PLANT PHYSIOLOGY-3 BY NIKHIL PURANIK
ABOUT MIE MY NAME IS NIKHIL PURANIK PURSUING B.E IN MECHANICAL ENGINEERING FROM RNSIT LIVE IN BENGALURU PROFILE :https://unacademy.com/user/nikhilrpuranik
TOPICS COVERED WATER MOVEMENT UP A PLANT TRANSPIRATION PULL TRANSPIRATION TRANSPIRATION AND PHOTOSYNTHESIS A COMPROMISE UPTAKE OF MINERAL IONS TRANSLOCATION OF MINERAL IONS PHLOEM TRANSPORT PRESSURE FLOW OR MASS FLOW HYPOTHESIS
WATER MOVEMENT UP A PLANT As various ions from the soil are actively transported into the vascular tissues of the roots, water follows (its potential gradient) and increases the pressure inside the xylem. This positive pressure is called root pressure, and can be responsible for pushing up water to small heights in the stem. Effects of root pressure is also observable at night and early morning when evaporation is low, and excess water collects in the form of droplets around special openings of veins near the tip of grass blades, and leaves of many herbaceous parts. Such water loss in its liquid phase is known as guttation.
TRANSPIRATION PULL Root pressure does not account for the majority of water transport; most plants meet their need by transpiratory pull. Despite the absence of a heart or a circulatory system in plants, the flow of water upward through the xylem in plants can achieve fairly high rates, up to 15 metres per hour -water is mainly pulled' through the plant, and that the driving force or this process is transpiration Transpiration is essentially evaporation of water from plant leaves] This is referred to as the cohesion-tension-transpiration pull model of water transport.
Palisade Xylem Phloem- TRANSPIRATION 0 Stomatal Guard Cell Diffuston into surrounding atr pore Transpiration is the evaporative loss of water by plants. It occurs mainly through the stomata in the leaves. Besides the loss of water vapour in transpiration, exchange of oxygen and carbon dioxide in the leaf also occurs through pores called stomata. Normally stomata are open in the day time and close during the night. The immediate cause of the opening or closing of the stomata is a change in the turgidity of the guard cells.
TRANSPIRATION AND PHOTOSYNTHESIS A COMPROMISE Transpiration has more than one purpose; it creates transpiration pull for absorption and transport of plants supplies water for photosynthesis transports minerals from the soil to all parts of the plant cools leaf surfaces, sometimes 10 to 15 degrees, by evaporative cooling maintains the shape and structure of the plants by keeping cells turgid
UPTAKE OF MINERAL IONS Unlike water, all minerals cannot be passively absorbed by the roots. Two factors account for this: (i) minerals are present in the soil as charged particles (ions) which cannot move across cell membranes and (ii) the concentration of minerals in the soil is usually lower than the concentration of minerals in the root. Therefore, most minerals must enter the root by active absorption into the cytoplasm of epidermal cells. This needs energy in the form of ATP.
TRANSLOCATION OF MINERAL IONS After the ions have reached xylem their further transport up the stem to all parts of the plant is through the transpiration stream The chief sinks for the mineral elements are the growing regions of the plant, such as the apical and lateral meristems, young leaves, developing flowers, fruits and seeds, and the storage organs. Xylem transports only inorganic nutrients while phloem transports only organic materials
PHLOEM TRANSPORT: FLOW FROM SOURCE TO SINK Food, primarily sucrose, is transported by the vascular tissue phloenm from a source to a sink. Usually the source is understood to be that part of the plant which synthesises the food, i.e., the leaf, and sink, the part that needs or stores the food. The direction of movement in the phloem can be upwards or downwards, i.e., bi-directional The direction of movement in the xylem is always unidirectional, i.e. upwards