Class 10 Science – Chapter 1- Life processes – Transportation in plants
Transportation in Plants – all green plants require, along with the food prepared by photosynthesis, other inorganic nutrients. These are absorbed from the soil by the roots as they are in contact with the soil.
The materials prepared by photosynthesis and the materials absorbed by the roots should be diffused to other parts of the plant and this process is called transportation in plants.
The two main vessels involved in transportation are xylem and phloem vessels. The transportation at the expense of energy is called active transport and that without the expense of energy is called passive transport.
Phloem, Sugar and Translocation Phloem consists of several types of cells: sieve tube cells (aqua sieve elements), companion cells and the vascular parenchyma.
Sieve cells are tubular cells with end walls known as sieve plates. Most lose their nuclei but remain alive, leaving an empty cell with functioning plasma.
Companion cells load sugar into the sieve element (sieve elements are connected into sieve tubes). Fluids can move up or down within the phloem and are transported from one place to another.
Sources are places where sugars are being produced and Sinks are areas where sugar is being consumed or stored. Food passes through the phloem by a Pressure-Flow Mechanism. Sugar moves from a source to a sink by osmotic pressure.
Translocation of sugar into a sieve element allows water to enter that cell, increasing the pressure of the sugar-water mix. The pressure develops the sap to flow towards an area of lower pressure, the sink. Then the sugar is extracted from the phloem by another energy-requiring step and usually converted into starch or metabolized in the sink.
Class 10 Science Notes
Transportation of water and minerals in plants.
Root hairs are thin-walled extensions of the epidermal cells in roots. They provide increased surface area and thus more efficient absorption of water and minerals. Water and dissolved mineral nutrients enter the plant via two roots.
Water and selected solutes pass through only the cell membrane of the epidermis of the root hair and then through plasmodesmata on every cell until they reach the xylem: intracellular route.
Water and solutes enter the cell wall of the root hair and pass between the wall and plasma membrane until it enters the endodermis, a layer of cells that they must pass through to enter the xylem: extracellular route.
Only when the concentration inside the endodermal cell falls below that of the cortex parenchyma cells, does the water flow into the endodermis and from there into the xylem. In the leaf cells, these raw materials are combined in the presence of solar energy by a series of chemical reactions.
These reactions take place in the chloroplasts with the help of many enzymes. The end products of these reactions are glucose and oxygen. Oxygen is released into the atmosphere through the stomata.
The glucose molecules get converted to another form of sugar called sucrose. Sucrose is easily transported to various parts of the plant body through phloem vessels and is stored in the form of starch.
The chemical process of photosynthesis can be summarized as follows: The leaf is well equipped for the process of photosynthesis. Green plants not only produce food for themselves but for the rest of the living world.
The soil is the natural and richest source of raw material for plants.
Raw materials like nitrogen, phosphorous and other minerals are absorbed by plants from the soil by roots.
Plants absorb water and minerals from soil by roots and transport to the leaves.
As the distance between roots and leaves is large, diffusion is not sufficient to provide raw materials to leaves and energy to roots.
Plants use slow transport system but large as required in tall plants to transport energy from leaves and raw materials from roots.
A group of special cells forming vascular tissue transport water and nutrients to all the cells of the plants.
Two types of vascular tissues are xylem and phloem.
Xylem transports water and minerals obtained from the soil.
Phloem transports products of photosynthesis from the leaves to other parts of the plant.
Fig.Xylem and phloem
Vessels, tracheids of the roots, stems, and leaves are connected to form a continuous system in xylem cells to transport water to all the parts of the plants.
Cells in the roots which are in contact with the soil take up ions which creates a difference in concentration between the roots and the soil and therefore water moves to the roots to eliminate the difference.
Water is moved into xylem of roots and from where it is pushed upward.
Plants use different mechanisms to pull water upwards through xylem like-
- Water which is lost through stomata is replaced by water absorbed by the roots.
- Evaporation of water from leaf creates a suction force which pulls water.
The loss of water in the form of water vapor is called
Importance of transpiration-
- Regulates temperature.
- Helps in absorption of water and upward movement of water and minerals.
When stomata are open during the day, a large amount of water is lost and thus upward movement of water also becomes more.
Phloem transports soluble products of photosynthesis, amino acids, and other substances.
The transport of soluble products of photosynthesis is called translocation.
The substances are transported to the storage organs of seeds, roots, and fruits.
The translocation takes place in the sieve tubes with the help of adjacent companion cells.
The movement of substances is bidirectional i.e both upward and downward.
Energy from ATP is utilized for translocation.
Fig. movement of water and nutrients upward and products of photosynthesis both upward and downward
Materials like sucrose move to phloem using energy, increasing the osmotic pressure of the tissue causing water to move and materials in the phloem to tissues according to the plant’s needs.
Example- when the buds grow these need energy and sugar stored in the root or stem would be transported to the buds as sugar is an energy giving molecule.
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