate to task, purpose, and audience.
    Draw evidence from literary or informational texts to support analysis, reflection, and research.

Mathematics: Practice Standards

    Make sense of problems and persevere in solving them. Students start by explaining to themselves the meaning of a problem and looking for entry points to its solution. They analyze givens, constraints, relationships, and goals. They make conjectures about the form and meaning of the solution and plan a solution pathway rather than simply jumping into a solution attempt. They consider analogous problems, and try special cases and simpler forms of the original problem in order to gain insight into its solution. They monitor and evaluate their progress and change course if necessary. Students check their answers to problems using a different method, and they continually ask themselves, “Does this make sense?” They can understand the approaches of others to solving complex problems and identify correspondences between different approaches.
    Model with mathematics. Students can apply the mathematics they know to solve problems arising in everyday life, society, and the workplace. Students who can apply what they know are comfortable making assumptions and approximations to simplify a complicated situation, realizing that these may need revision later. They are able to identify important quantities in a practical situation and map their relationships using such tools as diagrams, two-way tables, graphs, flowcharts and formulas. They can analyze those relationships mathematically to draw conclusions.
    Use appropriate tools strategically. Students consider the available tools when solving a mathematical problem. These tools might include pencil and paper, concrete models, a ruler, a protractor, a calculator, a spreadsheet, a computer algebra system, a statistical package, or dynamic geometry software. Students at various grade levels are able to identify relevant external mathematical resources, such as digital content located on a website, and use them to pose or solve problems. They are able to use technological tools to explore and deepen their understandings of concepts.


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