3.3 Transport In Plants Flashcards
What are dicotyledonous plants?
Plants with two seed leaves and a branching pattern of veins in the leaf
Define meristem
A layer of dividing cells
Define phloem
Transports dissolves assimilates
Define vascular tissue
Consists of cells specialised for transporting fluid by mass flow
Define xylem
Transports water and minerals
What’s tissues give vascular bundles strength?
Collenchyma and sclerenchyma
How are vascular bundles arranged in young root?
Xylem in x shape and phloem between arms
What is around the vascular bundle in you root?
Endodermis
What is in the inside layer of the endodermis?
Meristem cells that form the pericycle
How are vascular bundles arranged in non woody plants?
They are desperate and discrete
Near the outer edge
How are vascular bundles arranged in woody plants?
Seperatley in young stems
Continuous ring in older stems just under bark of tree
What is in between the xylem and the phloem?
Cambium
What is the cambium?
A layer of meristem cells that divide to produce new xylem and phloem
How are xylem and phloem arranged in the leaf?
Within each vein, the xylem is on top of the phloem
Spread away from midrib
What are companion cells
Cells that help to load sucrose into the sieve tubes
What are sieve tube elements?
Make up the tubes in phloem tissue that carry sap up and down the plant
Sieve tube elements are seperatley by sieve plants.
What are xylem vessels
The tubes which carry water up the plant
What does xylem tissue consist of?
Vessels
Fibres for support
Living parenchyma cells which act as packing tissue to separate and support the vessels.
How do xylem vessels develop?
Lignin makes cell walls waterproof
Cells die
Liginfication
What patterns am does lignin form in the cell wall and what do they do?
Spiral
Annular (rings)
Reticulate (network of broken rings)
Prevent it from being too rigid
What happens in areas where liginification is not complete?
Form bordered pits allow water to leave one vessel and enter the next
Leave xylem and pass into living parts of the plant
How is xylem adapted?
Continuous column
Narrow tubes, water column does not breadth easily and capillary action is effective
Bordered pits
Patterns allow stretch and bend
Why is the flow of water not impeded in xylem?
No cross walls
No cell contents
Lignin no collapse
Adaptations of companion cells?
Numerous mitochondria to produce ATP for active processes
What are plasmodesmata?
Gaps in cell wall containing cytoplasm thag connects two cells
What are the three possible pathways that water takes through a plant?
Apoplast
Symplast
Vacuolar
What is the apoplast pathway?
Through spaces in cell walls and between cells
Moves by mass flow
Mineral ions and salts can be carried
What is symplast pathway?
Enters cytoplasm through plasma membrane
Plasmodesmata
What is the vacuole pathway?
Can go in vacuoles too
What is water potential?
The measure of tendency of water to move from one place to another
Define potometer
A device that can measure the rate of water uptake as a leafy stem transpires
What is transpiration
The loss of water vapour from the aerial parts of a plant, mostly through the stomata in the leaves
Step one of water leaving the leaf
enters leaf through xylem
Moves by osmosis into cells of spongy mesophyll
May go down apoplast
Step 2 of water leaving the leaf
Evaporates from cell walls of spongy mesophyll
Step 3 of water leaving leaf
Water vapour moves by diffusion out through stomata
Uses difference in concentration of molecules in leaf and outside
Water vapour potential gradient
Why is transpiration important?
Transports useful mineral ions up the plant
Maintains cell turgidity
Supplies water for growth, elongation and photosynthesis
Supplies water that evaporates and keeps plant cool
What factors affect transpiration rate?
Light intensity Temperature Relative humidity Air movement Water availability
How does light intensity affect transpiration
Stomata open to allow gaseous exchange for photosynthesis
Increases transpiration
How does temperature affect transpiration?
Increase rate of evaporation for higher water vapour potential
Increases rate of diffusion through stomata because more KE
decreases relative water vapour potential in the air- more rapid diffusion
How does humidity affect transpiration?
Decreases rate of water loss
Smaller potential gradient
How does air movement affect rate of transpiration
Carry away the water vapour
Higher gradient
How does water availability affect transpiration rate?
If there is insuffieicint water, stomata close and leaves wilt
Define adhesion
The attraction between water molecules and the walls of the xylem vessel
Define cohesion
The attraction between water molecules caused by hydrogen bonds
Which pathway is blocked by the casparian strip?
Apoplast
How does water move up the stem?
Root pressure
Transpiration pull
Capillary action
How does water enter the xylem
Mineral ions actively transported
Lower water potential
Osmosis
How does transpiration pull work?
Water attached by cohesion
Low hydrostatic pressure
High tension
What protects against high tension in xylem?
Lignin
Define hydrophyte
A plant adapted to living in water or wet ground
Define xerophyte
Plant adapted to living in very dry conditions
How do plants minimise water loss?
Waxy cuticle prevent evaporation
Stomata under
Stomata closed at night
Lose leaves in winter
Adaptations of marram grass
Rolled leaf, humid reduces air loss Thick waxy cuticle Stomata on inner side Stomata in pits in lower epidermis with hairs Low surface area of mesophyll
Adaptations of cacti
Succulents that store water in stems that can expand
Leaves are spines
Stem is green
Wide roots
Other xerophytic features
Closing stomata
Low water potential with salt
Tap root
Adaptations of water lily
Air spaces in leaf for float
Stomata on upper epidermis
Oxygen can quickly diffuse to roots in air spaces
How do they transpire in humid conditions?
Tips of leaves have hydathodes
Release water droplets
Define assimilates
Substances which have become a part of the plant
Define sink
A plant of a plant where materials are removed from the transport system
Define source
A part of the plant that loads materials into the the transport system
What is translocation
The transport of assimilates throughout a plant
Example of sink
Roots
Example of source
Leaves
What are dicotyleoenous plants
2 seed leaves
What does the endodermis do?
help transport water into the xylem
Where is the pericycle?
just inside the endodermis
Describe structure of the stem
non-woody = discrete
woody = ring
xylem most central, then phloem with cambium in between them
then sclerenchyma
then collenchyma
parenchyma all between (all other tissue)
Describe structure of leaf
phloem below xylem within central midrib
Three things that xylem contains?
- vessels to transport H2O and minerals
- fibres to support plant
- parenchyma
Differences between transpiration and translocation
Translocation = active, relies on difference in hydrostatic pressure, 'push' of sugars, altered by poisons Transpiration = passive, relies on tension, 'pull' of water, affected by wind, air movement etc
