Name:________________________
YEAR 11 BIOLOGY: PRACTICAL INVESTIGATION
VASCULAR TISSUE IN PLANTS
INTRODUCTION
Tissues that are specialised for transporting substances through plants over long
distances are called vascular tissues. Few cells in plants are far from vascular tissue. One
tissue transports water and inorganic nutrients upwards through the plant and is called
xylem. The other tissue transports sugars (in solution) produced by photosynthesis and
other manufactured products throughout the plant and is called phloem.
In stems, xylem and phloem tissue form vascular bundles, with the phloem on the outer
surface of the bundle. A layer of cells called the cambium runs through the vascular
bundle separating the xylem and phloem.
Vascular tissue is easily visible in leaves. The parallel veins of grasses and the branching
veins in most other leaves are part of the vascular network of the plant. Vascular tissue
extends from the roots to the very tips of leaves, and into developing buds and fruit.
PURPOSE
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To investigate the pathway of water movement in the stem and leaves of a
flowering plant (angiosperm).
To examine the microscopic structure of the tissue through which water moves in a
plant.
To become familiar with the structure and function of a vascular bundle.
MATERIALS AND EQUIPMENT
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celery petioles (sticks)
dye solution
large beaker
iodine stain
stereoscopic microscope
high power microscope
forceps
TOTAL:
/45 marks
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two dissecting needles
microscope slides and coverslips
single-edged razor blade
dissecting board
paper towel and paper tissues
prepared slides of plant material
PREPARATORY ACTIVITY
Begin to fill in the following table before you begin the practical activity by writing your
understanding of each key term listed in the space provided. If there terms are unfamiliar
before you start, ensure that you research the terms and complete the table by the end of
the prac.
Key Term /
Concept
xylem
Definition
tracheid
vessel
phloem
sieve cells
companion
cells
transpiration
root pressure
(8 marks)
PROCEDURE
Day 1
1. Cleanly cut the end off two celery petioles (sticks).
2. Place the petioles in a beaker of dye solution.
3. After about half an hour, observe the movement of dye through the celery by
looking at it without dissection. Record these observations.
Day 2
1. Collect one of the dyed celery petioles. Rinse the dye from the end and examine the
petiole and leaves of the celery for evidence that the dye has been distributed. (Try
holding it up to the light.)
QUESTION 1
Describe the distribution of the dye. Has the whole stem changed colour or is the dye
found in particular places? Explain your answer.
(2 marks)
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2. Place the petiole on a dissecting board and, using the
razor blade, cut transverse sections 1-2mm thick in the
positions shown in the figure to the right.
Arrange the sections in order on a microscope slide. (A
coverslip is not needed.)
Put the slide under a stereoscopic microscope and
examine the cut surface of each section for the presence
of dye.
QUESTION 2
Draw diagrams of the three sections, showing the distribution of the dye.
(6 marks)
3. Cut a section of the petiole 1cm thick. Stand the section on its end and cut
lengthways down along one of the coloured areas. Examine this section under the
stereoscopic microscope.
QUESTION 3
Combining your observations of the transverse and longitudinal sections, draw a threedimensional diagram of the petiole, showing where the dye has moved.
(4 marks)
QUESTION 4
What assumption are we making in saying that the dye shows us where the xylem is?
(1 mark)
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QUESTION 5
What causes the dye to travel to the leaves? (2 marks)
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4. Collect a 3cm piece of undyed celery petiole.
Using the technique shown to the right, cut
several very thin cross sections.
Select the thinnest section, mount it on a slide
and stain it with iodine. Add a coverslip and
observe under a high power microscope using
the low power objective lens.
Look for some thick-walled cells in about the
same position as you found the dye. These are
xylem vessel cells and they form part of a vascular bundle. Water moves in xylem.
5. Cut a 1cm thick slice from the remaining undyed celery. Place it under a
stereoscopic microscope and, using a scalpel, cut out a small piece of the vascular
bundle and put this on a microscope slide with a drop of iodine. Make sure the slide
is on a piece of paper towel.
Use the dissecting needles to tease this piece of tissue apart. Add a coverslip, and
gently squash the bundle.
6. Use low power, then high power, to identify the cell types shown in the figures
below.
xylem vessel cells
phloem cells
QUESTION 6
The walls of xylem vessel cells are thickened by a material called lignin. You may also
observe spiral coils in the vessel cells. These too are made of lignin. What advantage
would both of these features of xylem have for a plant?
(2 marks)
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QUESTION 7
Make drawings of several xylem vessel cells and several phloem sieve tube and
companion cells under high power magnification.
(12 marks)
CONCLUSION
Using the observations made in this activity and information from your textbook, draw a
diagram showing the structure of a vascular bundle in a flowering plant. Use detailed
labels to describe the function of the following types of cells: xylem vessel cells, sieve tube
cells, companion cells, fibre cells.
(8 marks)