Transport in plants Flashcards
Dicotyledon
Plants with veins (like oak leaves)
Structure of cross section of dicotyledonous root
Root hair cell projections, epidermis, cortex, endodermis, casparian strip, endodermis, pericycle, phloem, xylem.
what runs through the endodermis?
Casparian strip
what is special about the casparian strip? what is it made of?
Its water proof! It’s made of SUBERIN
Apoplast
movement of water through the cell walls and gaps between cell walls.
symplast
movement of water through the cytoplasm and plasmadesmata
why is more water transported through the apoplast route?
water faces more resistance through the cytoplasm.
Water flows in one continuous stream through the cell wall due to cohesion.
explain how water travels in the cell wall..
cohesion, adhesion - capilliary action.
What happens at the casparian strip?
Why does this happen? how does this help?
Water travelling via apoplast passes into the cytoplasm and follows the symplast pathway. The casparian strip is waterproof. The cytoplasm can now control which substances enter.
Why does water move from root hair cell to the xylem?
Difference in water potential between root hair cell and xylem.
What is root pressure?
Active transport transports mineral ions into xylem to reduce the water potential.
two main cells that make up the PHLOEM?
Sieve tube element, companion cell.
after photosynthesis, what is glucose transformed into?
Sucrose
What do you call the leaves and storage organs and why?
Sources - because they’re the sources of sucrose
What do we call roots, storage organs, shoots and why
Sinks- because this is where sucrose is deposited (to be utilised).
how is sucrose loaded into phloem?
- H+ ions transported from cytoplasm of companion cell to cell wall of companion cell using ATP.
- Now, there is a concentration gradient of H+ ions moving from the cell wall into the cytoplasm.
- the H+ ions couple with sucrose and are transpoted into the cytoplasm by co- transporters.
- sucrose diffuses into sieve tube elements.
How does phloem sap move? (4)
- as sucrose moves into phloem, water potential decreases.
- water moves into phloem from xylem and other cells.
- now, hydrostatic pressure inside sieve tube element causes sap to move towards the sinks.
- this is mass flow.
What happens after phloem sap reaches the sink?
- at the sink, sucrose transformed to glucose.
- water potential increases inside sieve tube elements.
- water moves out of phloem by osmosis.
What are assimilates?
Products moved by the process of translocation
Where are meristem cells found in stems?
cambium
Structure of vascular bundle in stem?
(out to in)
Sclerenchyma, phloem, cambium, xylem.
explain cohesion tension theory… briefly…(2 points)
- Transpiration occurs at stomata, creating areas of low pressure at the top of the xylem where water is being deposited and evaporated.
- water molecules are pulled to this low-pressure area, creating tension. - cohesion between water molecules pulls water up the xylem.
what does cohesion tension theory create?
a transpiration stream
structure of a leaf top to bottom?
Upper epidermis, palisade cells, spongy mesophyl and valscular bundle, lower epidermis and stomata
explain, in detail, transpiration at the stomata and cells in the leaf
surface of cells coated by a layer of water.
This water evaporates into gaps in the leaf due to the difference in water potential between the air and the cells.
Because water potential of air space is now high, water will move out of the stomata along the concentration gradient.
Water potential in cells is now low, so water moves from xylem to cells.
The water from these cells moves to adjacent cells.
2 pieces of evidence for transpiration pull/ cohesion tension theory/ transpiration stream
- if a plant stem is cut, air will be sucked into it. no cohesion now, so water stops movin’.
- Diameter of tree trunk reduces at high transpiration.
evidence for translocation, 2 points
- radioactive labelling (C14) measures where the C14 is when it moves down the trunk.
- removing bark (which contains phloem and not xylem). a bulge will form above and below ring. Analuse contents of both bulges
how does light intensity affect stomata?
It increases the number of open stomata
How is transpiration reduced?
Water vapour buildup around stomata decrease the concentration gradient between humid air gaps in the leaf to outside the leaf.
What does dry wind do to transpiration?
Decrease water potential for the air around the stomata.
What are the chemical changes of guard cells in light conditions?
- K+ ions transported into guard cells
- water potential decreases
- water moves into guard cells
What chemical changes occur to the guard cells in drought?
Roots send hormonal signals to guard cells, making them close.
How are guard cells adapted?
2 points
- rings of cellulose around the width of guard cells prevent lysis.
- thicker cell wall on one side prevent guard cell from expanding evenly, causing a bend.
Two ways phloem can be loaded…
- symplast route - sucrose diffuses into sieve tube element via symplast route.
- apoplast route - sucrose moves from cell wall to cytoplasm if companion cell via active loading.
evidence for translocation…
- advances in microscopy= seeing adaptations of companion cell
- if mitochondria of companion cell are poisened translocation stops.
- flow of sugars 10 000 times faster than diffusion alone.
- aphids stylet (mouth bit) is cut. sap flows out, which demonstrated pressure differences near the sink compared with near the source.
