Absorption of water

Absorption of water

Water is highly essential for plants for various metabolic activities. Land plants get their water supply from soil which serves as the source of water and minerals to them. The way in which water from soil enters roots, particularly to the root xylem, is called "mechanism of water absorption". Both Active and Passive absorption have been proposed for mechanism of water absorption.

Contents

Active Absorption

It is absorption of water by roots with the help of metabolic energy generated by the root respiration.The force for water absorption originates from the cells of root due to root respiration.As the root cells actively take part in the process so it is called Active absorption. According to Renner, active absorption takes place in low transpiring and well-watered plants and 4% of total water absorption is carried out in this process. The active absorption is carried out by two theories which are, Active osmotic water absorption and Active non-osmotic water absorption.

Active osmotic water absorption

This theory was given by Atkins (1916) and Priestley (1921). According to this theory, the root cells behave as ideal osmotic system through which water moves up from soil solution to root xylem along an increasing gradient of D.P.D. (suction pressure which is the real force for water absorption). If solute concentration is high and water potential is low in the root cells, water can enter from soil to root cells through endosmosis. Mineral nutrients are absorbed actively by the root cells due to utilisation of ATP. As a result, the concentration of ions (osmotica) in the xylem vessels is more in comparison to the soil water. A concentration gradient is established between the root and the soil water.Hence, the solute potential of xylem water is more in comparison to that of soil and correspondingly water potential is low than the soil water.Otherwise stated, water potential is comparatively positive in the soil water. This gradient of water potential causes endosmosis. The endosmosis of water continues till the water potential both in the root and soil becomes equal. It is the absorption of minerals that utilise metabolic energy, but not water absorption. Hence, absorption of water is indirectly an active process.

Active non-osmotic water absorption

This theory was given by Thimann (1951) and Kramer (1959). According to the theory, sometimes water is absorbed against concentration gradient.This requires expenditure of metabolic energy released from respiration of root cells.There is no direct evidence, but some scientists suggest involvement of energy from respiration.In conclusion it is said that, the evidences supporting active absorption of water are themselves poor.

Passive absorption

This mechanism is carried out without utilisation of metabolic energy.Here only the root act as an organ of absorption or passage. Hence, sometimes it is called water absorption 'through roots', rather 'by' roots. It occurs in rapidly transpiring plants during daytime, because of opening of stomata and the atmospheric conditions. The force for absorption of water is created at the leaf end i.i. the transpiration pull. The main cause behind this transpiration pull, water is lifted up in the plant axis like a bucket of water is lifted by a person from an well. Transpiration pull is responsible for dragging water at the leaf end, the pull or force is transmitted down to the root through water column in the xylem elements. The continuity of water column remains intact due to the cohesion between the molecules and it act as a rope. Roots simply act as a passive organ of absorption. As transpiration proceeds, simultaneously water absorption also takes place to compensate the water loss from leaf end. Most volume of water entering plants is by means of passive absorption.

Conclusion

The water thus absorbed by the plants as described and most of the absorption is by passive absorption.

See also

Reference

  1. http://www.tutorvista.com/content/biology/biology-iv/plant-water-relations/absorption-water-by-plants.php
  2. http://www.springerlink.com/content/qw62632354v4nm77/
  3. http://www.ictinternational.com.au/appnotes/ICT101.htm
  4. http://www.jstor.org/stable/4353618
  5. http://www.wiziq.com/tutorial/70692-Biology-XI-11-Transport-in-plants-4-Mechanism-of-Water-Absorption

Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать курсовую

Look at other dictionaries:

  • absorption — noun 1) the absorption of water Syn: soaking up, sucking up; technical osmosis 2) by 1543, Scottish fears of absorption by England were allayed Syn: incorporation, assimilation, integration, appropriation, inclusion 3) her total absorption i …   Thesaurus of popular words

  • absorption — noun 1) the absorption of water Syn: soaking up, sucking up 2) her total absorption in the music Syn: involvement, immersion, raptness, preoccupation, captivation, fascination, enthralment …   Synonyms and antonyms dictionary

  • Water absorption — is a phenomenon in the transmission of electromagnetic radiation through a medium containing water molecules. Water molecules are excited by radiation at certain wavelengths and tend to selectively absorb portions of the spectrum while allowing… …   Wikipedia

  • Water heating — is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating. In industry, both hot water and water heated to steam have… …   Wikipedia

  • Water hammer — (or, more generally, fluid hammer) is a pressure surge or wave resulting when a fluid in motion is forced to stop or change direction suddenly (Momentum Change). Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline …   Wikipedia

  • Absorption refrigerator — The absorption refrigerator is a refrigerator that utilizes a heat source (e.g., solar, kerosene fueled flame) to provide the energy needed to drive the cooling system rather than being dependent on electricity to run a compressor. These… …   Wikipedia

  • Absorption (electromagnetic radiation) — An overview of electromagnetic radiation absorption. This example discusses the general principle using visible light as specific example. A white beam source emitting light of multiple wavelengths is focused on a sample (the complementary color… …   Wikipedia

  • Absorption spectroscopy — An overview of electromagnetic radiation absorption. This example discusses the general principle using visible light as a specific example. A white beam source – emitting light of multiple wavelengths – is focused on a sample (the complementary… …   Wikipedia

  • Water (molecule) — Chembox new Name = Water (H2O) ImageFileL1 = Water 2D labelled.png ImageSizeL1 = 120px ImageNameL1 = The water molecule has this basic geometric structure ImageFileR1 = Water molecule 3D.svg ImageSizeR1 = 100px ImageNameR1 = Space filling model… …   Wikipedia

  • Absorption (pharmacokinetics) — In pharmacology (and more specifically pharmacokinetics), absorption is the movement of a drug into the bloodstream. Absorption involves several phases. First, the drug needs to be introduced via some route of administration (oral, via the skin,… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”