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Monday, February 27, 2012

Transportation System for the Continuation of Living Organisms Part II

This post is the part two of previous post. in the previous post I wrote about Dormant Transportation or passive transportation. This post is about Active Transportation.

Active Transportation

You know that diffusion is due to a concentration gradient. Water enters living cells against to the concentration gradient too at certain times. Look at an example. There are more sodium ions than iodine ions in sea water. In certain marine plants there are less sodium ions than iodine ions. Sodium ions do not enter the plant though iodine ions enter. The number of potassium ions in the cells of the fresh water plant nitella is thousand times greater than the number of ions in the surrounding water. If the potassium ions enter the cell by diffusion from the surrounding medium, it can occur only till the concentrations of potassium ions inside and outside are equal. (For the ions of a lesser concentration to enter the cells, ions should move from a region with a higher concentration.) Therefore the sodium or iodine ions enter the cells against the diffusion process.

The passage of particles of matter through a plasma membrane into a cell or out of cell against the natural diffusion process is known as Active Transportation. Energy of metabolism is used up for this purpose.

This process occurs through carrier molecules. Carrier molecules are a type of molecules in the plasma. The mineral ions which are attached to these molecules enter the cytoplasm. Hence the plants have the ability of absorbing the required minerals only.

The water and the minerals absorbed by the root hairs are conducted to the various parts of the plant through the xylem cells in the roots and the stem. This occurs by the movement of substances from cell to cell by osmosis and active transportation.

The structure of a tender root

There are two types of plants. They are the dicotyledonous and the monocotyledonous. You can see some structural differences between them. The external layer called the epidermis is a layer of single cells. Some of these cells have protrusions coming out. These are known as root hairs. The cortex, which consists of circular cells is the inner layer next to the epidermis. There are inter cellular spaces between these two layers. There is a single layer of barrel-shaped cells next to the cortex and it is known as the endodermis. These cells are arranged close together. There are no intercellular spaces between them. Next to the endodermis, the pericycle is made out of a single layer of cells. The vascular system is underneath this layer. The xylem layer is in the form of a star and the phloem cells are in between the xylem layers. The cambium is in between the xylem and the phloem. The pith is in the center. This is a very small layer. The structure changes when the dicotyledonous plants undergo secondary thickening as they mature. The roots thicken with age.

The structure of tender root of a monocotyledonous plant too is similar to the root of a dicotyledonous plant. But there is no cambium and no secondary thickening. Hence roots do not thicken with age.

Adaptation of roots for the absorption of water and minerals

  • The roots of dicotyledonous plants are divided into many lateral roots.
  • The monocotyledonous plants have a large number of fibrous roots.
  • Presence of root hairs.
  • Presence of a fairly thin epidermis at the tip of the root.

Ascent of sap

    A column of water rises up from the roots of a plant to the leaves through the xylem vessels. This is a continuous column of water. There are no air bubbles inside this air column of water. Xylem vessels are similar to pipes. There are two reasons for continuity of this column of water.
    • The water particles are attracted to each other - Cohesion.
    • The water particles are tightly attached to the walls of the xylem vessels - Adhesion. 
    When water goes out from the leaves of a plant by transpiration, water flows up along the xylem vessels under the conditions. The flow of water from the roots to the leaves due to transpiration is known as transpiration pull.

    In the soil the minerals are dissolved in water as their salts. The roots absorb this water and the root system of a plant exerts a push on it and sends it up along the xylem tube. This push is known as the root pressure. It has been found out that the maximum height of water that can be pushed due to the root pressure is about 18m. The water rises up beyond this height only due to the transpiration pull. The process of transporting water and minerals dissolved in it through the xylem cells from roots up to the leaves is known as the transpiration of nutrients.

    How about this one? Great! Awesome! Or Nice Then just share with your friends and Comment your Idea Below. Appreciate it!

    1 comment:

    Phillips Kevin Michael said...

    Yes it was a great idea about the transportation system for the continuation of living organisms. But do you know about Electricity Supply in Singapore?

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