Transcript Transpiration

9.2 - Transport in
Angiospermophytes
Transport in Angiospermophytes
Minerals in the Soil
• Minerals must be able to move through the
soil to the roots of plants to be absorbed how do they do this?
1. Diffusion 2. Fungal hyphae 3. Dissolved in soil water -
9.2.2
Mineral Uptake
• Minerals are absorbed by the plant via
active transport
– Minerals include potassium, phosphate,
nitrates and other ions
– The concentration of ions is higher inside
the root cell than in the surrounding soil
– Move against the concentration gradient
– Allows for selective absorption of minerals
by plants
• Cortex cells absorb mineral ions that are
dissolved in water
• From cortex, minerals dissolved in water
travel through the endodermis and into
the vascular cylinder.
9.2.3
Mineral Uptake
9.2.3
Mineral Uptake
9.2.3
Vascular Tissue - Xylem
• Xylem – water and mineral conducting tissue
• At maturity, cells are dead and lack plasma
membranes – so water flows through freely
• End walls break down forming long tubes
• Pores in side walls allow water movement
between adjacent cells
9.2.6
Vascular Tissue - Xylem
• Composed of tracheids and/or vessel elements
• Tracheids:
– Narrow cells arranged in columns
– Overlapping ends help with support and water
movement
• Vessel Elements:
– Cell wall arranged in a helical pattern that enable
walls to withstand pressure and stretch as other living
cells grow
– Wide diameter allows for efficient water transport
– Only found in angiosperms
9.2.6
Vascular Tissue - Xylem
9.2.6
Vascular Tissue - Xylem
9.2.6
Transpiration
• Transpiration - the loss
of water vapor from the
leaves and stems
through evaporation
• Plants are adapted to
limit water loss – how?
9.2.5
9.2.6
Transpiration
Transpiration Stream
•
•
Transpiration stream - transpiration creates
a flow of water from the roots, through the
stems, to the leaves
Movement of water through plants depends
on the cohesion and adhesion of water
molecules - what are these properties?
– Water forms a column due to hydrogen bonding
9.2.6
Transpiration Stream
Steps in water movement:
1. Water evaporates from spongy mesophyll in
leaf tissue (transpiration)
2. Water is replaced with water from xylem
tissue in leaf veins
 Water moves into leaf tissue via capillary action
3. When water is pulled out of xylem, suction
develops, and more water is pulled up from
roots and stem – transpiration pull
– Like using a straw to suck up liquid
9.2.6
Transpiration Stream
9.2.6
Regulation of Transpiration
• Water evaporates out of the leaf tissue through the
stomata (transpiration)
• Guard cells control transpiration by opening and
closing the stomata
• Generally, guard cells open stomata during the day
and close them at night - why?
9.2.7
Regulation of Transpiration
•
Changes in turgor pressure in the guard cells
open and close the stomata:
1. Guard cells actively uptake potassium ions (K+) and
increase solute concentration
2. Water enters the guard cells by osmosis to balance
solute concentration and cells become turgid.
•
Turgid guard cell = open stomata
3. Reverse process makes guard cells flaccid and closes
stomata
•
Flaccid guard cell = closed stomata
9.2.7
Regulation of Transpiration
9.2.7
Regulation of Transpiration
9.2.7
Regulation of Transpiration
• Environmental factors and stressors can also
affect transpiration and opening and closing of
the stomata:
– When plants are water deficient, cells may lose
turgor and stomata close - why important?
– Abscisic acid, a plant hormone, signals stomata to
close during water deficiencies.
9.2.8
Factors Affecting Transpiration
Factors affecting transpiration:
1. Light – guard cells close in darkness, open in
light – why?
– Increased transpiration during day
2. Temperature – higher temperatures increase
transpiration
– Also decrease outside humidity – thus increase
diffusion out water out of leaf
9.2.9
Factors Affecting Transpiration
Factors affecting transpiration:
3. Humidity – lower humidity increases
transpiration – why?
4. Wind – air movement moves air saturated
with water vapor away from stomata –
thereby increasing transpiration
9.2.9
Xerophytes
• Plants adapted to grow
in very dry
environments
• Have evolved different
adaptations to help
reduce transpiration why?
9.2.10
Xerophytes
Adaptations of Xerophytes:
– Spines instead of leaves –
why?
– Thick stems with water
storage tissue
– Thick, waxy cuticle
– Vertical stems instead of
lateral reaching branches
– why?
– Wide-spreading network
of shallow roots – why?
9.2.10
Vascular Tissue - Phloem
• Phloem – sugar and amino acid conducting
tissue
– Formed from long chains of sieve-tube members
– Alive a maturity (however they lack nuclei and
ribosomes)
– End walls (sieve plates) have pores that allow for
flow of sugar between cells
– Each sieve tube cell has an adjacent companion
cell that helps serve sieve tube member
9.2.11
Vascular Tissue - Phloem
9.2.11
Translocation
• Translocation – movement of substances from
one area in a plant to another
• Moves sugars and amino acids from source
areas (photosynthetic tissue and storage
organs) to sinks (fruist, seeds, and roots)
• Active process that occurs in phloem
9.2.11
Translocation
How Translocation Works:
• Plasma membranes in sieve tube members pump
organic compounds into cell via active transport
• Creates high solute concentration inside sieve
tube member
– Therefore, water diffuses into sieve tube via osmosis forms sap (sugars dissolved in water)
– Creates pressure inside sieve tube and pushes sap
throughout plant
9.2.11
Translocation
9.2.11
Translocation
1. Sugar loading in sieve tube raises
solute concentration and draws in
water
2. Water influx increases pressure forcing
flow of sap
3. Sugar unloading lowers solute
concentration, water effluxes and
pressure decreases
4. Water pulled back up via transpiration
9.2.11
stream
Translocation
9.2.11