Aquatic plants like submerged and floating plants obtain support differently than terrestrial plants. Submerged plants are very flexible with air spaces to resist water flow and float close to the surface. Floating plants have broad, firm but flexible leaves and air tissues called aerenchyma for buoyancy. Terrestrial herbaceous plants get support from turgor pressure in cells and cell wall thickening. Trees and woody plants gain support from structural tissues like sclerenchyma, xylem, and wood formed during secondary growth. Roots also provide external support by growing into the ground.

1. BIOLOGY FORM 5
CHAPTER 2
LOCOMOTION & SUPPORT
PART 4

2. SUPPORT IN
PLANTS

3. • Support in Aquatic Plants
Submerged Plants
– Leaves very thin, narrow & very flexible.
– Little resistance to water flow.
– Can be tugged at and pulled by the current of water with
little damage.
– Lots of air sacs/air spaces inside leaves/stems
– Plants float close to the surface for maximum sunlight &
nutrients
– Supported by upthrust/buoyancy of water.
– Stems no woody tissues.
– When removed from water, become limp.

4. Floating Plants
– Broad leaves ,firm but flexible enough to resist
being torn by wave action.
– Upward thrust of water supports plants
to float on water surface.
– Aerenchyma tissues in stems/tissues
formed from parenchyma tissue
- has air sacs to give buoyancy so plants
can float on water
– Don’t need strengthening tissue in stem/leaves.

5. Support in Terrestrial Plants
Herbaceous Plants
– Support from turgidity of the
parenchyma and collenchyma cells.
– Turgor pressure of fluids in the central vacuole pushes
the cell contents & plasma membrane against the cell
walls
Maintains shape & give support
to stem/leaves/roots
– Support from
-Thickening of cells walls
with cellulose
-Pectin in collenchyma cells

6. Special Structural Adaptations FFoorr EExxtteerrnnaall SSuuppppoorrtt
Roots
 come out from lower part of trunk & grow into the ground.
 Provide support
 Different
 Important in breathing & growing.
(a) Prop roots (b) Storage roots(c) “Strangling” aerial
roots
(d) Buttress roots (e) Pneumatophores

7.  secondary walls with lignin
 Thick, rigid, non-stretchable cell
wall
 Support non-growing parts of
plants
 2 types- fibres, sclereids
 Fibres-Long thin, straight.
Found inside vascular bundles.
 Sclereids-Short small and
irregular shaped. Found in fruits
and seeds.
PARENCHYMA CELLS
Parenchyma cells 60 m
COLLENCHYMA CELLS
80 m Cortical parenchyma cells
Collenchyma cells
SCLERENCHYMA CELLS
Cell wall
Sclereid cells
in pear
25 m
Fiber cells
5 m
Walls composed of
layers of cellulose
impregnated with
lignin.
SSuuppppoorrtt IInn
TTeerrrreessttrriiaall PPllaannttss
-- WWooooddyy
PPllaannttss
SSuuppppoorrtt ffrroomm
SScchhlleerreenncchhyymmaa
XXyylleemm ttiissssuueess

8. XXyylleemm
 Primary Xylem
 After secondary growth, secondary xylem formed (wood)
 Cell walls of xylem vessels and tracheid are thickened with
lignin during secondary growth
 Function:Makes plant stronger
Provide mechanical support
WATER-CONDUCTING CELLS OF THE XYLEM
Vessel Tracheids 100 m
Tracheids and vessels
Vessel
Vessel elements weiltehment
partially perforated
end walls
Pits
Tracheids
SUGAR-CONDUCTING CELLS OF THE PHLOEM
Companion cell
Sieve-tube
member
Sieve-tube members:
longitudinal view
Sieve
plate
Nucleus
Cytoplasm
Companion
cell
30 m
15 m

10. THE END