Alternative Conceptions about Plants

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Common Misconceptions about Plants

Plants are one of the first science topics taught in elementary school. Students plant seeds, grow and measure plants, observe the life cycle, and learn about plant structures and functions. This is in keeping with the National Science Education Standards, which states that students in grades K-4 should understand that plants have basic needs, including air, water, nutrients, and light. Elementary students should also understand plants’ life cycles and that all animals depend on plants.

While these concepts seem easily taught through observation and care for plants, research shows that students do develop significant misconceptions about plants and their needs. Some of these misconceptions may be related to elementary students’ limited classification skills. Many others stem from students’ tendency to give plants human characteristics. Formative assessment can help teachers be aware of student thinking and mindful of their own understanding and explanations of concepts.

We’ve highlighted some common misconceptions about plant classification, plant parts, needs of plants, plant food, and photosynthesis and respiration. Rather than an exhaustive list, this is meant to get you thinking about the ideas and understandings your own students may have. We’ve also provided tools for formative assessment and ideas for planning instruction accordingly.

MISCONCEPTIONS

Plant Classification

Students tend to classify plants based on recognizable characteristics (green, grow in the soil) and parts (stem, leaves, flowers). For example, about half of students in a recent study misclassified a mushroom as a plant because its stalk resembles the stem of a plant. Students may also not consider trees to be plants. However, this may be due to students’ limited classification skills rather than an understanding of plants.

Researchers have found that when classifying animals, elementary students tend to use mutually exclusive groups rather than subsets of a larger group. This may be the same for plants.

Students may think… Instead of thinking…
Plants are not alive. Plants are alive, even though they are different from animals and humans in many ways.
Trees, grass, vegetables, and weeds are not plants. Plants have many different characteristics. There are many different types of plants throughout the world. Not all plants have the same structures (stems, leaves, flowers, roots).


Plant Parts

While most students recognize the stem, leaves, and flowers of plants, fewer identify roots as a common structure. Students may need more experiences observing root systems of various plants.


Students may think… Instead of thinking…
Plants take in all substances they need to grow through their roots. Plants take in air through their leaves. Chloroplasts in the plant absorb the sun’s energy for use in photosynthesis. Water and minerals are taken in through the roots.
Leaves take in water. Water is taken in through the roots.
Plants get their energy from the soil through roots. Chloroplasts in the plant absorb the sun’s energy for use in photosynthesis. Water and minerals are taken in through the roots.


Needs of Plants

Students also tend to give plants human characteristics, especially when it comes to considering what plants need to grow. They may describe plants as eating, drinking, or breathing, or believe that plants need things that are provided by people. This may be an unintended consequence of having students grow and care for plants. The role of light and nutrients in plant growth seems to be especially difficult for elementary students. For example, students may view sunlight as useful but not essential for plant growth.

Students may think… Instead of thinking…
Plants are not alive. Plants are alive, even though they are different from animals and humans in many ways.
Trees, grass, vegetables, and weeds are not plants. Plants have many different characteristics. There are many different types of plants throughout the world. Not all plants have the same structures (stems, leaves, flowers, roots).


Plant Food

Students tend to classify plants based on recognizable characteristics (green, grow in the soil) and parts (stem, leaves, flowers). For example, about half of students in a recent study misclassified a mushroom as a plant because its stalk resembles the stem of a plant. Students may also not consider trees to be plants. However, this may be due to students’ limited classification skills rather than an understanding of plants.

Researchers have found that when classifying animals, elementary students tend to use mutually exclusive groups rather than subsets of a larger group. This may be the same for plants.

Students may think… Instead of thinking…
Sunlight is helpful but not critical. Sunlight is essential for plant survival.
Sunlight helps plants grow by keeping them warm. Chloroplasts in the plant absorb the sun’s energy for use in photosynthesis.
Soil provides a support structure and food for plants. Some plants grow in soil-free environments. Plants take up water and minerals from soil, but not "food."
Plants need things provided by people (water, nutrients, light) While people often care for plants (especially those indoors), plants as a whole are not dependent on people for their needs.


Photosynthesis and Respiration

Again, the tendency to give plants human or animal characteristics leads to misconceptions. For example, students often believe that plants perform “reverse breathing” in which they inhale carbon dioxide and exhale oxygen. In reality, plants use and produce both carbon dioxide and oxygen through two processes: photosynthesis and respiration.

Photosynthesis is the process by which plants convert carbon dioxide and water into sugar and oxygen. Photosynthesis requires energy, and a plant’s chloroplasts absorb solar energy to fuel these reactions.

Photosynthesis can only happen during the day when sunlight is available. Respiration, on the other hand, is the breaking down of sugars (and oxygen) to provide energy for plant growth.

Respiration also produces carbon dioxide and water, essentially the opposite of photosynthesis. Respiration does not require light and can happen at night.

Plants do release oxygen into the atmosphere, as they produce more than they need during photosynthesis.

The word “respiration” is often used incorrectly to describe breathing, but the two processes are different. Breathing, which occurs in animals, is the process of obtaining oxygen and removing carbon dioxide via lungs or gills. Respiration, as previously described, is the release of energy from food and occurs in both animals and plants.

Students may think… Instead of thinking…
Plants breathe by inhaling carbon dioxide and exhaling oxygen. Plants take in air through their leaves. Both carbon dioxide and oxygen are used for different processes. Photosynthesis requires carbon dioxide, while respiration requires oxygen. While plants do release oxygen, it is a by-product of photosynthesis and is not released through breathing. Plants do not breathe. They absorb air through the stomata (pores) in their leaves.
Plants obtain their energy directly from the sun. Energy from the sun allows the plant to carry out photosynthesis and produce sugars. Respiration breaks down these products and provides energy for the plant.



This article was written by Jessica Fries-Gaither. For more information, see the Contributors page. Email Jessica at beyondpenguins@msteacher.org

Copyright March 2009 – The Ohio State University. This material is based upon work supported by the National Science Foundation under Grant No. 0733024. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. This work is licensed under an [1]Attribution-ShareAlike 3.0 Unported Creative Commons license