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Lesson Plan

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DNA: Expressions in Agriculture

Grade Level

6 - 8

Purpose

This lesson centers around the activity of extracting DNA from a strawberry while highlighting careers in biotechnology and agriculture. Grades 6-8

Estimated Time

Two 45-minute sessions

Materials Needed

Activity 1:

  • Strawberry DNA Extraction Lab activity sheet, 1 per student
  • Frozen strawberries, 3 per group
    • Frozen strawberries can thaw as students smash them in the ziploc bag. Fresh strawberries also work well if they are in season and more cost effective.
  • Ziploc sandwich bags, 1 per group 
  • DNA extracting solution 
    • Make one day ahead so there are no bubbles in the solution. In a gallon container mix:
      • 1/2 gallon (2000 ml) water
      • 1/2 cup (120 ml) clear dish detergent
      • 2 tablespoons (30 ml) salt
  • Tablespoon
  • Funnels,* 1 per group
  • Plastic cups,* 1 per group
  • 4" x 4" squares of cheesecloth,* 2 per group
  • Graduated test tubes,* 1 per group
  • Rubbing alcohol, chilled
  • Pipettes,* 1 per group
  • Microcentrifuge tubes,* 1 per student
  • Yarn,* 1 necklace-length piece per student

*These items are included in the Strawberry DNA Necklace Kit, which is available for purchase from agclassroomstore.com.

Activity 2:

Vocabulary

deoxyribonucleic acid (DNA): deoxyribonucleic acid; a self-replicating material present in nearly all living organisms as the main constituent of chromosomes; the carrier of genetic information

genetic engineering: the process of directly modifying an organism's genes using biotechnology to produce desired traits

genetically modified organism (GMO): any organism whose genetic material has been altered using genetic engineering techniques

Did You Know?
  • In 2013 about half of the total land used to grow crops in the United States was planted with genetically engineered crops.1
  • Corn, cotton, and soybeans make up the majority of the genetically engineered crops planted in the United States.1
  • More than 90% of the soybeans planted in the United States in 2013 were genetically engineered.1
Background Agricultural Connections

Prior to this lesson students should have a basic understanding of cells, cell organelles and their functions, and the structure of DNA.

Although principles of biotechnology have been in use for over 6,000 years, the scientific field of biotechnology is relatively new. Biotechnology can be broadly defined as the use of living organisms or biological processes to make a product. Applications of biotechnology include using microorganisms to clean oil slicks, finding cures for human diseases by identifying related DNA sequences, and improving crop yields by transferring DNA from one organism to another to modify the genetic makeup of that organism.

Gregor Mendel was the first person to trace the characteristics of successive generations of a living thing (peas), and his discoveries laid the foundation for biotechnology as it is practiced today. Mendel was not a world-renowned scientist in his day. Rather, he was an Augustinian monk who taught natural science to high school students. His discovery of trait transfer was, at first, a theory. Genetic theory is no longer questioned in anyone’s mind. Many diseases are known to be inherited, and pedigrees are commonly traced to determine inheritance patterns of disease. Plants are now designed in laboratories to exhibit desired characteristics. The practical results of Mendel’s research not only changed the way we perceive the world but also the way we live.

The modern processes of biotechnology allow scientists to select what types of traits an organism will have and create changes that would otherwise happen slowly, over many seasons in the field. In agriculture, biotechnology is being used to increase crop yields, produce insect- and weed-resistant plants, and enhance vitamin and mineral content in food. It is also used to increase milk production and make cheese. Many of these advancements have been achieved by directly manipulating the DNA of plants and microorganisms, a process known as genetic engineering. Plants and microorgansims with genetically engineered DNA are called genetically modified organisms (GMOs) or simply bioengineered. The process of transferring genetic information between plants was developed in 1973, and there is still debate regarding the benefits and risks of GMOs.

In this activity, students will model a process that scientists use to extract DNA strands. Deoxyribonucleic acid (DNA) is a long molecule that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. Yes, DNA is in all your food! The main role of DNA molecules is the long-term storage of information. DNA is often compared to a set of blueprints, a recipe, or a code because it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but DNA contains more than just genes. Other DNA sequences are involved in regulating the use of this genetic information, and others have structural purposes. For more information about genetics and easy to understand tutorials, visit the Genetic Science Learning Center.

In this lab, students will extract strands of DNA from the nuclei of strawberry cells. Mashing the strawberries will break the cells’ walls, exposing the inner membranes. The DNA extracting solution will disrupt the cell and nuclear membranes. Filtering the mixture gets rid of all the strawberry cell parts that are bigger than DNA. Finally, the alcohol causes the DNA to precipitate and come out of the solution. Participating in the extraction of DNA will help familiarize students with one aspect of the work biotechnologists do.

In terms of careers, a plant scientist or genetic engineer may use biotechnology as a tool; these scientists may also employ biotechnologists. Biotechnologists have diverse and interesting careers. They work with living organisms in manufacturing and industrial settings. Often biotechnologists do not work with the complete plant or animal, but rather focus on cells, tissues, and even microorganisms that may be contained within the larger plant or animal structure. Often, a biotechnologist works in a laboratory setting under carefully controlled conditions to make changes to the minute systems that exist within a single cell.

Biotechnologists can be hired to help develop new medicines and medical treatment options, assist in waste treatment or environmental remediation, or develop new characteristics in livestock and plants for agricultural use. Biotechnologists work in many different sectors, including hospitals and research facilities, private food or animal production companies, pharmaceutical companies, government agencies, and food processing plants. They come from backgrounds in science and engineering or a combination of several educational groups including chemistry, biochemistry, microbiology, life sciences, and pharmacy sciences.

Engage
  1. Tell your students that you are thinking of a specific food, you are going to give them a list of clues, and you want them to guess which food you are thinking of. Ask students to raise their hands when they think they know the answer.
    • This food comes from a perennial plant.
    • In the United States, California grows the most of this food.
    • This food is usually red but can also be yellow or white.
    • This food has seeds on the outside.
    • This food is a fruit.
    • This fruit provides vitamin C to our diet.
    • What is this fruit? Strawberries!
  2. Display the image below of various types of strawberries. Ask your students to list the similarities and differences they see among the pictures. Help students recognize that various colors, sizes, and shapes of strawberries exist. Strawberries are usually red, but they can also be white and yellow. Strawberries can also be small or large and oblong or round. 
  3. Point out to the students that while these strawberries have different characteristics, they are all still strawberries. Ask the students, "What makes each of these strawberries different?" Provide further guiding questions and draw on students' prior knowledge of genetics and traits to help them recognize that the DNA in each of these strawberries is slightly different, leading to variation in characteristics.
  4. Explain that strawberry farmers and plant breeders work together to create varieties of strawberries that meet our needs. 
Explore and Explain

Activity 1: Strawberry DNA Extraction

  1. Prepare the DNA extracting solution the day before the activity. 
  2. Review and discuss the information provided in the Background Agricultural Connections section of the lesson with students. Pass out a Strawberry DNA Extraction Lab activity sheet to each student.
  3. Divide students into groups of three or four and provide each group with the following materials: Ziploc bag containing 3 strawberries and 3 tablespoons of DNA extracting solution, funnel, plastic cup, 2 squares of cheesecloth, graduated test tube, pipette, test tube, 3–4 microcentrifuge tubes (1 per student), and 3-4 pieces of yarn (1 per student). 
  4. Guide students through the following instructions, which are also provided on their lab activity sheets:
    • Collect your materials.
    • Carefully remove most of the air from the Ziploc bag, and seal it well.
    • Gently mash the strawberries through the bag. Be careful not to break the bag, but mix the strawberry mash thoroughly.
    • Place the funnel in the plastic cup. It should sit on the rim of the cup.
    • Place the two squares of cheesecloth into the funnel, forming a liner for straining.
    • Carefully pour the strawberry mixture into the funnel, making sure to catch the solids with the cheesecloth. After filtering the mixture, remove the cheesecloth, and place it into the Ziploc bag for disposal.
    • Add 5 ml of the filtered strawberry extract to the graduated test tube using the funnel. Hold the tube near the top so that the heat from your hand does not affect the extraction.
    • Remove the funnel, and use the pipette to forcefully add 3 ml of the isopropyl or rubbing alcohol to the test tube. Take care not to tilt or tip the test tube; do not mix the two liquids.
    • Observe the line between the strawberry mixture and the alcohol. You will notice a white, thread-like cloud appearing at this line. This is the strawberry DNA. The DNA will clump together and float to the top of the alcohol layer.
    • Holding the tube still, observe the tubes of others around you. Do you notice any differences?
    • Using the pipette, add some DNA strands and some of the alcohol in the test tube to each person’s microcentrifuge tube. Repeat steps 6 to 8 if necessary to collect enough DNA for everyone’s microcentrifuge tube.
    • Close the cap of the microcentrifuge tube tightly around a piece of yarn and tie the ends of the yarn to make a necklace.
    • Clean up! Dump the remaining strawberry solution where instructed, throw away the Ziploc bags, and collect the cups, test tubes, funnels, and pipettes to clean so they can be used again.

Activity 2: Careers in Biotechnology

  1. Provide each student with the Biotechnology WebQuest activity sheet, and instruct them to answer the questions on a separate sheet of paper.
  2. Review the students’ responses to the activity sheet.
  3. Ask students what kinds of careers in biotechnology would rely on DNA extraction. Guide the conversation so that students make a connection between the DNA they have extracted and the scientists who rely on similar methods to research and create bioengineered seed varieties. 
  4. Ask students about some of the pros and cons of biotechnology.
  5. List careers that would use biotechnology tools and information. 
Elaborate

  • Watch the America's Heartland episode, Sweet Sweet Strawberries. This 5-minute video highlights strawberry production at a California farm, describes how strawberries are selectively bred for specific traits, and explains how strawberries are packaged for shipping all over the United States.

  • Now that students have a basic knowledge of DNA, see the lesson The Science of a GMO to teach them the scientific process of creating a genetically modified plant.

Evaluate

After finishing the activities, review the following key concepts:

  • Like all living things, every plant and animal used in agriculture has DNA.
  • The process of DNA extraction is an important component of agricultural biotechnology, allowing plant and animal breeders to more accurately select for desirable traits and allowing scientists to genetically engineer organisms for agricultural use.
  • There are a wide variety of agricultural career opportunities in biotechnology.

Sources
  1. http://www.ers.usda.gov/webdocs/publications/err162/43667_err162_summary.pdf
Recommended Companion Resources
Author

Debra Spielmaker and Denise Stewardson

Organization

Utah Agriculture in the Classroom

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