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- Cortex- primarily parenchyma (storage
- Endodermis-Casparian Strip-water-proofing band that runs through radial (side) and end walls; barrier
- Stele- vascular bundles(transport into plant)
Explain the symplast
- •Water can simply cross a root hair membrane and then move from cell to cell through cortex and across epidermis to the core.
- •Once across the root hair membrane, water's intercellular movement is unimpeded by further membranes because cytoplasm of adjacent plant cells often form an association of plasmodesmata (cytoplasmic channels) that interconnect contents of cells.
- •At Casparian strip it continues through cells
Explain the apoplast.
- Network of cell walls and intracellular spaces that leads from epidermis through cortex.
- -doesn’t enter cells
- Casparian strip prevents further apoplastic flow, so the water must now cross a cell membrane of the endoderm (osmosis).
Transport: Gas exchange
- –controlled movement of carbon dioxide in and water vapor and oxygen out
- –Occurs in stomata
- –movement of water and minerals from soil to leaf and then water moves into atmosphere
- –Occurs in xylem
- – movement of sugars and other organic material throughout the plant
- –Occurs in phloem
Mechanism for Stomata opening
- –each is surrounded by 2 guard cells with chloroplasts which produce ATP via photophosphorylation.
- • Proton pump and ATP
- – active transport of K+ into the cell.
- •Increase in osmotic pressure results in the cell swelling
- •Stoma are opened by: light , low CO2 and an internal clock within guard cells that follows a circadian rhythm.
- Stomata close when guard cell shrink
- •Factors that will cause guard cells to K+ leave and water follows and shrink
- –Water lost due to dehydration
- –high CO2 in the leaf
- –abscisic acid,
Cell types in Xylem
- CELL TYPES INCLUDE
- •Tracheids and Vessel elements
- –Mature vessel elements die, leaving behind an empty cell wall that acts as a pipeline for water.
How do vessels transport water?
- •1- Transpirational pull-Water evaporates from cells near stomata.
- – Since they are dryer (water potential is lower)than their neighboring cells, water moves from the moist cells into the dry cells.
- 2- Root pressure- results from the inward active transpot of solutes from the soil by root cells.
- •Water follows inward by osmosis
- •This causes a chain reaction all the way down to the roots.
- •3- Cohesive/adhesive properties of water
- • Water is pulled up through xylem cells in long, thin columns.
- •Phloem cells (which have cytoplasm but no nuclei or organelles) include sieve cells And companion cells
- • -must be alive to function
Movement in Phloem
- •The movement of food in the plant is called translocation.
- –translocation is not unidirectional.
- –location of sugar production
- –location sugar is stored or consumed.
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