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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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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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Lab 9 Transpiration Example 2 ap

Introduction

Most of the water a plant absorbs is not used for a plant’s daily functioning. It is instead lost through transpiration, the evaporation of water through the leaf surface and stomata, and through guttation, which is the loss of water from the vascular tissues in the margins of leaves.

There are three levels of transport in plants: uptake and release of water and solutes by individual cells, short distance cell to cell transport at tissue and organ levels, and long distance transport of sap by xylem and phloem at the whole plant level. The transport of water is controlled by water potential. Water will always move from an area of high water potential to an area with low water potential. This water potential is affected by pressure, gravity, and solute concentration.

Water moves into the plant through osmosis and creates a hydrostatic root pressure that forces the water upward for a short distance, however, the main force in moving water is the upward pull due to transpiration. This pull is increased by water’s natural properties such as adhesion and cohesion. Transpiration decreases the water potential in the stele causing water to move in and pull upward into the leaves and other areas of low water potential. Pressure begins to build in the leaves, so to prevent downward movement, guttation occurs. Guttation occurs through leaf openings on the leaf margins called hydrathodes. Loss of water through transpiration can be facilitated by the opening and closing of the stomata depending on environmental conditions.

There are three types of cells in plants: parenchyma, sclerenchyma, and collenchyma. Parenchyma cells are the most abundant and are not specialized. They are found in the mesophyll of leaves, the flesh of fruits, the pith of stems, and the root and stem cortex. Sclerenchyma are elongated cells that make up fibers. They have thick secondary walls and the protoplasts often die as they grow older. They are used for support and are found in vascular tissue. Collenchyma cells are living at maturity and have a thickened secondary wall.

In Lab 9A, all of the plants in this experiment will lose water through transpiration, but those affected by the heat sink and the fan will lose a larger amount of water due to the environmental conditions. This transpiration will pull water from the potometer into the plant. The structure and cell types of a stem cross-section can be observed under a microscope.

Exercise 9A: Transpiration

The materials needed for this exercise were a pan of water, timer, a beaker containing water (heat sink), scissors, 1-mL pipette, a plant cutting, ring stand, clamps, clear plastic tubing, petroleum jelly, a fan, lamp, spray bottle, a scale, calculator, and a plastic bag.

Exercise 9B: Structure of the Stem

The materials needed for this exercise were a nut-and-bolt microtome, single-edge razor blade, plant stems, paraffin, 50% ethanol, distilled water, 50% glycerin, toluidine blue O stain, a microscope slide and cover slip, pencil, paper, and a light microscope.

The tip of the pipette was placed in the plastic tubing and they were submerged in a tray of water. Water was drawn into the pipette and tubing until no bubbles were left. The plant stem was cut underwater and inserted into the plastic tubing. Petroleum jelly was immediately placed around the tube edging to form an airtight seal around the stem. The tubing was bent into a “U” shape and two clamps were used on the ring stand to hold the potometer in place. The potometer was allowed to equilibrate for ten minutes.

The plant was exposed to a fan, which was placed one meter away and set on low speed. The time zero reading was recorded and then it was continually recorded every three minutes for 30 minutes. After the experiment, all the leaves were cut off the plant and massed by cutting a one cm2 box and massing it.

A nut-and-bolt microtome was obtained and a small cup was formed by unscrewing the bolt. The stem was placed in the microtome and melted paraffin was poured around the stem. The paraffin was allowed to dry and the excess stem was cut off. The bolt was twisted just a little and then cut with the blade. The slice was placed in the 50% ethanol. The slices were left in the ethanol for five minutes. Using the forceps, the slices were moved to a dish of the toluidine blue O stain and left for one minute. The sections were rinsed in distilled water. The section was mounted on the slide with a drop of 50% glycerin. A cover slip was placed over the slide. The cross section was observed under a light microscope and drawn.

Table 9.1: Individual Potometer Readings

Class Potometer Readings

Mass of leaves = 1.1 g Leaf Surface Area = 0.0044 m 2

Table 9.2: Individual Water Loss in mL/m2

Table 9.3: Class Average Cumulative Water Loss in mL/m2

Analysis of Results

Calculate the average rate of water loss per minute for each of the treatments: Room: 1.67 mL/m2 Fan: 0.76 mL/m2 Light: 0.93 mL/m2 Mist: 0.83 mL/m2

Explain why each of the conditions cause an increase or decrease in transpiration compared with the control.

How did each condition affect the gradient of the water potential from stem to leaf in the experimental plant?

The light and the fan decreased the water potential in the leaves and water moved up the stem by transpiration pull. The room temperature had little or no effect on the water potential. The mist increased the water potential of the air causing less transpiration to occur from the leaves.

What is the advantage to a plant of closed stomata where water is in short supply? What are the disadvantages?

The closing of the stomata would prevent transpiration of water and minimize this loss if water was in short supply. It is a conservational adaptation. However, closing stomata prevents the exchange of gases in plants and limits their carbon supplies.

Describe several adaptations that enable plants to reduce water loss from their leaves. Include both structural and psychological adaptations.

Plants that are adapted to drier climates are called xerophytes. Some of these plants have adapted small, thick leaves with a reduced surface area. They may also have a thickened cuticle to protect themselves from the environment. The stomata may be sunken into pits. Some xerophytes shed their leaves during the driest seasons and others can store water such as cacti. CAM plants uptake CO2 at night and change it into crassulacean acid that can be broken down during the day for sugars. These plants can close their stomata during the day.

Why did you need to calculate leaf surface area in tabulating your results?

The surface area has to be calculated because this greatly affects the amount of water lost through transpiration. Smaller leaves may lose less water than the larger ones, but by calculated water loss by surface area creates comparable data that is constant and consistent.

Error Analysis

This lab had many opportunities for error. The potometer set up was a complicated procedure. If any air bubbles were present in the plastic tubing, it could cause drastic error to occur. Any miscalculations or inaccurate weighing could also account for error.

Discussion and Conclusion

Transpiration in plants is controlled by water potential. This change in water potential in leaves causes a gradient by which water can be moved upward. When the water potential of the air was increased by the mist and plastic bag, less water evaporated from the leaves, decreasing the water potential gradient between the root and stem. This decreased the transpiration pull. The fan and floodlight simulated environmental conditions such as wind, heat, and intense light. These conditions increase the amount of water transpired by plants. This in turn increased the water potential gradient causing more water to be pulled through the stem. The control plant should have had normal rates of transpiration.

The stem must have specialized cells for support and transport. The epidermis is the outermost layer of the stem. The xylem is a transport tube for water, and the phloem transports food and minerals through the plant. Parenchyma are non-specialized cells and are located in the interior. The tougher sclerenchyma and collenchyma make up the structural outer support of the epidermis and the transport tubes of phloem and xylem.

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

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.

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Process of Transpiration in Plant Cell: 17 Experiments

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The following points highlight the seventeen experiments on process of transpiration in plant cell. Some of the experiments are: 1. Determination of Stomatal Frequency (Or the Number of Stomata per Unit Area) of a Leaf 2. Measurement of Stomatal Pore 3. Determination of Changes of Stomatal Opening in Light, Dark and Under Desiccation 4. Effect of pH on Stomatal Opening and Closing and Others.

Determination of Stomatal Frequency (Or the Number of Stomata per Unit Area) of a Leaf

Measurement of Stomatal PoreDetermination of Changes of Stomatal Opening in Light, Dark and Under Desiccation

Effect of pH on Stomatal Opening and Closing

Determination of the Area of Leaves by Different Methods

Determination of the Percentage of Total Stomatal Aperture in Relation to the Area of the Whole Leaf

Demonstration of Law of Diffusion Through Small PoresDemonstration of the Phenomenon of Transpiration

Determination of Transpiration Index

Determination of the Rate of Transpiration

Quantitative Determination of the Differential Rates of Transpi­ration from the Two Surfaces of a Leaf (Cuticular and Stomatal)

Simultaneous Determination of the Amount of Water Absorbed, Retained and Transpired by a Plant

Demonstration of Suction Force Due to Transpiration or Tran­spiration Pulls

Determination of Stomata-Bearing Surface of a Leaf without Using a Microscope

Determination of the Effects of Environmental Factors on the Rate of Transpiration

Quantitative Determination of Transpiration Under Conditions of Different Experimental Errors Generally Encountered

Demonstration of Guttation

Experiment # 1

Determination of stomatal frequency (or the number of stomata per unit area) of a leaf :.

Experiment:

In order to determine the dimension of stomata and the area of field of vision, the ocular is first standardized with the help of a stage micrometer. One stage micrometer division is generally 10µ (it is indicated on the stage itself).

The length of the scale of the stage micro­meter is equal to 1 mm and 1 mm is equal to 1000µ. For standardiza­tion of the ocular micrometer, it is first placed inside the eye-piece and the stage micrometer on the stage of a microscope at a particular magnification. Now it is observed how many divisions of the ocular coincide exactly with those of stage micrometer.

Three such readings are taken and the average is determined. The value of one ocular division is calculated as follows:

If X stage divisions are equal to Y ocular divisions, then one ocular division becomes equal to 10X/Yµ (1 stage division = 10µ). Standardiza­tion in both low and high power of microscope is separately done.

The diameter of the field of vision of the microscope is determined with the help of the ocular or the stage. The area of the field of vision is calculated from the formula πr 2 , where r is the radius of the field of vision, i.e., half of the diameter (convert µ into centimeter and calculate area of the field of vision in square centimeter).

Epidermal peelings from the lower surface of Basella leaf are mounted on a slide and the number of stomata within the field of vision is counted. Three such readings are taken by moving the slide. Such readings are taken from the apical, middle and the basal portions of the leaf and the average number is calculated.

The number of stomata within the area of field of vision is determined and from it the number of stomata per square centimeter is calculated. This gives the stomatal frequency of the leaf.

Discussion:

Stomatal frequency is defined as the number of stomata per unit area of the leaf surface. Different species of plant have different stomatal frequencies and this varies with environment and age of the leaves.

In leaves stomata may occur in both upper and lower surfaces. In woody plants with dorsiventral leaves they are located mainly on the lower epider­mis and in herbaceous plants with isobilateral leaves they occur on both the surfaces, though more abundant on the lower side.

In an individual leaf stomata are more numerous near the apex and minimum near the base, the middle region having an average distribution. Stomatal fre­quency generally ranges between few thousands to a hundred thousands. In determining stomatal frequency of an isobilateral leaf the stomata of both the surfaces should be taken-into consideration.

Experiment # 2

Measurement of stomatal pore:.

There are several methods for determination of the state of stomatal opening. A few important methods are given below.

(a) Lloyd’s method:

By this method stomatal pore of leaves can be measured by using ocular (standardized) and the microscope. The epidermal peelings of leaf of a suitable species are taken and immediately fixed by immersing in hot alcohol.

The alcohol fixes the stomata prevent­ing any further movement of the guard cells. The peelings are examined under the microscope and the opening of the guard cells is then measured by a standardized ocular.

The area of the pore is determined. Since the area of the pore is somewhat ellipsoidal in nature, the area could be very approximately taken as equivalent to (πr/4) (ax b), where a and b represent the length and the breadth of the pore, and π = 3.142.

(b) Impression method:

The leaf is taken from a healthy potted plant and its lower surface is smeared with Durofix or Collodian (1gm of pyroxylin in 6 ml of alcohol and 20 ml of ether). It is kept for some time. After about half an hour the Durofix or Collodian is dried up into a thin papery film.

The film is now stripped off and the impres­sions of the stomata in. such films can be observed under a microscope. The exact area of the stomatal opening is calculated by the above method.

(c) Darwin’s porometer method:

Darwin’s porometer is a useful apparatus for following the changes in the stomatal aperture, i.e., the degree of opening of stomata. This is an indirect method for know­ing the degree of opening of stomatal aperture.

The Principle of the method is that the water vapour, which comes out of the stomatal pores, produces a pressure on the level of water column in a vertical tube pushing the level down at a rate at which water vapour comes out (Figure 10).

2. Before taking actual measurement of area from the outline drawn on a paper, zero of the lever vernier should be fixed at 35 mark of the tracer arm.

(b) By weighing method:

A leaf is placed on a card board or on a century board and its outline is drawn. The leaf area on the board is accurately cut and weighed. Now one square centimeter area is cut out from the board and is weighed. If weight of the area drawn on the board is X. gm and that of one square centimeter is Y gm, then the area of the leaf is X/Y sq. cm.

(c) By graph paper method:

This is the most convenient method which is generally used in laboratory experiments. The leaf is placed in a millimeter graph paper and its outline is drawn. The total number of large square blocks (one large square block is equal to one square centimeter) is counted.

The number of small squares (one small square is equal to one square millimeter) in the remaining area of the outline of the leaf is then counted and converted into square centimeter. All the values are added in order to get the total area of the leaf.

Experiment # 6

Determination of the percentage of total stomatal aperture in relation to the area of the whole leaf :.

Stomatal frequency (X) of the experimental ‘leaf is determined as in Expt. 1 and the area of the leaf (Y) is found out as in Expt. 5c. Now the average area (Z) of the stomatal pore is determined as in Expt. 2.a.

The product of X (stomatal frequency) and Y (area of the leaf) gives the total number of stomata. This product when multiplied by Z (area of the aperture) gives the total area of the stomatal aperture of the leaf. The percentage of the area of the stomatal aperture in relation to the entire leaf area is calculated.

Stomatal frequency varies with different species of plants, age of leaf of the same species and the conditions under which it is grown. When there are a few stomata per unit area of the leaf, they are usually large, if there are many they are generally small.

Calculations of stomatal areas as percentages of leaf areas, however, show no constant relation. The range is not very great and is usually between 0.4 to 0.2 percent of the leaf area calculated on the basis of one surface in case of dorsiventral or both the surfaces in case of isobilateral leaves.

Experiment # 7

Demonstration of law of diffusion through small pores :.

The law of diffusion through small pores can be studied by taking equal amounts of alcohol in two wide-mouthed bottles. The mouths of the bottles are covered with two polythene sheets having holes of different diameters.

Care should be taken that the holes are more or less widely spaced. The rate of evaporation is measured by weighing the bottles from time to time. The total diameter and perimeter in centimeter and area in square centimeter of all the pores are separately determined in the two sheets.

The area of the pores and the perimeter of the pores in each case are determined by applying the formulae πd 2 /4 and π × d respectively, where d is the diameter of the pore. The mean change in weight per unit time per unit area and per unit linear dimension of the pore (perimeter) gives the rate of evaporation through pores of different diameters. The results are entered in tabular form.

In quiet air the rate of diffusion is more nearly propor­tional with the linear dimension, i.e., the perimeter of the pores than to their areas. For this reason the rate of diffusion per unit surface of pore is higher in the smaller pores.

If the pores are uniformly scattered over a surface, the actual open area is highly reduced but there is slight reduction in diffusion rate. Thus the diffusion through a multi-perforate septum is higher as compared with that of a single opening with an area equal to the aggregate area of the pores.

Closely spaced pores bring interference in diffusion due to overlapping of humidity layers. It has been estimated that if pores are over 8 or 10 times diameter apart, interference is minimum and each pore allows for its maximum diffusion.

Interestingly, stomata are usually further apart than 8 times of their diameter. This is why the rate of diffusion through stomatal apertures is high even though the total area of stomatal opening is small.

Although, the open area of the stomatal pore only represents 1 % of the total leaf area, the diffusion of water vapour through the pores often exceeds 50% of that evaporating from free ‘ water surface.

N.B. In order to establish the degree of correlation between:

(i) The rate of evaporation and the perimeter of pores and

(ii) The rate of evapora­tion and the area of pores, results are tabulated and subjected to statistical analysis for degree of correlation.

Experiment # 8

Demonstration of the phenomenon of transpiration :.

(a) Bell jar method (qualitative):

A small healthy potted plant is taken and its soil is covered with a polythene sheet to check evaporation from the soil surface. The stem and leaves remain uncovered. The plant is now placed under a bell jar and the rim of the bell jar is sealed with Vaseline. The set-up is kept in a lighted place. Another set-up is similarly maintained where all the leaves from the plant are removed previously.

Observation:

In the first set-up droplets of water are seen on the inner walls of the bell jar. In the second set-up there is no condensation of water vapour on the inner wall of bell jar.

When leaves transpire water the water vapour comes out and after saturating the inner atmosphere of the bell jar it condenses in the form of droplets on the inner walls. In the case where all the leaves are removed from the plant before covering with bell jar, no condensation of water vapour takes place because the transpiring organs, that are leaves, are absent.

N.B. Instead of removing the leaves, Vaseline may be applied on both the surfaces of the leaves of the plant to prevent transpiration.

Effects of the presence of some poisonous gases (CO, CO 2 , HCL vapour, etc.) on transpiration may be studied by introducing the gas into the bell jar before covering the plant. The effect of light and darkness may also be studied by this method.

(b) Cobalt chloride paper method (qualitative):

A few pieces of filter paper are soaked in 5 % aqueous cobalt chloride (COCl 2 ) solution for a few minutes. The pieces are then taken out, excess solution is removed by hanging and pieces are dried in hot air oven at 60°C.

These are then cut into squares (2×2 cm) and kept in a desiccator containing fused CaCl 3 . The original colour of the wet papers is pale pink, when dried to a standard uniform shade, the colour becomes intense blue.

Now a piece of cobalt chloride paper thus prepared is placed at the lower surface of a leaf of a potted plant and the paper is covered with glass slides from both surfaces of the leaf the slides are made air-tight with Vaseline.

After some time the blue colour of the cobalt chloride paper turns pink.

As water vapour comes out of the stomatal pores (if they are open) it moistens the cobalt chloride paper changing its colour to pink. The treated blue dry paper is thus a moisture detector, turning pink when left in the air or when placed in contact or near an evaporating surface.

(c) By conical flask-water-oil-leaf method (quantitative):

A 250 ml conical flask is filled up to its neck with water and a-suitable petiolate leaf (cut under water in order to maintain conti­nuity of water column) is inserted within the conical flask in such a way that its petiole remain under water.

A sinker may be used to keep the leaf in position. Now oil is poured on the surface of water to check eva­poration from water surface. The whole set-up is weighed and allowed to stand in open air or in a well ventilated room having sufficient light. After 2 hours the set-up is reweighed.

The difference between the first and the second weights gives the amount of water transpired by the leaf in 2 hours. The results may be expressed in per unit time.

The loss in weight is due to loss of water in the form of water vapours through the leaf. Since the free evaporating surface is checked by oil film, the sole loss of water is only due to transpiration through the leaf.

(d) Hanging leaf method:

Two healthy leaves of a suitable plant are selected. One of the leaves is smeared with Vaseline on both the surfaces and to the petiole to check transpiration. The second leaf is left as such. The leaves are then weighed and kept hanging in bright sunlight for an hour. These are then taken out and reweighed.

After one hour it is seen that the first leaf remains turgid and fresh while the second leaf wilts. In the first leaf the difference bet­ween the initial and the final weights are negligible, but in the second leaf considerable loss in weight takes place.

Results indicate that the first leaf in which transpiration is checked, the loss of water is insignificant and the leaf remains turgid and fresh. While in the second leaf loss of water due to transpiration takes place in, appreciable quantity and the leaf wilts.

Experiment # 9

Determination of transpiration index :.

Transpiration index is defined as the ratio of the time (in seconds) required for a standard change of colour of dry cobalt chloride paper over a free evaporating surface (S) and the transpiring surface (E) and can be expressed as follows:

Transpiration index = S × 100/E

(The index is multiplied by 100 to obtain the loss of water from the leaf surface as a percentage of evaporation from free water surface).

Two equal pieces (2×2 cm) of cobalt chloride papers are taken. One is attached to the lower surface of a dorsiventral leaf as in Expt. 8.b and another is placed on a wire net which is kept over a petridish containing water. Time taken in seconds for a standard colour change of the cobalt chloride papers in both the cases is noted.

Transpiration index is calculated from the above mentioned formula.

Transpiration index gives an indication of the relative efficiency of the rate of transpiration with that of physical evaporation. It varies from species to species, with age of leaves and with different environ­mental conditions.

N.B. Transpiration index of upper and lower surfaces of a leaf, in light and dark, in young and old leaves and in different ecological types of leaves may be compared. The participation of conducting tissues in transpiration may also be studied from this experiment by separately removing xylem and phloem tissues.

Experiment # 10

Determination of the rate of transpiration :.

(a) Cobalt chloride paper method (qualitative):

Two pieces of cobalt chloride papers are affixed on both the surfaces of a dorsiventral leaf as in Expt. 8.c. The length of time required for the papers to turn pink indicates the rate of transpiration from the two surfaces of the leaf.

(b) Conical flask-water-oil-leaf method (quantitative):

Two dorsiventral leaves of equal and comparable sizes are taken. The upper surface of one leaf and the lower surface of the other are smeared perfectly with Vaseline. The experiment is then set-up as in Expt. 8.c.

The amount of water transpired per unit time divided by the area of the leaf (determined by graphical method as in Expt. 5.c) gives the rate of transpiration per unit time per unit area of the leaf.

The rate of transpiration is higher in lower surface than in upper surface because stomata are more abundant in lower surface than upper surface which is cuticularised. The rate of transpiration from the lower surface indicates stomatal transpiration and that from the upper surface indicates cuticular transpiration.

N.B. The rate of transpiration may be correlated with:

(i) Stomatal frequency,

(ii) A single stoma (amount of water transpired per unit time divided by the total number of stomata of the leaf),

(iii) Area of stomatal aperture (amount of water transpired per unit time by the total stomatal aperture),

(iv) Number of xylem vessels present in the petiole (a cross section of the petiole may be cut for estimation of total number of xylem; the total area of xylem vessels as determined from the formula πr 2 ) and correlated with the rate of transpiration), and

(v) Simple physical evaporation (rate of evaporation of water per unit time per unit area of a petridish is to be calculated taking area of petridish to be πr 2 ) and this may be compared with the rate of transpiration per unit area of the stomatal aperture.

(c) Potometer method (quantitative):

The rate of transpiration (expressed in gm per hour per square centi­meter of the leaf surface) can be measured with the help of an apparatus known as potometer. Determination of the rate of transpiration by different potometers, excepting Garreau’s, is an indirect one where both absorption and transpiration have been taken into consideration.

Potometers are designed on the principle that the rate of transpiration is nearly propor­tional to the rate of absorption of water by the plant, although it is not the general rule. There are many types of potometers; all working on the same principle excepting Garreau’s which gives a direct measurement of transpiration. The potometers described below are generally used in laboratory experiments.

(i) Darwin’s potometer:

Description:

This apparatus consists of a short glass tube from which a side tube bends upward ending in an open mouth (manometer tube) into which a plant twig is inserted through a cork.

The upper open mouth of the main tube is closed by a cork. The lower end of the tube is also fitted with a cork through which passes a long graduated (in ml) capillary tube. The end of the capillary tube dips in a beaker containing water (Figure 12).

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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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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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Shop Experiment Transpiration Experiments​

Transpiration.

Experiment #10 from 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.

Correlations

Teaching to an educational standard? This experiment supports the standards below.

Ready to Experiment?

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This experiment is #10 of 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.

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This experiment shows the result of plant transpiration.

Detailed Description

After a plastic bag is wrapped around part of a plant, the inside of the bag becomes misty with transpired water vapor.

Sources/Usage

Public Domain.

Related Content

Il ciclo dell'acqua, The Water Cycle, Italian

Evapotranspiration and the Water Cycle

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Investigating the effect of increasing temperatures on transpiration

April 6, 2022 By Emma Vanstone Leave a Comment

Transpiration is the loss of water from a plant. Transpiration mainly occurs from the leaves. Water vapour diffuses out of the stomata ( tiny pores mostly found on leaves ).

Loss of water from the leaves creates a pull on the water in the xylem cells drawing water up the plant. This movement of water from roots to leaves is called the transpiration stream .

Xylem cells form a  continuous tube  from the leaves of a plant to the roots, a bit like a drinking straw providing a continuous flow of water.

The transpiration stream transports minerals and water around the plant and keeps cells turgid ( full of water ) so they can support the plant without it wilting.

Rate of Transpiration Experiment

How does increasing temperature and airflow around a plant affect the rate of transpiration.

This simple investigation uses a hairdryer to increase the airflow and temperature around the leaves of a celery stick to find out how the rate of transpiration is affected.

You’ll need

Two celery stalks with leaves

Food colouring

A hairdryer

Instructions

Choose two stalks of celery with leaves that are similar in size.

Cut them to the same length.

Place each stalk in a container of water and food colouring. Make sure the same amount of water and food colouring is used for each sample.

Every 5 minutes for half an hour, blow warm air from a hairdryer over the leaves of one celery stalk.

After half an hour, remove the celery stalks from the water and carefully slice the stalks to find how far up the coloured water has reached.

How does increasing airflow and temperature affect the rate of transpiration

We found the celery sample that was exposed to heat from the hairdryer had a much faster rate of transpiration than the celery not exposed to heat.

The coloured water had travelled much further up the stalk of the sample exposed to heat than the one not.

How the movement of air affects transpiration

Air flow removes water vapour from around a leaf, creating a concentration gradient ( low concentration of water in the air and high concentration in the leaf ) between the leaf and air, increasing water loss from the leaf. If there’s not much airflow, the water vapour doesn’t move far from the leaf, so there’s a high concentration of water inside and outside of the leaf and so no concentration gradient for diffusion.

How temperature affects transpiration

Higher temperatures mean water molecules evaporate at a faster rate which increases the rate of transpiration.

What else affects the rate of transpiration

The amount of light also affects the transpiration rate. Stomata close in the dark so water cannot diffuse out.

More experiments to investigate transpiration

These colourful flowers look much more impressive than the celery, but the process is the same!

Water is transported up the stem of a plant by a process called capillary action . You can try this out by placing paper flowers into a tray of water and watching them open up.

You might also like my 3D model of a flower ! This is great for learning about the different parts of a flower.

Last Updated on January 20, 2023 by Emma Vanstone

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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.

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