UNIT 1 – PLANT’S STEM
PHYSIOLOGY OF STEM
1. ACTIVE TRANSPORT moves solutes (minerals) into SEIVE TUBES of the PHLOEM VESSEL.
2. Making SEIVE TUBES HYPERTONIC (increase in solute concentration)
3. They will attract WATER from nearby XYLEM VESSELS through OSMOSIS
4. As WATER moves into the SEIVE ELEMENTS, TURGOR PRESSURE builds up in those cells
5. TURGOR PRESSURE causes BULK FLOW (water and solutes move into the next cell whose solute concentration is
lower till they reach SINK REGION, regions of use)
6. WATER moves out of the SEIVE TUBES the goes into the SINK REGIONS or re-enters the XYLEM VESSELS
CONDUCTION OF MATERIALS BY THE XYLEM CONDUCTION OF MATERIALS BY THE PHLOEM
XYLEM: upward conduction of water and dissolves PHLOEM: to distribute the products of photosynthesis
nutrients (sap)- minerals and food stored in the roots via translocation
XYLEM CELLS: differentiated into tiny tubes which are
like capillary tubes
PULL FROM ABOVE MASS FLOW/ PRESSURE FLOW THEORY
TRANSPIRATION PULL ● flow of solutes in mass as a result of turgor pressure
● TRANSPIRATION is like a pull which causes water build up in the cells
and sap to go up and replace the lost water
● loss of water through the stomates and lenticles
due to:
TEMPERATURE HUMIDITY AIR CURRENT SOURCE REGIONS SINK REGIONS
● higher T= ● more humid= ● presence of ● sites of food production ● sites of use (other plant
higher rate of decrease rate air= increases in the plant (leaves) parts)
absorption of absorption evaporation
COHESION - ADHESION
1. Water has a tremendous property of cohesion,
each molecule clinging tenaciously to several
adjacent molecule
2. When the leaves transpire (water evaporates from
the stomates), water is lost in the leaves and aerial
parts molecule by molecule
3. Due to this water loss, the water in the vascular
tissue will move up to the leaves
COHESION ADHESION
● holding together of like ● holding together unlike
substances substances
4. water molecules will 5. adhesion of water
be linked together molecules to the walls of
forming a continuous the tracheids and vessels
string of water right down will cause water to move
to the root tip up the plant parts
PUSH FROM BELOW
ROOT PRESSURE
● result of the osmotic uptake of water into the
vascular elements of the root
● generated by the active absorption from the soil to
the xylem
● as long as water molecules continue to vacate
transpiration sites, replacement molecules are pulled
under tension and the root pressure then pushes
water up (the pressure is generated by the active
absorption of water)
GUTTATION
● HYDATHODES: special opening where excretion of
droplets of water by plants , located at the edges or
, Meristems
Cells are small in size, have thin cell wall, contain little or no vacuole
a. SHOT APICAL MERITEM produce stem and leaf tissues (vegetative structures)
b. APICAL MERISTEM can switch (by day length, temperature, and developmental stages) to a FLORAL MERISTEM and
produce flowers
Tissues of the Stem
c.
STEMS can be viewed as a series of concentric rings of various tissues
TISSUE LOCATION / FUNCTION
STOMATA ● External layer of cells
● Covered with a cuticle to reduce water loss
● Protect against invasion by pathogens
EPIDERMIS
TRICHOMES
● Protect internal tissues
● Replaced by a CORK LAYER
- stronger external surface
- more resistant to damage
- protective layer
● Layer of cells between the EPIDERMIS and VACULAR TISSUE
CORTEX
● Woody: function as a storage organ in many
● Transport system
● Organization is variable: form a complete ring
● Dicot: arranged as a circle of bundles
● Monocot: distributed (scattered) throughout the stem
● Outside of vascular bundle
● Distribute photosynthate (fixed carbon) from leaves (source) to the rest of the plant
SEIVE TUBE ● responsible for transport
PHLOEM
MEMBERS ● lack nucleus
● elongated cells with porous connections between the ends of cells (sieve plates)
COMPANION ● support the activity of the sieve tube
CELLS
VASCULAR TISSUE
VASCULAR ● Provide source of new cells for growth of vascular system: can produce either phloem or xylem cells after division
CAMBIUM ● meristematic tissue
● thin layer of undifferentiated cells between the phloem and xylem
● Essential for radial expansion of the stem
● Inside of the vascular bundle
● Required for transport of water and nutrients form root throughout the plant
● Die after differentiation
● cell walls are thickened for strength
Ring of LIGNIN provide reinforcement
XYLEM
● water and nutrients are moved through xylem vessels and tracheids arranged end to end
TRACHEIDS ● long thin
● primary component of SOFT WOODS including pines
XYLEM ● short and fat
VESSELS ● provide structural support
● important component of HARDWOODS
PITH ● innermost tissue of the stem
● comprised of undifferentiated PARENCHYMA CELLS
● storage tissue; sugar cane
● woody: may be lost or reduced
PHYSIOLOGY OF STEM
1. ACTIVE TRANSPORT moves solutes (minerals) into SEIVE TUBES of the PHLOEM VESSEL.
2. Making SEIVE TUBES HYPERTONIC (increase in solute concentration)
3. They will attract WATER from nearby XYLEM VESSELS through OSMOSIS
4. As WATER moves into the SEIVE ELEMENTS, TURGOR PRESSURE builds up in those cells
5. TURGOR PRESSURE causes BULK FLOW (water and solutes move into the next cell whose solute concentration is
lower till they reach SINK REGION, regions of use)
6. WATER moves out of the SEIVE TUBES the goes into the SINK REGIONS or re-enters the XYLEM VESSELS
CONDUCTION OF MATERIALS BY THE XYLEM CONDUCTION OF MATERIALS BY THE PHLOEM
XYLEM: upward conduction of water and dissolves PHLOEM: to distribute the products of photosynthesis
nutrients (sap)- minerals and food stored in the roots via translocation
XYLEM CELLS: differentiated into tiny tubes which are
like capillary tubes
PULL FROM ABOVE MASS FLOW/ PRESSURE FLOW THEORY
TRANSPIRATION PULL ● flow of solutes in mass as a result of turgor pressure
● TRANSPIRATION is like a pull which causes water build up in the cells
and sap to go up and replace the lost water
● loss of water through the stomates and lenticles
due to:
TEMPERATURE HUMIDITY AIR CURRENT SOURCE REGIONS SINK REGIONS
● higher T= ● more humid= ● presence of ● sites of food production ● sites of use (other plant
higher rate of decrease rate air= increases in the plant (leaves) parts)
absorption of absorption evaporation
COHESION - ADHESION
1. Water has a tremendous property of cohesion,
each molecule clinging tenaciously to several
adjacent molecule
2. When the leaves transpire (water evaporates from
the stomates), water is lost in the leaves and aerial
parts molecule by molecule
3. Due to this water loss, the water in the vascular
tissue will move up to the leaves
COHESION ADHESION
● holding together of like ● holding together unlike
substances substances
4. water molecules will 5. adhesion of water
be linked together molecules to the walls of
forming a continuous the tracheids and vessels
string of water right down will cause water to move
to the root tip up the plant parts
PUSH FROM BELOW
ROOT PRESSURE
● result of the osmotic uptake of water into the
vascular elements of the root
● generated by the active absorption from the soil to
the xylem
● as long as water molecules continue to vacate
transpiration sites, replacement molecules are pulled
under tension and the root pressure then pushes
water up (the pressure is generated by the active
absorption of water)
GUTTATION
● HYDATHODES: special opening where excretion of
droplets of water by plants , located at the edges or
, Meristems
Cells are small in size, have thin cell wall, contain little or no vacuole
a. SHOT APICAL MERITEM produce stem and leaf tissues (vegetative structures)
b. APICAL MERISTEM can switch (by day length, temperature, and developmental stages) to a FLORAL MERISTEM and
produce flowers
Tissues of the Stem
c.
STEMS can be viewed as a series of concentric rings of various tissues
TISSUE LOCATION / FUNCTION
STOMATA ● External layer of cells
● Covered with a cuticle to reduce water loss
● Protect against invasion by pathogens
EPIDERMIS
TRICHOMES
● Protect internal tissues
● Replaced by a CORK LAYER
- stronger external surface
- more resistant to damage
- protective layer
● Layer of cells between the EPIDERMIS and VACULAR TISSUE
CORTEX
● Woody: function as a storage organ in many
● Transport system
● Organization is variable: form a complete ring
● Dicot: arranged as a circle of bundles
● Monocot: distributed (scattered) throughout the stem
● Outside of vascular bundle
● Distribute photosynthate (fixed carbon) from leaves (source) to the rest of the plant
SEIVE TUBE ● responsible for transport
PHLOEM
MEMBERS ● lack nucleus
● elongated cells with porous connections between the ends of cells (sieve plates)
COMPANION ● support the activity of the sieve tube
CELLS
VASCULAR TISSUE
VASCULAR ● Provide source of new cells for growth of vascular system: can produce either phloem or xylem cells after division
CAMBIUM ● meristematic tissue
● thin layer of undifferentiated cells between the phloem and xylem
● Essential for radial expansion of the stem
● Inside of the vascular bundle
● Required for transport of water and nutrients form root throughout the plant
● Die after differentiation
● cell walls are thickened for strength
Ring of LIGNIN provide reinforcement
XYLEM
● water and nutrients are moved through xylem vessels and tracheids arranged end to end
TRACHEIDS ● long thin
● primary component of SOFT WOODS including pines
XYLEM ● short and fat
VESSELS ● provide structural support
● important component of HARDWOODS
PITH ● innermost tissue of the stem
● comprised of undifferentiated PARENCHYMA CELLS
● storage tissue; sugar cane
● woody: may be lost or reduced
