MECHANISM OF TRANSPORTATION IN PLANTS
Plants generally y require sufficient quantities of several minerals and other substances which are transported in them. Materials transported in plants include manufactured food, carbon dioxide, water, oxygen, nitrogenous waste products, latex, amino acids, glucose, Auxins and mineral salts. The medium of transport in plants is the latex or cell sap.
In aquatic, unicellular and simple multicellular plants, gases enter and leave the cells by simple diffusion. Water enters the cells of these plants by osmosis while manufactured food and waste products are transported by diffusion. In multicellular plants like flowering plants, the gases are mainly absorbed through the stomata in the leaves and lenticels in the stem while mineral salts and water are absorbed through the root system. Inside the plants, gases move by diffusion. They dissolve in water of the moist cells before entering the cells. Water, mineral salts and soluble food are transported in the vascular tissues of the plant. The vascular tissues of plants are made up of a network of long tubes called vascular bundles. A vascular bundle consist mainly of the xylem and the phloem tissues. But in the roots and stems of dicotyledonous plants, a layer called cambium exist between the xylem and the phloem tissues. Hence, the vascular bundles are found in the roots, stems and leaves of flowering plants.
FUNCTIONS OF THE CAMBIUM TISSUES
They are capable of dividing and multiplying thereby enabling the plants to produce secondary xylem and phloem. This then results in the growth in width or girth of the stems called secondary thickening.
2. THE XYLEM TISSUES: the xylem tissues consist mainly of dead cells with lignified cell walls.
FUNCTIONS OF THE XYLEM TISSUES
The xylem tissues transport water and dissolved mineral salts from the roots to other parts of the plants read here for osmosis and diffusion. It also gives support and rigidity to plants.
3. THE PHLOEM TISSUES: the phloem tissues consist of thin-walled living cells with dense cytoplasm which have perforated cross wall.
FUNCTIONS OF THE PHLOEM TISSUES
The phloem tissues transport manufactured food from the leaves mainly to other parts of the plant either for use or for storage.
PROCESS WHICH AID TRANSPORTATION IN PLANTS
Translocation is the process by which manufactured food substances are transported from where they are manufactured to tissues where they are needed or stored. Translocation normally begins from the leaves to other parts of the plant. Phloem is the tissue through which these manufactured food substances are translocated.
Substances or materials commonly translocated in plants include sugar, glucose or carbohydrates, oil, resins, proteins or amino acids, alkaloids and hormones.
The functions of these translocated substances include:
(i) Proteins or amino acids which are used for building up new tissues.
(ii) Sugar, glucose or carbohydrates which provides energy for synthetic process.
(iii) Oil provides energy.
(iv) Alkaloids, resins and steroids are protective in function and prevent herbivores from eating the plants as they are all waste products in plants
Aim: to show that translocation takes place through the phloem tissue (Ringing experiment)
Materials required: two plants marked X and Y, knife.
Procedure: the knife is used to remove the bark and phloem round one of the trees marked X while only the bark of the other tree marked Y is removed. (This tree marked Y serves as the control experiment). The plants are all left for about 2—5 weeks.
Observation: after the expiration of these weeks, it will be observed that swelling begins to appear gradually in the bark along the ring in plant X but no swelling in that of Y. The swelling in X is due to the accumulation of food substances which have passed down through the phloem from the leaves. After a long period of time, tree X will finally die because the root cannot obtain food manufactured in the leaves.
Conclusion: phloem is responsible for the translocation of manufactured food from the leaves to other parts of the plant.
Differences between transpiration and sweating
1. Occurs in plants through stomata or lenticels
2. Transpiration involves only loss of water
3. Water is lost in the form of vapour
4. Occurs during the day
1. Occurs in mammals/skin/through sweat pores
2. Loss of water, salts and nitrogenous
3. Water loss is liquid in form. see water cycle here
4. Occurs both day and night
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