Roots and Translocation: Structure of Roots, Process of Translocation and Evidence for it

Edited by Jamie (ScienceAid Editor), Taylor (ScienceAid Editor), Asutosha Sahu, Jen Moreau

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Root Structure

Below is a diagram of a cross section of a primary root.

cross section of a root, labeled
  1. 1
    Epidermis
    .
    The outside layer of the root that holds everything in place.
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  2. 2
    Parenchyma
    .
    Beneath the epidermis are the parenchyma [pah-ren-ki-ma]. They are packing cells and make up the bulk of the root. Generally they are responsible for storing starch and also respiration.
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  3. 3
    Endodermis
    .
    The endodermis is a layer around the vascular bundle. The cells here contain a casparian strip which helps to control water movement into the xylem.
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  4. 4
    Xylem & Phloem
    .
    These are arranged rather strangely. The xylem transports water, and the phloem transports sugar. We will go into more detail below.
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Translocation

This is the process of transporting sugar and takes place in the phloem. How we think it travels through them is called the mass-flow hypothesis.

diagram showing the process of translocation

The source is where food is produced. This would be the leaves. They produce glucose which is converted to sucrose which enters the phloem. This makes the water potential more negative, making water from the surrounding xylem enter.

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All of this extra material increases the pressure and forces the solution down and through the sieve plate. Then it gets to the sink where the sucrose is moved by active transport into the parenchyma; where it is made into insoluble starch so the water returns to the xylem.

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Therefore the solutes move from source to sink, but it is important to note that it can go in both directions. For example, at night when there is no light for the leaves to produce sugar by photosynthesis, energy has to come from storage.

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Evidence

Evidence for this theory comes from two sources.

  1. 1
    Radioactive Tracers
    .
    These show the direction of flow of sucrose, This method uses radioactive carbon dioxide where the C is 14C. Carbon dioxide - (CO2 = 1 carbon atom and 2 oxygen atoms). This radioactive carbon dioxide is put in a bag over a leaf and sealed. The carbon dioxide gets converted into glucose and an x-ray can be taken that will show where this radioactive material has moved to.
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  2. 2
    Ringing Experiments
    .
    diagram showing ringing
    In the ringing experiment, a ring of bark is scraped away that also removes the phloem. After a while sugar is trying to be transported down the stem but it is stopped by the ring. This means a bulge of sugar forms above the ring. This suggests that sugar moves down the stem in the phloem.
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Questions and Answers

Why ringing experiment cannot be performed in monocotyledon plants?

Who proposed ringing experiment &why ringing experiment cannot be performed in monocotyledon plants.?? Please tell me why ringing experiment cannot be performed in monocotyledon plants? I want the full note.

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The Ringing Experiment

The ringing experiment involves removing a selected part of a stem tissue in the form of a ring or a girdle. There are two types of ring tissues removed; one the phloem is removed only and the second one, the xylem is removed. Three plants are selected in the ringing experiment. The three selected plants are kept under sunlight to allow photosynthesis take place. Let the plants be Plant A, B, and C. After a short duration of sunshine, it is noticed that in plant B, the portion of the cut stem immediately bulges above the ring. On the other hand, plants A and C have no any sign of bulging. This works on the foundations of downward translocation taking place in the phloem as plant's B phloem was removed. Such instances didn't happen in plants A or C as the phloem was still intact. This suggests that the removal of xylem had no effect on the translocation as seen in A.

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In the next experiment, a similar procedure will be followed showing the upward translocation also conducted through the phloem. The procedure starts with the removal of the xylem in Plant A, removal of phloem in plant B and control in plant C. The shoots in A and B are defoliated above the rings. The cut part is kept in glass cylinder which is filled with water so as to keep the tissues moist. In plant A, where only the xylem was removed shows the stem elongation. This shows that there was an undisturbed movement of solutes through the phloem. In plant B, there is no elongation seen. This indicates that the stoppage of solute flow in the stem was removed.

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Tracer Experiment

Tracer studies with the sap analysis which clearly shows that sieve tubes are the main structures in which organic materials translocate within the plant. This is the method used to determine translocation in plants. In tracer experiment, the main aim is to know the flow of sucrose. This procedure utilizes radioactive carbon dioxide where C is treated as 14C. Carbon dioxide which simply means in CO2 there is only one carbon and two oxygen atoms. The radioactive carbon dioxide is placed in a bag over the experimenting leaf and sealed. After a while, the carbon dioxide will be converted into glucose form where an X-ray is taken so as to show where the radioactive material has moved clearly.

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Another experiment procedure is where a plant is grown in a lab and one leaf exposed to a carbon dioxide which contains radioactive isotope 14C. This 14CO2 is taken up by the plant during photosynthesis, and then the 14C is incorporated into sucrose and glucose. Later on, the plant gets frozen into liquid nitrogen so as to kill and fix it fast enough and then placed on a photographic film in the dark. The results show an autoradiograph outlining the compound location containing the 14C. The experiment shows how organic compounds are transported downwards from the leaves to the roots in a plant. The technique can be used to trace the ions, sugars or water.

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Explain how organic substances are translocated in plants?

No, I already found it. What I would like to have is the process of mass flow

Mass flow, simply put, is the movement of matter of one substance through a designated channel. In plant physiology, this often includes the upward movement from water in the soil into vascular plant tissue. The general movement of materials from exchange surfaces to the necessary cells through the plants mass transport system is accomplished by mass flow.

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Will I need this for AQA GCSE UNIT 3 END OF YEAR EXAM?

WILL I OR NAH? I am sitting exams soon and would like to know if this should be revised. cheers,Mughal. Becuase my question is unique, I used Ctrl f and typed it in, nothing came so its orignal. I have tried: Google and wikipedia and the school libary and I asked my mates but theyre pretty dumb. I think it was caused by: My teacher didn't explain the task so now I am lost

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What are the scientific methods to investigate transport in tracer and ringer experiments?

I have to write an essay on the question but I am not able to find enough information to actually fill the essay.

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Examples that disprove mass theory please please please?

May you provide me with some examples that disprove the theory of mass flow please. I.E experiments or methods that can be used to say that mass flow theory is incorrect. may you provide me with some examples that disprove the theory of mass flow please. I.E experiments or methods that can be used to say that mass flow theory is incorrect. may you provide me with some examples that disprove the theory of mass flow please. I.E experiments or methods that can be used to say that mass flow theory is incorrect

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Roots and Translocation: Structure of Roots, Process of Translocation and Evidence for it. (2017). In ScienceAid. Retrieved Apr 27, 2017, from https://scienceaid.net/biology/plants/translocation.html

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MLA (Modern Language Association) "Roots and Translocation: Structure of Roots, Process of Translocation and Evidence for it." ScienceAid, scienceaid.net/biology/plants/translocation.html Accessed 27 Apr 2017.

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Article Info

Categories : Plants

Recent edits by: Asutosha Sahu, Taylor (ScienceAid Editor), Jamie (ScienceAid Editor)

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