Lesson
Purpose of the work:
– understanding the mechanism and regulation of the transpiration process in plants
– determination of the influence of internal factors on water evaporation
Run time:
Expected results:
After completing the work, students can:
- develop teamwork skills
- be able to analyze and summarize the information received
- draw logical conclusions
Teacher’s Guide:
- Divide the students to 3 students in each group.
- Before starting laboratory work, please read the safety rules by following the link:
To download the worksheet, please follow this link:
Theoretical part
Like all living organism, plants also require an excretory system to discharge excess water from their body. This process of elimination of excess water from the plant body is known as transpiration. It is generally the evaporation of water from the surface of the leaves.
Some internal factors influencing this process are:
Degree of stomatal opening: Holes can be open or closed. When the stomata are open, transpiration increases, and when they are closed, it decreases.
Presence of a waxy layer: Some plants have a thin layer of wax on the surface of the leaves. This helps to reduce transpiration because the wax prevents water from evaporating quickly from the leaf surface.
Cell structure of the epidermis: The epidermis is the topmost layer of leaf cells. If the cellular structure of the epidermis changes, this can affect the rate of transpiration.
The shape and size of the stomata: holes can be of different shapes and sizes. The leaves of some plants may have more or less lobes, which also affects transpiration.
Leaf surface area: Plants with larger leaves are more breathable, so they can evaporate more water.
Sources:
- Изображение от <a href=”https://ru.freepik.com/free-photo/top-view-of-different-leafs-concept_7666445.htm#query=%D1%80%D0%B0%D0%B7%D0%BD%D1%8B%D0%B5%20%D1%84%D0%BE%D1%80%D0%BC%D1%8B%20%D1%80%D0%B0%D1%81%D1%82%D0%B5%D0%BD%D0%B8%D0%B9&position=21&from_view=search&track=ais“>Freepik</a>
- https://ru.freepik.com/free-vector/diagram-showing-plant-cell-with-stomata-and-guard-cell_5983941.htm
Practical part
Step 1 Prepare a 3% cobalt chloride solution. To do this, stir 5 g of cobalt chloride in 100 ml of distilled water.
Step 2. Place pieces of filter paper in the prepared solution. Do not take paper strips with your hands! Use tweezers.
Step 3. After the solution is completely absorbed, place the papers in a Petri dish and dry under the sun. After drying, the color of the filter paper should turn blue. These blue indicator strips turn bright pink when interacting with water molecules.
Step 4. Dry paper strips should be stored in a vial with a stopper.
Step 5 Take one of the strips of paper and cut it into equal squares.
Research part
Use a fresh, well-watered plant for this experiment.
Step 6. First put the indicator paper on the top and then on the bottom surface of the plant leaf and cover both sides with a glass slide. Secure slides with tape or rubber band.
Step 7. Put the leaves under the sun for 10-15 minutes.
After given time, observe the changes. Answer the questions:
- What changes were observed in the pieces of paper located on the upper and lower sides of the leaf?
- According to the results of the experiment, on which leaf surface does transpiration proceed intensively?
Conclusion
In this experiment, students observed the process of transpiration in plant parts. Students were able to see that the intensity of water evaporation in each part of the plant is different. This laboratory work allows us to better understand the mechanisms of regulation of plant transpiration and its significance in the life of plant organisms. The results obtained are of practical importance and can be used to optimize plant care in agriculture, horticulture and landscape design.
