Plant Organs
Roots & Stems
I. Roots
A. F(x)s = grow underground
1. Absorb water &
nutrients
from soil
2. Anchor plant in the soil
3. Make hormones
important for
growth
& development
I. Roots
B. Structure
1. Root cap
F(x) = protects apical
meristem
I. Roots
B. Structure
2. Root hairs
F(x) =
increase surface area
for absorption
I. Roots
B. Structure
3. Casparian Strip
F(x) =
*channel water &
dissolved nutrients into
vascular tissue
*allow movement only
into roots
I. Roots
C. Types of Roots
1. Taproots
a. Large main root that can store food
b. F(x) = absorption,
anchoring
E.g.
beet
carrot
C. Types of Roots
2. Fibrous roots
a. Numerous small roots
b. Grow near surface
c. F(x)= absorption,
anchoring
c. E.g. grass
C. Types of Roots
3. Prop or
Adventitious roots
a. Grow down to soil
from stem,
above ground
b. F(x)s =
support,
absorption
c. E.g. corn,
banyon tree
C. Types of Roots
4. Aerial Roots
a. Grow without soil,
in air
b. F(x) = absorb water
from
moist air
c. E.g. orchids in
tropical
rainforest
II. Stems
A. F(x)s
1. Hold leaves up to sunlight
2. Transport water & nutrients from
roots to leaves
3. Food storage in some plants
II. Stems
B. Stem Structures
1. Node – place where
one or more leaves are
attached
Note: At the point of attachment of each leaf,
there is a lateral bud with
an apical meristem
capable of developing
into a new shoot
II. Stems
B. Stem Structures
2. Internode –
part of stem
between nodes
II. Stems
C. Specialized stems
1. Rhizome = horizontal
underground stem
2. Tuber =
 Underground stem w/ buds
 Food storage

E.g. potato, parsnip
II. Stems
C. Specialized stems
3. Bulb =

large bud w/ layers

Food storage

Many edible

E.g. onion, garlic
II. Stems
C. Specialized stems
4. Corm =
 Upright, thickened underground stem
 Food storage
 Not usually edible
 E.g. shamrock plant (Oxalis)
II. Stems
C. Specialized stems
5. Some plants almost
all stem,
no leaves
E.g. cactus
II. Stems
D. Stem growth
1. Growth in Length – only at tips of
stems where new primary growth
occurs via apical meristems
2. Growth in Circumference –
width via
lateral meristems
II. Stems
E. Primary Growth in Stems
1. Vascular tissue arranged in
vascular bundles
2. Dicots – bundles in a ring around
outside edge
3. Monocots – bundles scattered
throughout stem
II. Stems
Dicot stem CS
Vascular bundles
II. Stems
E. Primary Growth in Stems
4. Pith – center of the stem
5. Cortex – ground tissue btwn.
Vascular Bundles & epidermis
Vascular bundle
dicot
monocot
II. Stems
F. Secondary Growth in Stems
¿Which get wider year after year,
monocots or dicots?
DICOTS!
**Most monocots have no secondary growth.
1. ↑stem width in dicots due to cell ÷ in
vascular cambium
II. Stems
2. Vascular Cambium
arises in vascular
bundle btwn. xylem &
phloem
3. Cylinder formed by
cambium,
then secondary
xylem inside,
then secondary
phloem on outside of
cylinder
II. Stems
G. Woody Stems
1. Heartwood
2. Sapwood
3. Bark
DRAW THIS!
II. Stems
G. Woody Stems
1. Heartwood
 Dark color
 Center of tree trunk
 Dead xylem , no longer transports water
 F(x) =
support
II. Stems
G. Woody Stems
2. Sapwood
 Lighter in color
 Nearer to outside of tree trunk
 F(x) = transport (live xylem)
Note: In a large diameter tree, heartwood gets
wider, sapwood stays relatively same width
II. Stems
G. Woody Stems
3. Bark
 F(x) = protection
 Made of cork, cork cambium & phloem
II. Stems
H. Stem F(x)s
1. Phloem moves sugars
a. Translocation – sugars moved from
source (photosynthesis in leaves)
to sink (where they are stored)
b. Products of Photosynthesis can move
in ____?___ direction
ANY
II. Stems
H. Stem F(x)s
1. Phloem moves sugars
c. Pressure – Flow Hypothesis
i. Sugars PUMPED into sieve tubes
@ the source
ii. Turgor = pressure increase due to
water entering sieve tubes by
osmosis
II. Stems
H. Stem F(x)s
2. Xylem moves water & nutrients
a. Cohesion-Tension Theory
combination of 3 processes:
i. Transpiration
ii. Cohesion
iii. Adhesion
Transpiration




In leaves, release of excess water to
atmosphere
Creates negative pressure in xylem
Replacement water pulled from xylem
Water enters roots to replace lost water
Cohesion


Water molecules stick to each other & pull
each other up narrow xylem tubes
Water is a polar molecule, therefore
Water molecules attract each other!
Adhesion

Water molecules strongly attracted
to xylem wall
II. Stems
b. Final words on water movement in plants
i. Varies with time of day
ii. Midday – stomata open, rapid movement
iii. Night – stomata closed movement stops
Exception: cacti stomata open @ night
¿Why?
to minimize water loss