National Agricultural Literacy Curriculum Matrix


In Search of Essential Nutrients (Grades 9-12)

Grade Level(s)

9 - 12

Estimated Time

1 hour


Students will learn about the essential elements found in soil, compare and contrast the essential element requirements of plants and humans, explain why plants cannot use elemental nitrogen found in the atmosphere, and identify the sources for each essential element needed by plants.


Activity 1:

  • Master 1.1, Essential Elements (1 to project)
  • Master 1.2, The Periodic Table (1 per student and 1 to project)
  • Master 1.3, Essential Elements for Plants (1 to project)
  • Master 1.4, Essential Elements for Humans (1 to project)
  • 1 colored pencil per student

Activity 2:

  • Master 1.5, Sources of Essential Elements (1 per student and 1 to project)
  • Master 1.6, Using Nitrogen (1 per student)

Optional Extension:

  • Master 1.7, Food Label (1 per student)

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


macronutrient: a nutrient that must be present in a relatively large amount to ensure the health of the organism. Macronutrients are building blocks used to make essential biomolecules.

micronutrient: a nutrient required in small quantities to ensure the health of the organism. Micronutrients are often used as cofactors for enzymatic reactions.

nutrient: any of 17 essential mineral and non mineral elements necessary for plant growth

Background Agricultural Connections

Plants and Their Essential Elements

All organisms must take in matter from their environment in order to survive. There are 92 naturally occurring elements on Earth. Living things need only a minority of them. For example, humans require about 21 different elements to be healthy. Almost all of the mass of our bodies comes from just six of those elements (carbon, hydrogen, oxygen, nitrogen, phosphorus , and calcium). These are the elements used to construct the carbohydrates, nucleic acids, proteins, and other molecules that make up our cells and carry out their chemistry. Other elements critical to our health are needed in very small amounts. Often, such elements are cofactors required by enzymes to catalyze specific chemical reactions. Regardless of whether elements are needed in large or small amounts, they must be obtained from the environment. Furthermore, it not enough that essential elements are present in the environment; they must be available in a chemical form that our bodies can use.

Not surprisingly, the situation in plants is similar. They, too, must carry out thousands of different chemical reactions, many of which are similar to those of humans. Scientists have identified 17 elements that are essential for plants (see Table 9). An element is described as being essential to the plant if the following conditions are met:

  • The element must be required by the plant to complete its life cycle.
  • The element cannot be replaced by another element.
  • The element must be required for a specific biological function.
  • The element must be required by a substantial number of different plant species.

Essential elements can be classified as mineral or non-mineral nutrients. Carbon, hydrogen, and oxygen are classified as non-mineral nutrients because they are obtained from the atmosphere and water. Mineral nutrients can be further classified as being either macronutrients or micronutrients. As the name implies, macronutrients are needed in relatively large amounts. Nitrogen, phosphorous, and potassium are called primary macronutrients, while calcium, sulfur, and magnesium are called secondary macronutrients. The rest of the essential elements are called micronutrients because they are needed in small amounts. It is important to note that despite their name, micronutrients are just as essential to plant health as are macronutrients.

Plants absorb most of their essential elements from water in the soil. Usually the essential elements are taken up as a positively charged cation or a negatively charged anion.

The Nitrogen Cycle

Although the atmosphere is about 78 percent nitrogen, plants cannot make use of nitrogen gas (N2). Instead, plants need to obtain their nitrogen by taking up the cation ammonium (NH4+) or the anion nitrate (NO3–) in the soil. These ionic forms of nitrogen are generated by the breakdown of organic material in the soil or through a process called nitrogen fixation that is carried out by soil microbes. Some crop plants (legumes such as peas, beans, peanuts, and soybeans) live in close association with nitrogen-fixing bacteria that live in their roots and convert N2 gas to a form that plants can use. Such crops have a steady source of nitrogen and do not require nitrogen-containing fertilizers.

The nitrogen cycle describes the processes by which nitrogen moves between its various chemical forms. Biological or physical processes can cause these chemical conversions. Four processes are essential to the nitrogen cycle.

  • Nitrogen fixation refers to the process by which atmospheric nitrogen (N2) is converted to nitrogen–containing compounds that are usable by plants. Nitrogen fixation can be accomplished through the action of lightning or bacteria in the soil.
  • Ammonification refers to the process by which bacteria and fungi convert decomposed nitrogen-containing compounds into ammonium ions (NH4+).
  • Nitrification refers to the process by which bacteria convert ammonium ions into nitrite (NO2-). Other bacteria convert nitrite to nitrate (NO3-). This is important because nitrites can reach levels that are toxic to plants.
  • Denitrification refers to the process by which bacteria convert nitrates back to N2.

So, let us summarize the nitrogen cycle. First, recall that plants cannot use the nitrogen in the air that is so plentiful. When plants and animals die and decompose, they add nitrogen to the soil. Bacteria in the soil convert the nitrogen into compounds that plants can use. Plants take in these nitrogen-containing compounds through their roots and use them to grow. Animals eat the plants, use the nitrogen, and return it to the soil when they die and decompose.

Interest Approach – Engagement

  1. Ask students questions to assess their prior knowledge. Questions could include:
    • What is an essential element?
    • What nutrients are essential to life? Are they the same for plants and humans?
    • Where do these nutrients come from?
  2. Inform students that after this lesson they will be able to:
    • define an essential element,
    • compare and contrast the essential element requirements of plants and humans,
    • explain why plants cannot use elemental nitrogen found in the atmosphere, and
    • identify the sources for each essential element needed by plants.


Activity 1: Essential Elements

In this activity, students use the periodic table to express their prior knowledge about what plants need to survive. Their predictions are compared to a list of essential elements known to be important to plant health.

  1. Begin the lesson by explaining that scientists who are interested in studying human health must understand the specific needs of the body. Ask students, “What do humans need to live?”
    • Accept all answers. Write student responses on the board or on chart paper. Direct the discussion to elicit air (oxygen), water, and food. Some students may realize that sleep is also required for survival. Other students may suggest environmental conditions such as temperature and pressure or material things such as clothing and shelter.
  2. Remind students that life requires energy for its existence . Ask students, “What do people take into their bodies from the environment to help them survive?”
    • Students should recognize that from the list generated in the previous step air, water, and food are obtained from the environment.
  3. Ask students, “Why do we need each of these (air, water, and food) to survive?”
    • Students should:
      • report that oxygen in the air is needed for cellular respiration.
      • be able to explain that our cells are mostly made of water. Water is the medium in which life has evolved. It is required for the chemistry of life.
      • recognize that food has two critical functions: as a source of chemical energy and as a source of chemical building blocks needed by our cells.
  4. Remind students that humans (and animals) eat plants and other animals to obtain chemical energy and provide them with the building blocks needed by their cells. Ask students, “What about plants; do plants need food?”
    • Some students may respond that plants do not need food, because they can obtain energy from photosynthesis. Other students may mention that plants need water or that they obtain nutrients from the soil. If not mentioned by a student, remind the class that fertilizer can be considered “food” for plants, because it provides nutrients that plants need to live and grow.
    • Teacher note: In many things you may read online, the terms “essential elements” and “essential nutrients” are often used interchangeably. A nutrient is a substance that organisms need to live and grow. In this activity, the term essential elements will be the preferred term because students will be looking at the periodic table of elements. Elements often combine into larger molecules that living things use. For example, water is an important nutrient for organisms; water is made up of the elements hydrogen and oxygen.
  5. Explain that they will now investigate the chemical elements that are essential for plant growth.
    • Project Master 1.1, Essential Elements. Ask different students to read aloud the criteria that describe an essential element.
  6. Pass out to each student a copy of Master 1.2, The Periodic Table. Instruct the class to think about the definition of “essential element” and use a colored pencil to shade those elements on the periodic table that they think are essential for healthy plant growth . If possible, students should think of an example of how a given element is used by the plant (such as the plant using nitrogen to make protein or phosphorus being used to make ATP).
    • Give students about 10 minutes to complete this task. Students likely will not be able to suggest a function for elements needed in trace amounts. Many such elements are needed as cofactors for enzymes. It is not important to discuss the uses of each element, but it is important that students understand that these elements are needed to build cell structures and to carry out the cell’s chemistry through enzymatic reactions.
    • This step gives you an opportunity to assess how well students can relate their knowledge of chemistry to biology. For example, students may respond that carbon is used to make carbohydrates, such as sugar.
  7. Project Master 1.2, The Periodic Table. Ask a student volunteer to read aloud the elements shaded on his or her periodic table . Have the volunteer explain why the selected elements were chosen. Have additional students add to the list with their predictions.
    • As the elements are read off, shade them in or circle them on the projected copy. Students are not expected to identify the complete list of essential elements. Their responses however, will reflect their relative knowledge about the biology of plants.
  8. Explain that you are now going to reveal which elements have been shown to be essential for plant growth and compare them with students’ predictions. Project Master 1.3, Essential Elements for Plants.
    • Students likely will be surprised that so many elements are essential for plant growth. The comparison between the elements predicted by the students and the accepted ones should show some overlap. Students should be expected to identify carbon(C), hydrogen(H), nitrogen(N), oxygen(O), phosphorus(P), and sulfur(S) because these elements serve as building blocks for biomolecules. If necessary, ask guiding questions to connect these elements to the synthesis of proteins, nucleic acids, and carbohydrates.
  9. Ask, “Do you think that humans require the same essential elements as plants?”
    • Responses will vary. Some students may think that since humans and plants are very different from each other, they will need different sets of elements. Others may reason that since plants and humans are each made of cells that contain similar biomolecules, the essential elements needed by both will be similar.
  10. Project Master 1.4, Essential Elements for Humans. Ask students to comment on how similar or dissimilar this pattern of elements is compared with that shown previously for plants.
    • Students should notice that the two patterns are more alike than different. To make this point clearer, you can project copies of Masters 1.3, Essential Nutrients for Plants and 1.4, Essential Nutrients for Humans side-by-side for students to compare.

Activity 2: Sources of Essential Elements

In this activity, students consider from where plants obtain essential elements.

  1. Explain that you will conclude the lesson with a brief activity that explores where plants obtain their essential elements.
  2. Pass out to each student a copy of Master 1.5, Sources of Essential Elements. Explain that the handout lists the 17 essential plant elements. Instruct students to think about where a corn plant obtains these essential elements. Students should indicate the source—air, water, and soil—for each element (that is, each chemical element) by checking the appropriate boxes on the handout.
    • For the purpose of this activity, students should think about water as rainfall (before it reaches the ground). It therefore should not include those elements found in soil that may dissolve in water. Students are free to check more than one box for any element. Give students about 5 minutes to complete this task.
  3. Project Master 1.5, Sources of Essential Elements. Ask a student volunteer to describe which elements he or she listed as coming from water.
    • Put a “W” next to the elements named by the students. Of course, students should mention hydrogen and oxygen. Actually, rainwater may contain small amounts of other elements derived from atmospheric gases and dust particles. Other elements that could be mentioned include C, Cl, N, and S.
  4. Ask another volunteer to describe which elements he or she listed as coming from the air.
    • Put an “A” next to the elements named by the students. Students should recognize that the corn plant obtains carbon and oxygen (via CO2) from the air. Some students may know that most of the atmosphere is nitrogen. Most students will not realize that nitrogen gas is not available to the corn plant in a usable form. Do not correct this misconception yet. This issue will be addressed in Step 7. As with water, small amounts of other elements also may be present due to air pollution.
  5. Ask another volunteer to describe which elements he or she listed as coming from the soil.
    • Put an “S” next to the elements named by the students. Students should list most if not all of the essential elements. The soil not only contains many elements that reflect its geological history, but it also contains organic material from once-living plants and animals as well as from the abundant life (both macro and micro) that resides there.
  6. Ask students to help you summarize where the corn plant gets its essential elements.
    • Students should report the following:
      • Water: Hydrogen and oxygen.
      • Air: Carbon and oxygen.
      • Soil: All essential elements.
    • Ask students to work individually or in pairs to write a short summary before holding a class discussion. This will allow students to gather their thoughts before speaking and for you to assess each student’s understanding.
  7. Explain that nitrogen is an essential element that plants need in relatively large amounts. Pass out to each student 1 copy of Master 1.6, Using Nitrogen. Instruct students to read the description and answer the questions.
  8. After students have completed their tasks, ask them, “In light of what you just read, would you change your prediction of where the corn plant obtains its nitrogen?”
    • Students should change their answer, if necessary, to indicate that the corn plant must obtain its nitrogen from the soil rather than from the air.
  9. Ask for volunteers to read his or her answers to Question 1 and 2 on Master 1.6, Using Nitrogen.
    • Question 1: What do you think is responsible for converting most of the nitrogen used by plants into a usable form?
      • Answer: Students should conclude that bacteria are responsible for fixing most of the nitrogen used by plants. Some nitrogen also is fixed by lightning and industrial processes, but these are much smaller amounts
    • Question 2: Why is this ability of legumes to carry out their own nitrogen fixation important to farmers?
      • Answer: Because the symbiotic bacteria in legumes fix additional nitrogen for plants to use, farmers can be less concerned with replenishing the soil using nitrogen-containing fertilizers.

Concept Elaboration and Evaluation

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

  • To grow healthy crops, farmers need to know which essential elements are found in the soil and how much of each is present.
  • Essential elements are found in the soil. 
  • Essential elements in the soil come from multiple sources that include:
    • natural ones, such as the erosion of rocks;
    • the action of lightning;
    • the decomposition of plant and animal material;
    • human-associated activities, such as runoff from fertilizers used by farmers and the public as well as from waste that humans produce; and
    • emissions from industry and automobiles

Optional Extension Activity: Humans, Food, and Essential Elements

This activity requires a variety of different food labels and access to the Internet if carried out in the classroom. Alternatively, it can be assigned as homework.

  1. Ask students to recall that plants get their essential elements mostly from the soil. Ask, “What about people? From where do they get their essential elements?
    • Students should respond that people get most of their essential elements from food, though water gives us hydrogen and oxygen just as it does for plants.
  2. Instruct students to obtain a food label from a nutritious food for analysis.
    • Since this activity is concerned with diet and essential elements needed for good heath, food labels should come from healthy foods and not from snacks.
  3. Have students retrieve their copies of Master 1.4, Essential Elements for Humans. Pass out to each student a copy of Master 1.7, Food Label and instruct them to follow the directions on the handout.
    • Some elements, including sodium, calcium, and magnesium are listed on food labels. However, most of the ingredients listed on a food label are chemical compounds and not individual elements.
  4. After students have completed their tasks, ask volunteers to list the essential elements found on their food labels. List them on the board as well as the chemical compound they come from.
  5. Ask if other students found any additional essential elements to add to the list. As before, list the ingredient in which each essential element is found.
  6. Ask students to compare the list of essential elements from their food labels to those shaded as essential on the periodic table on Master 1.4.
    • Students will see that the nutrition facts label on foods includes data about elements, such as calcium, iron, zinc, or manganese content. Students will see that food ingredients are the source of the 6 elements (C, H, N, O, P, and S) that are needed to make important biomolecules when they research the molecular formula. For example, they will see that carbohydrates and fats are made up of carbon, hydrogen, and oxygen. Proteins also contain nitrogen, phosphorus, and sulfur. Many of the other essential elements that are not structural components of biomolecules are needed as cofactors for enzymes and are present in very small amounts.
  7. Conclude the activity by asking, “What did this exercise teach you about health and diet?”
    • Students should recognize that their diet needs to contain a variety of foods to supply all the essential elements. Plants, as well as people, need a “balanced diet.”

Essential Links

Enriching Activities

Suggested Companion Resources

Agricultural Literacy Outcomes

Agriculture and the Environment

  • Understand the natural cycles that govern the flow of nutrients as well as the way various nutrients (organic and inorganic) move through and affect farming and natural systems (T1.9-12.h)

Food, Health, and Lifestyle

  • Accurately read labels on processed food to determine nutrition content (T3.9-12.a)

Education Content Standards


Plant Science Systems Career Pathway

  • PS.01.01
    Determine the influence of environmental factors on plant growth.
  • PS.01.02
    Prepare and manage growing media for use in plant systems.
  • PS.01.03
    Develop and implement a fertilization plan for specific plants or crops.
  • PS.03.02
    Develop and implement a management plan for plant production.


APHG Topic 5A: Agriculture, Food Production, and Rural Land Use: The development of agriculture led to widespread alteration of the natural environment.

  • Learning Objective 2
    Learning Objective 2
    Explain the connection between physical geography and agricultural practices.


HS-ESS3: Earth and Human Activity

  • HS-ESS3-4
    Evaluate or refine a technological solution that reduces impacts of human activities on natural systems.

HS-ETS1: Engineering Design

  • HS-ETS1-2
    Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

HS-LS2 Ecosystems: Interactions, Energy, and Dynamics

  • HS-LS2-4
    Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.

Common Core Connections

Speaking and Listening: Anchor Standards

    Integrate and evaluate information presented in diverse media and formats, including visually, quantitatively, and orally.
    Make strategic use of digital media and visual displays of data to express information and enhance understanding of presentations.

Language: Anchor Standards

    Determine or clarify the meaning of unknown and multiple-meaning words and phrases by using context clues, analyzing meaningful word parts, and consulting general and specialized reference materials, as appropriate.
    Acquire and use accurately a range of general academic and domain-specific words and phrases sufficient for reading, writing, speaking, and listening at the college and career readiness level; demonstrate independence in gathering vocabulary knowledge when encountering an unknown term important to comprehension or expression.


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