Transcript PPT3 - Ycmou

Online Counseling Resource
YCMOU ELearning Drive…
School of Architecture, Science and Technology
Yashwantrao Chavan Maharashtra
Open University, Nashik – 422222, India
SBT/SBI/SGS011-CP3-03
Introduction
Programmes and Courses
 SEP –SBT011 -U3-CP3
 SEP –SBT011 -U3-CP3
 SEP – SGS011-U3-CP3
School of Science and Technology, Online Counseling Resource…
Credits
 Academic Inputs by
Sonali Alkari
Faculty YCMOU Nagpur Centre,
Faculty LAD college P.G. D of Biotechnology
Research officer Ankur Seeds Pvt Ltd
[email protected]
[email protected]
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School of Science and Technology, Online Counseling Resource…
How to Use This Resource

Counselor at each study center should use this presentation to deliver
lecture of 40-60 minutes during Face-To-Face counseling.

Discussion about students difficulties or tutorial with assignments should
follow the lecture for about 40-60 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.
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Learning Objectives
After studying this module, you should be able
to:
 Describe plant transport mechanism
 Describe transpiration
 Describe cohesion theory
 Describe translocation.
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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.
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School of Science and Technology, Online Counseling Resource…
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.
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School of Science and Technology, Online Counseling Resource…
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.
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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).
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.”
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School of Science and Technology, Online Counseling Resource…
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.
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School of Science and Technology, Online Counseling Resource…
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.
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School of Science and Technology, Online Counseling Resource…
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.
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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.
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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.
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School of Science and Technology, Online Counseling Resource…
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.
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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.
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School of Science and Technology, Online Counseling Resource…
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.
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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.
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School of Science and Technology, Online Counseling Resource…
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.
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School of Science and Technology, Online Counseling Resource…
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.
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School of Science and Technology, Online Counseling Resource…
Critical Thinking Questions
1. Describe is water movements in plants.
2. Describe food transport in plant.
3. Write a short note on transpiration.
4. Write a short note on stomata
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Hints For Critical Thinking Question
1. Describe importance and mechanism of
water transport-cohension theory.
2. Describe importance and mechanism of
food transport- pressure flow theory.
3. Importance
of
necesaary evil.
transpiration
,
4. Role in water loss, phytosythesis
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School of Science and Technology, Online Counseling Resource…
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
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School of Science and Technology, Online Counseling Resource…
Study Tips
www.en.wikipedia.org
Microsoft Encarta Encyclopedia
http://en.wikipedia.org/wiki/
Wikipedia the free encyclopedia
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School of Science and Technology, Online Counseling Resource…
End of the Presentation
Thank You
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