Water Properties

What are the special water properties the xylem tissue uses?


Water is a unique compound and, as such, has some unique properties. If you fill a glass to the brim with water, you may notice how the water is actually above the edge of the glass. How does this happen? Why doesn’t the water overflow? It will eventually, but water is very attracted both to itself and to other substances. This helps water “hold on” to the glass (adhesion) and to itself (cohesion) so it does not overflow as quickly as you may think it will.

A12.2 Water sits above the edge of the glass.


© dnak, via Wikimedia Commons
A12.3 Water droplets on a leaf
Cohesion is the property of water that allows it to be attracted to itself. Image A12.3 shows water molecules that have attached to each other to form small water droplets on the surface of a leaf. This is a great example of cohesion.

Water molecules are slightly polar in nature. This means one end of the water molecule has a very slight positive charge while the other end has a very slight negative charge. Remember, opposites attract, so the positive end of one water molecule is attracted to the negative end of another, allowing the molecules to cling to each other. If we look back at the glass, this attraction can only hold for so long. Eventually the weight of all the water particles clinging together will become too much and the water will overflow from the glass.


© Jü, via Wikimedia Commons
A12.4 Oxygen is slightly positive and the hydrogens are slightly negative

  Did You Know?


 A12.5 Gerridae insect sitting on the surface of a lake

A variety of bugs use the property of cohesion to sit on the surface of the water without sinking. They have adapted so they do not break the bonds used in cohesion when they sit on the surface.


©Horla Varlan via flickr
A12.5 Water along the edges of the glasses is higher than in the middle
Adhesion is the property of water that allows it to be attracted to other substances. This property is also due to water’s polar nature. The positive and negative ends of the water molecule are attracted to the slightly positive and negative ends in other substances. If you look closely at water in a glass, you will see the water along the glass itself is higher than the water in the middle of the glass. This is because the water is attracted to the glass, so more molecules are found along the glass wall. This causes the water to sit higher as there are more water molecules in that location. Water can actually “climb” a short distance by using this property. The water molecules that are higher up on the glass wall pull other water molecules up behind it due to the cohesion property.


  Read This

Please read the section called “Cohesion and Adhesion” on page 316 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how the properties of cohesion and adhesion work. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.

  1. If you were to place droplets of water on a penny, which property keeps the droplets from falling off the penny? How does it work?

Cohesion helps to keep the water droplets from falling off the penny. Cohesion works by keeping the water molecules attracted to each other so they hold on to each other rather than falling off the penny.

You could also suggest adhesion helps to keep the water droplets from falling off the penny. Adhesion keeps the water attracted to the surface of the penny so the droplets do not slide off the penny.
  1. How does water “climb” up the side of a glass?
Water uses the properties of both adhesion and cohesion to move up the side of the glass. The water molecules are attracted to the side of the glass, so they all try to align themselves along that surface. This pushes the molecules up the side of the glass. The property of cohesion keeps the water molecules attached to each other, so as the molecules are pushed up the side of the glass, they pull other molecules with them.