VCE Biology Unit 1
Water transport in Plants
Water is of vital importance to plants; it accounts for about 75% of their composition.
It is needed by plants for many reasons including:
 As a reactant in photosynthesis
 Turgor pressure gives plants support
 Solvent that enables transport of carbohydrates as sucrose
The source of water for land plants is the water in the soil solution. Land plants have to
have a way of taking up this water effectively and efficiently delivering it to even its most
remote cells. For some large trees these cells may be in the leaves many, many meters
above the ground.
This task is designed to help you to understand the journey that water molecules take from
the moment they are absorbed across the surface of root hairs and roots until they are
either used by plant cells or evaporated from the surface of plant.
We will explore
 The structure of water conducting tissues; xylem and tracheids
 The structure of the phloem
 The mechanism by which plants transport water
 The means by which plants loose water to the environment
 The means by which plants control water loss
We will observe:
 The path of water movement in roots, stem and leaves and thus determine the
location of vascular tissues within these structures.
 To observe the difference in structure of stem and root between a monocotyledon
and a dicotyledon.
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VCE Biology Unit 1
Activity 1
Water loss from celery
Look at the uncovered celery and the celery in the cylinder covered by the plastic bag. When these
were set up the level of eosin dye in each was 100 ml. They have been sitting in the eosin dye
solution overnight.
As a group we will record the results for set up A. The celery from set up A can then be used to cut
and observe. The first group at this station will cut a cross section (transverse section) through the
celery 5 cm from the end placed in the dye.
In the table below record the current eosin level for set up A and B:
Table 1: Uptake of eosin by covered and uncovered celery shoots
Set up of the celery
Celery uncovered
Celery covered by plastic
bag
Initial Eosin level
ml
A
B
mean
100
100
100
100
100
100
Final Eosin level
ml
A
B
mean
Average volume of
Eosin taken up
ml
( 2 marks)
1. Examine the leaves of the uncovered and covered celery and compare these. Describe what
you noticed.(1 mark)
This is only one mark so any one point of comparison is acceptable.
The red dye in the leaves of the uncovered celery is much more concentrated than in the
leaves of the covered celery
OR
The red dye in the uncovered leaves is spread throughout the tissues of the leaf which in
the covered celery the dye is mainly in the veins of the leaves.
2. Look at the results for the average volume of eosin taken up by the celery in each treatment
group. Account for the difference between the two. Explain your answers fully.(4 marks)
Much more dye was taken up by the uncovered celery than the covered celery (using your
results you should quote data regarding the difference as well as stating it was more)
Answer is the explanation as to why this happened below

Eosin is a water soluble dye. Water uptake is determined by rate of transpiration,
/evaporation of water from leaf surface.(1)

There is relatively high water vapour gradient between the dry air and the air
spaces in the leaves for the uncovered celery this resulted in a relatively high rate
of diffusion of water from the leaves OR a relatively high rate of transpiration(1)
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VCE Biology Unit 1


The bag traps evaporated water and creates a humid environment around the
covered celery leaves. (1)
Thus there is a relatively low water vapour gradient between the environment and
the air spaces in the leaves for the covered celery, thus a slower transpiration rate,
so less water taken up compared to uncovered leave.(1)
Activity 2
Cross sections of celery and carrot
You have been provided with a stalk of celery and a carrot. Both of these have been soaked
overnight in coloured dye. Both have leaves on them.
1. One of these is a mostly root and the other is a stem. Which is which?
Carrot= mostly root
Celery=mostly stem
Using the blade provided, carefully take a cross section of the celery and the carrot, and
note the position of the coloured areas.
Draw labelled diagrams below to record your observations:
Diagram 1
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VCE Biology Unit 1
Diagram 2
Cut a longitudinal section down the celery stalk. Draw a labelled picture indicating what
you saw.
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VCE Biology Unit 1
2. Name the tissue that you would expect to be identified by the red staining. Explain
your reasoning



Xylem
Eosin is a water soluble dye and is carried up the plant with water
Water is transported in the xylem.
Activity Three
Water movement through a plant
4 factors influence the transport of water through plant:
Watch the following You Tube videos and use the information and your class notes
and text to assist you in answering the following
http://www.youtube.com/watch?v=At1BJJDcXhk
http://www.youtube.com/watch?v=mc9gUm1mMzc
1) Transpiration
What is transpiration?
The evaporation of water from the surface of a plant, (mainly via the stomata of
the leaf)
Explain how this assist with moving water from roots to leaves?
Water molecules are attracted to each other by cohesive forces and water moves
as a continuous column in the xylem. As water molecules are evaporated this
pulls water molecules adjacent to these along and so on down the column.
So transpiration provided a pulling force on the column of water in the xylem.
2) Root pressure
What creates root pressure?
The movement of water into the roots by osmosis.
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VCE Biology Unit 1
3) Cohesion:
Water is a polar molecule. The Hydrogen end of the molecule is slightly positive and
the oxygen end of the molecules is slightly negative. The polar nature of water
molecules means that they will be attracted to one another. Because they are
attracted to one another water molecules are described as cohesive; they “stick”
together.
To demonstrate that water molecules are cohesive, charge up a plastic rod and
place it near to, but not touching, a very slow running stream of water.
a) What happens?
(try this using a plastic ruler at home if you haven’t done it)
The water will move towards the rod.
b) How does this demonstrate that water molecules are cohesive?
The water molecules nearest the rod are attracted to the charged rod, but the
whole water stream moves as one towards the rod because the water molecules
are attracted to each other.
c) How does the cohesion of water molecules assist in moving water up the xylem
of a plant?
Water molecules are attracted to each other and as water molecules in the leaf
are evaporated this pulls water molecules adjacent to these along and so on down
the column.
4) Adhesion and capillarity: Water molecules are also attracted to the walls of the
xylem vessels. This property is known as adhesion. Adhesion results in water being
drawn a small distance up the xylem and this assists with its transport.
DEMONSTRATE this by dropping a small volume of water on the bench and place a
piece of paper towel just touching the side of the puddle. Observe and describe
what happens.
The image to the right shows the
effect of adhesion of water
molecules to the sides of tubing of
different diameter.
Xylem vessels have extremely
small diameters.
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VCE Biology Unit 1
How does this increase the effect of the adhesion between the water molecules and
the xylem walls?
The narrow diameter of the xylem means that there will be a great surface area of vessel
in direct contact with water molecules. The effect of adhesion in this situation will be very
pronounced. Water will be drawn up the wall of the xylem a large distance and this force
will stop the column of water falling due to gravity when transpiration is low.
Activity Four
Discuss the following and as a group come up with a suggested reason for each of the
following. Record your answers.
1. After transplanting a plant it is a good idea to remove some of the leaves.

Removing leaves will reduce the rate of transpiration and limit water loss.

Roots will be damaged in the transplanting process which is reduce the plants
ability to absorb water from the soil

It is important to limit water loss because the amount of water the plant could
replace would be limited because of root damage.
2. Water moves up a stem more quickly on a hot dry day than on a cool wet day.
Water molecules have more kinetic energy on a hot day and will diffuse faster than on a
cool day.
On a dry day there is a higher water vapour gradient between the inside of the leaf and
the environment than on a wet day.
So on a hot dry day the rate of evaporation of water from the leaf surface will be faster
than on a cool day due to faster rate of diffusion of water due to faster molecule
movement and larger water vapour concentration gradient, thus water will move up stem
more quickly in this circumstance.
3. Plants tend to wilt more easily when it is really windy



Wind moves water vapour away from the stomata and continually replaces it with
drier air.
This maintains a relatively high water vapour gradient between inside the leaf and
the environment
thus transpiration is higher and the leaves are more likely to lose water faster
than it can be replaced, causing wilting
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VCE Biology Unit 1
4. In order to show how the air stomata of a plant open, a student makes artificial
stomata as follows. She fills two short lengths of dialysis tubing with a 20% sucrose
solution and ties the ends together as show below (left). She then places the
artificial stoma in a dish of distilled water and leaves it there for three hours. A the
end of the three hour period it looks like the diagram on the right (below)
a) What structures do the two lengths of dialysis tubing represent?
Guard cells
b) Explain how the change in appearance has been brought about.
Water entering the dialysis tubing by osmosis
c) Mention two ways in which the working of this artificial stoma differs from a real
one.



Real guard cells can actively control their solute concentration according to light
intensity and photosynthesis rate, but the artificial guard cells cannot.
Water enters real guard cells due to high concentrations of potassium, not
sucrose,
Real stomata can pump K ions out to make water move out of them and the
stomata close, this artificial system cannot do this.
Any other feasible comparison
d) What part do the stomata play in the movement of water through a plant?
Transpiration is the biggest force moving water through the xylem of plant.
Rate of water loss is related to the size the stomata as these are the openings through
which most evaporation of water occurs
For example if stomata are fully open, the rate of water loss will be higher than if the
stomata are partially or fully closed.
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VCE Biology Unit 1
Activity 5
Root cross section
Look at the root cross sections of the Zea mays (a monocotyledon) and the Ranunculus (a
dicotylendon) under both low and high power. Identify the following tissues
Epidermis, cortex, vascular bundle, xylem, phloem
DRAW and LABEL a diagram showing the location of each tissue in each type of root.
Diagram 1:
Diagram 2:Rununculus
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VCE Biology Unit 1
3 marks
1. Where in the root is the xylem located in a monocotyledon, compared with a
dicotyledon?
In the very centre of a dicot forming and X or Y shape, whereas it forms
a ring near the centre in the monocot
2 mark
2. What is the function of the xylem.
Transport of water AND mineral ions
1 mark
4. Describe the function of the phloem.
Transport of sucrose and re-translocation of ions in a plant.
1 mark
5. Why is starch often present in the cortex of the root.

Product of p/s is glucose which is transported to the cortex of the root for
storage

Glucose is used to form the polymer starch which is stored in the cortex
tissue of the root.

Plants have energy store in the roots for use by the plant when energy needs
are not met via photosyntheis
3 marks
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VCE Biology Unit 1
Activity 7 : Stem cross section
Look at the stem cross sections of the Zea mays (a monocotyledon) and the Ranunculus (a
dicotylendon) under both low and high power. Identify the following tissues
Epidermis, cortex, vascular bundle, xylem, phloem
DRAW and LABEL a diagram showing the location of each tissue in each type of stem.
Diagram 1:
3 marks
Diagram 2:
3 marks
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VCE Biology Unit 1
6. What do the terms monocotyledon and dicotyledon mean?
Monocotyledon refers to a group of plants who seedling has one leaf, while Dicotyledons
refers to a group of plants whose seedlings have two seed leaves.
Each type has a number of characteristics that they share in common, such as number of
petals, types of veins in leaves and arrangement of vascular tissue in roots and stems.(see
table below.
2 marks
7. Describe the differences in arrangement of vascular bundles in the stems of the
Ranunculus and Zea mays.
Zea Mays has its vascular bundles scattered, while Ranunculus has them arranged in a
ring around the edge of the stem
2 marks
8. Is celery a monocotyledon or a dicotyledon? Explain, making reference to your
results.
 Dicotylendon
 Its vascular bundles are arranged in an orderly half ring (as in dicots)along the
edge of the stem, they are not scattered.(like monocots)
2 marks
9. Is the carrot a monocotyledon or a dicotyledon? Explain, making reference to your
results.
 Dicot
 Its Xylem was in the very centre of the root. Not in a ring as it would be if it
was a monocot.
2 marks
Summary of Comparisons between plants that are monocots and those that are Dicots
Monocots
Dicots
Embryo with one cotyledon (seed leaf)
Embryo with two cotyledons
Flower parts in multiples of three
Flower parts in multiples of four or five
Major leaf veins are parallel
Major leaf veins are branched
Roots are fibrous
Taproots
Stem vascular bundles are scattered
Stem vascular bundles are in a ring
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VCE Biology Unit 1
Annotate the following diagram to summarize the transport of water through a plant from
roots to leaves.
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