photosynthesis
Misconceptions
about photosynthesis
When teaching, it is always important to be aware of an misconceptions that students might have about any given topic. When teaching anything about plants there are commonly a lot of misconceptions since students generally do not know a lot about them. On this page, I have listed four common misconceptions that students have about photosynthesis. I have also provided some ideas on how you, as a teacher, can address with these misconceptions in your classroom.
Plants are green because they absorb green light
This is a common misconception amongst students. As students are not required to take any physics prior to taking SBI4U, they may not have a strong background in the electromagnetic spectrum and how humans see colours. It is important to go over this with students in order for them to understand why plants are green.
To overcome this misconception there are many things you can do as a teacher. Some of these strategies include:
To overcome this misconception there are many things you can do as a teacher. Some of these strategies include:
- Spend a lesson teaching students about the electromagnetic spectrum
- Show students the visible portion of the electromagnetic spectrum using a prism
- Conduct a laboratory demonstration to show students that chlorophyll absorbs red light (see activity below)
Demonstration: Fluorescence of Chlorophyll
![Picture](/uploads/6/0/8/4/60840857/2477695_orig.png)
You can show your students that plants absorb red wavelengths of light by using this demonstration. By extracting chlorophyll from leaves, you can show your students that red light is released by electrons without the presence of an Electron Transport Chain.
Materials:
Procedure:
Materials:
- Spinach leaves
- 95% ethanol
- Mortar and pestle
- Filter paper
- Erlenmeyer flask
Procedure:
- Tear the spinach into tiny pieces
- Cover the leaves with 95% ethanol
- Crush the leaves with a mortar and pestle
- Use filter paper to filter the solution into an Erlenmeyer flask
- Shine light onto the solution to see the red light being emitted-- this is best done by shutting off lights in the room and shine a light from a flashlight or an overhead projector
Explanation:
In the plant, when chlorophyll absorbs red light, electrons become excited and are passed through an Electron Transport Chain. When chlorophyll is extracted from the spinach leaves, the electrons become excited but do not have anywhere to do. Since they do not have anywhere to go, the energy from the photon is released in the form of red light and the electron returns to its ground state. When the photon is release, the chlorophyll solute fluoresces red light.
In the plant, when chlorophyll absorbs red light, electrons become excited and are passed through an Electron Transport Chain. When chlorophyll is extracted from the spinach leaves, the electrons become excited but do not have anywhere to do. Since they do not have anywhere to go, the energy from the photon is released in the form of red light and the electron returns to its ground state. When the photon is release, the chlorophyll solute fluoresces red light.
Di Giuseppe (2003)
'dark reactions' do not require sunlight
This is a common misconception in the way the stages of photosynthesis are worded. Typically known as the light reactions (light-dependent reactions) and dark reactions (light-independent reactions), students believe that the "dark reactions" do not require sunlight in order to proceed.
However, this is untrue. The "dark reactions", or light-independent reactions, still require the products from the "light reactions" in order to proceed. Although indirectly, these reactions still require energy from the sun in order to occur. Many students are led to believe that these reactions occur at night, when it is dark.
To counter this misconception, it is important that the correct vocabulary is used. Although some textbooks still refer to the light-independent reactions as "dark reactions" it is important that this misconception is explained to students throughout the course of teaching photosynthesis.
A way that this misconception could be taught to students would be to have students conduct an inquiry-based literature review to discover for themselves whether or not these reactions actually occur in the dark. This would be a good way to get students to explore real-world studies surrounding photosynthesis and to learn a bit about the history of the research.
However, this is untrue. The "dark reactions", or light-independent reactions, still require the products from the "light reactions" in order to proceed. Although indirectly, these reactions still require energy from the sun in order to occur. Many students are led to believe that these reactions occur at night, when it is dark.
To counter this misconception, it is important that the correct vocabulary is used. Although some textbooks still refer to the light-independent reactions as "dark reactions" it is important that this misconception is explained to students throughout the course of teaching photosynthesis.
A way that this misconception could be taught to students would be to have students conduct an inquiry-based literature review to discover for themselves whether or not these reactions actually occur in the dark. This would be a good way to get students to explore real-world studies surrounding photosynthesis and to learn a bit about the history of the research.
All Plants Are Photosynthetic
Since many plants photosynthesise, many students believe that ALL plants photosynthesise. However, this is untrue. There are three main types of plants:
- autotrophic plants
- photosynthetic
- use carbon dioxide and solar energy to produce glucose
- example: maple trees
- insectivorous plants
- catch and slowly digest insects for energy
- example: Venus fly trap
- semiparasitic plants
- take food and nutrients from autotrophic plants
- example: mistletoe
Watson (2014)
Photosynthesis is the exact opposite of cellular respiration
Many students think that photosynthesis is the exact opposite reaction of cellular respiration. This is a common misconception because the reactions of photosynthesis and cellular respiration are often oversimplified. The simplified reaction equations are seen below:
photosynthesis: 6CO2 + 6H20 --> C6H12O6 + 6O2
cellular respiration: C6H12O6 + 6O2 --> 6CO2 + 6H20
These simplified reactions are not an accurate depiction of the major steps of photosynthesis and cellular respiration. These reactions imply that both photosynthesis and cellular respiration occur in one step, which is largely untrue. As discussed in the Content section of this resource website, there are many steps to photosynthesis just as there are in cellular respiration.
It is important to discuss this misconception with students in order for them to understand that they are not direct inverses of each other.
An activity that could counter this misconception would be to have some students write out all of the steps of photosynthesis while other students write out all of the steps of cellular respiration on large chart paper. After you put all chart paper beside each other, it will be vert obvious to students that photosynthesis is not the direct opposite reaction of cellular respiration.
photosynthesis: 6CO2 + 6H20 --> C6H12O6 + 6O2
cellular respiration: C6H12O6 + 6O2 --> 6CO2 + 6H20
These simplified reactions are not an accurate depiction of the major steps of photosynthesis and cellular respiration. These reactions imply that both photosynthesis and cellular respiration occur in one step, which is largely untrue. As discussed in the Content section of this resource website, there are many steps to photosynthesis just as there are in cellular respiration.
It is important to discuss this misconception with students in order for them to understand that they are not direct inverses of each other.
An activity that could counter this misconception would be to have some students write out all of the steps of photosynthesis while other students write out all of the steps of cellular respiration on large chart paper. After you put all chart paper beside each other, it will be vert obvious to students that photosynthesis is not the direct opposite reaction of cellular respiration.
Hershey (2004)