[Biology Class Notes] on Plant Water Relations Pdf for Exam

Water is essential to both animals and plants, so understanding plant water relations is important. Through the dissolution of substances, water plays an important role in life. The plants consume enormous amounts of water daily and lose a significant amount of it through transpiration. Different types of plants have varying water requirements.

Osmosis

Water moves across a semipermeable membrane, which is called osmosis. The water moves from a region of higher concentration towards one of lower concentration in order to reach equilibrium. This again involves two processes called endosmosis and exosmosis.

The endosmosis reaction occurs when water diffuses inwards through a semipermeable membrane when the surrounding medium is less concentrated whereas the exosmosis reaction takes place when water diffuses outwards through a semipermeable membrane when the surrounding medium is highly concentrated.

Water Potential

In addition to having kinetic energy, water molecules possess other properties. Water has kinetic energy or water potential in direct proportion to its concentration in a system. A molecule of water moves from a system with higher energy to a system with lower energy when two systems containing water are in contact. Pascale is the unit for expressing the potential energy of water. Water at standard temperature has a zero potential energy value.

A certain amount of solute is added to pure water, resulting in the concentration of water decreasing and the water potential declining. Solute potential describes how much the water potential decreases with added solutes. This is always negative and with a rise in dissolved solute concentration, the value of solute potential decreases. Pure water has a higher potential value when it is under more pressure than atmospheric pressure. In plants, a turgid cell is one whose walls are pressured by water entering the cell by diffusion. As a result, pressure increases within the cell. In general, this is a positive value. Solute potential and pressure potential are the two components of water potential.

Imbibition

In the imbibition process, the seed, semi-permeable, or permeable substances like wood or colloid absorb water from the soil. E.g., if you have hay or wooden pieces in the field in which you have grown a farm, you will have to use more water on a regular basis because the dry grass and wooden pieces imbibe some water. Apart from the fact that these things are permeable, their surface area, their support of capillarity, and surface tension also contribute to the imbibition process.

Plasmolysis

The process of plasmolysis involves the expulsion of water from a cell and the shrinkage of the cell membrane. This occurs when the cell is exposed to an overly tonic solution (which contains more solutes). Cytoplasmic water is lost, followed by vacuole water. An isotonic solution does not allow water to move into the cell, while a hypotonic solution will allow water to move into the cell and exert pressure on its walls, which is known as the turgor pressure.

Water and Osmotic Potential

Potential energy is the amount of energy contained in water molecules. Considering the volume and purity of water as well as the energy contained in each molecule, one can calculate the energy contained in water. Using the purest form of water with a specific volume at a given temperature as a standard can result in better predicting other variables. 

As a result of several factors including gravity, osmosis, mechanical pressure, capillary action, etc., water has the potential to flow or move from one place to another. 

Through the action of osmosis, water flows through a semipermeable membrane. Water moves from the high concentration region to the low concentration region in this process. We can learn about plants’ relationship with water by studying these different types of potentials.

The Water Intake Process

Plants require water as one of their most basic requirements. Approximately 90% of the body of a plant is water. With the help of water, green plants perform processes such as photosynthesis; they absorb carbon dioxide from the atmosphere and give out oxygen as a result. 

Additionally, water provides nutrients like nitrogen through nitrate, potassium, phosphorus through phosphate, chlorine, magnesium, zinc, calcium, molybdenum, iron, sulfur, copper, and boron through diffusion through the soil. 

In addition to keeping cell walls turgid, water also helps keep them flexible. Turgor pressure helps to increase cell size; cell division aids in the growth of plants.

Therefore, water is essential for the enlargement of cells. Toxins are transported from the leaves by water. Stomata produce low pressure in the vacated space, allowing more water to fill the void; this allows nutrients to move freely. The transpiration process is another useful use of water in plants that prevents the plant from drying out. Furthermore, water is an essential ingredient in nitrogen fixation.