Test: Transportation In Plants - 1

• The xylem tracheary elements consist of cells known as tracheids and vessel members, both of which are typically narrow, hollow, and elongated.
• Tracheids are less specialized than the vessel members.
• Main function of xylem – upwards water transport.
• The xylem, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plants.
• The system transports water and soluble mineral nutrients from the roots throughout the plant.
   

• Xylem cells form long tubes that transport materials, and the mixture of water and nutrients that flows through the xylem cells is called xylem sap.
• These substances are transported through passive transport, so the process doesn’t require energy.
• The phenomenon that allows xylem sap to flow upwards against gravity is called capillary action. This occurs when surface tension makes liquid move upward.
• Water is also aided in moving up through the xylem by adhering to the xylem cells. However, it gets harder to work against gravity to transport materials as a plant grows taller, so xylem sets an upper limit on the growth of tall trees.

Osmosis is the concept that involves in the moment of solutions inside and outside of the cell. If the cell is placed in isotonic solution, the net change will be zero.

• Plants have two transport systems - xylem and phloem .
• Xylem transports water and minerals. Phloem transports sugars (sucrose) and amino acids dissolved in water.

• Guttation is the exudation of drops of xylem sap on the tips or edges of leaves of some vascular plants, such as grasses, and a number of fungi.
• Guttation is not to be confused with dew, which condenses from the atmosphere onto the plant surface.

Steroid hormones are made up of fats and they are not soluble in water. They are hydro phobic in nature. Hence they can easily pass through the plasma membrane by simple diffusion.

Raisins when soaked in water swell up due to imbibition. As a result of absorption or imbibition of water, the size of the raisins increases. The difference in mass between the swollen and dry raisins gives the amount of water imbibed by the raisins.

In spring, new buds are formed. These buds need more energy to grow than other parts of the plant. This energy comes from the sugar stored in the root or stem tissue to the buds by phloem. Thus, buds need the sugars in springs. 

• In angiosperms, water is conducted through vessels and tracheids.
• Xylem is a complex tissue composed of xylem vessels, xylem tracheids, xylem fibers, and xylem parenchyma. 
• Xylem vessels: Xylem vessels comprise a vertical chain of lengthened, dead cells known as vessel elements.
• Xylem vessels are long hollow chains of tough long-dead xylem cells.
• Xylem tissue is the water transporter cells of plants. It carries water around a plant. The presence of vessels is a characteristic feature of flowering plants.
• Xylem vessels work because of the transpiration stream. It is caused by the evaporation of water from the cells in the leaf to the atmosphere. The resulting surface tension causes pressure in the xylem that pulls the water from the roots and soil. This is called capillary action.

• Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel elements being the other. Tracheids, unlike vessel elements, do not have perforation plates.
• Tracheids provide most of the structural support in softwoods, where they are the major cell type. Because tracheids have a much higher surface to volume ratio compared to vessel elements, they serve to hold water against gravity (by adhesion) when transpiration is not occurring. This is likely one mechanism that helps plants prevent air embolisms.

Transpiration is physiological evaporation of water . It is same as evaporation of water from living system. More the temperature more will be evaporation. Hence, transpiration will be more at high temperature.

• Root pressure, in plants, force that helps to drive fluids upward into the water-conducting vessels (xylem). It is primarily generated by osmotic pressure in the cells of the roots and can be demonstrated by exudation of fluid when the stem is cut off just above ground. It is partially responsible for the rise of water in plants.
• Root pressure is the positive pressure that develops in the roots of the plants by active absorption of nutrients from the soil. The active absorption depends on the active accumulation of solute in xylem sap.
• Root pressure in maximum when transpiration is very low and absorption is high because transpiration is the output of water from a plant, and absorption is the input of water into a plant. If the output is low and input is high, the pressure will be at its greatest.

The opening and closing of the stomata is controlled by the guard cells. In light, guard cells take up water by osmosis and become turgid. Because their inner walls are rigid they are pulled apart, opening the pore. In darkness, water is lost and the inner walls move together closing the pore.

The loss of water in the form of vapour from living plants, particularly from the aerial parts, is known as transpiration. The process is in principle one of evaporation and diffusion. Loss of water vapour may occur from any part of the plant which is exposed to the air.

Plants: Plants do not move. They have a large proportion of dead tissues. Some plants are very tall. So, plants generally have relative slow transport system.

The phloem is arranged in long, continuous strands called vascular bundles that extend through the roots and stem and reach into the leaves as veins. vascular bundles also contain the xylem, the tissue that carries water and dissolved minerals from the roots to the shoots.