1. Online Counseling Resource YCMOU ELearning Drive…
14-Apr-17
Online Counseling Resource YCMOU ELearning Drive…
School of Architecture, Science and Technology
Yashwantrao Chavan Maharashtra Open University, Nashik – , India
© 2006, YCMOU. All Rights Reserved.

2. SBT/SBI/SGS011-CP3-03 Introduction
14-Apr-17
SBT/SBI/SGS011-CP3-03 Introduction
Programmes and Courses
SEP –SBT011 -U3-CP3
SEP – SGS011-U3-CP3
© 2006, YCMOU. All Rights Reserved.

3. Credits Sonali Alkari Faculty YCMOU Nagpur Centre,
Academic Inputs by
Sonali Alkari
Faculty YCMOU Nagpur Centre,
Faculty LAD college P.G. D of Biotechnology
Research officer Ankur Seeds Pvt Ltd
© 2008, YCMOU. All Rights Reserved.

4. How to Use This Resource
14-Apr-17
How to Use This Resource
Counselor at each study center should use this presentation to deliver lecture of minutes during Face-To-Face counseling.
Discussion about students difficulties or tutorial with assignments should follow the lecture for about minutes.
Handouts (with 6 slides on each A4 size page) of this presentation should be provided to each student.
Each student should discuss on the discussion forum all the terms which could not be understood. This will improve his writing skills and enhance knowledge level about topics, which shall be immensely useful for end exam.
Appear several times, for all the Self-Tests, available for this course.
Student can use handouts for last minutes preparation just before end exam.
© 2008, YCMOU. All Rights Reserved.
© 2006, YCMOU. All Rights Reserved.

5. © 2008, YCMOU. All Rights Reserved.
14-Apr-17
Learning Objectives
After studying this module, you should be able to:
Describe plant transport mechanism
Describe transpiration
Describe cohesion theory
Describe translocation.
© 2008, YCMOU. All Rights Reserved.
© 2006, YCMOU. All Rights Reserved.

6. © 2008, YCMOU. All Rights Reserved.
Transport mechanism
In plant transport mechanism in needed mainly for
Water transport
Food transport
Water transport is from root to different plant parts
The main conduction tissue for water transport in xylem.
Whereas food transport in mainly from leaf to different parts of plants .
The main conducting tissue for food transport in phloem.
© 2008, YCMOU. All Rights Reserved.

7. Water Movement in Plants-1
Long-distance water movement is crucial to the survival of land plants.
Although plants vary considerably in their tolerance of water deficits, they all have their limits, beyond which survival is no longer possible.
About 85 percent of the fresh weight of leaves can be water.
On a dry, warm, sunny day, a leaf can evaporate 100 percent of its water weight in just an hour.
© 2008, YCMOU. All Rights Reserved.

8. Water Movement in Plants-2
Water loss from the leaves must be compensated for by the uptake of water from the soil.
Water transport is important for the uptake of essential mineral nutrients from the soil.
Shortages of mineral nutrients such as nitrogen, potassium, and phosphorus are often limiting to plant growth, which is why fertilizers are often added to the soil to improve plant productivity and appearance.
The major mechanism for long-distance water transport is described by the cohesion-tension theory.
© 2008, YCMOU. All Rights Reserved.

9. Cohesion-Tension Theory-1
As per the cohesion-tension theory, the driving force of transport is transpiration, that is, the evaporation of water from the leaf surfaces.
Water molecules cohere (stick together), and are pulled up the plant by the tension, or pulling force, exerted by evaporation at the leaf surface.
Water will always move toward a site with lower water potential, which is a measure of the chemical free energy of water.
By definition, pure water has a water potential of 0 MegaPascals (MPa).
© 2008, YCMOU. All Rights Reserved.

10. Cohesion-Tension Theory-2
In contrast, at 20% relative humidity, the water potential of the atmosphere is -500 MPa.
This difference signifies that water will tend to evaporate into the atmosphere.
The water within plants also has a negative potential, indicating water will tend to evaporate into the air from the leaf.
The leaves of crop plants often function at -1 MPa, and some desert plants can tolerate leaf water potentials as low as -10 MPa.
The water in plants can exist at such low water potentials due to the cohesive forces of water molecules.
© 2008, YCMOU. All Rights Reserved.

11. Cohesion-Tension Theory-3
The chemical structure of water molecules is such that they cohere very strongly.
By the cohesion-tension theory, when sunlight strikes a leaf, the resultant evaporation first causes a drop in leaf water potential.
This causes water to move from stem to leaf, lowering the water potential in the stem, which in turn causes water to move from root to stem, and soil to root.
This serves to pull water up through the xylem tissue of the plant.
© 2008, YCMOU. All Rights Reserved.

12. © 2008, YCMOU. All Rights Reserved.
From Root to Leaf-1
Plants have root hairs and often mycorrhizal fungi at the root surface, both of which serve to filter the soil water as it enters the plant.
Mycorrhizae are symbiotic associations between plant roots and fungi.
The root cells and mycorrhizal fungi both actively uptake certain mineral nutrients.
Mycorrhizae can be particularly important for the uptake of phosphate.
The active uptake of minerals by living cells of the root and the subsequent transfer of minerals to the xylem can result in positive root pressures, with water potentials above 0 MPa.
© 2008, YCMOU. All Rights Reserved.

13. © 2008, YCMOU. All Rights Reserved.
From Root to Leaf-2
This occurs only under certain conditions, such as at night or during rainstorms, when water loss from the leaves is minimal.
Such positive root pressures disappear with the onset of leaf transpiration water molecules move from the soil into living cells of the root, and eventually into the transport cells of the xylem, known as tracheids and vessels.
These xylem cells are dead and hollow, allowing rapid water transport.
They also have hardened cell walls to help them resist the tendency to collapse as water is sucked through them.
© 2008, YCMOU. All Rights Reserved.

14. © 2008, YCMOU. All Rights Reserved.
From Root to Leaf-3
The long-distance transport of the water molecule occurs first within the xylem cells of the root, then the xylem of the stem and branch, and then into the xylem of a leaf midrib and vein.
Driven by transpiration, the water molecule is pulled from the nonliving tracheids and vessels of the xylem in the living cells of the leaf mesophyll (middle layer) and to the surface of mesophyll cell walls.
The water molecule then evaporates into a leaf intercellular air space and finally out of a stomatal pore and into the atmosphere.
© 2008, YCMOU. All Rights Reserved.

15. © 2008, YCMOU. All Rights Reserved.
The Role of Stomates-1
Leaves of land plants are covered with a waxy cuticle that prevents watercloss and gas exchange.
The stomates at the leaf surface have guard cells that open and close the stomate to regulate the uptake of carbon dioxide and release of oxygen, as required for photosynthesis.
They also serve to regulate water loss from transpiration.
During the day, the stomates normally open up in response to sunlight, allowing for photosynthetic gas exchange, but also allowing for transpiration.
© 2008, YCMOU. All Rights Reserved.

16. © 2008, YCMOU. All Rights Reserved.
The Role of Stomates-2
At night, the stomates normally close,preventing unnecessary water loss.
When excessive water loss occurs during the day, drops in leaf water potential can cause stomates to close.
Were it not for stomate closure in response to water stress, the leaves would suffer excessive water loss, the leaf cell membranes and photosynthetic apparatus would be destroyed, and “cavitation” would occur in the xylem cells.
Cavitation, which is a break in the water column, occurs when air is pulled into the xylem vessel or tracheid. This can make the xylem cell unable to conduct water.
© 2008, YCMOU. All Rights Reserved.

17. © 2008, YCMOU. All Rights Reserved.
Transpiration
The stomata's open up to allow for photosynthesis to occur, and during the process of letting carbon dioxide into the leaf, water vapor is lost to the atmosphere.
Instead, most water is lost by transpiration through the stomates.
The transpirational water loss allows for uptake of mineral nutrients from the soil.
However, much of the water loss that land plants exhibit can be viewed as a “necessary evil.”
© 2008, YCMOU. All Rights Reserved.

18. © 2008, YCMOU. All Rights Reserved.
Translocation-1
Translocation is the movement of materials from leaves to other tissues throughout the plant.
Plants produce carbohydrates (sugars) in their leaves by photosynthesis, but non photosynthetic parts of the plant also require carbohydrates and other organic and nonorganic materials.
For this reason, nutrients are translocated from sources (regions of excess carbohydrates, primarily mature leaves) to sinks (regions where the carbohydrate is needed).
Some important sinks are roots, flowers, fruits, stems, and developing leaves.
© 2008, YCMOU. All Rights Reserved.

19. © 2008, YCMOU. All Rights Reserved.
Translocation-2
Leaves are particularly interesting in this regard because they are sinks when they are young and become sources later, when they are about half grown.
The tissue in which nutrients move is the phloem.
The phloem is arranged in long, continuous strands called vascular bundles that extend through the roots and stem and reach into the leaves as veins.
Vascular bundles also contain the xylem, the tissue that carries water and dissolved minerals from the roots to the shoots.
© 2008, YCMOU. All Rights Reserved.

20. © 2008, YCMOU. All Rights Reserved.
Translocation-3
When plants increase in diameter (secondary growth) they do so by divisions of a layer of cells just under the bark; this cell layer makes new xylem to the inside (forming the wood of the tree trunk) and a thin, continuous cylinder of new phloem to the outside.
Phloem sap is composed largely of sugar dissolved in water.
All plants translocate sucrose and stachyose, or sugar alcohols such as sorbitol.
Many other organic compounds are found, including amino acids, proteins, and hormones.
Glucose, the sugar found in the circulatory system of animals, is not translocated.
© 2008, YCMOU. All Rights Reserved.

21. © 2008, YCMOU. All Rights Reserved.
Translocation-4
In order to accommodate the flow of sap, the internal structure of the conducting cells of the phloem, the sieve elements, is drastically altered.
As the sieve elements mature, they lose many of the organelles commonly found in living cells and they modify others. The nucleus disappears, as do the vacuoles, microfilaments, microtubules, ribosomes, and Golgi bodies.
Therefore, the inside (lumen) of the cell is left essentially open. The sieve elements are greatly elongated in the direction of transport and are connected to one another to form long sieve tubes.
© 2008, YCMOU. All Rights Reserved.

22. © 2008, YCMOU. All Rights Reserved.
Translocation-5
Some sieve elements can live for a long time, as many as one hundred years in palm trees, even though they have no nucleus or any of the machinery needed for protein synthesis.
Cells closely associated with them, called companion cells, apparently keep them alive.
The association of sieve elements and companion cells is one of the most intimate and complex in nature, and one of the least understood.
It now appears that both small and large molecules can move from companion cells to sieve elements through the plasmodesmata that connect them.
© 2008, YCMOU. All Rights Reserved.

23. Pressure-Flow Mechanism-1
The rate of translocation in angiosperms is approximately 1 meter per hour.
In conifers it is generally much slower, but even so this is far too fast to be accounted for by diffusion.
Instead, the sap flows, like Translocation river of dilute syrup water .
What is the force that drives the flow of material in the phloem?
It is pressure, generated in the sieve elements and companion cells in source tissues.
© 2008, YCMOU. All Rights Reserved.

24. Pressure-Flow Mechanism-2
In leaves, sugar is synthesized in mesophyll cells, and is then actively pumped into the phloem, using metabolic energy.
By using energy, the sugar is not only transferred to the phloem but is also concentrated.
When a solute such as sugar is concentrated inside cells, water enters the cells by osmosis.
Since the plant cells have a rigid cell wall, this influx of water creates a great deal of internal pressure, over ten times the pressure in an automobile tire.
The pressure causes sap to move out through the pores of the sieve element, down the tube.
© 2008, YCMOU. All Rights Reserved.

25. Pressure-Flow Mechanism-3
At the other end of the transport stream, in the sinks, sugar is constantly leaving the phloem and being used by surrounding cells.
Some is consumed as an energy source, some is stored as sugar or starch, and some is used to make new cells if the sink tissue is growing.
Since sugar leaves the phloem in the sink, water exits too (again by osmosis) and the pressure goes down. Therefore, there is a difference in pressure between source and sink phloem.
This causes the solution to flow, just as water flows along a pressure gradient in a garden hose. This process is known as the pressure-flow mechanism.
© 2008, YCMOU. All Rights Reserved.

26. Sugar Loading and Unloading
When sugars and other nutrients arrive in sink tissues they unload from the phloem and enter surrounding cells, either through plasmodesmata or by crossing from one cell to another across the cell walls.
The size and metabolic activity of the different sinks determines the amount of material that is delivered to them.
Thus, the use of sugar in the sinks determines how much sugar flows to them.
© 2008, YCMOU. All Rights Reserved.

27. © 2008, YCMOU. All Rights Reserved.
What You Learn-1…
You have learnt that…
Water transport is important for the uptake of essential mineral nutrients from the soil.
The major mechanism for long-distance water transport is described by the cohesion-tension theory.
As per the cohesion-tension theory, the driving force of transport is transpiration, that is, the evaporation of water from the leaf surfaces.
Water is lost by transpiration through the stomata, viewed as a “necessary evil.”
The stomates at the leaf surface have guard cells that open and close the stomate to regulate the uptake of carbon dioxide and release of oxygen, as required for photosynthesis.
They also serve to regulate water loss from transpiration.
© 2008, YCMOU. All Rights Reserved.

28. © 2008, YCMOU. All Rights Reserved.
What You Learn-2…
Translocation is the movement of materials from leaves to other tissues throughout the plant.
Phloem sap is composed largely of sugar dissolved in water.
Many other organic compounds are found, including amino acids, proteins, and hormones.
In order to accommodate the flow of sap, the internal structure of the conducting cells of the phloem, the sieve elements, is drastically altered.
In leaves, sugar is synthesized in mesophyll cells, and is then actively pumped into the phloem, using metabolic energy.
There is a difference in pressure between source and sink phloem.
This causes the solution to flow, just as water flows along a pressure gradient in a garden hose. This process is known as the pressure-flow mechanism.
© 2008, YCMOU. All Rights Reserved.

29. Critical Thinking Questions
14-Apr-17
Critical Thinking Questions
Describe is water movements in plants.
Describe food transport in plant.
Write a short note on transpiration.
Write a short note on stomata
© 2008, YCMOU. All Rights Reserved.
© 2006, YCMOU. All Rights Reserved.

30. Hints For Critical Thinking Question
Describe importance and mechanism of water transport-cohension theory.
Describe importance and mechanism of food transport- pressure flow theory.
Importance of transpiration , necesaary evil.
Role in water loss, phytosythesis
© 2008, YCMOU. All Rights Reserved.

31. © 2008, YCMOU. All Rights Reserved.
Study Tips
Book1
Title:The Living World
Author: George Johnson
Book2
Title: ABC Of Biology
Publisher: Holy Faith
Book3
Title: Biological Science
Author: Taylor, Green & Stout
© 2008, YCMOU. All Rights Reserved.

32. © 2008, YCMOU. All Rights Reserved.
Study Tips
Microsoft Encarta Encyclopedia
Wikipedia the free encyclopedia
© 2008, YCMOU. All Rights Reserved.

33. End of the Presentation
Thank You
© 2008, YCMOU. All Rights Reserved.