Transportation in plants refers to the movement of water, nutrients, and other essential substances throughout the plant’s various parts. Plants have specialized structures and tissues that facilitate this transportation process. The two main types of transportation in plants are:
- Water Transport: Water is crucial for plants, as it is involved in various physiological processes such as photosynthesis and nutrient uptake. The movement of water in plants occurs through two main processes:
a. Transpiration: Transpiration is the loss of water vapor from the aerial parts of the plant, primarily through small pores called stomata on the leaves. As water evaporates from the leaf surfaces, it creates a negative pressure (tension) that pulls water upward from the roots through the xylem vessels.
b. Capillary Action: Capillary action, also known as capillarity, is the ability of water to move upward through narrow tubes due to the combined forces of adhesion (water molecules sticking to the xylem walls) and cohesion (water molecules sticking to each other). This process aids in the movement of water against gravity in the xylem vessels.
The xylem is a specialized tissue responsible for transporting water and dissolved minerals from the roots to other parts of the plant.
- Nutrient Transport: Besides water, plants also need various nutrients (such as nitrogen, phosphorus, potassium, etc.) to support growth and metabolism. These nutrients are obtained from the soil through the roots and transported throughout the plant via the phloem.
The phloem is another specialized tissue responsible for translocating sugars, amino acids, hormones, and other organic compounds produced in the leaves during photosynthesis to the rest of the plant. This process is called translocation and occurs in both upward (from leaves to other parts) and downward (from leaves to roots) directions.
Together, the xylem and phloem form the vascular system of the plant, facilitating the transport of water, nutrients, and other substances essential for the plant’s survival and growth. This transportation system allows plants to maintain their structure, carry out metabolic processes, and respond to environmental stimuli.
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.
perennial crop, cocoa tree
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.
mechanism of transportation in plants
Inside the plants, gases move by diffusion. They dissolve in the 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.
- THE CAMBIUM TISSUES: they are made up of narrow living cells with thin walls and dense cytoplasm.
FUNCTIONS OF THE CAMBIUM TISSUE DURING TRANSPORTATION IN PLANTS
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 walls which are means of transportation in plants.
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
Transportation of materials in the plant is aided by the following processes:
(i) Translocation.
(ii) Transpiration.
(iii) Absorption of water and mineral salts.
(iv) Transport of water in the xylem tissue.
Translocation
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 provides energy for the 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
Experiment to show transportation 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
Transpiration
- Occurs in plants through stomata or lenticels
- Transpiration involves only loss of water
- Water is lost in the form of vapour
- Occurs during the day
Sweating - Occurs in mammals/skin/through sweat pores
- Loss of water, salts and nitrogenous
- Water loss is liquid in form. see water cycle here
- Occurs both day and night
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