TRANSPORT IN VASCULAR PLANTS (Water and Nutrients)
Plants absorb nutrients and water through their roots, but photosynthesis occurs in the leaves therefore, plants need to get water and nutrients from the ground up through their stems to the cells in their leaves.1Like animal, plants also contain vascular tissues: the xylem and the phloem1
  • Xylem transports water and nutrients up from the roots to the leaves.1
  • Phloem transports sugar molecules, amino acids, and hormones both up and down through the plant.1

Moving water and nutrients from the surface of the roots all the way to the cells in the leaves is a complex process.2 Water and Nutrient transport involves three stages:
  1. From the soil into the roots2
  2. From the roots into the stems2
  3. From the stem to the leaves2


Table of Contents

1. Phase l: transport into the roots
2. Phase ll: transport into the stem
3. Phase lll: transport to the leaves
4. Interesting Facts
5, Glossary
6. Quiz
7. References

Transport into the Roots

Water enters the root cells by osmosis-- The cells of a plant has a lower concentration of water molecules than the water in the soil therefore, the plant cell membrane allows water molecules to enter freely.2Water molecules can also enter the roots and move through the spaces between the cells before being absorbed by osmosis.2Once the water has entered the cells, the water molecules move towards the vascular cylinder.2

Nutrients enter the root cells by active transport-- The cells of a plant has a higher concentration of nutrients than the water in the soil therefore, the nutrients do not enter the roots by diffusion but by active transport.2 Once the substances are in the outer root cells they move through the cells of the cortex towards the endodermis, from which they pass the pass the casparian strip into the vascular cylinder.2From here the nutrients are pumped across cell membranes into the xylem.2
casparianstrip.jpg
Image 2: Transport of Substances Through the Casperian Strip into the Xylem



1.71.jpg
Image 1: Transport of Water and Nutrients into the Root Cell



Image 13 and Image 24

Water moves through the cortex by flowing between the cells or by osmosis. Nutrients are taken in by active transport and move from cell to cell until they reach the endodermis. Here, the casparian strip prevents substances from leaking back into the cortex and forces them to pass through the cell membrane.2 Nutrients enter the xylem by active transport.2


Transport into the Stems

Once in the xylem, the substances form a liquid called xylem sap, this sap then moves up the root towards the stem.2 As more nutrients enter the xylem their concentration increases and water molecules follow by osmosis, this creates root pressure which helps push the xylem sap upwards.2 Capillary action also helps the upward movement of the xylem sap.2 In the xylem tube, the sap is held together by weak attractive forces between the different water molecules and it rises upward due to the attractive forces between the water molecules and the sides of the cell walls.2 Xylem sap can move from one xylem tube to another and as well as move out of an xylem tube into the surrounding tissue; this ensures that water and nutrients reaches all the cells in a plants body.2

capillaryyyyyyy.jpg









Image 35


Capillary action increases as the diameter of the tube decreases.2

Transport to the Leaves

The most impotent force of transport up the xylem comes from the leaves of a plant.2 In grade 10 science we learned that the epidermis of leaves contains many stomata, which are the pores formed by guard cells. Transpiration occurs when the stomata is open, releasing water vapour.2 When a water molecule moves upward in the xylem, it pulls a another molecule with it which in turns pulls the one behind it, this occurs down the length of the xylem.2 If a plant does not transpire, the water column will not move.2

As we have all observed before in our lives, if a plant does not have enough water it wilts. The central vacuole of a plant stores water and dissolved substances, when it is full, it experts pressure against the cell wall.2 This is called turgor pressure; turgor helps support the plant however when the plant is unable to take up water from the soil, the vacuole will release its water causing low turgor pressure which in turn causes the plant to wilt.2

Turgor Pressure in Action6





Interesting Facts

  1. Today's oldest vascular plant is the Lycopods which dominated the landscape 400 million years ago.7
  2. Vascular plants first developed around 410 million years ago, during the mid-Silurian period of history.7
  3. Unlike xylem, the phloem are made of living cells; however, these cells are unique in that they have no nucleus.7



Glossary

Word

Definition

Osmosis
The tendency of molecules of a solvent to pass through a semipermeable membrane from a less concentrated solution into a more concentrated solution.2
Active Transport
The transportation of materials through a cell membrane using energy from the cell, substances are transported from an area of low concentration to an area of high concentration.2
Cortex
The region of tissue in a root or stem lying between the epidermis and the vascular tissue.2
Endodermis
The innermost layer of cells in the cortex of a root.2
Casparian strip
The wax like strip that runs through the cell wall of an endodermal cell.2
Vascular Cylinder
The central portion of a root that contains the xylem and the phloem.2
Root Pressure
The osmotic force pushing xylem sap upward in root vascular tissue.2
Capillary Action
The tendency of a liquid to rise or fall because of attractive forces between the liquids molecules.2
Transpiration
Evaporation of water through the stomata of plant leaves.2
Turgor Pressure
Pressure caused by the fluid contents of the central vacuole, which pushes against the wall of a plant cell.2


Quiz

(Answer are Found Below the References)


1:True or False
Osmosis is when molecules of a solvent to pass through a semipermeable membrane from a higher concentrated solution into a lower concentrated solution.
2: True or False
Necessary substances enter the vascular cylinder before they enter the cortex.
3: True or False
Active transport is the transportation of materials through a cell membrane using energy from the cell, substances are transported from an area of low concentration to an area of high concentration.
4: True or False
Low turgor pressure prevents a plant from wilting.


References

  1. How plants get water and nutrients- for dummies. [homepage on the Internet]. 2010 [cited 2012 Jun 18]. Available from: http://www.dummies.com/how-to/content/how-plants-get-water-and-nutrients.html
  2. Dulson, Jacqueline, Maurice Giuseppe, and Douglas Fraser. "Transport in Vascular Plants" In Nelson biology 11: university preparation, 549-552. Toronto: Nelson Education, 2011.
  3. Root cross section. [homepage on the Internet]. 2009 [cited 2012 Jun 18]. Available from: http://turfgrass.cas.psu.edu/education/turgeon/Modules/10_AnnualBluegrass/Annual_Bluegrass_Module/1.71%20root%20cross%20section.html
  4. The Endodermis and the Casparian Strip. [homepage on the Internet]. 2009 [cited 2012 Jun 18]. Available from: http://www.uic.edu/classes/bios/bios100/lectf03am/casparian.htm
  5. Biochemistry, [homepage on the Internet]. 2009 [cited 2012 Jun 18]. Available from: http://library.thinkquest.org/28751/review/biochem/2.html
  6. Turgor Pressure in Celery Stalks. [Video on the Internet]. 2009 [cited 2012 Jun 18]. Available from: http://www.youtube.com/watch?v=fhsurzE_-J0
  7. Facts About Vascular Plants. [homepage on the Internet]. 2009 [cited 2012 Jun 18]. Available from: http://www.gardenguides.com/86897-vascular-plants.html




Answers to the Quiz
  1. False
  2. False
  3. True
  4. False