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How fast is water transported from roots to leaves?

How fast is water transported from roots to leaves?



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I understand basically how water transport from roots to leaves through the xylem works, but I have no idea of the timescales involved.

How long does it take for water to get from root tips to leaves? How does this speed change in different parts of the plant? How does it differ between different plant types? How is it affected by plant size?

Also, I guess it changes from relatively fast in the middle of the day to almost zero at night, but how does it change during a normal sunny day (e.g. sinusoidal? More like a square wave?)


You can find some answers for your questions in this paper (it is only for Ricinus communis, but you may follow the cited by from google and find for other plants):

http://onlinelibrary.wiley.com/doi/10.1046/j.1365-3040.2001.00704.x/full

velocity in the phloem (0·250 ± 0·004 mm s−1) xylem in the light (0·401 ± 0·004 mm s−1), in the dark (0·255 ± 0·003 mm s−1)

Graphs on daily change are on the paper.


How fast is water transported from roots to leaves? - Biology

By the end of this section, you will have completed the following objectives:

  • Define water potential and explain how it is influenced by solutes, pressure, gravity, and the matric potential
  • Describe how water potential, evapotranspiration, and stomatal regulation influence how water is transported in plants
  • Explain how photosynthates are transported in plants

The structure of plant roots, stems, and leaves facilitates the transport of water, nutrients, and photosynthates throughout the plant. The phloem and xylem are the main tissues responsible for this movement. Water potential, evapotranspiration, and stomatal regulation influence how water and nutrients are transported in plants. To understand how these processes work, we must first understand the energetics of water potential.


Investigation: Examining water uptake by the stem

To examine water uptake by the stem.

Apparatus

  • water
  • food colouring dye (available at supermarket)
  • white flower on a stem, e.g. Impatiens, carnation or chrysanthemum
  • scissors
  • two jars, cups or measuring cylinders
  • plastic tray
  • sticky tape

Method

  1. Fill one jar with plain water, and one with water containing several drops of food colouring dye.
  2. Take the flower and carefully cut the stem lengthwise, either part way up the stem or right up to the base of the flower (try both, the results will be different!)
  3. Put one half of the stem into the jar containing plain water and one half of the stem into the jar containing food colouring dye. To make it easier to insert the stalks without breaking them, it helps to wedge paper underneath the jars so that you can tilt them towards each other. Tape the jars or cylinders down onto a tray so that they do not fall over.
  4. Observe the flowers after a few hours and the next day, and note where the dye ends up in the flower head. You can leave the flowers up to a week but be sure to make sure that they have enough water.

Variation: Instead of using one cylinder with water and one with food dye, use two different colour food dyes (e.g. blue and red). At first the flower will show two separate colours, but as time goes by the whole flower will show both dyes. This is because water can move sideways between xylem vessels through openings along their length. The ability of water to move laterally between vessels is useful for when air becomes trapped in a vessel, causing a blockage. If you cut the stem right up to the base of the flower, this will limit movement between the xylem vessels.

Variation: Try using celery stalks with leaves. Cut open the celery stalk (cross-section) and you will see darker-coloured little holes/ spots. These are the vessels.

Results

Record your observations and results

Conclusions

What did you conclude from this experiment?

[Attributions and Licenses]

This modified article is licensed under a CC BY-NC-SA 4.0 license.

Note that the video(s) in this lesson are provided under a Standard YouTube License.


The Pathway of Minerals

Minerals enter the root by two pathways.

  • By active transport into the symplast of epidermal cells then moving toward and into the stele through the plasmodesmata connecting the cells.
  • By passively moving through the apoplast until they reach the Casparian strip where they are transported into the cells of the endodermis.

In both cases, minerals enter the water in the xylem from the cells of the pericycle (as well as of parenchyma cells surrounding the xylem) through specialized transmembrane channels.


GCE O Level Biology

n    The inner wall is strengthened by a hard substance called ___________ that is deposited on it.

Different patterns of lignification

n    Conducts ______________________________ from the roots to the stems and leaves.

n    Provides _______________________________ for the plant.

n    A continuous lumen without any _________________________to prevent the flow of water and mineral salts.

n    Walls are lignified to prevent the _____________________________________.

n    Consists of _____________________________.

n    A sieve tube consists of columns of elongated, thin-walled living cells called the _____________________________.

n    Cross-walls separating the cells are perforated by minute pores like a sieve called ________________________.

n    Matured sieve tube cells do not have vacuole, organelles and nucleus, except a thin later of cytoplasm.

n    Substances are transported by __________________________________.

n    It accompanies each sieve tube cell.

n    It is a narrow, thin-walled cell with many ______________________________.

n    It ______________________________________________________________.

n    Transport _____________________________________________ from the leaves to other parts of the plant.

n    The sieve plates are perforated to enable food substances to pass through them to be transported to various parts of the plant.

n    Companion cells have many mitochondria to __________________________ __

Organization of vascular tissues in stems

Vascular bundles in roots

Cross-section of a dicotyledonous root

Organization of vascular tissues in roots

9.2 Studying the Movement of Substances in Plants

Translocation in plants

n    Transport of _______________________________________________.

n    Occurs in the _____________.

1.   Sugars formed in leaf cells are ___________________ by companion cells (loaded) into phloem.

2.   Bulk flow of water pushes sap to sinks.   Sink cells actively remove ________, and convert them to ________.   Water is recycled through xylem.

Using aphids in translocation studies

Aphids are insects which feed on plant juices. They penetrate phloem tissue with their ______________. Aphids are anaesthetized with __________________ while feeding. The body is cut off, leaving the proboscis in phloem.

Using isotopes in translocation studies

Providing a leaf with __________________________ .

Stem is cut off, and a section is exposed onto an X-ray photographic film.

Assignment 9.3 & 9.4    Chapter 9 Transport in Plants

9.3 Entry of Water into a Plant

Entry of water through the roots

n    This takes place at the ____________________.

n    Root hair grows between the soil particles with close contact with water.

n    Mineral salts are dissolved in soil water.

n    Sap of root hair cells has a __________________________________________.

n    Since the surrounding soil particles have a high water potential , water from the soil ___________________________________ .

Adaptations of the root hair cell to absorption

n   Increases surface area to volume ratio

n   Increases the ______________________ of water and mineral salts.

n   Water enters root hair cell by osmosis.

n   Generates energy from cellular respiration

n   ______________________ can take place.

9.4 Moving Water against Gravity

Entry of water up the stem by:

_________________________

n    By using active transport, ions in the living cells ________________________ in the root are pumped into the vessels.

n    Water potential in the xylem vessels is _______________.

n    Water passes from the living cells into the xylem vessels by osmosis and flows upwards.

_________________________

n    Water moves up inside fine capillary tube by ____________________.

n    Water molecules attract other water molecules by ________________________.

n    Water sticks to the upper inner surface of the xylem vessels by _____________.

n    The water moves up the plant into the leaves.

________________________

n    Transpiration is the ______________________________________________, especially through the stomata of the leaves.

n    The suction force caused by transpiration is called ______________________. It is the main factor that causes the movement of water up the xylem.

Importance of transpiration

n    Transpiration pull draws __________________________ from the roots to the stems and leaves.

n    Evaporation of water from the cells in the leaves removes _______________________________. This cools the plant, preventing it from being scorched by the hot sun.

n    Water transported to the leaves can be used in photosynthesis to _______________________________. Turgid cells keep the leaves spread out widely to trap sunlight for photosynthesis.

n    Instrument that can be used to _______________________________.

Factors affecting the rate of transpiration

A rise in the temperature of the surroundings increases the ___________________, thus increasing the rate of transpiration.

Air inside leaf is saturated with water vapour

Increasing the humidity of the air will _____________________________________ between the leaf and the atmosphere, therefore decreasing the rate of transpiration. When the atmosphere’s humidity decreases, the rate of transpiration increases.

Adaptations of plants living in dry conditions

1.             __________________________ to reduce surface area exposed to evaporation

When light intensity is increases, stomata open, increasing the rate of transpiration. When light intensity is reduced, stomata close. An increase in light intensity ____________________________________.

Blows water vapour away at the surface of leaves. Maintains _________________________________ between the leaf and the atmosphere. The stronger the wind, the faster the rate of transpiration. When the air is still, transpiration reduces or stops. Rapid transpiration occurs under __________________.

n    The turgor pressure in the leaf mesophyll cells helps to ___________________ and __________________________ to absorb sunlight for photosynthesis.

n    In strong sunlight, when the __________________________ exceeds the rate of absorption of water by the roots, the cells lose their turgor, become flaccid and the plant wilts.

n    Wilting also occurs in the soft stems of certain plants in which the stem mesophyll cells lose water.

Advantages of Wilting

n    When the leaf folds up, the surface area that is exposed to sunlight is reduced, causing the ____________________________________.

n    ______________________ and the rate of transpiration is decreased.

Disadvantages of Wilting

n    The rate of photosynthesis is reduced because ___________________________.

n    As the stomata close, the amount of _____________________________ is also reduced. Carbon dioxide becomes a limiting factor, thereby decreasing the rate of photosynthesis. 


Water Transport in Plants

Water is essential for all living things, including plants. Vegetation relies on water in the ground surrounding its roots. After you&rsquove watered a wilted plant, you&rsquove probably noticed how the plant&rsquos stem and leaves straighten up in only a couple hours. But how does the water in the roots get up to the upper parts of the plant?

The answer is the xylem tubes. The xylem tubes are similar to your blood vessels. In both, water and some nutrients are transported around the organism&rsquos body. Plants don&rsquot have a heart to pump liquids around their bodies, so they rely on physical forces to move liquid up to the highest leaf. Two of the most important forces are cohesion and adhesion. Cohesion is the attraction of one like molecule to another. Adhesion is the attractive force between different molecules. Within the xylem tubes, the forces of cohesion and adhesion are stronger than the force of gravity, allowing the water to reach the top of a house plant, or towering redwood tree.

Problem

How is water transported in plants?

Materials

  • 3-4 Water Glasses
  • Water
  • Food coloring
  • 3 or 4 fresh white carnations
  • Ruler
  • Sharp knife
  • Cutting board

Procedure

  1. Fill each of the three water glasses with a half cup of water.
  2. Add twenty drops of food coloring.
  3. Stir the food coloring into the water.
  4. Ask a grown-up to help you cut the last centimeter off the white carnation. You should cut the stem at a 45 degree angle.
  5. Immediately put the flower in the food coloring.
  6. Do not disturb the flowers. Observe them after 2, 4, 8, 24, and 48 hours, paying special attention to the bottom of the stems.
  7. If desired, cut 4 or so centimeters off the stem of one of the finished flowers to observe it more closely.

Results

After just a couple hours, you might notice the food coloring in the stem. After twelve or so hours, the food coloring should tint the vessels within the flower. Your results will vary depending on the quality of your flowers and cutting. When you observe the bottom of the stem, you will probably notice the round xylem tubes are filled with food coloring.

You cut off the last centimeter of the stem at the beginning of the experiment to make sure that the xylem tubes exposed to the colored water weren&rsquot damaged. The colored water moved up the stem by cohesion and adhesion. Water regularly evaporates from the surface of the flower. As water molecules go into the atmosphere, water molecules behind them are pulled upward. In cohesion, one end of one water molecule is attracted to the other end of another water molecule. The attraction of the water molecules to the side of the xylem tube is called adhesion. Since the food coloring is mixed in, it gets to ride up the stem along with the water.

Going Further

Suppose you want to make flowers for 4 th of July. You could split the carnation stem vertically, leaving the flower intact. Then, you can dip one side of stem in blue colored water, and the other in red.

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Transport of water into the plant (OCR A-level Biology)

A Science teacher by trade, I've also been known to be found teaching Maths and PE! However, strange as it may seem, my real love is designing resources that can be used by other teachers to maximise the experience of the students. I am constantly thinking of new ways to engage a student with a topic and try to implement that in the design of the lessons.

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pptx, 2.27 MB docx, 16.57 KB

This detailed lesson describes the transport of water into the plant as well as the movement across the cortex to the endodermis and to the xylem. Both the engaging PowerPoint and accompanying resource have been designed to cover the first part of point 3.1.3 (d) as detailed in the OCR A-level Biology A specification.

The lesson begins by looking at the specialised features of the root hair cell so that students can understand how these epidermal cells absorb water and mineral ions from the soil. Moving forwards, students are introduced to key terminology such as epidermis and root cortex before time is taken to look at the symplast, vacuolar and apoplast pathways that water and minerals use to transverse the cortex. Discussion points are included throughout the lesson to encourage the students to think about each topic in depth and challenges them to think about important questions such as why the apoplast pathway is needed for the water carrying the ions. The main part of the lesson focuses on the role of the endodermis in the transport of the water and ions into the xylem. Students will be introduced to the Casparian strip and will learn how this layer of cells blocks the apoplast pathway. A step by step method using class questions and considered answers is used to guide them through the different steps and to support them when writing the detailed description.

This lesson has been specifically written to tie in with the next lesson on the pathways and mechanisms by which water and mineral ions are transported to the leaves and then out into the air surrounding the leaves.

Get this resource as part of a bundle and save up to 33%

A bundle is a package of resources grouped together to teach a particular topic, or a series of lessons, in one place.

Module 3: Exchange and transport (OCR A-level Biology A)

This bundle contains 18 detailed and engaging lessons which cover the following specification points in module 3 (Exchange and transport) of the OCR A-level Biology A specification: 3.1.1: Exchange surfaces * The need for specialised exchange surfaces * The features of an efficient exchange surface * The structures and functions of the components of the mammalian gaseous exchange system * The mechanism of ventilation in mammals * The mechanisms of ventilation and gas exchange in bony fish and insects 3.1.2: Transport in animals * The double, closed circulatory system in mammals * The structure and functions of arteries, arterioles, capillaries, venules and veins * The formation of tissue fluid from plasma * The external and internal structure of the heart * The cardiac cycle * How heart action is initiated and coordinated * The use and interpretation of ECG traces * The role of haemoglobin in transporting oxygen and carbon dioxide * The oxygen dissociation curve for foetal and adult haemoglobin 3.1.3: Transport in plants * The structure and function of the vascular systems in the roots, stems and leaves * The transport of water into the plant, through the plant and to the air surrounding the leaves * The mechanism of translocation As well as the detailed A-level Biology content of the PowerPoint slides, the resources contain a wide range of tasks including guided discussion points, exam-style questions and quiz competitions which will engage and motivate the students


Transpiration can be regulated through stomatal closure or opening. It allows for plants to efficiently transport water up to their highest body organs, regulate the temperature of stem and leaves and it allows for upstream signaling such as the dispersal of an apoplastic alkalinization during local oxidative stress.

Summary of water movement:

The water passes from the soil to the root by osmosis. The long and thin shape of root hairs maximizes surface area so that more water can enter. There is greater water potential in the soil than in the cytoplasm of the root hair cells. As the cell's surface membrane of the root hair cell is semi-permeable, osmosis can take place and water passes from the soil to the root hairs. The next stage in the transpiration stream is water passing into the xylem vessels. The water either goes through the cortex cells (between the root cells and the xylem vessels) or it bypasses them – going through their cell walls. After this, the water moves up the xylem vessels to the leaves through diffusion: A pressure change between the top and bottom of the vessel. Diffusion takes place because there is a water potential gradient between water in the xylem vessel and the leaf (as water is transpiring out of the leaf). This means that water diffuses up the leaf. There is also a pressure change between the top and bottom of the xylem vessels, due to water loss from the leaves. This reduces the pressure of water at the top of the vessels. This means water moves up the vessels. The last stage in the transpiration stream is the water moving into the leaves, and then the actual transpiration. First, the water moves into the mesophyll cells from the top of the xylem vessels. Then the water evaporates out of the cells into the spaces between the cells in the leaf. After this, the water leaves the leaf (and the whole plant) by diffusion through stomata.


Practical Work for Learning

Class practical

Observing plants in different situations allows students to make inferences about water movement through the plant material.

Lesson organisation

This could be set up as a circus of observations – depending how many of the plant setups you choose to use. Or you could run the ‘dye in stems’ section as a class practical, with the ‘plant in polythene bag’ and/ or the ‘cuttings in dye and water’ as demonstration practicals.

Apparatus and Chemicals

For each group of students:

Microscope slides and coverslips

Dropping pipette and water

White tile or dissection board

Scalpel or sharp cutting tool

For the class – set up by technician/ teacher:

Coleus cuttings, with roots partly in dye and partly in water or air (needs 2-3 weeks advance preparation, Note 1)

Plant in pot, covered in polythene bag – set up an hour or two before lesson

Celery stalks or Busy Lizzie (Impatiens) stems in dye (Note 3)

Health & Safety and Technical notes

Take care with sharp scalpels.

Make a risk assessment of the chosen dye.

1 Coleus cuttings: Strike cuttings from Coleus two or three weeks in advance – using hormone rooting powder to encourage root formation and to reduce chance of infection of plants with fungus. Include liquid fertiliser in the water to encourage healthy growth. Coleus with lemon-coloured leaves are best as any dye will show up well in their tissues.

Two hours before the lesson, place some cuttings with part of their new root system in dye (Note 2) and the other part in water. Support another set of cuttings with part of their root system in dye and the other part in air. Rub off any stray roots so that all the roots are in a solution (for the water/ dye example). Plastic boxes used to hold indicator papers are ideal for this set-up. Stick two pairs of boxes together and cut a little way down the dividing wall. See diagram below.

2 Suitable dyes are dilute (0.1%) methylene blue solution, a blue food dye, 0.5% eosin or ink. Details of stains are on Hazcard 32. Methylene blue is described as harmful by skin contact whereas eosin is described as irritant. In either case, avoid skin contact.

3 Make a note of the time when you place the stems in dye. Ideally some samples should be set up at 24, 12, 2 and one hours before use. Alternatively, If celery stems are left to wilt and then placed in dye during the lesson, dye will move up the stem and into the leaves over a few minutes.

4 Celery can be difficult to cut neatly into sections, whereas Busy Lizzie is easy to slice thinly. The thickness is not critical – aim for about 1 mm and part of the section is likely to be thin enough. Make a small pool of water at the cut end and the slices will float.

Procedure

SAFETY: Take care with sharp scalpels.
Avoid skin contact with some dyes.

Preparation

a Set up plants in advance. Put the plant in the polythene bag in a sunny place for an hour or so. Put the other stems in dye up to 24 hours ahead of the lesson as described in Notes 1 and 3.

b Cut thin sections of celery or Busy Lizzie (Note 4).

Investigation

c Observe the plant in the polythene bag. The inside of the bag will be cloudy as water evaporating from the leaves condenses on the inside of the bag.

d Observe the stem of celery or Busy Lizzie. Use a sharp blade to cut across the stem at 1 cm intervals starting at the top and working down. Each time, use a hand lens to examine the cut surface for signs of the dye.

e Work out how fast the dye travels up the stem.

f Use a paint brush to transfer a thin slice of celery or Busy Lizzie (Note 4) to a microscope slide. Add enough water to make a complete layer between the slide and coverslip. Examine with a microscope.

g Describe what is seen.

h Observe the Coleus cuttings and note which parts of the leaves the dye has reached.

Teaching notes

Water travels up tall plants at about the same speed as the lifts that carry people to the top of a tall office block.

Typically, a coppice of beech of around 400 trees will raise about 20 tonnes of water a day from the soil to the leaves, 20 metres or so above the ground.

Although the process of transpiration is well understood in terms of plant structures, capillary action in narrow tubes and the process of osmosis of water through plant cell membranes, there are still some questions about transpiration that remain unanswered. For example, why is so much water moved from roots to leaves and then out into the air? Is it to keep the plant cool, or to transport sufficient dissolved minerals? And how do the tallest plants raise water to their highest leaves?

There are several opportunities here to make clear the difference between a description of what we observe and an explanation of the events that have resulted in what we see.

For example, in the cutting with half its roots in water and half in dye solution, some leaves show dye in their veins while others do not. In the other cutting, with one set of roots left in air, the dye appears throughout the veins. This is a description of our observation.

This is explained if, normally, each set of tubes from the roots supplies a particular area of leaf with water. However, when the need arises (such as when there is no water at all around a particular root) water can be transferred from one tube to another and so get to all parts of the leaves. This is an explanation of the observation above.

This diagram shows the likely position of the dye in the stem.

Health & Safety checked, September 2009

Downloads

Download the student sheet Observing water moving through plants (0.9 MB) with questions and answers


Summary

Water potential (&Psi) is a measure of the difference in potential energy between a water sample and pure water. The water potential in plant solutions is influenced by solute concentration, pressure, gravity, and matric potential. Water potential and transpiration influence how water is transported through the xylem in plants. These processes are regulated by stomatal opening and closing. Photosynthates (mainly sucrose) move from sources to sinks through the plant&rsquos phloem. Sucrose is actively loaded into the sieve-tube elements of the phloem. The increased solute concentration causes water to move by osmosis from the xylem into the phloem. The positive pressure that is produced pushes water and solutes down the pressure gradient. The sucrose is unloaded into the sink, and the water returns to the xylem vessels.


Watch the video: THE UPTAKE AND TRANSPORT OF WATER AND MINERAL IONS BY ROOT SYSTEM (August 2022).