structures responsible for transportation and translocation in flowering plants

What are the structures responsible for transportation and translocation in flowering plants?

Transportation in plants: is the process in which plant absorbs water from roots and transports it different parts of the plants.

Translocation in plants: is the process that conducts synthesized food in different parts of the plant.

Structures that are responsible for transportation and translocation:

Plants make their food in leaves and transport in all parts of the plant including roots. In the same way water is absorbed by the roots and transpoted through out all the parts of the plant.vascular bundles are the specialized tissues that are responsible for transpoting synthesized food and water through out the plant.

Vascular bundles consist of:

    • Xylem
    • Phloem

Structure of Xylem:

    • Long, hollow tubes.
    • The cells in the xylem that carry water become vessels.
    • A vessel is made up of a series of long cells joined end to end stretching from roots till leaves.
    • These vessels are dead cells which consist of dead cell walls and a deposition called lignin.
    • lignin makes the cell wall very strong and impermeable.

Types of xylem vessels:

    • Lignin is present in spiral, ring or pit forms.
    • These tubes lack cytoplasm and nuclei.
    • Xylem tubes are unidirectional from down(soil) to up(leaves and stems).

Functions of xylem vessels:

    • Xylem vessels conducts water and dissolved mineral salts from the roots to the stems and leaves.
    • Provides mechanical support for the plant.

 

How is the structure of xylem adapted to carryout its function?

    • Xylem vessels are Tublar:

Joined end to end from roots till leaves and stem.

    • Xylem have Narrow lumen:

Capillary action takes place easily.

    • No nucleus and cytoplasm present:

No resistance for the movement of water and dissolved minerals.

    • No end plates/attached end to end:

No cross walls so supported by lignin.

    • Lignin deposition:

Provide mechanical support to the plant.

Structure of Phloem:

Phloem consists of :

    • Sieve tube elements:

      • cylindrical cells
      • cell walls are made up of cellulose,
      • consists of perforated end plates which are perforated called sieve plates.
      • Mature sieve cell consist of only a thin layer of cytoplasm.
      • Lacks of central vacuole, nucleus and most organelles.
    • Companion cells:

      • Narrow and thin walled.
      • Contain cytoplasm and nucleus.
      • Many mitochondria are present.
      • Carries out metabolic activities/ processes needed to keep sieve tube cells alive .
      • Phloem tubes are bidirectional.

Function of Phloem:

    • Translocate organic material(sucrose and amino acid) in all parts of the plant.

How is the structure of phloem adapted to carryout its function?

Companion cells are present: Companion cells contain many mitochondria that provide energy for the companion cell to load sugars from the mesophyll cells into the sieve tubes by active transport.

Holes are present in sieve plates: allows rapid flow of manufactured food substances through sieve tubes.

Positions of Xylem and Phloem in a leaf, stem and root of a dicotyledonous plant:

    • In a leaf , xylem lies on upper side while phloem lies on lower side.

    • In stem, xylem lies on lower side while phloem lies on upper side.

    • In root, xylem and phloem lies alternative in a star shape in the center.

Structure and adaptations of root hairs for its function:

Structure of root hairs:

    • Each root hair is a projection of an epidermal cell, which lives for only a few days.
    • It is very minute just a few mm in length.
    • As the root grows, new root hairs are produced. Old root hairs degenerate and die. Absorption of water and mineral salts occur in new areas of the root.
    • Root hairs only exist in the root hair zone immediately behind the root cap.
    • The absorption of water occurs mainly through root hairs.
    • Root hair is surrounded by cell wall made up of cellulose which is fully permeable.
    • It is a living cell of the plant cell that contains nucleus, protoplasm, a big vacuole filled with cell sap.
    • It is a cell of a plant cell but it does not contain chloroplast as it does not make food because it lies under the soil where the sunlight does not reach.

How is the root hair adapted for its function?

    • Root hair is elongated and narrow so increases the surface area for absorption.
    • Lots of mitochondria is present in cytoplasm so can produce energy for active transport.
    • They do not have cuticle as this would prevent water absorption.
    • They have large vacuoles to absorb water and pass it to the next cells.
    • Root hair cell contains concentrated cell sap which means it has low water potential so water enters in root hair through the process of osmosis.
    • Cell wall prevents deformation or bursting of cell because of hydrostatic pressure.
    • Partially permeable membrane helps to maintain diffusion gradient and ensures water uptake.

Describe an experiment to show which tissue in a stem conducts water/dissolved mineral salts  from roots to leaves?

    • Take a young bean seedling and placed in a beaker with its roots immersed in water with any dye.(eosine dye that is red in colour)
    • Leave the seedling undisturbed in dye for few hours in sunlight.
    • When the dye becomes visible in the leaf stalks and leaf veins, remove the seedling.
    • Cut very thin slices/sections of root and shoot.
    • Examined under the microscope.
    • It was observed that xylem tissues in roots and shoots are dyed.
    • This shows that xylem is responsible for transport of water from roots to leaves.

Explain how a plant stem is able to support the leaves, flowers and fruits?

    • A plant contains xylem tissues that are dead tissues.
    • Xylem tissues consist of long vessels with thick lignified cellulose walls.
    • This lignified thickening make the stem strong enough to support the softer and fragile tissues of the leaves, flowers and fruits against the gravity and wind.

Functions of water in a plant:

    • It is important for the process of photosynthesis.
    • It also help in many hydrolytic reactions(process of breaking bonds in the presence of water).
    • It is an essential constituent of protoplasm.
    • It acts as an solvent for mineral salts, nutrients and certain organic compounds.
    • It transports the dissolved minerals, nutrients and some organic compounds.
    • It provides an important medium for chemical reactions to take place.
    • It helps in heat loss.(after evaporation of water through leaves , temperature drops)

Test yourself:

    • What is translocation?
    • Name the tissue responsible for translocation.
    • Name the tissues present in vascular bundles?
    • What is lignin?
    • Name the tissue in which lignin is present.
    • Why is xylem a tissue not a cell?
    • Which tissue gives mechanical support to the stem and other fragile parts of the plant?
    • Why do roots not take part in the process of photosynthesis?
    • From which cells, roots emerge.
    • Which features make the roots best adapted for the process of absorption?
    • Name the cells that help the phloem to carry out their function.
    • List down different functions of water.
    • What is the difference between glucose, sucrose and starch as a food of a plant?
    • Why water enters into root hairs by the process of osmosis?
    • Why companion cells have lots of mitochondria?
    • What is a hydrolytic reaction? Give one example.
    • Why do roots have no chloroplast?
    • What do you mean by unidirectional and bidirectional?
    • Why phloem is bidirectional and xylem is unidirectional?
    • Explain the difference between transportation and translocation?

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