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BIOLOGY DEPARTMENT

Unit 2 - Transport in Plants

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Transport in Flowering plants

Plants don’t have a circulatory system like animals, but they do have a

sophisticated transport system for carrying water and dissolved solutes to

different parts of the plant, often over large distances.

TASK 1: Sketch the outline of a plant and label what is transported around

the plant from their sites of uptake or synthesis. Draw arrows to show in

which direction these substances are transported.

Learners should be able to demonstrate and apply their knowledge and understanding of:

a) the structure of the dicotyledon root, including examination of microscope slides of T.S. dicotyledon root

b) the absorption of water by the root c) the movement of water through the root: apoplast, symplast and

vacuolar pathways d) the structure and understand the role of the endodermis e) the detailed structure of xylem as seen by the light and electron

microscope, including examination of microscope slides of T.S. dicotyledon primary stem

f) the movement of water from root to leaf including the transpiration stream and cohesion-tension theory

g) the effect of environmental factors affecting transpiration h) the adaptations shown by some angiosperms: hydrophytes,

xerophytes, including examination of microscope slides of T.S. leaves of marram grass and water lily

i) the detailed structure of phloem as seen by the light and electron microscope

j) understand the translocation of organic materials from source to sink, including the ideas surrounding phloem transport: diffusion; cytoplasmic strands; mass flow models; experimental evidence that solutes e.g. sucrose, are carried in the phloem; use of aphids and autoradiographs.

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Vascular tissue in plants

The vascular system in plants is made up of the xylem and the phloem.

TASK 2: Using a textbook or the internet, write down the substances that

are transported in these tissues.

Xylem -

Phloem -

Vascular tissue is found in specific positions in the root and in the stem of a

dicotyledonous plant.

TASK 3:

Using slides or a textbook, draw low power diagrams of a dicotyledonous root

and stem, labelling all tissues clearly.

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Xylem and phloem are specialised tissues made from several types of cells

with different functions.

TASK 4: Write down the functions of each cell type in the table below.

Xylem Tissue

Vessels

Tracheids

Fibres

Phloem Tissue

Sieve tubes

Companion Cells

Fibres

Parenchyma

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Xylem has a lignified cell wall and rings of thickening. Vessels and tracheids

have pits where the cell wall is not lignified.

TASK 5: Explain why xylem has this structure.

TASK 6: Look at slides of TS stem and locate vascular tissue. Label the

xylem vessels, parenchyma, phloem sieve tubes and companion cells on the

photograph below.

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How does water get into a plant?

Most absorption of water is through the root hairs.

TASK 7: Sketch a root hair from pictures in a textbook/internet. What

features do root hair cells have to allow them to do their job efficiently?

Complete: Some ions such as _________ (NO3-) and __________ (PO4

3-)

enter cells by __________ __________ against the concentration

gradient. This can lower the water potential inside plant cells so that water

moves in by _________.

Once inside a root, water can travel through it via 3 pathways

• Apoplast pathway

• Symplast pathway

• Vacuolar pathway

TASK 8: Use a textbook or try the websites below and draw these three

pathways on the diagram on the next page. Annotate your drawings.

http://www.kscience.co.uk/animations/transpiration.swf

https://highered.mheducation.com/sites/9834092339/student_view0/chap

ter38/animation_-_water_uptake.html

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TASK 9: Complete the sentences below:

Water can travel through three pathways through the cortex. It can move

through the cytoplasm of cells via the plasmodesmata; this is the

_________ route. Water can also travel through the cell vacuoles; this is

the _________ pathway. The third route is called the apoplast pathway;

water travels through the _____ _______.

Water travels in this way until it reaches the ___________, a layer of cells

which surround the vascular tissue (_________ and _________). In the

_____________, the apoplast route is blocked by the ___________ band

made of water proof _________. At the ____________ band, water

passes across the plasma membrane and continues along the _________

route. Ions must be taken up by ________ ________ which allows the plant

to selectively take up ions into the xylem. This _______ the water potential,

causing water to move into the xylem by _________. This creates a

hydrostatic pressure forcing water upwards called _______ _________.

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TASK 10: Draw the casparian strip and the route that water takes to the

xylem on the diagram on the previous page.

What happens inside the xylem?

Water molecules are polar and form hydrogen bonds between other

molecules. When molecules of the same type stick together this is called

cohesion.

TASK 10: Draw a picture of several water molecules below to show cohesion

by hydrogen bonding.

Because of the polar nature of water, it also binds to other substances. This

is called adhesion. This can be shown when a capillary tube is put into

coloured water.

TASK 11: Explain why the water rises in this experiment.

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Xylem vessels and tracheids form a continuous system of channels for water

transport. Water passes through the root, up the stem to the leaves where

it evaporates. The columns of water are held up by the cohesive forces

between molecules and the adhesive forces between water and the

hydrophilic lining of the xylem vessel.

As water is lost from the leaves this creates a tension causing a pull on the

water column. This is called transpiration and the column of water is called

the transpiration stream. The opening and closing of stomata can alter water

loss through transpiration.

TASK 12: Make sure you add information about transpiration to your

diagram on page 7.

http://www.phschool.com/science/biology_place/labbench/lab9/concepts1.ht

ml

Practical Task: Investigation into transpiration using a simple potometer.

Make sure that you complete the appropriate pages in your lab book.

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Measuring Transpiration

Transpiration can be measured by using a potometer.

Transpiration can be affected by various external factors such as

temperature, light, humidity and air movement.

TASK 13: Complete the table below to explain how and why transpiration is

affected.

External Factor How and why is transpiration affected?

Temperature

Light

Humidity

Air Movement

TASK 14: Explain what the boundary layer of a leaf is and its significance in

transpiration.

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Adaptations of Angiosperms

Some angiosperms (flowering plants) have adaptations depending on whether

they live in an environment with little available water or a watery

environment.

TASK 15: Define the following terms:

Mesophyte –

Hydrophyte –

Xerophyte –

TASK 16: Annotate the cross sections of a marram grass leaf and a water

lily leaf to explain how each is adapted to survive in its environment. List any

other adaptations below each picture.

Marram grass leaf Water Lily leaf

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Translocation

The products of photosynthesis are transported in a soluble form (sucrose)

to all parts of the plant via the phloem. The leaves are the source of sugars

and the growing tissues act as sinks. The mass flow hypothesis suggests

that there is a passive flow of sucrose from source to sinks.

TASK 17: Look at the animation (second half) using the link below and try to

explain the mass flow hypothesis using diagrams.

https://highered.mheducation.com/sites/9834092339/student_view0/chap

ter38/animation_-_phloem_loading.html

Evidence for translocation The mass flow hypothesis does not account for all observations such as

movement of sucrose and amino acids in opposite directions at the same time

and at different rates. Other hypotheses have been proposed such as

diffusion and cytoplasmic streaming.

Evidence for the translocation of solutes was obtained from several

experiments:

• Ringing Experiments

• Radioactive Tracing combined with using aphid mouthparts

• Use of radioisotope labelled CO2 combined with autoradiography

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TASK 18: Find out what happens in these experiments and what they tell us

about translocation. Summarise this information in the table below.

Experiment What happens and conclusions

Ringing

Radioactive tracing

using aphid

mouthparts

Radioisotopes and

autoradiography

A good source of information for translocation experiments is on the

website below:

http://www.biologymad.com/master.html?http://www.biologymad.com/a2biol

ogy.htm

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Folder Check: Transport in plants

Check whether you have detailed notes on

following.

Notes

complete?

Teacher/Student

Comments

Drawings of dicotyledon stem and root with tissues identified.

Detailed knowledge of the cells in phloem and xylem tissue.

Description of the transport of water into a plant including the symplast, apoplast and vacuolar pathways.

Explanation of the importance of the endodermis.

Description of the cohesion-tension theory of water movement from root to leaf.

Description of the use of a potometer to measure transpiration.

Description of factors that affect the rate of transpiration.

Description of the adaptations of different angiosperms (hydrophytes and xerophytes).

Description of translocation of sucrose from source to sinks (mass flow hypothesis).

Description of evidence that supports the mass flow hypothesis.

General Organisation Y or N Student/teacher

comments.

Are student notes up to date?

Are their notes accurate?

Is the folder organised?

Is there evidence of independent learning? Has all homework been handed in?