1. UNIT 5: SUPPORT AND TRANSPORT
SYSTEMS IN PLANTS
(CAMPBELL & REECE (2010) CHAPTER 35 &36)
2. 1. ANATOMY OF
DICOTYLEDONOUS PLANTS
• Plants, like multicellular animals, have
organs composed of different tissues,
which in turn are composed of cells
• Three basic organs evolved: roots, stems,
and leaves
• They are organized into a root system and
a shoot system
6. Dermal tissue
• In nonwoody plants, the dermal tissue
system consists of the epidermis
• A waxy coating called the cuticle helps
prevent water loss from the epidermis
• In woody plants, protective tissues called
periderm replace the epidermis in older
regions of stems and roots
• Trichomes are outgrowths of the shoot
epidermis and can help with insect defence.
7. Vascular Tissues
• The vascular tissue system carries out
long-distance transport of materials
between roots and shoots
• The two vascular tissues are xylem and
phloem
• Xylem conveys water and dissolved
minerals upward from roots into the shoots
• Phloem transports organic nutrients from
where they are made to where they are
needed
8. Ground Tissues
• Tissues that are neither dermal nor
vascular are the ground tissue system
• Ground tissue internal to the vascular
tissue is pith; ground tissue external to the
vascular tissue is cortex
• Ground tissue includes cells specialized for
storage, photosynthesis, and support
13. 2. SECONDARY GROWTH
(Chapter 35 p.751-754)
• Secondary growth occurs in
stems and roots of woody plants
but rarely in leaves
• The secondary plant body
consists of the tissues produced
by the vascular cambium and
cork cambium
14.
15.
16.
17. a. The Vascular Cambium and
Secondary Vascular Tissue
• The vascular cambium is a cylinder of meristematic
cells one cell layer thick
• It develops from undifferentiated parenchyma cells
• Secondary xylem accumulates as wood, and
consists of tracheids, vessel elements and fibers.
• Early wood, formed in the spring, has thin cell walls
to maximize water delivery.
• Late wood, formed in late summer, has thick-
walled cells and contributes more to stem support.
18. a. The Vascular Cambium and
Secondary Vascular Tissue
• Tree rings are visible where late and early wood
meet, and can be used to estimate a tree’s age
• Dendrochronology is the analysis of tree ring
growth patterns, and can be used to study past
climate change.
• As a tree or woody shrub ages, the older layers of
secondary xylem, the heartwood, no longer
transport water and minerals.
• The outer layers, known as sapwood, still
transport materials through the xylem.
20. 3. UPTAKE OF WATER AND
MINERALS INTO THE ROOTS
• The plasma membrane directly controls the
traffic of molecules into and out of the cell.
• In most plant tissues, the cell wall and cytosol are
continuous from cell to cell.
• The cytoplasmic continuum is called the
symplast.
• The cytoplasm of neighboring cells is connected
by channels called plasmodesmata.
• The apoplast is the continuum of cell walls and
extracellular spaces.
21. Water and minerals can travel through
a plant by three routes:
Transmembrane route: out of one
cell, across a cell wall, and into
another cell.
Symplastic route: via the continuum
of cytosol.
Apoplastic route: via the cell walls
and extracellular spaces.
23. Pathway 1: Transmembrane route
Water and minerals move from the soil (high
WP) through the cell wall, plasmamembrane
and into the cytoplasm of the roothair.
Through the cell wall, plasma membrane
and into the cytoplasm of the cortex cells.
Through the cell wall, plasma membrane
and into the cytoplasm of the endodermis
Through the cell wall, plasma membrane
and into the cytoplasm of the pericycle.
Through the cell wall, plasma membrane
and into the xylem of the plant.
24. Pathway 2: symplastic route
Water and minerals flow from the high
WP in the soil, through the cell wall,
plasma membrane and into the
cytoplasm of the roothair.
Through the plasmodesmata linking the
cytoplasm of the cells into the cytoplasm
of the cortex cells.
Flowing through the plasmodesmata
into the cytoplasma of the endodermis
cells and pericycle and into the xylem.
25. Pathway 3: Apoplastic route
During the Apoplastic route the water and
minerals travel along the cell walls of the
roothairs, cortical cells, and endodermis, but
the endodermis has Casparian strips that
prevent further movement of water, therefore
water enter the cytoplasm of the endodermal
cells and then take the symplastic route
(through cytoplasm and plasmodesmata that
link cytoplasm of cells) into the xylem of the
root.
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27. Transport of minerals across an
endodermal plasma membrane
Minerals follow the same routes as water when it moves
through the roothair and cortex cells.
But when it moves through the endodermal plasma
membrane it does it in the following way:
An ATP driven pump removes hydrogen ions from the
cell.
This establishes an electrochemical gradient that
allows potassium ions and other positively charged
ions to cross the membrane via a channel protein.
Negatively charged mineral ions can cross the
membrane by way of a carrier when they “hitch a
ride” with hydrogen ions, which are diffusing down
their concentration gradient.
29. 3. TRANSPORT OF WATER AND
MINERALS TO THE LEAVES
What makes the upward movement of water
in the xylem of the stems and leaves possible?
Root pressure
Cohesion-adhesion-tension
Transpiration
30. • Water entering root cells creates a positive
pressure called root pressure.
• It occurs at night and tends to push xylem
sap upwards.
I) Root pressure
31. Upward movement of water requiring no
energy.
Cohesion- Tendency of watermolecules to
cling together and form a continuous water
column.
Adhesion- Tendency of water molecules to
cling to the sides of the container (xylem)
they are in. It gives the water column extra
strength and prevents it from slipping back
II) Cohesion-adhesion-tension
model
34. Transpiration is the loss of water vapour through
the stomata of the leaf.
The water molecules that evaporate from the cells
into the intercellular airspaces are replaced by
other water molecules from the leaf xylem.
Because the water molecules are cohesive,
transpiration exerts a pulling force, or tension, that
draws the water column through the xylem to
replace the water lost by the stomata.
This is also a mechanism by which minerals are
transported throughout the plant body.
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III) Transpiration
35. High temperature – faster transpiration
High light intensity – faster transpiration
Windy – faster transpiration
High humidity – slower transpiration
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Environmental factors that influence
the speed of transpiration
37. What is guttation and what causes it?
Root pressure is responsible for guttation.
Guttation is when drops of water are
forced out of the vein endings along the
edges of leaves called hydathodes.
38. 4. TRANSLOCATION OF SUBSTANCES FROM
THE LEAVES TO THE REST OF THE PLANT
(Chapter 36 p. 779-780)
The products of photosynthesis are
transported through phloem by the
process of translocation.
Phloem sap is an aqueous solution that is
high in sucrose.
It travels from a sugar source to a sugar
sink
39. A sugar source is an organ that is a net
producer of sugar, such as mature leaves
A sugar sink is an organ that is a net consumer
or storer of sugar
Sugar must be loaded into sieve-tube elements
of the phloem.
Sugar then moves by symplastic or both
symplastic and apoplastic pathways.
At the sink, sugar molecules diffuse from the
phloem to sink tissues and are followed by
water.
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Ground tissue of roots, consisting mostly of parenchyma cells, fills the cortexThe innermost layer of the cortex is called the endodermis – a cylinder 1 cell thick that forms the boundary with the vascular system (selective barier).Pericycle – outermost cell layer in vascular cylinder adjacent to & just inside endodermis – from which lateral roots ariseLateral roots cannot originate near the roots surface because its vascular system must be continuous with the vascular cylinder at the center of the established root.Casparian strip – waxy material impervious to water & dissolved minerals
Ground tissue consists mostly of parenchyma butcollenchyma just beneath the epidermis provides strength for stems.Sclerenchyma cells, especially fiber cells, also provide support in those parts of the stems that are no longer elongating.Vascular cambium (lateral meristem) – cylinder of dividing cells for growth in thickness – adds layers of vascular tissue called secondary xylem and secondary phloem
Ground tissue of a leaf, a region called the mesophyll is sandwiched between the upper and lower epidermal layers.Mesophyll consists mainly of parenchyma specialised for photosynthesis, including pallisade and spongy mesophyll.
Vascular cambium and cork cambium = lateral meristems for secondary growth (thickness)Vascular cambium adds layers of vascular tissue: secondary xylem (wood) & secondary phloemCork cambium (adds secondary dermal tissue)replaces the epidermis with the thicker, tougher periderm.
Primary growth from activity of apical meristem nears completion – vascular cambium forms.Secondary growth begins – stem thickens as vascular cambium forms secondary xylem to the inside and secondary phloem to the outside.Some initials give rise to vascular rays – connect the secondary xylem with the secondary phloem, move water and nutrients, store carbohydrates and aid in wound repair.Secondary phloem can’t keep pace as cells no longer divide – as a result these tissues & epidermis will ruptureCork cambium develops – produces cork cells which replace epidermis
