This is the new updated edition of the first book in the bestselling Uncovering Student Ideas in Science series. Like the first edition of volume 1, this book helps pinpoint what your students know (or think they know) so you can monitor their learning and adjust your teaching accordingly. Loaded with classroom-friendly features you can use immediately, the book includes 25 “probes”—brief, easily administered formative assessments designed to understand your students’ thinking about 60 core science concepts.

Access this probe as a Google form: English | Español

Download this probe as an editable PDF: English | Español

The purpose of this assessment probe is to elicit students’ ideas about plant growth. The probe is designed to find out whether students recognize that plants use their stored food to grow in the absence of light.

Friendly talk

Growth, behavioral response, tropism, phototropism, food

Although there can be exceptions because plant growth depends on several conditions, the best answer is Carl’s: “I think the plants in the dark closet will be the tallest.” Plants may grow taller in a dark place for a limited time. They respond to the lack of light by growing “taller” and more spindly, and the plant stem and leaves may be yellow and not as leafy. The growth in the dark is caused by auxins, which are plant hormones that regulate plant growth. Auxins are found in young tissue called the apical meristem, which is at the end of a shoot or stem, and are transported downward from the tip of the stem or shoot. Auxins stimulate plant cells to elongate, resulting in an increase in plant height.

Light is the form of energy plants capture to make food from carbon dioxide and water. This food can be used to carry out life processes and to build new structures for growth or repair, or it can be stored for later use. The plant in the dark uses the food it has made to continue growing taller as the cells continue to elongate. It may grow faster than the plant on the windowsill, although the growth will be spindly and etiolated. If the plant is in the dark for an extended period of time, eventually its food will be used up because it cannot photosynthesize more food without light, and the plant will no longer have the energy and building material from food that it needs to live and grow.

Elementary Students

Elementary students have varied experiences investigating the growth of plants. Knowing that plants require light is a grade-level expectation in state standards. In later elementary grades, students begin to understand why plants need light beyond just knowing that they need it to survive. The idea that light is needed for survival may imply that plants stop growing and soon die when placed in the dark.

Middle School Students

In middle school, students design their own experiments with plants that allow students to identify, manipulate, and control variables. They develop an understanding that plants make food and that this food can be used immediately for energy and building material for growth and repair, or it can be stored and used by a plant later when needed. They also begin to learn about behavioral responses of animals and plants, including plant tropisms. This probe is useful in determining whether students can link ideas about storing food and making food for growth.

High School Students

At this level, students are more systematic in investigating plant functions. Their knowledge of plant physiology and behavioral response includes the role of auxins and plant tropisms. Although students may understand how plants respond to a lack of sunlight, they may still revert to their intuitive beliefs about plants being unable to grow in the dark.

This probe can be used with students in grades 3–12. It can be extended by having students draw before and after pictures of the plant in the light and the plant in the dark. Have them use their drawings to explain what happened.

• Students appear to accept the idea that light is needed for all the stages of plant growth. However, they may not understand that light is used to make food for the plant and is not a condition for growth itself (Driver et al. 1994).
• A study conducted by Roth, Smith, and Anderson (1983) found that students held strongly to the idea that light is always required by plants, even in the face of contrary evidence such as plants growing taller in the dark.
• In a study conducted by Wandersee (1983), secondary students were asked to draw their predictions for a plant that was grown in a dark cupboard and one that was kept on a windowsill where the light could shine through. Almost 90% of the students drew the plant on the windowsill as large and healthy, leaning toward the light—which showed some understanding of phototropism. Eighty-five percent of the students drew the plant in the cupboard as being stunted. Only 11% of the students drew the plant in the cupboard as tall and spindly.

Barman, C., M. Stein, N. Barman, and S. McNair. 2001. Students’ ideas about plants: Results from a national study. Science and Children 41 (1): 46–51.

Damonte, K. 2005. Plants on the move. Science and Children 42 (7): 49–50.

Tolman, M., and G. Hardy. 1999. Teaching tropisms. Science and Children 37 (3): 14–17.

West, D. 2004. Bean plants: A growth experience. Science Scope 27 (7): 44–47.

• This probe can be followed up with an investigation in which students test their predictions. Once they have gathered and analyzed their findings, encourage them to explain their findings. Challenge them to revise their initial ideas based on their evidence and what they now know from their sensemaking discussion about plant growth and plant responses.
• Revisit this probe after students have had the opportunity to investigate and learn about how plants respond to the absence of light and construct a scientific explanation. As they revise their initial explanation, ask them to use the crosscutting concept of cause and effect in their scientific explanations.
• Provide students with an opportunity to test their ideas with different types of plants so that their ideas about plant growth are not limited to only one kind of plant.
• Ask students to describe situations in which they have seen plants growing in the absence of light, such as grass under a board or a houseplant left in a basement. Describe how the plant looks compared with a plant grown under ordinary light conditions.
• Be careful when developing the idea that plants need light to live. Clarify the need for light to make food and that food is sometimes stored by plants and used later for growth, repair, and the energy to carry out life processes when the ability to carry out photosynthesis is limited.
• Challenge older students to figure out and explain why a plant turns yellow in the absence of light.