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,

1. BIOLOGY AS LEVEL
REVISION 02

2. 7. Plant Transport
And Phytotomy

3. Phytotomy
 Root System
- Roots
 Shoot System
- Node – Wear plants grow outward
- Internodes
- Leaves

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

7. Transport of Oxygen

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

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

15. Spongy Mesophyll
 Aerenchyma – parenchyma that is specialized for
gas exchange/ diffusion

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

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

22. Vascular Tissue
 Xylem
 Phloem

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

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

32. TRANSPIRATION

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

43. Translocation

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