The development of Vascular plant allows the kingdom of plant to not only spread but conquer the world. The fascinating efficiency of the plant transport system is one that should be a joy for anyone to study,
4. Why do plants need
transport system?
Small surface area: volume ratio – diffusion is
inefficient
Large amount of nutrient requirement for growth
Large amount of nutrient requirement for repair
5. Roles of the plant transport
system
Move substances from area of absorption – to area
of uses (root – xylem - leaf)
Move substances from area of production
(SOURCE) to area needed for metabolism (SINK)
(leaf – phloem – stem for growth/ cell wall
building)
Move substances from area of production to area of
storage (leaf – phloem - root)
6. Transport of Carbon
dioxide
Diffusion through plant cells (phospholipids
membrane as it is non-polar)
Carbon Dioxide --- absorbed through stomata
(controlled by guard cells)
Plant leaves have large surface area to receive as
much of the gas as possible – diffusion from the air
8. Plant Tissues
Dermal Tissues: Protection, prevent water loss
- Epidermis, Periderm
Ground Tissues: metabolism, Storage, Growth
- Parenchyma, Collenchyma, Sclerenchyma
Vascular Tissue: Transport
- Xylem and Phloem
9. Epidermis
Continuous layer on the outside of the plant
One-Cell thick
Provides protection
Waxy Cuticle – made of cutin – protects organ from
frying out of water loss
Leaves: Stomata – for gas exchange
Roots: Root Hair
10.
11.
12. Parenchyma
Thin-walled cell – they are packing tissues
Isodiametric (allow tight packing)
Metabolically active
The turgidity helps support plant
Storage of starch
Has air spaces between cells – allow gas
exchange
Water and minerals are transported between
walls and the living content of the cell
Made up the cortex in roots/ stems
Pith in stems
13. Mesophyll
Meso = middle, Phyll = Leaves
Specialized parenchyma cells – photosynthesis
PALISADE MESOPHYLL – near to the upper
surface – hence has more chloroplast
SPONGY MESOPHYLL
14. Palisade Mesophyll
Chlorenchyma – A parenchyma
specialized for photosynthesis
Many chloroplast
Large vacuole – storage
Starch grains
Arranged end-on to pack in as
much of the cell as possible
Elongated – located nearer to the
surface to receive maximum
sunlight
16. Collenchyma
Parenchyma cell is modified to form collenchyma
Extra cellulose deposited at the corners of each cell
Adds extra strength
The midrib is the collenchyma
Ridged stems
The layer just below the epidermis
Celery – mostly collenchyma
17. Collenchyma
Allows plant to bend in the wind (more deposition
of cellulose)
Cells are living/ non-lignified – allows flexibility/
stretching
Usually not found in roots – they are not exposed to
wind
18. Sclerenchyma
Dead cells with rigid lignified walls
They cannot stretch
1. Fibres (Long, narrow, thick walled, narrow lumens,
tapering ends) – mechanical strength – protection
to non growing parts [XYLEM/ PHLOEM]
2. Schlereids – shorter/ fatter than fibre – provides
mechanical strength – exist isolated in cortex, pith,
xylem/phloem or in groups in testa/ walnut shells
19.
20. Endodermis
Once cell thick layer
Before the Pericycle
Surrounds the vascular tissue in stems and roots
21. Pericycle
One or several cell thick
Between the endodermis and the vascular tissue
New roots grow out of this
In stems – formed from sclerenchyma cells – dead
lignified cell
23. Xylem Vessel element
Vessel elements – long tube like
structure
No end-wall between cells
No cytoplasm – no organelles (More
room/ uninterrupted flow)
Lignified – support the xylem as it
doesn’t have the turgidity provided
by vacuole – withstand negative
pressure – waterproofing
Pits – lateral movement of water
Angiosperm – vessels very important
– large leaves = high water losses
24. Xylem vessels - Tracheid
Dead hollow cells – narrower lumens than xylem
vessel elements
Found in conifers – do not lose as much water
Narrow lumen = more capillarity
Tapering end walls – provide mechanical strength
25.
26. Phloem
Sieve tube elements
Companion cells
Parenchyma
– provide turgidity
Fibres
- Provide support/
protection
27. Sieve Tube Elements
Living, no lignified
Tubular – linked end to end
Perforated end walls
Thin cytoplasm
Few organelles, no nucleus
Cellulose Cell Walls
Plasmodesmata connecting with
Companion Cells
28. Sieve Tube Elements
Bidirectional flows of solutes/ hormones
Perforated walls – allow movement of substances
Few organelles with no nucleus/ thin cytoplasm –
no impediment of phloem sap’s flow
Cellulose cell wall – allows exchange of substances
Plasmodesmata – exchanges of substance with
companion cells
29. Companion Cells
Has nucleus and a lot of other
organelles
Nucleus – control activities both of the
cell + sieve tube elements
Ribosomes – production of enzymes/
co-transporters/ carriers proteins
Mitochondria – produces ATP for
active transport
30. Stem Vs. Root
STEM
1. Vascular bundle in a ring –
provide flexibility/ support
2. Sclerenchyma – vascular
bundle cap
3. Collenchyma – cortex beneath
epidermis – flexible support
against wind
4. Chlorenchyma/ Palisade –
under epidermis – for new
growth – may have stomata
5. No endoderm
31. Stem Vs. Roots
Roots
1. Vascular bundle in the central –
reduces damage from friction with
soil
2. No sclerenchyma – soil provides
support
3. No collenchyma – no wind to
withstand
4. No Chlorenchyma – not exposed to
sunlight
5. No stomata – most gas exchange
occur with root hair cells
6. Endodermis surrounds vascular
bundle
33. Transpiration
The loss of water vapor at the surface of the leaf
through the stomata by the process of diffusion
down the water potential gradient. The loss of water
vapor from plants to the environment.
34. Water movement through
a leaf
Transpiration at the surface of the leaf – reduces
water potential in the leaf
Water EVAPORATES from the mesophyll cell wall
into the air space
35. Root
Xylem is in the center
Root hair is where water is absorbed
Water moves through the cortex – enters the xylem
Due to water potential gradient
36. Root – The 2 Pathways
Water can take two routes through the root cortex
1. The Apoplast pathway: Cell wall is made of fibre
crisscrossing each other – water can soak in easily.
Hence water seep from wall to wall without
entering the cytoplasm
2. The Symplast pathway: Water moves into
cytoplasm/ vacuole of cortical cell by osmosis –
move into adjacent cells through plasmodesmata
37. Root – Entering the Xylem
Sometimes – mineral ions secreted into the xylem water –
reducing the water potential gradient = ROOT
PRESSURE
In the roots – xylem in the center
Water moves through the cortex following the water
potential – through symplast/ apoplastic pathway
It reaches the endodermis where there is a suberin layer
on the cell wall called the Casparian strip
This is waterproof
38. Root – Entering the Xylem
This forces water to move through cell membrane – may help
in generation of root pressure or help in controlling what’s
going into the xylem
When plants grow old, some cells become fully suberized –
leaving only the passage cells that can allow water to pass
through
Water moves through the Pericycle and into the pits and into
the xylem
Root hair increases surface area for water absorption
Mycorrhiza has a similar function – it is a fungi that receives
nutrient from plant while helping it in water transport
(mutualism)
39. Xylem
Water moves in continuous column
Major force: Hydrostatic pressure
Move by mass flow
Water molecules – attracted by hydrogen bonding
Cohesion and adhesion – allows this type of movement
Air lock happens when there’s an air bubble that breaks
the flow of water up the tube – the small diameter of the
lumen prevents this
Pits connect xylem to the other cells
40. Leaf
Transpiration is the loss of water from the leaves to
the atmosphere
Evaporation of water from the leaves
Reduces water potential in the leaf
41. Leaf
Cells: Mesophyll (not tightly packed) – many air
spaces
Air inside usually saturated
Sir inside has contact with air outside through
stomata
Potential gradient causes movement of air out
42. Xerophytes Adaptations
Reduction of surface area: Needle leaves
Swollen stems for water storage
Reduction in water potential gradient: Sunken
stomata, infold of cell membranes, leaves folding,
Trichomes
44. Translocation
Movement of assimilates (substances which plants
make) from source to sinks
In this case – mostly sucrose
Transported in sieve elements helped by companion
cells, parenchyma and fibre
45. Phloem Sap
Content: Sucrose, Potassium ions, Amino acids, Chloride
ions, Phosphate ions, Magnesium ions, Sodium ions,
ATP
Usually it is hard to extract phloem sap
There is a clotting technique
When the phloem is cut, the sap surges up to the cut but
is blocked by the sieve plate
The sieve plate is then sealed with carbohydrate callose
The speed of flow and the amount triggers this
mechanism
46. How Translocation
happens
Moves as mass flow
1 m per hour on average
ACTIVE TRANSPORT from source (organ of production) to sink (organ
that needs the sucrose)
At source: caused by active loading of sucrose into the phloem vessel
Causes water to diffuse into phloem down the water potential gradient
gradient
Raises hydrostatic pressure
At sink: Active unloading of sucrose
Causes water to move out
Lowers the pressure – maintains the gradient
47. How Translocation
happens
Photosynthesis produces triose sugar
Water moves through the mesophyll – apoplastic or symplastic
Here, the companion cell pumps Hydrogen ions into its wall –
using ATP
Excess of hydrogen – causes hydrogen to move back by their
concentration gradient through carrier protein – Co-transporter
protein
This Co-transporter transports sucrose with it
Sucrose then moves into sieve tube element via plasmodesmata
At unloading points – same method is used – enzyme invertase
converts sucrose into glucose and fructose – reducign the
concentration of glucose – setting up the gradient
48. Sieve Tubes Vs. Xylem
Active transport and Passive transport
Living cells required, non living cells requires
(membranes needed to control entry/ loss of
solutes)
Lignified cell wall for xylem
Entirely empty tube for xylem – flow unimpeded –
strong walls
Sieve plates which allow self healing
