Topic 6 Plant Structure

Compiled Notes for the following outcomes:

Identify plant structure
Describe the functions for each plant structure
Explain the transportation of water and nutrients in xylem
Explain the transportation of nutrients in phloem

1. TOPIC&6:&
PLANT&STRUCTURES&

2. Learning&outcomes&
• Iden=fy&plant&structure&
• Describe&the&func=ons&for&each&plant&structure&
• Explain&the&transporta=on&of&water&and&nutrients&in&xylem&
• Explain&the&transporta=on&of&nutrients&in&phloem&

4. Plant&Organs&
• Flowering&plants&have&two&major&
components&to&their&structure.&
1. A&root&system;&extends&
below&ground&
2. A&shoot&system;&composed&
of&the&stem,&leaves,&and&
reproduc=ve&organs.&
• At&the&end&of&the&root&and&shoot&
system&is&a&terminal&bud&from&
which&ver=cal&growth,&called&
primary&growth,&occurs.&

6. Content&
1. Leaf:&Structure,&func=on&and&adapta=on&
2. Stems:&Structure,&func=on&and&adapta=on&
3. Roots:&Structure,&func=on&and&adapta=on&
4. Transporta=on&
1. Xylem&
2. phloem&

7. &&&1.&Leaf&
! plants&make&carbohydrates,&occurs&
in&the&leaves&via&photosynthesis.&&&
! To&conduct&photosynthesis,&leaves&
need&solar&energy,&water,&and&
carbon&dioxide.&
! Photosynthe=c&leaves&share&
similar&structural&components.&
! The&blade,&the&wide&part&of&the&
leaf&
! The&pe=ole,&the&stalk&
connec=ng&leaf&to&stem.&

8. The&blade:&
! the&wide&part&of&the&leaf&
! Have&maximum&surface&
area&for&the&collec=on&of&
energy&&&absorb&CO
2&
The&pe5ole:&
! &the&stalk&connec=ng&leaf&
to&stem.&
! &receive&H
2
O&from&the&root&
by&way&of&vascular&=ssue&
that&terminates&in&the&
leaves&

9. • There&is&tremendous&
diversity&in&leaf&
structure&between&
plant&species.&&&
• In&some&plant&species,&
leaves&may&serve&
addi=onal&func=ons,&
such&as&storage.&
• Some&plants&are&
deciduous&(they&drop&
their&leaves&during&
certain&seasons.)&

10. Leaves&adapta5ons&
• Modified&as&tendrilsY&that&
allow&the&plant&to&aZach&
to&objects.&
• The&leaves&of&cactus&are&
spines&that&reduce&H2O&
loss&&&protect&the&plant&
from&&browsing&animals.&
• The&leaves&as&traps&for&
catching&insects.&

11. Organiza5on&of&Leaf&&
• The&top&and&boZom&of&a&typical&eudicot&
leaf&is&composed&of&epidermis&
– The&epidermis&o[en&has&hairs&or&
glands.&
– Stomata&are&located&on&the&lower&
epidermis.&
• The&interior&of&the&leaf&is&composed&of&
photosynthe=c&mesophyll&cells.&
– The&spongy&mesophyll&is&arranged&
randomly&to&increase&surface&area&
for&gas&exchange.&
– The&palisade&mesophyll&is&
comprised&of&elongated,&ver=callyY
oriented&cells.&Contain&the&most&
chloroplast.&

14. 2.&Stems&
• The&stem&is&the&main&axis&of&
the&plant.&
• Stems&can&produce&side&
(lateral)&branches&from&lateral&
(axillary)&buds.&
•&&Nodes&are&the&points&where&
leaves&aZach&to&stems.&
• An&internode&is&the&region&
between&nodes.&

15. • The&stem&also&contains&the&vascular&5ssue&that&transports&water&and&
nutrients&to&leaves&(&to&support&photosynthesis).&
• In&some&plant&species,&stems&may&also&carry&out&photosynthesis&or&
serve&as&a&storage&organ&(e.g.&tuber)&
Sweet potato- tuber plant

16. Monocotyledon&Versus&Dicotyledon&Plants&&
Vascular&5ssue:&
! The&arrangement&of&the&vascular&=ssue&differs&between&monocots&and&
eudicots.&
! Plants&have&two&types&of&vascular&=ssue.&
1. The&xylem&transports&water&and&minerals.&
2. The&phloem&transports&organic&nutrients.&
! The&vascular&=ssues&serve&as&a&type&of&circulatory&system&for&plants.&

17. Monocot&vs.&Dicot&&
Vascular&Tissue&Arrangement&&
Scattered Forming a ring

18. &&3.&Roots&
• Roots&system&supports&
the&plant&by&anchor&
plants&to&the&soil.&
• Roots&also&absorb&water&
and&nutrients&from&the&
soil.&
• The&surface&area&of&
roots&is&greatly&
increased&by&the&
produc=on&of&root&hairs.&&&

19. Root&Hair&

20. • There&are&different&types&of&root&systems.&
1. Some&plants&have&a&single&taproot.&
2. Grasses&have&fibrous&root&systems.&
3. Some&plants&have&prop&roots;&a&type&of&adven55ous&root&
for&support.&
Root&system&

21. • For&perennial&plants,&the&roots&act&as&a&storage&order&that&
allows&the&shoot&system&to&regrow&each&year.&&&
grow and bloom over the spring and
summer, die back every autumn and
winter, and then return in the spring
from their root-stock

22. TRANSPORTATION&OF&WATER&&&
MINERALS&:&XYLEM&

23. Xylem:&Tracheids&and&Vessel&Members&
• Water&and&dissolved&
mineral&ions&flow&through&
conduc=ng&tubes&of&xylem&&
• Interconnected,&
perforated&walls&of&
tracheids&and&vessel&
members&(dead&cells)&
form&the&tubes&

25. 1. The&water&and&nutrients&
taken&up&by&roots&and&root&
hairs&through&soil&water.&
2. H
2
O&enter&the&root&by&
osmosis&
3. H
2
O&+&nutrients&are&
transported&to&leaves&via&
the&interconnected&vessel&
elements&of&the&xylem.&
4. H
2
O&+&nutrients&
transported&to&leaves&

26. 1.&Root&Pressure&
• The&water&and&nutrients&taken&
up&by&roots&and&root&hairs&
through&soil&water.&
• This&movement&is&provided&in&
part&by&root&pressure,&a&
posi5ve&pressure&created&
when&water&enters&the&root&by&
osmosis.&&&
• Soil&hypotonic&!&root&
hypertonic& Root pressure

27. 2.&Transpira5on&
• Transpira=on&
– Evapora=on&of&water&from&
plant&parts&(mainly&though&
stomata)&into&air&&
– pulls&water&upward&
through&xylem&by&causing&
con=nuous&nega=ve&
pressure&(tension)&from&
leaves&to&roots&
• root&hypotonic&!&leaves&
hypertonic&

28. 3.&CohesionVTension&Theory&
• The&cohesionVtension&model&
explains&how&water&travels&up&
the&xylem&to&leaves.&
• leaves&have&numerous&
openings&called&stomata.&
• When&these&stomata&are&open,&
water&evaporates&from&the&
interior&of&the&leaf&to&the&
outside&air,&a&process&called&
transpira=on.&

29. CohesionVTension&Theory&
1. As&plant&leaves&transpire&water,&a&
tension&is&created&that&pulls&water&
from&roots&to&leaves.&
2. This&tension&is&maintained&because&
water&molecules&display&an&aZrac=on&
to&one&another&called&cohesion.&
3. Hydrogen&bonds&among&water&
molecules&resist&rupturing&(cohesion)&
so&water&is&pulled&upward&as&a&
con=nuous&fluid&column&
4. Water&also&adheres&to&the&xylem&
elements&in&a&process&called&adhesion.&&
5. Hydrogen&bonds&break&and&water&
molecules&diffuse&into&the&air&during&
transpira=on&
Cohesion &
adhesion
Transpiration

30. Root pressure
created when
water enter root
cells via osmosis
Water rises through xylem
vessels because :
1. Cohesion: Water
molecules are
attracted to each
other
2. Adhesion: Water
molecules form
hydrogen bonds with
the xylem cell wall
Transpiration
Evaporation of water from
stomata creating a tension
that pulls the water column
from root to leaf
** Because of cohesion, new water molecules is drawn from the xylem which is
replaced by water from the roots

31. Opening&and&Closing&of&Stomata&
! The&opening&and&closing&of&the&leaf&stomata&is&controlled&by&
turgor&pressure&within&the&guard&cells.&
! As&water&enters&the&guard&cells,&these&cells&swell,&opening&the&
stomata.&
! As&water&exits&the&guard&cells,&the&loss&of&turgor&causes&the&
stomata&to&close.&&&

32. Water&Conserva5on&
• Cu5cle&&
– Waxy&covering&that&
protects&all&plant&
parts&exposed&to&
surroundings&
– Helps&the&plant&
conserve&water&

33. Water&Conserva5on&
• Environmental&signals&cause&stomata&
to&open&and&close&&
• Closed&stomata&limit&water&loss&(but&
prevent&gas&exchange&for&
photosynthesis&and&aerobic&
respira=on)&
• Some&plant&like&CAM&plant&adapt&for&
water&conserva=on&and&
photosynthesis&by&opening&their&
stomata&at&night&to&allow&CO
2
&for&
photosynthesis&and&close&stomata&
during&the&day&to&prevent&
dehydra=on.&
The pineapple
is an example
of a CAM plant.
CAM= Crassulacean acid metabolism

34. TRANSPORTATION&OF&ORGANIC&
NUTRIENT:&PHLOEM&

35. Phloem:&SieveVTube&Members&

36. perforated end
plate of sieve-tube
Cell (sieve plate)
one of a series of
living cells that abut,
end to end, and form
a sieve tube
companion cell (in
the background,
pressed tightly
against sieve tube)
Phloem:&SieveVTube&Members&

37. Organic&Nutrients&in&the&Phloem&

38. • As&mature&leaves&
photosynthesize,&phloem&load&
sucrose.&&
• Phloem&is&considered&source&
of&sugar&(Source&cell).&
• The&phloem&transported&
sugar&to&=ssues&that&require&
sugars,&called&sink&=ssues&
(Sink&cell).&
• Sugar&are&unloaded&at&sink&
region&(ac=vely&growing&or&
storage&parts&of&the&plant&)&

39. Pressure&flow&theory&
• Phloem&&
– Translocate&photosynthe=c&
products&down&the&gradient&
of&pressure&and&solute&
concentra5on&&
• Transloca5on&Process&
– Distributes&sucrose&and&other&
organic&compounds&
throughout&the&plant&
– An&energyVrequiring&process&
– Can&be&elaborate&by&
PressureYflow&theory&&
Translocation

40. 1. Source&cells:&produce&glucose/&
organic&molecules&&(by&
photosynthesis)&&
2. Glucose&is&converted&to&sucrose&
for&transport&
3. Companion&cell&loads&sucrose&
4. Water&follows&from&xylem&by&
osmosis&
5. Sap&volume&and&pressure&
increased&&
6. Sap&flow&within&phloem&
7. Unload&the&organic&molecules&by&
the&companion&cell&
8. Sucrose&is&stored&in&sink&cell/
=ssues&(as&starch)&
9. Water&diffuses&into&xylem&
10. Water&recycles&as&part&of&
transpira=on&to&re&supply&the&
sucrose&loading&&
(1)
(2)
(3)
(4)
(5)
(7) (8)
(9)
(10)
Pressure&flow&theory&
(6)
glucose

41. https://www.youtube.com/watch?
v=MxwI63rQubU
https://www.youtube.com/watch?
v=60SgZgK3Gss