Investigation into the strength of various plant fibres


The experiment is being performed in order to determine the strength of various plant cell fibres.

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The xylem is surrounded by spirals and rings of lignin that provide strength to the cells. The sclerenchyma is also very tough and provides the plant with some strength. Both of these cells are found in the vascular bundle. This should make these cells the strongest in the stem of the plant. The other fibres that will be tested are less rigid and therefore should hold less weight, before snapping


Dependant Variable:

The dependant variable is the factor that will be measured due to the outcome of the experiment. In this experiment, the dependant variable is the mass at which the fibres give way, when having masses hung off of them.

Independent Variables:

These are the factors that will be changed in order to measure the dependant variable. In this experiment there is only one independent variable; the type of fibre being used. I am predicting that the vascular bundle, which contains the lignified xylem and sclerenchyma, will be the strongest fibres. The other fibre being used is the general tissue. This contains no lignin and no supporting structures. This will cause it to be weak and should break at a much lower mass in comparison to the vascular bundle

Controlled Variables:

These are the factors that could influence results but are not required in the experiment. They need to be controlled and maintained as best as possible, in order to achieve the most accurate results. The controlled variables in this experiment are:

1. The length of the fibres being tested. Longer fibres will be capable of sustaining more weight as the load would be spread over a much larger area, as opposed to using a smaller length of fibre.

2. The thickness of fibres used, same as above in which the area upon the weight is acting is spread out over a larger area in thicker fibres. The thickness must be kept to within a very small degree.

3. The bulldog clips used to hold the strands in place must be identical and used for each experiment without being changes. This is because the fibres may become damaged in the bulldog clip, creating a weak point. This cannot be overcome, so if the same clips are used, then all experiments will be affected in the same way by the bulldog clips.

4. The length of time that the test fibres are out of the water, this could affect results as the fibres may begin to dry out and become brittle over time, affecting the results. Each fibre should not be removed from the plant until it is ready to be tested.

5. The plant that each fibre comes from should be the same to ensure that there are no differences involving weakness. Environmental or genetic differences could influence the strength of the plant


In the interests of accuracy, all experiments should be performed 3 times and an average taken from them. In order to maintain a larger degree of accuracy, the controlled variables must be observed and maintained. If this is not achieved, the results may be compromised and therefore invalid, preventing me from getting any realistic conclusion from the data.


* clamp stand (x2)

* Boss (x2)

* Clamp (x2)

* Bulldog clips (x2)

* Bunch of celery (quantity required will vary with different experiments)

* Set of masses (0-10g and 10-100g)

* Tile

* Razor blade

* Ruler

* Forceps


1. Set up the apparatus as shown above.

2. Cut a length of the desired fibre from the celery stem. (this could be the xylem, schlerenchyma or entire vascular bundle) ensuring that all strands are the same length and width.

3. Place on end of the fibre in the bulldog clip on one of the clamps and the other end in the other clip (ensure that no extra pressure is exerted onto the fibre through the bulldog clip as this may cause more damage.

4. Suspend the smallest weight onto the fibre roughly in the middle.

5. Add extra weights one at a time until the fibre breaks

6. Record weight which results in breakage.

7. Repeat 3 times for each type of fibre.

8. Perform same experiment for the other fibres.

Diagram above shows where to extract fibres from.


Type of fibre


Mass held

Before breaking (g)
















The results show that the vascular bundles are the strongest fibres within a celery stalk. This is due to the lignin, which encircles the xylem, and the sclerenchyma (as shown on the left). These two fibres give the plant strength and rigidity. There are only two different areas that fibres could be taken from. The vascular bundle and the areas that do not contain vascular bundles are the only places within the plant that fibres could be taken from, that are of equal diameter. When using these two fibres, the results show that the vascular bundles are the strongest fibres for resisting weight, supporting my hypothesis, “This should make these cells (xylem and sclerenchyma) the strongest in the stem of the plant.”

The sclerenchyma also have lignin in their cell walls. This lignin forms and kills the cell, leaving behind a tough and strong lignified dead cell. Even though the cell is dead, it has a lot of strength. All of the vascular bundle fibres broke whilst sustaining a weight that exceeded the other fibres by between 50 and 350g.

There was a lot of variation between all of the results, by over 160g for the vascular bundle fibres. This could have been caused by damage sustained during extraction of the fibre from the plant. All fibres were extracted from the same celery, so genetics and environment should not have been a factor. The force with which the weights were placed onto the fibre which may have created weak points on the fibre which could have affected the results. The fibres should be knotted around the clamp to prevent any weak spots being creates where the bulldog clips are gripping them.

In order to see if the above factors had an effect on the experiment, I would need to conduct the experiment more times and take an average from the results acquired. Due to time issues, this could not be performed in this experiment. This makes our results very inaccurate as can be seen from the values. A conclusion can be drawn from the results but not an accurate one.

The vascular bundle which contains the lignified xylem and sclerenchyma is the strongest part of a celery plant. The other areas of the celery do not have as much tensile strength.

The fibres should be knotted around the clamp to prevent any weak spots being creates where the bulldog clips are gripping them.

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