In any country, the transport system comprises land transport through bicycles, trains, motor vehicles and beasts of burden, water transport by boats and ships, and air transport by airplanes. The basic function of the transport system is to take goods, persons and materials from one place to the other. Generally different agricultural products are acquired in bigger quantities in certain portions of a country than in others.
In animals and plants, there are transport systems. They take materials from different parts of the organisms where they are formed or obtained to the parts where they are employed or eliminated from the body. This lecture note mainly deals with the materials which are transported, the routes all along which they are transported, the procedure or mechanisms through which they are transported in the flowering plants and the procedure of transpiration.
Transport in plants:
In a common plant like an alga, materials enter or depart the cells in its body through diffusion. In the cell itself, materials are distributed through the circular streaming movement of the cytoplasm. In higher plants, special conducting tissues, termed as vascular tissues, carry out transport. Such vascular plants comprise all flowering plants and non-flowering plants like gymnosperms and ferns.
Materials for Transportation:
The main materials transported in plants are mineral salts, water, manufactured food, oxygen and carbon-dioxide, gases and necessary chemicals like pigments and hormones.
1) The absorbed water from the soil is carried to the leaves and other parts of the body for the process of photosynthesis and other functions.
2) Prepared food is transported from the leaves to all living cells of the body for tissue respiration or to storage tissues for storing the food.
3) Absorbed mineral salts from the soil are transported to all cells of the body where they are employed in the production of food, protoplasm and other body substances.
4) Excretory products like carbon-dioxide and water are transported from all the living cells to where they are expelled.
Mechanism of transportation in plants:
Plants usually need adequate quantities of several minerals and other substances that are transported in them. The materials transported in plants comprise prepared food, carbon-dioxide, oxygen, water, nitrogenous waste products, amino-acids, latex, glucose, Auxin and mineral salts. The mode of transport in plants is the latex or cell sap.
In aquatic, unicellular and simple multi-cellular plants, gases enter and depart the cells through simple diffusion. Water comes in the cells of such plants through osmosis whereas manufactured food and waste products are transported through diffusion.
In multi-cellular plants such as flowering plants, the gases are mostly absorbed via the stomata in the leaves and lenticels in the stem whereas mineral salts and water are absorbed via the root system. Within the plants, gases moved through diffusion. They dissolved in the water of the moist cells prior to entering the cells. Water, soluble food and mineral salts are transported in the vascular tissues of the plant. The vascular tissues of plants are formed of a network of long tubes termed as vascular bundles. Vascular bundles comprise mainly of the xylem and phloem tissues. However in the roots and stems of dicotyledonous plants, a layer termed cambium exists among the xylem and the phloem tissues. Therefore the vascular bundles are found in the stems, leaves and roots.
Absorption of Water by Roots of Plants:
The roots hairs of flowering plants have direct contact with water in the soil. The cell sap in the root hairs is more concentrated as compared to the soil water; therefore water is capable to pass from the soil into the root hairs through osmosis. The water passes via the thin layer of cytoplasm or cell membrane that is selectively permeable into the vacuole of the root hairs. The extra water increases the tugor pressure of the vacuole or decreases the osmotic pressure and forces water out into the cell walls to the cortex. The cell subsequent to the root hair cell inside consists of a lower tugor or higher osmotic pressure; therefore water will pass into it through osmosis. In this manner, the water absorbed will get to the vessels of xylem.
Translocation is the method by which prepared food substances are transported from where they are required or stored. Translocation generally starts from the leaves to other parts of the plant. Phloem is the tissue via which such prepared food substances are translocated. Materials or substances generally translocated in plants comprise glucose, sugar or carbohydrates, resins, oil, proteins or amino acids, alkaloids and hormones.
The functions of such translocated substances comprise:
a) Proteins or amino-acids that are employed for building up new tissues.
b) Glucose, Sugar and carbohydrate provides energy for synthetic procedure.
c) Alkaloids, steroids and resins are defensive in function and prevent herbivores from eating the plants as they are all waste products in the plants.
Transpiration is stated as the elimination of surplus water from plants into the atmosphere in the form of water-vapor. Plants are capable of loosing surplus water via:
a) The stomata in the leaves which is termed as stomata transpiration.
b) By the use of lenticels in the stem which is termed as lenticular transpiration.
c) By the use of cuticle of the leaf surface which is known as cuticular transpiration.
Conditions influencing the rate of Transpiration:
The rate at which water vapor is lost through a plant based on a number of factors which comprise:
1) The size of stomata pores: If stomata open due to turgidity of the guard cells, then transpiration occurs while flaccidity of the cells causes the guard cells to close and foil transpiration from occurring.
2) Humidity: The higher the humidity of atmosphere the slower the rate of transpiration whereas the lesser the humidity the high the rate of transpiration.
3) Temperature: Rise in temperature gives increase to high rate of transpiration whereas low temperature gives mount to the low rate of transpiration.
4) Light: High light intensity outcome in high rate of photosynthesis and as a result leads to raise in temperature, thus giving mount to high rate of transpiration and vice-versa.
5) Wind: The high the rate or speed of wind the higher the rate of transpiration and vice-versa.
6) Soil water: The high the level of soil water the higher the rate of absorption and as a result the higher the rate of transpiration and vice-versa.
Significance or benefits of transpiration to Plants:
Transpiration has the given significance or benefits to plants:
a) It lets plants to absorb water and mineral salts from the soil.
b) It makes easy the movement of soil water.
c) The evaporation of water due to transpiration from the plants cools the plants.
d) It aids to eliminate surplus water from the plants.
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