Monai Elnaasani
Describe how to determine the tensile strength of plant fibres practically.
Past paper - June 2011, January 2016
1. Take two fibres of the same length, thickness and mass extracted by the same
retting method
2. Attach a piece of fibre to a tensometer apparatus
3. Place 5g weight on the tensometer
4. Note the force generated
5. Repeat the steps with 10g, 15g, 20g and 25g weights or till the fibre breaks
6. Note the force after adding weight
7. Exclude anomalous result and redo for that mass
8. Repeat for each fibre and calculate the mean
9. Compare and draw a graph with two different fibre variables taken into account
Tensile strength - the force a fibre can take without breaking, or the force required to
make a fibre break
- Units are pascals Nmˆ-2
Independent variable;
• Types of fibers or their cross section (depends on the experiment)
Dependent variable;
• force needed to break fibre, maximum tensile strength
Control;
• Fibre length using a ruler
• Diameter of fibre using a micrometer πrˆ2
• Retting method
• Mass
• Age
• Region taken from plant - to remove genetic variation, so same composition, source
of fibre and age to give a valid comparison of results
• Temperature by using chamber, air conditioning or incubator at fixed temperature
• Stored for same length of time
• Same way of applying masses
• Same humidity using beaker of water in chamber or any suitable solution or by air
conditioning
• Water content of fibre
• Soaking time using a stopwatch
Safety;
• Use goggles to protect eyes incase tensile breaks and flies away slapping you in the
face
• Put soft cloth below the weight so that weigh doesn’t land on foot and cause injury
when fibre breaks
• Use gloves to prevent contamination or poisoning from stings of spines on fibre
Pearson Edexcel Advanced Level Biology Unit 3 - notes for success
Describe how to determine the tensile strength of plant fibres practically.
Past paper - June 2011, January 2016
1. Take two fibres of the same length, thickness and mass extracted by the same
retting method
2. Attach a piece of fibre to a tensometer apparatus
3. Place 5g weight on the tensometer
4. Note the force generated
5. Repeat the steps with 10g, 15g, 20g and 25g weights or till the fibre breaks
6. Note the force after adding weight
7. Exclude anomalous result and redo for that mass
8. Repeat for each fibre and calculate the mean
9. Compare and draw a graph with two different fibre variables taken into account
Tensile strength - the force a fibre can take without breaking, or the force required to
make a fibre break
- Units are pascals Nmˆ-2
Independent variable;
• Types of fibers or their cross section (depends on the experiment)
Dependent variable;
• force needed to break fibre, maximum tensile strength
Control;
• Fibre length using a ruler
• Diameter of fibre using a micrometer πrˆ2
• Retting method
• Mass
• Age
• Region taken from plant - to remove genetic variation, so same composition, source
of fibre and age to give a valid comparison of results
• Temperature by using chamber, air conditioning or incubator at fixed temperature
• Stored for same length of time
• Same way of applying masses
• Same humidity using beaker of water in chamber or any suitable solution or by air
conditioning
• Water content of fibre
• Soaking time using a stopwatch
Safety;
• Use goggles to protect eyes incase tensile breaks and flies away slapping you in the
face
• Put soft cloth below the weight so that weigh doesn’t land on foot and cause injury
when fibre breaks
• Use gloves to prevent contamination or poisoning from stings of spines on fibre
Pearson Edexcel Advanced Level Biology Unit 3 - notes for success
