Evaluation of Mass Flow Theory

Created by: Betsy_2018
Created on: 02-06-17 15:19


	Mass Flow Theory to Explain Translocation
	Advantages sap is released from the sieve tubes when they are cut, which suggests that not only do they carry sugar, there is a pressure in the tubes that causes it to flow sucrose concentration is greater at the leaves than the sinks, which suggests that there must be a mechanism to get it from the leaves to the sources there is a downward flow in the phloem during the day, which stops by night. This suggests that translocation is dependent on light - photosynthesis creates lots of sugars which need to be transported away when a plant's metabolism is inhibited, translation also stops which suggests that in one or more stages of translocation, ATP is needed companion cells have many mitochondria and readily make lots of ATP. Cell specialisation would suggest that these cells have evolved this way for a purpose	Disadvantages the function of sieve plates is unknown, implying that Mass Flow Theory is not comprehensive not all solutes move at the same rate in solution, which goes against the theory, which claims that solutes move at a rate at which they are needed, not on which they individually are capable of sucrose moves at a standard speed, and does not appear to change dependent on concentration gradient sieve plates should in theory actually inhibit mass flow as their perforated surfaces should inhibit the desired pressure changes to make the solution travel
	Evaluation Mass Flow Theory is the most widely accepted and the most likely explanation for translocation. However, little is known about the specific jobs of the sieve elements.

Mass Flow Theory to Explain Translocation

Advantages

sap is released from the sieve tubes when they are cut, which suggests that not only do they carry sugar, there is a pressure in the tubes that causes it to flow
sucrose concentration is greater at the leaves than the sinks, which suggests that there must be a mechanism to get it from the leaves to the sources
there is a downward flow in the phloem during the day, which stops by night. This suggests that translocation is dependent on light - photosynthesis creates lots of sugars which need to be transported away
when a plant's metabolism is inhibited, translation also stops which suggests that in one or more stages of translocation, ATP is needed
companion cells have many mitochondria and readily make lots of ATP. Cell specialisation would suggest that these cells have evolved this way for a purpose

Disadvantages

the function of sieve plates is unknown, implying that Mass Flow Theory is not comprehensive
not all solutes move at the same rate in solution, which goes against the theory, which claims that solutes move at a rate at which they are needed, not on which they individually are capable of
sucrose moves at a standard speed, and does not appear to change dependent on concentration gradient
sieve plates should in theory actually inhibit mass flow as their perforated surfaces should inhibit the desired pressure changes to make the solution travel

Evaluation

Mass Flow Theory is the most widely accepted and the most likely explanation for translocation. However, little is known about the specific jobs of the sieve elements.

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Evaluation of Mass Flow Theory

Mass Flow Theory to Explain Translocation

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Disadvantages

Evaluation

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