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Identifying structures in a stem CPAC 6
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- PEARSON (PEARSON)
Full CPAC 6 write up which achieved passing grade and fulfilled all necessary criteria for Biology Edexcel
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Name: Hiba Majid 12E (P:\Science\Mr Alim\Year 12\AS Biology(Core Practical: 5)
Title: Identifying plant fibres within a stem using light microscope (Rhubarb) PART A
METHOD
1. Carry out instructions given (or those you have produced and researched) to complete the practical
(CPAC1)
2. List apparatus below and describe techniques used when measuring quantities with a particular piece
of apparatus:
Piece of apparatus Purpose of piece of Comment on how piece of equipment was Appendix 5c
apparatus used accurately/appropriately/safely technique
Light microscope To view the vascular (Medium risk) There are glass components
bundles and if it falls off a high place, it will break.
It should be kept from the edge, in the
middle. It should be kept away from
water, as it is an electrical device.
Microscope slide To observe rhubarb under (Low risk) May cut someone if it is broken
the microscope as it is made of glass. To ensure this
doesn’t occur it should be kept without
any pressure on it for it to break.
Coverslip To keep the bundle still (Low risk) The coverslip should be held
under the light microscope tight to avoid it falling off. it should also be
dealt with carefully to ensure it does not
break. To avoid air bubbles, it should be
placed at 45° and not just placed on top
2 mounted needles To tease vascular bundles (High risk) It is a sharp object, leading to
apart injury. It should be put away after use and
the pointed sharp end kept away from
myself and others
Forceps To pick out vascular bundles (Low risk) No way for the forceps to injure
out of the rhubarb so long as they are used sensibly
Watch glass To place rhubarb onto (Medium risk) If it falls off the edge, it will
break. It should be kept away from edge of
table to prevent it falling off
Methylene blue (1% To differentiate the cells, to (Medium risk) It can lead to staining. It
solution) make bundles visible should only be opened when needed and
closed tightly after use. It should be
dropped carefully. You should also wear a
lab coat.
50% glycerol To make the cells clear and Only opened when needed and dropped
visible carefully
Filter paper To absorb the excess dye No risk. Small chance of injury
from the rhubarb
(CPAC a2a, 2b, 2d, 3a, 3b)
Mr Alim
, Name: Hiba Majid 12E (P:\Science\Mr Alim\Year 12\AS Biology
3. Summarise the method used, pointing out any difficulties in carrying out the practical and any
changes that were necessary from the original plan and why they were made. Draw an appropriate
diagram as necessary. (CPAC 2c)
Preliminary method:
1. Take a small piece of tinned rhubarb and place in a watch glass. From the block of tissue, pick
out 1 or 2 vascular bundles (using forceps) and place them on a microscope slide
2. The vascular bundles should be teased apart using a mounted needle
3. Place a drop of methylene blue onto the tissue and leave for 5 minutes
4. remove extra stain with filter paper. place a drop of dilute glycerol on the fibres and place
under a cover slip. Place this side on a piece of filter paper and press down with you thumb,
in order to separate the tissue. do not move the coverslip sideways.
5. Begin with a low magnification under the microscope and then change to a medium and high
magnification.
6. Look for vascular bundles amongst separated tissues
Difficulties and changes made:
● In order to ensure the best were taken, we took 3 vascular bundles
● Due to time constraints, we left the vascular bundles with the dye for less than 5 minutes
● Filter paper was not absorbing methylene blue efficiently and so we used tissues to blot and remove
excess methylene blue as there was too much added
Measurements
50% glycerol Only 1-2 drops used, using a pipette
Methylene blue Only 1 drop. Excess absorbed by filter paper
Thinned piece of rhubarb Used forceps to take small pieces out then
teased with a mounted needle
RESULTS
1. Use your results above to determine the value being investigated. Show your workings clearly,
drawing a relevant graph as necessary. (ATTACHED AT BACK ON SEPARATE PAPER)
EVALUATION AND CONCLUSION:
1. Evaluate how well you think the experiment went. Refer to accuracy, reliability, uncertainties and
how you could have improved each of these. (refer to results as necessary)
2. Write a brief conclusion of your results
The experiment went well and a clear image of the rhubarb cells was successfully produced. The vascular
bundle was highly magnified and visible so it was easy to distinguish the different cells. It also allowed us to
identify structures within the stem such as the parenchyma. We managed to view vivid images of vascular
bundles within the rhubarb under a light microscope at both low and high power. It was clear where the
Xylem and Phloem tubes were positioned within the bundles. The methylene dye made it easy to view these.
(Core Practical: 5)
Mr Alim
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