Practical assesment about biology: To determine the water potential of potato tuber cells

Essay by Nirmala February 2004

download word file, 14 pages 3.9

Downloaded 125 times



To determine the water potential of potato tuber cells.

Background knowledge

Osmosis is defined as the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. Osmosis is considered in terms of water potential and solute potential.

Water potential is a measure of the kinetic energy of water molecules. Here, water molecules are constantly moving in a random fashion. Some of them collides with cell membrane, cell wall, creating a pressure on it known as water potential. The higher their kinetic energy the more they move and hits the membrane, therefore higher the water potential. Water potential also depends on the number of molecules of water present. Solute restricts the movement of water, so a strong sugar solution with lots of solute particles will lower the kinetic energy and hence water potential. In osmosis water moves down a water potential gradient until the equilibrium is reached between two regions.

The amount of solute molecule that lowers the water potential in a solution is called solute potential. The highest water potential is found in pure water, where no solutes restricts the movement of water. The water potential of pure water is given a value of 0 kilopascals. Adding solutes lowers the water potential to a negative value. The more solute particles added, the lower the water potential becomes which means that the more negative value.

For example,

Pure water = 0 Kpa (highest water potential)

Dilute sugar solution = -100Kpa

Concentrated sugar solution = -350Kpa (lower water potential)

Therefore, the nearer the value to 0 Kpa, the higher the water potential.

Potato tubers are made of plant cells. Plant cells always have a strong cell wall surrounding them. They also contain partially permeable cell membrane. They both have...