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Transpiration Made Simple!

• One plant will be placed in continuous light for 24 hours. 
• One plant will be placed in front of a blowing fan for 24 hours.
• One plant will be placed inside a plastic bag that had previously been spritzed with water (high humidity inside the bag). 
• The fourth plant will serve as a control.

3 comments:

Thank you so much for this post. I did a recent transpiration experiment with my kids at home and couldn't have explained the science behind it better than what you have provided here! They loved it. We posted on our blog and linked back to your post here.

Thank you. I homeschool my eight year old son, who can never get enough science! This will be a wonderful activity to encourage his latest fascination with plants and how they function.

Thank you so much for this I will use this approach and I love the lab!

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Transpiration Experiment – Colour Changing Flowers

May 7, 2024 By Emma Vanstone 26 Comments

Do you know you can change the colour of white flowers by placing them in a pot of food colouring and water? This easy colour-changing flower science experiment is great for learning about transpiration and transport in plants .

Easy Transpiration Experiment

How to make colour-changing flowers

You’ll need.

White flowers

Food colouring – we’ve found Wilton gel colours work well. Natural food colourings DO NOT work in our experience.

Small jar or vase

Transpiration experiment – instructions

Trim the flowers at the stalks.

Fill a vase or jar with water and add a little food colouring.

Place the flowers in the jar and leave for a few hours.

Usually, you will see the flowers change colour within a few hours.

Extra Transpiration Challenges

Try carefully splitting a stem in half with a sharp knife ( ask an adult to do this )

Place one half of the stem in one colour water and the other in a different colour. After a few hours, you should have a flower two different coloured petals!

What is Transpiration?

The white petals change colour because of something called the transpiration stream . Transpiration is the movement of water up the stem of a plant from root to leaf when water is lost from the plant due to evaporation and diffusion of water from a plant’s surface. Firstly, water is absorbed by the root and moves through root hair cells via the process of osmosis . It then moves into the xylem vessel, which is the tube that carries the water up the stem. Water moves up the xylem vessel by adhesion (being attracted to the side of the vessel) and cohesion (water molecules being attracted to each other).

When water evaporates from the surface of the leaves, the pressure change pulls the column of water upwards to replace the water lost. There’s a constant transpiration stream of water through the plant.

The best way to consider this is to imagine you have a thick milkshake – the straw can’t carry the milkshake up itself, but if you suck from the top, the milkshake is sucked up the straw. It moves in a column because water molecules are attracted to each other.

What affects the speed of transpiration?

The rate of transpiration is affected by environmental factors

Factors affecting transpiration

Transpiration is faster when there’s more sunlight. Stomata ( tiny pores on the surface of a plant ) close when it’s dark as they don’t need to be open when photosynthesis is not happening. Photosynthesis also needs sunlight. When the stomata are closed, water cannot escape from the plant’s surface.

Temperature

Transpiration happens at a faster rate in higher temperatures. In warm weather, water particles evaporate and diffuse through the stomata faster, increasing the transpiration rate.

Air movement around the plant

When airflow around a plant is good, transpiration is faster as the water vapour that has just diffused and evaporated from the leaf is moved away, increasing the concentration gradient between the air and the inside of the leaf. Diffusion is faster when the concentration gradient is more significant.

The effect of increasing airflow on the rate of transpiration can be demonstrated using celery, food colouring, water and a hair dryer!

What food colouring should I use?

We have found that natural food colours don’t work, but these Wilton gel colours work every time.

If you liked this experiment, don’t forget to try my other plant science experiments .

Contains Affiliate Links

Last Updated on May 7, 2024 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Reader Interactions

September 26, 2011 at 8:55 pm

I did this for my kids this summer. We used daisy’s…it didn’t work. I have done it with carnations before and it worked, but not sure why daisy’s didn’t work!

October 12, 2011 at 9:13 pm

I think the stem structure can vary somewhat and only certain flowers work effectively. Definitely try carnations next time!

September 28, 2011 at 8:50 am

Thanks for the tip! I’m going to try this one out!

September 29, 2011 at 6:12 pm

It is great! x

September 28, 2011 at 1:32 pm

Yet another fabulous experiment to explore with children! I remember always wanting to try this but never getting round to it.. I WILL with my kids! 😉

Thank you for liking to Kids Get Crafty!

Thanks Maggy

September 30, 2011 at 9:47 pm

You have so many great ideas on your blog. I would love if you would link some of them up to my Weekend Wonders blog hop!

October 12, 2011 at 9:18 pm

Is that a Sat or a Sunday? Can you send us the link, as that would be great! Thanks for stopping by, we are so pleased you like it! 🙂

October 01, 2011 at 6:52 am

I don’t know of a child that doesn’t find this utterly fascinating! It’s such a great idea! I have to have a go at this with Little One!

Thank you for linking up to #handmadethursday x

October 12, 2011 at 9:19 pm

Thank you kindly! Let us know if you do have a go! 🙂 x

October 03, 2011 at 9:43 pm

What a great experiment! Will definitely be giving this one a go! Well done girls, another simple but fun experiement my children will love.

Thank you lovely! x

October 04, 2011 at 11:02 am

I love this experiment – it works really well in the spring as well with Daffodiles we always used to have multi coloured daffs in the house in spring.

October 04, 2011 at 12:33 pm

Thank you! We will definitely have a go with daffodils in the spring.

October 06, 2011 at 8:42 pm

thanks so much for sharing on Craft Schooling Sunday!

October 12, 2011 at 9:12 pm

Thank you so much. We will stop by. If you have craft posts yourself come and link to our fun sparks on a Thursday! 🙂

October 12, 2011 at 9:17 pm

We are all linked up so thank you! A beautiful sea or turquoise if ever I saw!

January 02, 2012 at 4:44 pm

I remember doing these as a kid with my grandmother – so fun! Thanks for reminding me to do them with my own kids!

January 02, 2012 at 7:55 pm

oh wow! Thats great. It is a really fab experiment! x

January 09, 2012 at 9:39 pm

How long does it take for you to see the change in color?

January 09, 2012 at 10:54 pm

Usually by the end of the day!

March 12, 2012 at 6:28 am

Wondering…If I dye 6 carnations, seperately, a different color each (like the colors of the rainbow), could I then combine them in one vase of plain water after the petals have changed color?

November 05, 2012 at 1:03 am

Hi I tried this but it didn’t work I used a white flower or should I wait longer.

November 05, 2012 at 8:39 am

Make wait longer, or make your coloured solution stronger. Good luck.

January 30, 2014 at 9:23 pm

This is really interesting – am sure my boys would really love this.

April 17, 2018 at 9:56 am

It is a very colourful science topic and also interesting to play around with it

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Science project, transpiration experiment.

Do plants sweat? Not quite, but they do lose water. Track down the missing mass in this experiment by learning how plants lose water to the air through transpiration.

How much water can a plant lose through transpiration?

• Three small, thin-leafed plants
• Three small, broad-leafed plants
• Small watering can
• 6 plastic bags large enough to fit completely around each plant pot
• Masking tape
• Get six small plants, three with wide leaves and three with narrow leaves. Use the masking tape and pen to give each one a number.
• Water the plants until water comes out of the bottom of the pot. If the plants are really dry when you start, water them thoroughly and wait a few minutes. Then, water them again. When the water has soaked in and the pot is full of water like a squishy sponge, it’s time to weigh the plants. Create a table that shows how much each plant weighs before and after the experiment.

• Create a hypothesis by addressing these questions:
• If you water plants and then put them in the sun, what will happen to the water?
• Would anything change if you put a plastic bag around the base of the plant?
• How would adding the bag change your experiment?

• Put the plants in full, warm sunlight for an hour, then take off the plastic and weigh each plant again. Record the weight in the table. Is the weight different? The same? Why do you think that this is the case? Did different plants lose different amounts of weight, or did they lose around the same amount? Why?
• Dry off the inside of each plastic bag. Re-seal the bags over the plants, return the plants to the sunny spot, and continue timing and weighing for several hours without adding any more water. What happens?

During your transpiration experiment, the plants will lose water, even though they are in the bags. The broad-leafed plants will lose a little more than the thin-leafed plants, but depending on the size of the plant, it may not be measurable.

So how did the water sneak out of the plants?

When it’s a hot day, you might get a little sweaty. Plants “sweat” as well. Similar to how we lose water through our skin, plants lose water through their leaves.

Although you might not be able to see them, plants have small pores, or holes, on their leaves. Take a look at the bottom of a leaf under a microscope, and you will be able to see these holes, which are known as stomata . This is where plants can lose water through transpiration.

Even though it’s an invisible process, the loss of water from plants through transpiration is an important part of the water cycle because it adds a lot of water to our air. In just one year, every leaf on earth can send out much more than its own weight in water. In fact, a large oak tree can contribute 40,000 gallons of water a year to the air!

You probably water the plants in your house so that they’ll stay healthy—so if plants need water, then why do they lose it? Transpiration happens in part because plants need to breathe. Plants need to take in carbon dioxide, and to do this, they need to open their stomata. When this happens, water comes out. You’ve probably experienced this when you breathe as well: on a cold day, you can even see the water from your breath as it makes clouds in the air.

Transpiration also helps plants by cooling them down, much like how sweating helps us regulate our body temperatures. Transpiration also plays a big role in helping water move around the plant by changing the water pressure in plant cells. This helps minerals and nutrients move up the plant from the roots.

Going Further

What would happen to a plant if you were to put petroleum jelly on the leaves?  How about olive oil? Try placing different substances on the leaves and weighing the plant, then do the experiment again. What would happen in a warmer room? Would there be more or less transpiration?

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Shop Experiment Transpiration Experiments​

Transpiration.

Experiment #9 from Advanced Biology with Vernier

Introduction

Water is transported in plants, from the roots to the leaves, following a decreasing water potential gradient. Transpiration , or loss of water from the leaves, helps to create a lower osmotic potential in the leaf. The resulting transpirational pull is responsible for the movement of water from the xylem to the mesophyll cells into the air spaces in the leaves. The rate of evaporation of water from the air spaces of the leaf to the outside air depends on the water potential gradient between the leaf and the outside air.

Various environmental factors, including those conditions which directly influence the opening and closing of the stomata, will affect a plant’s transpiration rate. This experiment will measure transpiration rates under different conditions of light, humidity, temperature, and air movement. The data will be collected by measuring pressure changes as the plant takes up water into the stem.

In this experiment, you will

• Observe how transpiration relates to the overall process of water transport in plants.
• Use a Gas Pressure Sensor to measure the rate of transpiration.
• Determine the effect of light intensity, humidity, wind, and temperature on the rate of transpiration of a plant cutting.

Sensors and Equipment

This experiment features the following sensors and equipment. Additional equipment may be required.

Ready to Experiment?

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Get answers to your questions about how to teach this experiment with our support team.

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Purchase the Lab Book

This experiment is #9 of Advanced Biology with Vernier . The experiment in the book includes student instructions as well as instructor information for set up, helpful hints, and sample graphs and data.

Potometer Experiment

A Potometer experiment is performed to estimate the transpiration rate in different plants. A potometer is an apparatus used to determine the transpiration rate of the cut shoot at the desired time. It is also called a transpirometer .

Using the potometer, we can record the readings of water uptaken by the cut shoot. There are two causes of water uptake. Plants uptake water to perform two major activities. One is transpiration, and the other is photosynthesis.

Transpiration is the evaporation of water by the leaves through the stomatal activity. Plants absorb sunlight, CO2 and H2O to give oxygen and carbohydrates during photosynthesis .

Thus, we can only get a rough idea about the transpiration rate using a potometer. But, the actual transpiration rate may be lower than the value indicated by the potometer. Because water loss can be due to both transpiration and photosynthesis.

Bubble and mass potometers are common devices used to measure transpiration in plants. A bubble potometer measures water absorbed by the shoot. Mass potometer measures the water loss by the shoot.

The working of a potometer depends upon the amount of water absorbed by the plant. This post discusses the purpose, design and working of the photometer. Also, the aim, requirements and steps are explained to measure transpiration using Ganong’s photometer.

Content: Potometer Experiment

Requirements of the potometer experiment, potometer experiment steps, factors affecting transpiration.

• Calculation

Precautions

Limitations, what is potometer.

A potometer is a set-up that helps in estimating the transpiration rate and factors affecting transpiration. We can measure the transpiration rate in plants by knowing the amount of water absorbed by the plant. Here, the amount of water absorbed is equal to the water loss during the transpiration by plants. Also, we can study the effect of different external variables on transpiration rate.

What is the Purpose of the Potometer?

A potometer aims to measure the water absorbed by the plant, which is equal to the value of transpiration.

What is the Design of the Potometer?

• Capillary tube : Here, a bubble travels a distance due to water absorption by the plant. We can measure water uptake through regular gradations on the tube.
• Reservoir : It is like a funnel with a tap. We can reset the bubble by turning on the tap. Some potometers also use a syringe in place of a reservoir.
• End tube : It holds the shoot. The stem end must be in touch with the water. Additionally, we need to fix the cork Bauer on the end tube to avoid air bubbles.

How does a Potometer Work?

There are two main types of potometers.

• In a bubble photometer , we require a leafy shoot fixed within the end tube. Then, over a specific time, an air bubble travels a distance that is equal to the water uptaken by plants.
• In a mass photometer , we require a plant with its root submerged in a beaker. This beaker is then placed on a digital balance. Readings depend upon the amount of water lost by the plant.

Thus, we can measure transpiration by recording the change in the volume of water taken up or the change in mass.

• Potometer to conduct the experiment and to take out the readings.
• Water bucket to submerge the apparatus.
• Healthy shoot to study the rate of transpiration.
• Vaseline seals all the connection points.
• Cutter cuts the shoot.
• Adhesive tape secures the airtight seal.
• Stopwatch is used to set the time.

• Bench lamp to know the effect of light intensity.
• Table fan to know the effect of wind speed.
• Polythene to know the effect of humidity.
• Dryer to study the effect of temperature.
• First, submerge the whole apparatus in the sink or water tray to remove air bubbles.
• Then, cut the plant shoot underwater and insert it into the hole of the cork Bauer fixed to the end tube. This step should be quick to avoid entering any air into the plant’s xylem.
• After that, attach the whole unit to the capillary tube underwater.
• Then, use vaseline at all the connections to ensure an airtight environment. Also, we could use adhesive tape to secure the airtight seal.
• After that, we can take out the potometer apparatus and mount it on the wooden base. Note : If any bubbles appear, restart the whole procedure to get accurate results.
• Then, place the open end of the capillary tube into a beaker. The capillary tube has graduations in millimetres.
• Add colour to the water to see the distance travelled by the air bubble within the capillary tube.
• Introduce an air bubble by dipping the capillary tube out of and back into the beaker containing water.
• Note down the distance of an air bubble before the experiment. Then set the time in the stopwatch. Allow the air bubble to move at a given time.
• Finally, record the reading by looking at the distance an air bubble moved.
• We can also repeat the experiment by refilling the system by turning the glass stop cock. During this stage, we can reset or adjust the air bubble.

We can also investigate the transpiration rate under different environmental factors. Below, we will discuss the effect of different variables on transpiration.

Light Intensity

We can study the effect of light intensity by using a bench lamp at different distances. High light intensity causes turgidity of guard cells, allowing stomatal opening. It permits more water loss .

To know the effect of wind speed on transpiration, we can use a table fan . By using an inch tape, we could place the fan at different distances to study the effect of high and low wing speed. More wind speed removes water vapour from the air surrounding the leaf. Thus, it generates a steep concentration gradient between the leaf and water. It leads to an increase in water loss or transpiration.

We can wrap a polythene bag around the leaves to know how the humidity affects transpiration. When the humidity is high , the air concentration saturated with water vapour is high. As a result, the diffusion of water vapour from the leaves reduces. Here, the concentration gradient is smaller, resulting in a less net flow of water vapours .

Temperature

To know how the temperature affects transpiration, we can use a dryer . Higher temperature increases the water molecules’ kinetic energy, resulting in high transpiration rate . Water molecules evaporate from the mesophyll and diffuse away faster.

How does a potometer measure transpiration?

Using a potometer, we could estimate the transpiration rate in two ways:

• Indirect Method : Here, we need to measure the reduction in the volume of water in the capillary tube over some time.
• Direct Method : Here, we need to measure the loss in mass of the potometer over some time.
• Plant shoot must be fresh and healthy.
• The whole apparatus must be airtight.
• The cut stem must be fixed to the end tube underwater.
• Leaves of the desired shoot must be dry before cutting.
• There should not be any air bubbles in the apparatus.
• It measures the transpiration rate by estimating water uptake by the plant.
• It helps to study the effect of variables like light, humidity, temperature and wind speed on the transpiration rate.
• It isn’t easy to set up, as an air bubble may alter the results.
• The potometer does not give accurate results. Because not all the water that the plant takes is used for transpiration. Plants may take water for photosynthesis or to maintain cell turgidity as well.
• The cut shoot does not remain active for a long time.
• The air temperature outside may change the position of the air bubble within the capillary tube.

Thus, a potometer is used to calculate the amount of water that the cut shoot has uptaken. The water uptake by the plant gives the value of water loss or transpiration rate in a given plant.

Related Topics:

• Corolla in Plants
• Life Cycle of Bryophytes
• ATP Synthase in Photosynthesis
• Characteristics of Mushrooms

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Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

Observing earthworm locomotion

Practical Work for Learning

Published experiments

Transpiration in plants.

Accurate quantification of the movement of water into plants is possible with a potometer. Assessing the impact of changing humidity and air movement on plant uptake of water provides essential experience for understanding plant adaptations. Some species of plant develop with differing densities of stomata according to their environmental conditions. Measuring stomatal density provides a tool for investigating this variation.

Experiments

• A window on the past: Measuring stomatal density
• Estimating rate of transpiration from a plant cutting
• Measuring rate of water uptake by a plant shoot using a potometer

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SCIENCE EXPERIMENTS FOR KIDS

Exploring transpiration.

Get out of the house and into nature with this simple backyard project

This animal is not on exhibit in the habitats.  It is one of our Animal Ambassadors and is used in public and school programs.

Download a PDF of this experiment

By using just a few plastic bags and the plants in your own garden, on your windowsill or just outside your door, you can explore the process called transpiration. Plants take up water through roots and then release it through microscopic holes called stomata. A big plus: You’ll get a nice dose of fresh air and some sun to add to your indoor studies.

GATHER THIS:

• Large, clear plastic bags

THEN DO THIS:

• For the fastest results, do this activity midday on a warm, sunny day.
• Chose several different types of plants you have access to that do not have any water or dew on them.
• Slide a plastic bag around a branch or some of the leaves in the sun and secure it with the twist tie. (Option: Repeat on the same type of plant in the shade.)
• Make sure there are some leaves in each bag and that the twist tie is snug to the branch. *Do not remove the branch or leaves from the plant
• Repeat on different types of plants.
• Make initial observations of each bag.
• Come back every 30 min for the next couple of hours. Make more observations.
• Remove the bags after a few hours and feel what has accumulated inside the bag.
• Try on a plant with thick or shiny leaves; on a plant with large, broad leaves; on a plant with fuzzy or hairy leaves; on a plant with leaves that aren’t green.
• Which plant transpired the least/most?
• What does the inside of the bag look like after 30 min? 60 min? 90 min?
• Bonus: Add a thermometer to the inside of a bag and let sit for 30 min.
• Try this during the night!

WHAT IS HAPPENING?

Transpiration is the process by which water is pulled from the roots of the plant through the stems and leaves and released through microscopic holes in the leaves called stomata. The water is pulled up, against the force of gravity because of the interplay of two forces: cohesion and adhesion. Cohesion is the force that causes water molecules to stick to each other and adhesion is the force that causes water to stick to other materials. Cohesion keeps the water in the xylem of a plant stuck together so that when a water molecule evaporates out of the stomata, it pulls on the water molecule behind it, and so on, all the way down to the roots. Additionally, the water sticks to or adheres to the xylem walls and exhibits capillary action whereby water rises into a narrow tube against the force of gravity.

The rate of transpiration is directly related to the number and size of the stomatal openings, and to the evaporative demand of the atmosphere surrounding the leaf. The atmospheric conditions that influence the evaporative demand and the rate of transpiration are light intensity, temperature, humidity and wind speed. A fully grown tree may lose several hundred gallons of water through transpiration on a hot, dry day. The rate of transpiration also depends on the type of plant. Succulent plants have much slower transpiration rates because of a thick, waxy coating on the leaves. That thick, waxy coating is why succulent plants are well adapted to live in arid regions like deserts with minimal water.

WHAT THIS TEACHES:

Skills: Observations skills

Themes: Plants, adaptations, water

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Transpiration Experiments: Learn Demonstartion and Measurements

Transpiration Experiments: In the article, we will learn about transpiration in plants’ experiments through jar bells and polythene bags, etc. Plants absorb the water through roots, and the xylem transports the water to the stem, leaves, and other parts of the plant. The leaves utilise only about 2 % of the absorbed water in photosynthesis. The leaf surface contains tiny pores called stomata, through which the water transpired into the atmosphere. The loss of water through the surface of leaves is called transpiration.

Several experiments have been performed to demonstrate the process of transpiration. The experiment related to transpiration is based on the concept of loss of water in the form of droplets. Certain weighing experiments have also been performed to demonstrate the loss in volume of water from the source during transpiration. Let’s read the article to study the experiments related to transpiration in detail.

What is Transpiration?

The loss of water in the form of water vapour through the aerial parts of the plants is called transpiration. A large amount of water is lost through the leaf surfaces. Leaves contain several minute pores called stomata on their upper and lower surfaces. The stomatal pores open into intercellular spaces of the leaf and provide an uninterrupted path from the interior of the leaf to the external environment.

Important Facts About Transpiration

Transpiration is, however, concerned with the loss of water in the plants through stomata but serves as a necessary evil for the plant. This can be discussed as follows:

1. Transpiration creates a suction pull or force on the roots to absorb more water from the soil.

2. Transpiration pull facilitates the upward movement of water through the xylem.

3. The cohesive property of water can be easily determined due to the process of transpiration.

4. It regulates the temperature of the plant parts and prevents the wilting of the leaves through the continuous pull of water.

5. Transpiration contributes to the cyclic flow of water in the atmosphere and therefore maintains the temperature of the surroundings.

6. The excess accumulation of water may cause waterlogging in the roots of the plants. Transpiration prevents the water from logging in the roots and therefore contributes to the survival of plants to some extent.

Experiment Related to Demonstration of Transpiration

1. Polythene bag or Bell jar Experiment Aim: Demonstration of transpiration through the stomatal pores of the leaves. Materials required: A well-watered potted plant, a polythene bag or a bell jar, greasy substance. Procedure: The demonstration of transpiration  can be done by following the below-mentioned steps in a sequential manner: I. A well-watered potted plant is taken, and the plant is covered with a transparent polythene bag. The bag is tied up to make the setup airtight. A bell jar can also be used instead of a polythene bag, and the grease or vaseline can be used to make the experimental setup airtight. II. The covered plant is further placed in the sunlight for about two to three hours.

Observation: A few drops of water can be observed on the inner surface of the polythene bags.

Conclusion: The water droplets that appear on the inner surface is due to the condensation of water vapour into liquid water. It proves the loss of water through the surface of leaves during transpiration.

Fig: Polythene bag experiment to demonstrate transpiration (Transpiration Experiment Plastic Bag)

2. Cobalt chloride Experiment: Aim: Demonstration of the transpiration by using cobalt chloride paper. Materials required: A well-watered potted plant, a polythene bag, a bell jar, cobalt chloride paper.

Procedure: The experiment can be demonstrated in the following steps: I. A plant with broadleaf is preferably taken to perform the experiment. The plant is supplied with sufficient water and further covered with the polythene bag to escape water vapour from the pot. II. The entire setup is placed into the bell jar. A piece of cobalt chloride paper is also placed in the bell jar along with a polythene-wrapped plant. III. Another control setup is designed as a control experiment in which a cobalt chloride paper is alone placed in a jar without the plant.

Fig: Cobalt chloride paper experiment to demonstrate transpiration

Observation:

I. The observation is marked by the change in the colour of cobalt chloride paper from blue to pink because of the reaction of cobalt chloride with water. II. While the cobalt chloride paper of another setup remains blue and does not show any colour change as there is no water for the reaction with cobalt chloride paper.

Conclusion: The change in the colour of the cobalt chloride paper ensures the occurrence of transpiration in the plant.

3. Four-Leaf Experiment: Aim: Demonstration of transpiration through stomata. Materials required: four leaves, vaseline, string. Procedure: I. The four fresh leaves are taken and labelled as A, B, C, D, and E. II. Leaf A is coated with Vaseline on both surfaces. III. The lower surface of leaf B is coated with Vaseline. On the contrary, the upper surface of leaf C is coated with Vaseline. IV. The leaf D kept uncoated. V. Vaseline closes the stomata and therefore prevents the loss of water through the stomata. VI. The leaves are tied in a similar sequence on the string. The setup is then placed in the sunlight for about one or two days.

Observation: The following observation has been found: I. Leaf A is fully coated with vaseline and remains fresh and green. II. The leaf B shrivelled a little. III. The leaf C shrivelled comparatively more. IV. The leaf D is completely wilted.

Conclusion:

I. Leaf A shows that no transpiration has occurred through leaf A as stomata were closed due to the application of vaseline. II. The leaf B shows a little transpiration as the lower surface contains fewer stomata, and the upper surface is coated with vaseline. III. The leaf C shows comparatively more transpiration as its upper surface is exposed to transpiration. IV. The leaf D shows the maximum rate of transpiration. It can be concluded that transpiration occurs through stomata as the fully vaseline coated leaf remains fresh due to the absence of transpiration, while those partially coated show a little transpiration hence become shrivelled. The non-coated leaf completely wilts as transpiration through stomata occurs to its maximum extent.

Fig: Four-leaf experiment to demonstrate transpiration

Experiment Related to the Measurement of Transpiration

1. Weighing Experiment I: Aim: Demonstration of loss in the volume of water due to transpiration. Materials required: Small potted plant, weighing machine. Procedure: I. A small potted plant is supplied with a sufficient amount of water and then weighed on the weighing machine. II. Further, the plant is kept in the sunlight for about an hour. The soil surface and the pot should be covered to prevent the evaporation of water from any other surface. III. After an hour, the plant is again weighed on the weighing machine.

Observation: It has been observed that the plant weight is reduced after placing in the sunlight due to the loss in the volume of water.

Conclusion: The loss in plant weight occurs due to the loss of water. It shows that transpiration occurs through the aerial parts of the plant since all the possible ways for evaporation have already been checked.

2. Weighing Experiment II: Aim: Measurement of transpiration by a gradual decrease in the water level. Materials required: Leafy shoot, water, test tube, oil, weighing machine. Procedure: I. A test tube filled with water is taken. II. A leafy shoot is immersed in the test tube so that the roots remain submerged in the water and the shoot and leaves remain out from the water. III. A small amount of oil is now added to the test tube. The oil forms a thin film over the water surface and thereby prevents water loss by evaporation. IV. The experimental setup is then weighed, and the weight is noted. V. The setup is further placed in the sunlight to allow transpiration. VI. The plant is again weighed after some time.

Observation: A difference in the weight is observed. The water level in the test tube also falls down.

Conclusion: The difference in the weight and water level in the test tube ensures transpiration through the plant since the evaporation is already interrupted.

Fig: Weighing method to measure the transpiration

3. Potometer Experiment: Potometer is a device that measures the amount of water absorbed by the plant. The amount of water intake is almost equal to the amount of water loss through transpiration. There are a number of potometer that have been designed to measure the rate of transpiration. These are named as follows: I. Garreau’s Potometer is used to demonstrate transpiration from both the surfaces of the leaves. II. Darwin’s Potometer is used to demonstrate the suction force created by transpiration. III. Farmer’s Potometer and Gangong’s Potometer is used to measure the amount of water intake. Aim: Measurement of the rate of transpiration through Ganong’s potometer. Materials required: small plant twig, water, Ganong’s potometer. Procedure: I. A small twig of a plant is cut obliquely to larger the surface for water intake. II. The apparatus is filled with water, and the twig is placed in the vertical arm of the potometer and fixed with the help of a one-hole cork. III. Grease is applied to all the joints to make the apparatus airtight to escape the loss of water through evaporation. IV. An air bubble is inserted in the horizontal graduated tube of the apparatus by slighting lifting the bent capillary tube. V. The initial reading of the bubble on the graduated tube is noted. VI. The experimental setup is then placed in the different surrounding conditions.

Fig: Measurement of transpiration through Ganong’s potometer

Observations: I. In the experimental setup, if placed in the sunlight, the reading in the graduated tube is the maximum, i.e., the distance travelled by the bubble is the maximum due to the greatest suction force that is created by the maximum water loss. Moreover, in a windy atmosphere along with the sunlight, the rate of water loss even exceeded more. II. In the experimental setup, if placed in the shade, the reading on the scale is the minimum, i.e., the distance travelled by the bubble is the minimum due to the least suction force applied to the twig. III. In the experimental setup, if placed in the complete dark, the distance travelled by the bubble is negligible since the loss of water through the twig is nullified.

Conclusion: The distance travelled by the bubble and the suction force created for the absorption of water determines the rate of transpiration through the leaves in the different surrounding conditions. The more the loss of water, the more is the absorption of water.

Limitations of potometer: I. It is difficult to insert a single air bubble in the capillary tube. II. The twig may not remain alive for a longer period of time to demonstrate the change in the rate of transpiration in different environmental conditions.

Transpiration is the loss of water through the aerial parts of the plant. It is an essential process as it creates a suction force to form a continuous column of water from the roots to the leaves of the plant and therefore prevent the wilting of the leaves. A number of experiments have been performed to demonstrate transpiration in plants and to measure the rate of transpiration in plants. Since the leaves are responsible for the maximum water loss, therefore transpiration can be determined by placing a polythene covered plant in the sunlight.

Moreover, a four-leaf experiment is also performed to determine the occurrence of transpiration, where the transpiration through the upper and the lower surface of the leaf is controlled by Vaseline coating. The rate of transpiration is almost equal to the rate of absorption of water. Based on this concept different scientists contribute to demonstrate the rate of transpiration in accordance with the rate of water absorption with the help of a device called the potometer.

FAQs on Transpiration Experiments

Below are the most frequently asked questions on Transpiration Experiments:

Q.1: Why did we tie the bag around the leaves of the potted plant? Ans: The potted plant covered with the polythene bag is placed in the sunlight. The water lost through the leaves becomes condensed, and the water droplets that appear on the inner surface of the polythene prove the occurrence of transpiration.

Q.2: Why is a potometer used? Ans: A potometer is used to measure the rate of transpiration that is equal to the amount of water absorbed by plants.

Q.3: What is the role played by the bubble in Ganong’s potometer? Ans: The bubbles travel a distance in the capillary tube along with the suction of water and therefore determine the rate of transpiration by the plant.

Q.4: How is the air bubble introduced in the Ganong’s potometer? Ans: Air bubbles are introduced in the Ganong’s potometer by slightly lifting the bent tube.

Q.5: What is the main limitation of Gangong’s potometer? Ans: It is difficult to insert a single bubble in the tube.

We hope this detailed article on transpiration experiments is helpful. If you have any queries drop them in the comment section below and we will revert with answers.

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Experiments on Transpiration in Plants | Botany

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List of top nine experiments on transpiration in plants:- 1. Measurement of Leaf Area 2. Demonstration of Transpirational Water Loss by Potometers 3. Determination of the Rate of Transpiration by Simple Method (Conical Flask Method) 4 . Determination of the Rates of Stomatal and Cuticular Transpiration and a few others.

Experiment # 1. Measurement of Leaf Area :

The loss of water in the form of vapour from the aerial parts — particularly through leaves — is termed “transpiration”. On absorption from the soil by roots, the water is trans-located via the xylem tissue to the mesophyll cells of the leaves.

The excess water is lost through stomatal opening or through the diffusion process from leaf surface. For determination of the rate of transpiration, measurement of leaf area, i.e. transpiring surface, is highly essential. The leaf area can be measured by different methods.

Method I: By Graph Paper Method:

Requirements :

1. Graph paper (mm); 2. Scale, pencil, leaf, etc.

Procedure :

1. Place leaf on a millimeter graph paper and draw its outline with a pencil (Fig. 3.11).

2. Then count the total area covered by the leaf from the marked outline of the leaf and express it as square centimeter.

Observation :

The leaf area measurement procedure is shown in Fig. 3.11.

Method II: By Weighing Method:

1. Card-board

2. Leaf, pencil, rubber, blade, balance with weight box.

1. Place a leaf on a cardboard and draw its outline. Then cut the board along the line-mark of drawing and take its weight.

2. Now cut one square centimeter area from the board and take the weight. Observation

The weight of the board cut to the size of leaf area is x gms. The weight of one square centimeter area of the board is y gms. Then the area of leaf is x/y sq. cm (Fig. 3.12).

Method III: By Planimeter Method:

1. Planimeter — a simple instrument, having two major parts — a tracer arm having a tracing point and a carriage with a measuring wheel and also the pole arm attached to the pole, around which the instrument revolves (Fig. 3.13).

2. A platform, leaf, pencil etc.

1. Place the leaf on a platform in a fixed position and draw the outline of the leaf by a pencil.

2. Place the pole weight close to the outline of the leaf and move the tracer point along the margin of the leaf.

3. Record the initial reading from the scale and final reading after the tracing of leaf.

4. Compute the total leaf area by denoting the data from the main scale and also from vernier scale.

5. Record the vernier scale reading in the following ways before final computation:

First coincide the zero of the measuring wheel with zero of the vernier scale. Find out the number of divisions of the vernier scale that coincides with that of the measuring wheel.

Suppose 10 vernier divisions = 9 divisions of measuring wheel. So, 1 vernier division = 9/10 or 0.9 division of the measuring wheel. Vernier unit = 1 – 0.9 = 0.1 sq. cm small division of the measuring wheel = 1 sq. cm and 1 div. of the counter dial = 100 sq. cm.

Thus total reading = (Counter dial reading × 100) + (Measuring wheel reading × 10) + (vernier reading × 0.10) sq. cm.

Experiment # 2. Demonstration of Transpirational Water Loss by Potometers:

The water loss by the process of transpiration can be demonstrated by several types of glass apparatus, called Potometers. In most of the potometers, the rate of transpiration can be measured directly and expressed in gms per hour per sq. cm of leaf area.

But these methods are not accurate because of the fact that the amount of water absorbed by the twig (which is measured by the apparatus) is not actually transpired at the same time.

The description and working of some potometers are given below:

(A) Ganong’s Proto-Meter (Fig. 3.14):

This is a glass apparatus fitted with a wooden stand. It is one of the most suitable potometers used for the demonstration or determination of the rate of transpiration.

It consists of a narrow graduated horizon­tal limb which holds two vertical wide-mounted tubes — one of which is fitted with a rubber cork through which passes a leafy twig while the other acts as a reservoir of water which is fitted with a stopcock in the connecting tube to control water supply. The other ends of horizontal limbs bend at right angle and at the opposite side of the vertical wide mouthed tube.

Materials Required :

1. Ganong’s potometer

2. Water, beaker, leafy twig, knife, etc.

3. Graph paper, pencil, etc.

1. Fill the apparatus with water and insert a leafy twig (cut under water) through the cork of the vertical tube. The twig should always be cut under water to prevent air-clogging.

2. Keep some water in the reservoir funnel and close the stopcock and make all the connections air-tight by proper sealing.

3. Introduce a drop of air bubble in the horizontal limits of the apparatus.

4. Allow the twig to transpire for 1-2 hrs. under bright sunshine.

As water is lost by transpiration, the bubble will move in the horizontal graduated tube towards the transpiring twig. The rate of movement of the bubble in the horizontal tube is proportional to transpira­tion rate (assuming that the rates of absorption and transpiration are the same).

The rate of transpiration can be determined in the following ways:

Initial position of the bubble on the scale — X cm

Final position of the bubble after a given time — Y cm

Therefore, the distance traversed by the bubble in time t is equal to (Y – X) cm.

Now the volume of water transpired in a given time (t) is equal to tit 2 (Y – X) ml where ‘r’ is the radius of the bore of the horizontal tube.

So, the amount of water transpired by per unit area of the leaves of the twig per unit time is equal to

(Y – X)/ t x total leaf area * ml/min/sq. cm.

[* The leaf area can be measured by graph paper method.]

(B) Farmer’s Potometer (Fig. 3.15):

The apparatus consists of a wide-mouthed bottle fitted with a rubber stopper having three holes. The bottle is filled with water up to the neck. In one hole leafy twig can be introduced while in another a water reservoir having a stopcock is fitted. The third hole is fitted with a narrow bent tube which has a horizontal graduated tube with a centimeter scale.

1. Farmer’s potometer

3. Water, leafy twig, pencil, graph paper etc.

1. Fill the apparatus with water and keep some water in the reservoir.

2. Introduce a freshly cut (cut under water) twig within the bottle and make all connections air-tight by proper sealing.

3. The bent end of the narrow tube is to be immersed in a beaker containing water.

4. Keep the whole set-up under bright sunshine for transpiration at a steady state.

Observe the movement of the air-bubble within the hori­zontal tube towards the twig. The rate of movement of air-bubble is proportional to the rate of transpiration (assuming that the rates of absorption and transpiration are equal).

Same as in Ganong’s potometer.

(C) Darwin’s Potometer (Fig. 3.16):

The apparatus consists of a short glass tube from which a side tube bends upward ending in an open mouth into which a plant twig is inserted through a hole in a rubber cork.

The upper open mouth of the main tube is also closed by a cork. The lower end of the tube too is fitted with a cork through which passes a long graduated capillary tube, fitted with the help of a rubber tubing. The end of the capillary tube dip in a beaker containing.

1. Darwin’s potometer

2. Beaker, leafy twig, water, graph paper, pencil etc.

1. At the beginning of the experiment, fill up the apparatus with water.

2. Insert a fresh leafy twig (cut under water) through the cork of the side tube.

3. Make all joints air-tight.

4. Introduce an air-bubble within the water column of the capillary tube.

5. Allow the whole set to transpire under bright light after fixing it with stand and clamp.

As transpiration occurs from leaves of the twig water is absorbed by the twig from the side tube and this produces a suction force which sucks up water from the capillary tube. As a result, the air-bubble within the capillary tube gradually moves upward.

The rate of upward movement of air bubble is recorded from the initial and final readings of the position of the air-bubble in the capillary tube. The rate of transpiration is then expressed as in case of Ganong’s Potometer (ml of water transpired per minute per unit area of the leaf).

(D) By Garreau’s Potometer (Fig. 3.17):

It consists of two small bell jars placed one above an­other in-between which a leaf is placed while still attached to a potted plant. At the narrow end of the two bell jars, weighed amounts of anhydrous CaCl 2 are placed in two very small tubes. At the two ends of the bell jars, are attached two oil manometers which ensure the maintenance of con­stant vapour pressure within the bell jars.

Materials and Equipment’s :

1. Garreau’s Potometer

2. Vaseline, Anhydrous CaCl 2 salt

3. Potted plant, stand with clamps

4. Balance with weight box

1. Place a leaf of a potted plant inside two bell jars and make it airtight by vase-line.

2. Clamp the whole arrangement of the apparatus in vertical position and place it in sunlight.

3. Before the onset of the experiment place measured quantities of anhydrous CaCl 2 salt in the tubes and take the final weight after a considerable period of transpiration (at least two hours).

The difference between the two weighing’s is a measure of the amount of water lost from the upper and lower leaf surfaces.

Hence transpiration by both the surface of a leaf can be directly measured sepa­rately and simultaneously by Garreau’s potometer:

Initial weight of CaCl 2 in the upper tube — W 1 gms

Initial weight of CaCl 2 in the lower tube — W 2 gms

Final weight of CaCl 2 in the upper tube — W 3 gms

Final weight of CaCl 2 in the lower tube — W 4 gms

Amount of transpired water by upper leaf surface — (W 3 – W 1 ) gm.

Amount of transpired water by lower leaf surface — (W 4 – W 2 )

Rate of upper leaf surface transpiration i.e. cuticular transpiration (in case of dorsiventral leaf) = (W 3 – W 1 ) gm. total leaf area (sq m) and time (min)

Rate of lower leaf surface transpiration i.e. stomatal transpiration = (W 4 – W 2 ) gm. total leaf are (sq m) time (min)

Experiment # 3. Determination of the Rate of Transpiration by Simple Method (Conical Flask Method) :

The loss of water from the leaf surface of terrestrial plants is a normal physiological process. It is either transpirational loss, i.e., in the form of water vapour, or guttation i.e., in the form of water droplets.

Transpiration normally takes place through stomatal openings of leaves or through particular openings of stem surface or through the cuticu­lar surface, or a combination of paths mentioned above. This transpirational water loss is a necessary evil for plant life.

Transpirational water loss can be determined by the conical flask method — a very simple method.

Materials and Equipments :

1. A fresh leafy twig

2. Beaker, conical flask, knife, glass rod, thread etc.

3. Water, oil, balance with weight box

4. Graph paper, pencil, stop-watch etc.

1. Take a 100 ml conical flask and fill it with water up to the neck.

2. Insert a freshly cut petiolate leaf (leaf cut under water within a breaker) and tie the cut end of the petiole with a glass rod by thread so that the leaf cannot be displaced from the conical flask by wind.

3. Then put some oil over the water of conical flask so that the exposed water surface will be covered.

4. Weigh the experimental set (conical flask – water-oil-leaf) in a chemical balance and record the initial weight.

5. Place the experimental set under bright sunshine for 1 hour and weight finally in a chemical balance.

6. Record the final weight and calculate the water loss by transpiration.

7. Record the total transpiring area of the leaf by Graph paper method.

8. Determine the rate of transpiration in the following way:

Stomatal Index (S.I.) = No. of stomata in a given area (S)/Total no. of cells of the area (epidermal) + S × 100

6. Determine the total area of the leaf by graph paper method and then calculate the total number of stomata of the said leaf.

7. Determine the area covered by each stomata with the help of ocular micrometer (value of each division is standardized before by the stage micrometer by the formula):

1 ocular division value = Stage div./Ocular div. × 10µ.

Then calculate the total stomatal area of the given leaf.

8. Determine the transpiration index by recording the time (in sec) required for standard change of the dry cobalt chloride paper over the evaporating surface (S) and transpiring surface (E) by using the formula:

Transpiration index = S/E × 100

In this process, take two equal pieces (2 × 2 cm) of dry cobalt chloride paper and then place one of them under the lower surface of dorsiventral leaf of a twig by cello tape. Place the other over a wire net which is kept over a petridish containing water. Record the time (in sec) for a standard colour change of the cobalt chloride papers in both the cases (the paper turns pink when it absorbs water vapour moisture).

Area of the field of vision = x sq cm (calculate it by the formula πr 2 , where ‘r’ is the radius of the field)

Number of stomata per field = a

Total leaf area (from graph paper) = y sq cm

Stomatal frequency = a/x

Total number of stomata of the leaf = a/x × y

Stomatal index = No. of stomata in a given area(S)/Total no. of epidermal cell (E) + S = S/E + S x 100

Area of a stomata = π/4 (b x c) sq cm

Where ‘b’ and ‘c’ represent the length and the breadth of the pore.

Total stomatal area of leaf = π/4(b x c) x (a/x × y) sq cm

[S = Time taken to change the colour of cobalt chloride paper from a free evaporating surface; E = Time taken to change the colour of cobalt chloride paper from a free transpiring surface.]

Experiment # 6 . Determination of the Amount of Water Absorbed and Transpired by a Plant:

Absorption of water and subsequent loss of it in the form of vapour by the aerial parts of plants are two essential interlinked physiological processes. There is positive correlation between the two processes.

In normal situation the amount of water absorbed is much higher than the amount of water tran­spired. But under stressed conditions the amount of water transpired may be higher than the amount of water absorbed.

The relationship between the two processes mentioned above can be determined by two experimen­tal procedures:

(a) Direct determination with the help of glass apparatus.

(b) By conical flask-water-oil-leaf experimental sets.

(a) Direct Measurement Method:

Materials and Equipment’s:

1. Glass apparatus:

This is a simple apparatus consisting of a wide-mouthed bottle with a graduated side tube (in ml) attached to its base through a cork. The mouth of the bottle is fitted with a cork through which a small plant can be introduced (Fig. 3.19).

2. A small rooted plant or a fresh twig

3. Oil, water, sealing wax, etc.

1. Fill the apparatus completely with water.

2. Introduce a rooted plant or a fresh twig (cut under water) in the wide-mouthed bottle through the cork).

3. Seal the cork to make air-tight.

4. Put a few drops of oil on the surface of water of the graduated side tube to check surface evaporation.

5. Record the initial weight and initial water level on the side tube.

6. Keep the whole set under sunshine for 2 hours.

7. Record the final weight and the level of water in the side tube.

8. Calculate the amount of water transpired (in gms). (Initial weight – final weight) and the amount of water absorbed (in ml) (initial reading – final reading of the side tube).

The volume of water absorbed may be converted to gm. by multiplying the density of water at that temperature from a standard temperature density table.

Initial weight of the experimental set — W 1 gms

Final weight of the experimental set — W 2 gms

Thus the amount of water transpired = (W 1 – W 2 ) gm. = x gm.

Initial reading of side tube = 0 ml

Final reading of side tube = p ml

Thus the amount of water absorbed = (o – p) ml = Q ml

If the density of water is d, so Q ml of water = Q × d gm. = y gms

So the ratio of water transpired and water absorbed is x: y.

(b) By Conical Flask-Water-Oil-Leaf Method (Fig. 3.18) :

Materials and Equipment’s Required :

1. Conical flask, glass rod, thread etc.

2. Water, oil, leafy twig etc.

3. Balance with weight box

1. Take a conical flask (100 ml), fill it up to the neck with water.

2. Put a very little amount of oil over the water surface and take the initial weight (W 1 ) gms.

3. Slowly incline the flask and insert a fresh petiolate leaf (cut under water) tied to a short glass rod with a thread. Care must be taken that oil does not stick to the cut surface of the leaf.

4. Take the second weight (W 2 gms) of the set (conical flask – water-oil-leaf).

5. Place the experimental set under sunshine for 1 hour for transpiration and then take the final weight of the set with leaf – (W 3 gms) and without leaf – (W 4 gms).

6. Now calculate the amount of water transpired and amount of water absorbed.

Amount of water absorbed = (W 1 – W 4 ) gms

Amount of water transpired = (W 2 – W 3 ) gms

The difference between the two values gives the amount of water retained by the leaf or the excess water transpired — as the case may be.

Experiment # 7 . Compare the Rate of Transpiration With the Rate of Evaporation :

The process of vaporization of water from the exposed surface of water and that from the leaf surface are called evaporation and transpiration, respectively. The former is a physical while the latter is a physiological process.

The rate of evaporation is dependent on environmental factors like temperature, humidity, wind velocity, etc. while the rate of transpiration is dependent on both environmental and plant factors, particularly the water retention capacity of the plant concerned.

1. Conical flask, petridish, balance with weight box, glass rod, thread, etc.

2. A leafy twig

3. Water, oils, graph paper, pencil, etc.

1. Prepare a transpirational experimental set (conical flask-water-oil-leaf) in the usual way.

2. Take a petridish and fill it with water up to 2/3 of its volume. This is the evaporation experi­mental set.

3. Take the initial weight of the sets.

4. Both the sets are placed under sunshine for 1 hour.

5. Take the final weight of the sets and measure the area of transpiration surface and evaporation surface.

6. Calculate the rate of transpiration per min per sq cm of leaf area, and also the rate of evapora­tion per min per sq cm.

(a) Transpiration set:

Initial weight — W 1 gm.

Final weight — W 2 gms

Amount of water transpired = (W 1 – W 2 ) gm. = x gm.

Total transpiring surface (from graph paper) = y sq cm

Time — 1 hour

Rate of transpiration = x/y × 60 gm. per min per sq cm

(b) Evaporation set:

Initial weight — W 3 gms

Final weight — W 4 gms

Amount of water evaporated = (W 3 – W 4 ) = p gm.

Total evaporating surface (from graph paper) = Q sq cm

(Apply the formula Hr 2 to find out the total evaporating surface)

Time — 1 hour.

Rate of Evaporation = P/Q × 60 gms per min per sq cm

Ratio of Transpiration and Evaporation = X/60Y: P/60Q.

Experiment # 8 . Determination of the Effect of Antitranspirant Chemical on Transpiration :

The term “antitranspirant” is used to designate any material applied to plants for the purpose of retarding transpiration. There are different groups of antitranspirant chemicals — some of them simply act as permeability barrier, some may act as metabolic inhibitors, while some may also act through permeability changes of the guard cells.

Phenyl mercuric acetate is one of the potent antitranspirant chemicals that causes the partial closure of stomatal pores and, thereby, regulates the transpiration process.

1. Healthy leafy twig

2. Phenyl mercuric acetate solution (10 2 M Stock solution)

3. Quick-fix.

4. Conical flasks, beakers etc.

5. Oil, water, graph paper etc.

6. Balance with weight box

1. Prepare 4 sets of transpiration apparatus (conical flask-water-oil-leaf) using fresh petiolate leaves (leaves are cut under water).

2. Treat each set separately by spraying water (as control) or different concentrations of phenyl mercuric acetate solution (10 -3 M, 10 -4 M, 10 -5 M) on both surfaces of leaf.

3. Place the experimental sets under sunshine for 2 hrs.

4. Record the initial and final weights before and after transpiration in each set to determine the amount of water transpired by the leaf of each set.

5. Calculate the rate of transpiration for each set separately.

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Transpiration

Instructor prep, student protocol.

• Comparing Transpiration Rates of Leaves
• To begin the experiment to measure the transpiration rates of leaves from different plant species, you will first create a tool called a potometer, using a piece of plastic tubing and 5 mL calibrated pipette.
• To assemble the device, simply attach the rubber tubing to the tip of the pipette.
• Then, submerge the device into a bucket of water and move the pipette around under the water to fully fill the tube, taking care not to create bubbles.
• Next, cap the open end of the tube with a pipette bulb to keep the water in.
• Now, taking care not to spill water from the potometer, use a clamp and stand to hold the capped end of the pipette around 1 – 3 inches below the pipette bulb.
• Then, use a second clamp attached lower on the same stand to secure the open end of the rubber tubing.
• Next, use a transfer pipette or dropper to remove water from the open end of the tubing until the water level in the pipette portion of the potometer rests at the zero line. HYPOTHESES: In this experiment, the experimental hypothesis might be that leaves from plant species more adapted to hotter or arid environments will have lower transpiration rates than those from humid or wet regions. The null hypothesis would be that leaves of the different plant species will not differ in their transpiration rates.
• To begin the experiment, carefully use scissors to cut the end of the petiole, or stalk, of the first leaf and then insert the leaf into the tubing.
• Then, place a layer of lubricant around the area where the plant stem and rubber tubing meet to make a watertight seal.
• Next, remove the pipette bulb and taking care not to disturb the setup, let the experiment run for the appropriate experimental period, typically 30 – 60 minutes.
• At the end of the allocated time, record the level of the water in the pipette, noting how much the level dropped in milliliters.
• Then, refill and reset the potometer water level to zero, and then repeat the procedure for each of the remaining test leaves until the transpiration rates of all four leaves have been measured.
• Next, to determine the surface area of the leaf samples, lay each leaf on a blank piece of paper and carefully trace the outlines.
• Then, cut the outlines out and record the mass of each tracing.
• Finally, cut out and weigh one four by four centimeter square of the same type of paper used to make the leaf tracings. This will act as a reference with known area and weight.
• Next, you will need to quantify the number of stomata per unit area on each leaf. To do this, first prepare a slide mount by painting at least one square centimeter of the underside of each leaf with clear nail polish. IMPORTANT: Ensure you paint the bottom of the leaf, since the majority of the stomata are located there.
• When the nail polish is completely dry, carefully press a small piece of cellophane tape directly onto each patch and then gently peel off the tape to remove the painted on polish. NOTE: Use a piece of tape that is smaller than the microscope slide.
• Then, place each impression and tape onto a separate, clean microscope slide. HYPOTHESES: In this exercise, the alternative hypothesis could be that the leaves of the plants adapted to drier environments will have fewer stomata per unit area than the leaves of plants adapted to wetter environments. The null hypothesis might be that all plants species will have an equal number of stomata per unit area.
• To observe each impression under the microscope, first use a low magnification to find areas of the leaf impression that contain stomata. These will appear as darker dots or impressions.
• Then, switch to a higher magnification, keeping the sample viewing window centered on the stomata-containing area.
• Draw and label your observations, making sure to label each sketch with the plant species.
• Then, count and record the number of stomata in the field of view. You should perform this count a total of four times in four different areas of the leaf impression, and then determine the average number of stomata per counted area on the leaf.
• To calculate the number of stomata per mm 2 , place a transparent plastic ruler on the microscope stage under the objective and measure the diameter of the field of view.
• You can then use this number, the diameter or D, to calculate the area of the field of view in mm 2 .
• First, calculate the surface area of the 4×4 cm paper square to obtain the number of square centimeters.
• Then, divide the weight of the paper square by the number of centimeters squared it covers to obtain the weight of 1 cm 2 of paper.
• Finally, to calculate the surface area of each leaf, divide the weight of the leaf tracing by the weight of 1 cm 2 of paper. This will give you leaf area in centimeters squared.
• You should now convert this number to meters squared, the standard unit used for calculating transpiration rate.
• To calculate the transpiration rate for each leaf, divide the total water loss you measured in the potometer in mL by the time the experiment was run for in minutes.
• Then, divide this by the surface area of the leaf in m 2 .
• Make a bar graph with the four different leaf species on the X axis, and their corresponding transpiration rates on the Y axis. Do these rates appear different?
• Next, add a second Y axis to your chart and plot the average number of stomata per millimeter squared for each leaf that was observed under the microscope. Do you see a correlation between transpiration rate and number of stomata? If so, does this seem to have any relationship to the native environment the tree would typically inhabit?

Syllabus Edition

First teaching 2014

Last exams 2024

Skills: Experiments Investigating the Rate of Transpiration ( DP IB Biology: HL )

Revision note.

Biology & Environmental Systems and Societies

Practical 7: Potometers & the Rate of Transpiration

• Because the amount of water used in photosynthesis is so small in relation to the total amount of water that passes through a plant, the rate of water uptake can reasonably be used to represent the rate of transpiration
• The position of the air bubble is recorded at the start of an experiment , and then a researcher can either measure how far the bubble moves in a set amount of time , or time how long it takes for the bubble to move a certain distance
• Mass potometers measure the change in mass of a water-filled test tube connected to a plant shoot as it loses water over a set amount of time
• Light intensity
• Temperature

Investigating the effect of light intensity on the rate of transpiration

• Plant shoot
• Cutting board
• Scalpel/scissors
• Paper towels
• Volume scale
• Capillary tube
• This is done to prevent air from entering the xylem ; this could block the movement of water through the plant
• Set up the apparatus as shown in the diagram , ensuring that it is airtight , and using vaseline to seal any possible gaps
• Any water present on the leaves might affect the rate of transpiration as it could block the stomata
• Remove the capillary tube from the beaker of water to allow a single air bubble to form and then place the tube back into the water
• This could be achieved by varying the light bulbs used or by varying the distance between the light source and the plant shoot
• Allow the plant to adapt to the new environment for 5 minutes
• Record the starting location of the air bubble, leave for a set period of time , and then record the end location of the air bubble
• Change the light intensity by a measurable amount e.g. moving the lamp 10cm further away from the plant shoot
• Reset the bubble by opening the tap below the reservoir
• Repeat the experiment at the new light intensity, and again at a range of different intensities

The Effect of Temperature & Humidity on Transpiration Rates

• A potometer can be used to test hypotheses about the effect of various environmental factors , including temperature or humidity, on transpiration rates
• A fan on different settings could be used to vary the flow of air around a plant shoot
• Enclosing the plant shoot in a plastic bag can increase the humidity
• A humidifier or dehumidifier could be used to give a measurable variation in humidiy
• A lamp at different distances or with different types of light bulb can be used to vary light intensity
• A thermometer or temperature probe can be used to find surroundings with different air temperatures
• A heater or air conditioner can be used to give a measurable variation in temperature
• A researcher would need to be aware of the importance of controlling any variables other than the variable of interest to ensure that any results were valid e.g. placing a plant shoot in different rooms could be a way of varying temperature, but might bring the risk of also varying light levels and humidity; these variables would need to be controlled

Factors affecting the rate of transpiration

• The air outside a leaf usually contains a lower concentration of water vapour than the air spaces inside a leaf, causing water vapour to diffuse out of the leaf
• When the air is relatively still, water molecules can accumulate just outside the stomata, creating a local area of high humidity
• Less water vapour will diffuse out into the air due to the reduced concentration gradient
• Air currents, or wind, can carry water molecules away from the leaf surface , increasing the concentration gradient and causing more water vapour to diffuse out
• An increase in temperature results in an increase in the kinetic energy of molecules
• This increases the rate of transpiration as water molecules evaporate out of the leaf at a faster rate
• If the temperature gets too high the stomata close to prevent excess water loss
• This dramatically reduces the rate of transpiration
• Stomata close in the dark and their closure greatly reduces the rate of transpiration
• Stomata open when it is light to enable gas exchange for photosynthesis; this increases the rate of transpiration
• Once the stomata are all open any increase in light intensity has no effect on the rate of transpiration
• If the humidity is high that means the air surrounding the leaf surface is saturated with water vapour
• At a certain level of humidity, an equilibrium is reached; water vapour levels inside and outside the leaf are the same, so there is no net loss of water vapour from the leaves

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Author: Alistair

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

• Biology Article
• Comparitive Study Of The Rates Of Transpiration In The Upper And Lower Surface Of Leaves

Comparative Study - Rates Of Transpiration In The Surface Of Leaves

Compare the rates of transpiration in the upper and the lower surface of leaves.

Read more:   Transpiration

What is Transpiration?

It is the process of water movement through a plant which evaporates through the aerial parts of the plant into the atmosphere. It occurs through specialized openings known as stomata that are present on leaves which are chiefly concerned with a gas exchange during the process of respiration and Photosy n thesis . The stomata are girdled with specialized cells that govern the closing and the opening of the stomata known as guard cells. They assist in the regulation of the rate of transpiration.

Explore more: Photosynthesis

Material Required

• A potted plant
• Filter paper strips
• 3% cobalt chloride solution
• Binder clips
• Glass Slide
• Into the Petri dish, pour the cobalt chloride solution
• Dip a few strips of filter paper into the solution
• Allow the strips to stay in the solution for a few minutes, watch them turn pink in colour
• With the help of forceps, separate the strips
• Allow the strips to dry by placing them on the wire gauze
• Upon drying, the strips turn blue in colour
• Pluck a healthy leaf from the potted plant, clean it to remove excess droplets with the help of filter paper
• After drying on the wire gauze, set the dried strips one on the upper surface of the leaf and one on the lower surface.
• Now place 2 glass slides on each surface of the leaf, i.e., the upper surface and lower surface.
• With the help of binder clips, secure the slides.
• Observe and make note of the time that is consumed by the paper to switch its colour from blue to pink.

Observation

Through the experiment carried out, it is observed that the amount of time taken for the colour change of the cobalt chloride paper from blue to pink on the lower surface of the leaf is lesser than the upper leaf surface.

The rapid switch of the colour of the cobalt chloride paper on the lower surfaces depicts that rate of loss of water vapour is higher on the lower surface than the upper surface.

Precautions

• The plant that is used in the experiment should always be a healthy and well-watered plant
• The paper should always be handled with forceps or well-dried hands
• The leaf should completely be wiped off excess water before placing the strips

Viva Questions

Q.1. List the importance of the process of transpiration. Any two points.

A.1. Following is the significance of the process of transpiration:

• It helps the plant to absorb water from the soil, which is transported from roots to leaves and impacts the transpiration pull.
• During the process of evaporation, it cools down the surface of plants.

Explore more: Transpiration pull.

Q.2. What are some environmental factors affecting the rate of transpiration?

A.2. Transpiration can be affected by the following:

• Transpiration is quicker in the presence of light
• Transpiration is rapid at higher temperatures as it aids the evaporation of water
• Rate of transpiration is low when the relative humidity of the surroundings is higher
• Rate of transpiration decreases when there is no breeze as the leaf surface turns humid.

Q.3. Why is water loss greater in the lower surface of the plant in comparison with the upper surface?

A.3. It is because usually the distribution and number of stomata vary in the lower and upper surface of leaves. The lower surface of leaves has a greater number of stomata to carry out the process of transpiration.

Q.4. Why is this experiment a comparative study?

A.4. It is a comparative study as the rate of transpiration of both the leaf surfaces i.e., the upper and the lower surface is compared.

Q.5. Why is cobalt chloride paper used in this experiment?

A.5. It is because this paper turns into a pink colour when it reacts with water. Hence this property of the paper can be used to demonstrate the process of transpiration.

Q.6. How is the rate of transpiration estimated in this experiment?

A.6. It can be estimated by taking into account the time the paper takes to switch its colour from blue to pink.

Learn more in detail about the transpiration, rate of transpiration, other related topics and experiments at BYJU’S Biology .

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