Plant biology (photosynthesis)

How do plants solve the problems of energy, growth, and reproduction?

Biology for Future Elementary Teachers

Here's my current syllabus for an introductory college biology course for undergraduates planning on entering elementary teaching. This is NOT your traditionalcollege biology course. The goal of this course is ...

Project - Raising Plants

To study the life cycle and structure of plants, students grow plants from seed, fertilize them, and collect seed, starting the process over again. With the right growing conditions, almost ...

7. Flower Dissection


  • Flowers, possibly of several different species for cross-species comparisons. Almost any flower may be used although the anatomy is more easily distinguished in some flowers than others. Some common flowers with clearly differentiated parts include:Sarracenia flower dissection: Image courtexy of Noah ElhardtSarracenia flower dissection: Image courtexy of Noah Elhardt
    • Lily
    • Iris
    • Daffodil
    • Tulip
    • Wisconsin fast plant
    • Peas
    • Poppies
    • Gladiolus
  • Paper plates/plastic trays
  • Scissors or razor blade (to open the ovary)
  • Hand lens
  • Optional: tweezers
  • Optional: dissecting scope

7. Flower and Frog Dissection

Sarracenia flower dissection Image courtexy of Noah Elhardt Leopard frog in duckweed Image courtesy of Steven Dunlop To learn about the structure and function of living things, it is essential to ...

6. Cell Energy - Colorful Respiration

Blow through a straw into bluish liquid and watch it turn green then yellow before your eyes. Put some plants into the yellow liquid, leave it in a sunny window, come back the next day and the liquid is green. What if you leave the plants in the dark? What if you put some pond snails in? What if you put both pond snails and plants? What’s going on?

The liquid is bromthymol blue (BTB) a non-toxic acid-base indicator that can be used to indirectly measure levels of dissolved carbon dioxide (CO2). The amount of CO2 in a solution changes the pH. An increase in CO2 makes a solution more acidic (the pH gets lower). A decrease in CO2 makes a solution more basic (the pH gets higher). The reason for this is that carbon dioxide that is dissolved in water is in equilibrium with carbonic acid (H2CO3).

CO2 + H2O ↔ H2CO3

In any solution, while the majority of CO2 stays as CO2, some of it is converted to H2CO3, turning the solution slightly acidic. If CO2 is added to the water, the level of H2CO3 will rise and the solution will become more acidic. If CO2 is removed from the water, the amount of H2CO3 falls and the solution becomes more basic. Thus, acid-base indicators such as BTB can indirectly measure the amount of CO2 in a solution.

For more than you ever wanted to know about carbonic acid, see the Wikipedia article on carbonic acid. For the example lesson plans developed by Bob Culler through Access Excellence at the National Health Museum. For a great time lapse video showing BTB color changes using elodea and snails, see Activity C13 from Addison-Wesley’s Science 10 curriculum.


  • Bromthymol blue (BTB can be ordered from any science supply company such as Flinn Scientific $9 for 1 liter 0.04% BTB solution).
  • Several 2 liter soda bottles
  • Test tubes
  • 500 ml beakers or disposable plastic or paper cups
  • Water (since the pH of tap water varies, you may wish to use distilled water for your master BTB solution)
  • Drinking straws
  • Plastic wrap
  • Elodea
  • Pond snails


  1. Before the lesson, the teacher should mix a master BTB solution in one or more 2 liter soda bottles. For each 2 liter bottle, mix 120 ml 0.04% BTB with 1800 ml water. The end result should be a medium blue master BTB solution, dilute enough to be safe for plants and snails but dark enough to see the color changes.
  2. Pour 200 ml diluted BTB in a beaker or cup.
  3. Take a deep breath then blow bubbles in the BTB solution through a drinking straw. What happened? Why?
  4. Set up a test tube rack with 3 tubes. In tube #1 put unbubbled BTB solution (blue). In tube #2 put bubbled BTB solution (yellow). Tubes #1 and #2 will be your comparison tubes. In tube #3 you have a choice of what to do. Choose one option from each of the following columns:
    BTB solution Living things
    Light conditions
    bubbled BTB (yellow) spring of Elodea Sunny window/bright light
    unbubbled BTB (blue) 5 pond snails Dark closet/drak heavy cloth
    both Elodea and 5 pond snails  
  5. Make a hypothesis about what will happen to your tube.
  6. After 24 hours, check the color of your tube. What happened? Why?

Going Further

6. Cell Energy - Photosynthesis in a Jar

These experiments use a bell jar (or any other very large, clear, glass jar) to determine the identity of the gas produced by plants. It mirrors the famous experiments of Joseph Priestley and Jan Ingenhousz from the 1700’s that first demonstrated the existence of oxygen and its importance to plants and animals.

In 1771 and 1772, Priestly conducted a series of experiments using a bell jar. It was known that a candle placed in a sealed bell jar would eventually burn out and could not be relighted while still in the jar. Priestly discovered that a plant can survive indefinitely within a jar. Thus, he tried placing a plant into the jar with the burning candle. The candle went out as before and could not be relit right away. Priestly waited several days and tried again. The candle could be relit! The plant had restored the air inside the jar! (Do not try the next series of experiments since it harms animals!) Next priestly investigated what would happen to animals. He found that a mouse placed inside a sealed jar will eventually collapse. However, a mouse can survive in a sealed jar with a plant since the plant restores the air. Priestly was the first to demonstrate that oxygen is necessary for fire and animals but that given time, plants can create oxygen, allowing fires to burn and animals to breathe.

6. Cell Energy - Bubbling Plants

Elodea nuttallii: Image courtesy of Christopher Fischer.Elodea nuttallii: Image courtesy of Christopher Fischer.Summary
Students often believe that only animals “breathe”, but all things exchange gases with their environment. It’s just that the process is not so obvious in plants. Elodea is a very common water plant that can be found in aquarium stores. As photosynthesis occurs, oxygen is produced as a by-product. Elodea releases bubbles of oxygen as it photosynthesizes. In fact, the number or volume of bubbles in a certain amount of time can be used as a rough measure of photosynthetic rate.

6. Cell Energy - Plant Pigments

Chlorophyll extractionChlorophyll extractionSummary
Chlorophyll is the pigment in plants that captures sunlight energy and uses it to drive photosynthesis. While chlorophyll does give plants their characteristic green color, chlorophyll actually comes in many colors and subtypes ranging from green to yellow to orange to red. In this experiment, students use paper chromatography to separate the many pigments from one another. First the pigments are extracted from the plants by simply crushing the plant cells open on the filter paper with the edge of a penny. When the filter paper is then immersed in rubbing alcohol, the pigments are carried upwards through capillary action. The smallest pigments travel more quickly and thus separate from the larger pigments that remain closer to the origin line.

6. Cell Energy (photosynthesis and respiration)

Here you will find a toolbox full of inquiry investigations on photosynthesis and respiration. Rather than the detailed lesson plans provided elsewhere at My Science Box, each experiment only contains ...

1. Is it alive?

What does it mean to be alive? Is a cactus alive? Is a seed alive? Is the air we breathe alive? What are the necessary characteristics? To hook students into ...