Topic 3 - Mass Transport in Plants Flashcards
What is the phloem?
Plant vessels that transport sugars.
What are sieve tube elements?
- cells that make up phloem vessel
- living cells - contain cytoplasm but no nucleus
- walls made of cellulose
What are companion cells?
- connected to sieve tube elements via plasmodesmata
-> allows cytoplasm to be shared between these + sieve tube - have a nucleus
What are sieve plates?
- at either end of sieve tube elements
- have large pores -> allows sap to move
- allows sugars to be transported
What is translocation?
Proceeds where sugars produced in photosynthesis are transported from plant leaves to other parts
What are the steps of translocation? (Summary)
- Active transport of sucrose
- Diffusion of Sucrose
- Osmosis 1.
- Unloading of Sucrose
- Osmosis 2.
What are the steps of Translocation (detailed)?
- mass flow hypothesis
- Sucrose produced at source AT into companion cells (energy provided by mitochondria in CC.)
—> H+ AT out of CC and then diffuses back into CC with sucrose (Cotransport.) - Loading of sucrose into phloem causes concentration of sucrose to increase.
—> sucrose diffuses from CC into sieve tube elements. - Inc sucrose conc in phloem
Explain how pressure is generated inside the phloem tube during mass transport.
- Sucrose is AT out of source into phloem
- Lowering the WP in the phloem
- so water moves by osmosis from xylem into phloem
- generates hydrostatic pressure
Why is phloem pressure reduced during the hottest part of day? ( use knowledge of transpiration and mass flow to explain )
- transpiration is at higher rate during hottest part of day
- because water lost through stomata at quicker rate
- causes less movement of water from xylem to phloem
- so phloem pressure reduced
Give other two measurements to calculate the rate of water movement.
- initial and final mass
- no. of xylem vessels
During practical measuring uptake of water by roots (plant in beaker of water) why is a layer of oil used ontop of the water?
- so water doesn’t evaporate from the beaker making results incorrect
Explain why water moves up the stalks of plants.
- water evaporates (from leaf of top of stalk (depending))
- WP gradient creates tension + pulls up water
- H bonds through cohesion maintains upwards moving column of water
Describe how to handle a scalpel safely in practical
- blade down
- cut away from self
- against flat surface
Suggest how a plant may be able to survive without xylem tissue?
Short diffusion pathway to cells
Ringing experiment for plants (seeing effect of removing phloem). Explain how a control sample is used?
Compare to the effects of other treatments
Using ringing experiments to evaluate whether different treatments effect root growth.
- any substances not required for root growth?
- does any substance inc root growth?
- does any substance move through the plant?
Using ringing experiment evaluate whether the movement of substances through phloems can be explained by the mass flow hypothesis.
Support:
- do any show phloem is involved?
- do any show if AT is involved?
Against:
- no role for osmosis?
- do roots still grow without functioning phloem?
Using diagram explain how you can see if heat treatment damaged the phloem, by using CO2 with radioactively labelled carbon.
- radioactively labelled C in CO2 will be converted into sugar during photosynthesis
- which plant has radioactive all throughout?
- if only one plant without treatment then heat treatment does affect phloem
Explain how the scientists could’ve concluded that the heat treatment did not affect the xylem. (using graph)
- if given compare water content of leaves
- if given SDs overlap no significant diff
- would mean water still be transported by xylem
- or converse
Using graph what could you try to conclude about Fe Ions in barley plants by using results from heat treatment?
- heat treatment damaged phloem
- does Fe ions move up or down the plant
- does heat treatment have a bigger effect on older or younger leaves
- is there a higher ratio of Fe ions in treated or untreated leaves
Describe the cohesion-tension theory of water transport in the xylem.
- water is lost from xylem by transpiration
- lowers WP of mesophyll cells
- so water is pulled up the xylem (creating tension)
- water molecules cohere using H bonding forming a water column
- adhesion of water molecules to walls of xylem
Outline a method to find a rate of water loss per mm^2 of surface area of the leaves of the shoot
- trace around both sides of leaf on graph paper
- count squares to calculate area
- divide rate by SA
Why might the rate of water through a shoot in a potometer may not be the same as the rate of water movement through the shoot of a whole plant?
Plant has roots
Describe the mass flow hypothesis for the mechanism of translocation in plants
- Sucrose AT into phloem
- by CC ( have mitochondria to release ATP)
- lowers WP of sieve cell and so water diffuses by osmosis out6 of xylem into phloem
- increase in hydrostatic pressure causes mass movement towards sink
- sucrose converted in root for respiration for storage
