Topic 3 - Mass Transport in Plants Flashcards
(25 cards)
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 so dec WP in phloem. So water moves by osmosis from xylem into phloem.
- Generates hydrostatic pressure causing mass flow of sucrose to the sink where it is untaken by diffusion. Due to conc gradient of sucrose.
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
