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CareerStart lessons: Grade eight
This collection of lessons aligns the eighth grade curriculum in math, science, English language arts, and social studies with potential career opportunities.
Page 5.4

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Essential question: Why do plants need sunlight to carry on cell respiration and photosynthesis?

Learning outcomes

Students will understand the effect of sunlight on cell processes.

Teacher planning

Materials needed

  • Phenol red (Dilute with water if concentrated; blow bubbles with a straw until it turns orange or neutral. If it is in solid powdered form mix with isopropyl alcohol to turn into a solution.)
  • Elodea (water plant) or a small leaf of any house plant
  • 4 test tubes with stoppers
  • Aluminum foil or saran wrap
  • Test tube holder

Time required for lesson

One class period (50-55 minutes), plus observations taken over one week.


  1. Anticipatory Set: Ask students the following questions:
    • Why do farmers plant certain crops directly in sunlight and others in the shade?
    • What does a horticulturist study?
    • How could the amount of sun exposure affect crop yield?
    • Why do plants die in the dark?
  2. Draw the process of photosynthesis and respiration on the board. Discuss the process of plants taking in sunlight to produce food and to give off oxygen during cellular respiration. Examples of photosynthesis and respiration diagrams can be found at the following websites:
  3. Since animals give off CO2, discuss why it is important to have plants in our environment and the necessity of sunlight for photosynthesis.
  4. To observe the effect of sunlight on photosynthesis, have students conduct an acid/base test according to the lab instructions below. The lab will enable students to test for the presence of low or high H ions. The higher the H ions, the more CO2 being used during cellular respiration.
  5. Have students construct a table in their laboratory journals to record what they observe:
    Plant with phenol red
    in sunlight
    Plant with phenol red
    in the dark
    Phenol red (only)
    in the sunlight
    Phenol red (only)
    in the dark
  6. After students set up the lab for observation, discuss careers that require specialized knowledge of plants. (See “Career Information” below.)
  7. As students make their observations, share with them the information about cell respiration. (See “Teacher Information” below.)

Student lab instructions

  1. Place a small amount of phenol red in the bottom of each test tube.
  2. Using a cutting from the water plant (Elodea) or household plant, place a small amount inside each test tube, one for light and the other for the dark. The two remaining test tubes will act as a control.
  3. Seal the top of the test tubes with stoppers and additional saran wrap or aluminum foil.
  4. Place one set of test tubes in direct sunlight and the other two in the dark.
  5. Record observations in the chart. (The change may take several days to occur, depending on available sunlight.)
  6. Follow-up: Explain your findings in a letter to the local horticultural society or 4H club. Detail the importance of sun exposure to plant health and reduction in environmental stress.

Teacher information

  • Plants take in CO2 and give off O2 during cell respiration.
  • The presence of CO2 will turn phenol red acidic causing it to turn yellow (indicating high H ion concentration).
  • As the presence of CO2 decreases the phenol red will become basic, or alkaline, turning pink (indicating a low H ion concentration).
  • When the phenol red is orange it is neutral.
  • In this experiment, as the amount of CO2 in the environment is used by the plant during photosynthesis, the phenol red will turn pink.
  • If the CO2 concentration decreases, the H ion concentration will also decrease and the solution will change to pink, becoming basic.
  • If the CO2 concentration increases, the H ion concentration will also increase and the solution will change to yellow, becoming acidic.
  • Neutral solutions of phenol red will be orange.


Have students research different types of horticulture and the career options each branch of study promotes. (For example: arboriculture, floriculture, landscape horticulture, olericulture, polomogy, viticulture)

Career information

Career information comes from the Bureau of Labor Statistics’ Occupational Outlook Handbook.

Horticultural specialty farmers
Oversee the production of fruits, vegetables, flowers, and ornamental plants used in landscaping, including turf. They also grow nuts, berries, and grapes for wine. Specialize in improving crop health and yield; plant diversity; and drought-, insect-, and disease-tolerant plants.
Agricultural managers
Manage the day-to-day activities of one or more farms, ranches, nurseries, timber tracts, greenhouses, or other agricultural establishments for farmers, absentee landowners, or corporations.
Aquaculture farmers
Cultivate kelp and seaweed for production and raise fish and shellfish in marine, brackish, or fresh water, usually in ponds, floating net pens, raceways, or recirculating systems. (Specialists in aquaphonics)
Practitioners of forestry, the science of managing forests. Foresters may oversee the growth and harvesting of timber for industry, manage reforestation efforts, or remove dead and diseased trees from forested land.
Study plants and their environments. Botanists may study algae, fungi, lichens, mosses, ferns, conifers, and flowering plants; others specialize in areas such as identification and classification of plants, the structure and function of plant parts, the biochemistry of plant processes, the causes and cures of plant diseases, and the interaction of plants with other organisms and the environment


Optional resources for more information on the topics covered in this lesson

Photosynthesis Notes
These well-organized notes and diagrams depict photosynthesis, light dependent reactions, and the Calvin cycle at the molecular level.
Careers in Horticulture
Students can explore career opportunities through stories, photos, and audio files on this page by the American Society for Horticulture Science.
NCSU Department of Horticulture Science
NC State University describes the different degree options in the field of horticulture so that students can select the best choice for their goals.
What Can I Do with a Major in Horticultural Science?
Kansas State University explains what students can do with a major in horticultural science and lists required courses, career-related experiences and internships, and sample careers and possible work settings.

  • North Carolina Essential Standards
    • Science (2010)
      • Grade 6

        • 6.L.1Understand the structures, processes and behaviors of plants that enable them to survive and reproduce. 6.L.1.1 Summarize the basic structures and functions of flowering plants required for survival, reproduction and defense. 6.L.1.2 Explain the significance...

North Carolina curriculum alignment

Science (2005)

Grade 8

  • Goal 6: The learner will conduct investigations, use models, simulations, and appropriate technologies and information systems to build an understanding of cell theory.
    • Objective 6.01: Describe cell theory:
      • All living things are composed of cells.
      • Cells provide structure and carry on major functions to sustain life.
      • Some organisms are single cell; other organisms, including humans, are multi-cellular.
      • Cell function is similar in all living things.
    • Objective 6.04: Conclude that animal cells carry on complex chemical processes to balance the needs of the organism.
      • Cells grow and divide to produce more cells.
      • Cells take in nutrients to make the energy for the work cells do.
      • Cells take in materials that a cell or an organism needs.