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 full note

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ScienceAid QnA. This section is not written yet. Want to join in? Click EDIT to write this answer.

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

ScienceAid QnA. This section is not written yet. Want to join in? Click EDIT to write this answer.

Referencing this Article

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APA (American Psychological Association)
Roots and Translocation: Structure of Roots, Process of Translocation and Evidence for it. (2017). In ScienceAid. Retrieved Mar 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 Mar 2017.

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Chicago / Turabian ScienceAid.net. "Roots and Translocation: Structure of Roots, Process of Translocation and Evidence for it." Accessed Mar 27, 2017. https://scienceaid.net/biology/plants/translocation.html.

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Article Info

Categories : Plants

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

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