1. SUPPORT AND TRANSPORT IN PLANTS
ANATOMY OF DICOT PLANTS

2. ADVENTITIOUS ROOT SYSTEM
The Root
Two types of root systems
- tap root system
- adventitious root system
TAP ROOT SYSTEM
ADVENTITIOUS ROOT SYSTEM
- Arises from the radicle of the embryo
- Arises from any part of the plant except from the radicle of the embryo
- Main root can be distinguished
- Main root cannot be distinguished

3. Functions of the roots They anchor the plant firmly to the ground.
They absorb water and mineral salts.

4. External Structure of Root Tip
Root cap is made up of parenchyma cells. It protects the inner layers of the root.
The growing point is made up of meristematic cells. Some of the new cells produced replace the parenchyma cells of the root cap which were damaged.
Region of elongation – the cells comes from the growing point which begin to elongate.
The root hair region has root hairs, which absorb water and mineral salts.
Internally the cells in this region begin to differentiate into epidermis, parenchyma, sclerenchyma, xylem and phloem
Mature region has side roots and fully differentiated tissues.

5. Transverse section of young dicot root, in plan

6. Transverse section of a young dicot root in detail

7. Enlarged Root Hair

8. Functions of the various root tissues
. The root hairs of the epidermis absorb water and mineral salts.
The parenchyma of the cortex stores starch and the intercellular spaces allow water and mineral salts to pass through
The passage cells of the endodermis direct water into the xylem of the stele.
The pericycle gives rise to side roots
The xylem transports water and mineral salts from the roots to the stem and leaves. It also provides strength to the plant.
The phloem transports manufactured food from the leaves to the roots.
The vascular cambium gives rise to additional xylem and phloem as the root grows in thickness

9. The Stem Functions of the stem:
They hold the leaves in a favourable position to receive light for photosynthesis.
They hold the flowers in a favourable position for pollination.
Most stems contain chlorophyll and they therefore manufacture food by the process of photosynthesis.
They store food and water
They transport water and mineral salts from roots to leaves
They transport food from the leaves to the roots

10. External structure of a dicot stem

11. Transverse section of a young dicot stem in plan

12. Transverse section of a young dicot stem in detail

13. Functions of the various stem tissues
The cuticle reduces water loss through transpiration
The cuticle is transparent allowing light to pass through for photosynthesis.
The epidermis may have guard cells to allow gaseous exchange while at the same time reducing water loss through transpiration.
The hypodermis of sclerenchyma or collenchyma strengthens the stem and helps keep it upright.
The parenchyma of the cortex stores food.
The intercellular air spaces between the parenchyma cells allow for transport of water and gases.
The endodermal cells stores starch.
The sclerenchyma fibres gives strength to the plant and help to keep it upright.
Xylem transports water and mineral salts from the roots to the leaves
Phloem transports manufactured food from the leaf to the roots

14. Secondary growth of the stem
Increase in thickness of the stem is called secondary growth or secondary thickness.
Secondary thickness takes place in 3 steps:
Formation of secondary xylem and secondary phloem
Formation of cork
Formation of lenticels

15. Formation of secondary xylem and secondary phloem
Parenchyma cells between the vascular bundles begin to divide. This with vascular cambium forms a complete ring of cambium
Entire cambium divides to form secondary xylem on the inside and secondary phloem on the outside.
Every year a new ring of secondary xylem is formed. These are called the annual rings. (can tell the age of the tree by counting annual rings)
The xylem cells making up the older annual rings becomes clogged and are no longer able to transport water and mineral salts. They become heartwood.

16. Transverse section of stem after a complete ring of cambium has been formed

17. Formation of Cork
Certain parenchyma cells in the cortex begin to divide and form cork cambium
The cork cambium divides to form cork cells on its outside.
The cork cells have suberin laid down on their cell walls.

18. Annual Rings

19. Formation of Lenticles
In woody stems the stomata are blocked by the presence of cork cells
The epidermis of woody stems breaks up to form tiny pores called lenticles which allow gaseous exchange.

20. XYLEM
Xylem tissue is made up of four types of cells
- xylem vessels
- xylem tracheids
- xylem sclerenchyma
- xylem parenchyma
Xylem vessels and xylem tracheids are highly specialised cells.
Xylem vessels are dead cells. They are long, cylindrical cells.
Their cross walls are perforated or completely absent and form continuous tubes from roots to leaves.
Xylem vessels have thick walls made up of lignin.
Lignin is laid down in various patterns
Annular thickening ( lignin laid in circles)
Spiral thickening ( lignin laid in spiral)
Scalariform thickening (laid in ladder form)
Pitted thickening (laid in pits)
Xylem tracheids are similar to xylem vessels except that the ends are tapered and cross walls are always present

21. Xylem Vessels Xylem Tracheids Pitted Thickening Scalariform Thickening
Annular thickening
Spiral
Thickening
Xylem Tracheids

22. Adaptation of xylem to transport
Cross walls are perforated or completely absent – this forms xylem roots forms continuous tubes with the xylem stems and leaves.
Xylem vessles have no living contents – allows the water to flow freely inside.
The walls of the xylem vessels and tracheids are not completely thickened – the unthickened portions and bordered pits allow water to move across the root and stem
Adaptation of xylem to provide strength
the vessels and tracheids are thick-walled – they have a secondary wall of lignin
the vessels and tracheids are round in cross-section – round structures give additional strength

23. Phloem Phloem tissue is made up of four types of cells: Sieve tubes
Companion cells
Phloem parenchyma
Phloem sclerenchyma
Sieve tubes and companion cells are highly specialised cells
Sieve tubes are living cells with long cylindrical cells.
Their cross walls are perforated to form sieve plates
They are thin walled cells
They contain strands of cytoplasm which run through the sieve plates from one cell to the next
Companion cells lie next to the sieve tubes – they are thin walled, with cross walls and has a well-defined nucleus

24. Phloem tissue

25. The function of phloem tissue
The sieve tubes transport manufactured food from the leaves to the all parts of the plant.
The companion cells probably control the activities of the sieve tubes

26. Collenchyma and Sclerenchyma

27. Absorption and Transport of water and mineral salts by plants
Water enters the root hairs of the epidermis of roots by osmosis
POINTS TO REMEMBER
THE SOIL WATER IS THE DILUTE SOLUTION
THE CELL SAP HAS CONCENTRATION SOLUTION BECAUSE OF HIGH CONCENTRATION OF SALTS.
THE CELL MEMBRANE AND TONOPLAST IS SEMI-PERMEABLE MEMBRANE
OSMOSIS: MOVEMENT OF WATER MOLECULES FROM HIGH
WATER POTENTIAL TO LOW WATER POTENTIAL
THROUGH SEMI PERMEABLE MEMBRANE.

28. Lateral transport of water and mineral salts to the stele of the root

29. Upward movement of water and mineral salts through the stem from Roots to Leaves

30. Forces responsible for the upward movement of water
Transpirational pull
Root pressure
Capillarity

31. Forces responsible for the upward movement of water
Transpirational Pull:
Water evaporates from leaves
Creates diffusion pressure gradient between outside air and xylem
Tension exists in the water column extending from the roots to the leaves
Adhesive and cohesive forces keep the column continuous
Thus water is continually being pulled upward as water evaporates from the leaves
Upward pull = transpirational pull

32. Forces responsible for the upward movement of water
Root pressure
Cell sap of root hair always has low water potential when compared to soil water
Water enters root hair by osmosis
Continuous osmosis causes pressure forcing water a short distance up the stem
Capillarity
Spontaneous movement of water up narrow tubes because of adhesion and cohesion is called capillarity
Lumen of xylem vessels and tracheids are very narrow therefore capillarity takes place
Upward distance is very short

33. Structural modifications of leaves to reduce water loss (Internal factors limiting transpiration)
Sunken stomata: In some plants stomata may be sunken or small.
Thickened cuticle: A thick cuticle on the surface of leaves reduces the rate of transpiration.
Hair on leaves: the sheen r shine of the hairs of some leaves reflect sunlight and reduces transpiration. Hairs also trap water vapour, restricting water loss.
Shape, size and arrangement of leaves: The shape and size of leaves determine the total surface area exposed to the environment, and hence influence the rate of transpiration. The leaves of some plants are arranged in such manner that they shade each other or overlap each other. In this water loss is restricted

34. Environmental factors affecting the rate of transpiration
Humidity: High humidity decreases transpiration rate
Wind: Increases evaporation and thus transpiration
increases. Wind removes the water vapour around leaf thus increasing water vapour pressure gradient.
Temperature: Increases evaporation and thus transpiration
Light: generally causes an increase in the rate of transpiration

35. Wilting: Loss of turgidity of the cells results in leaves and
Sometimes the stems, becoming limp, causing them to droop.
Then the plant is called wilting.
Guttation: Loss of liquid water through tiny pores, called
hydathodes on margin of leaf.
Guttation
Wilting Plant

36. Economic uses of plants related to their anatomy:
Paper
Clothing
Timber for furniture-making and building construction
Basket-making
Thatching, matting and broom-making

37. This powerpoint was kindly donated to www.worldofteaching.com
Is home to well over a thousand powerpoints submitted by teachers. This a free site. Please visit and I hope it will help in your teaching 37