What are the properties of cohesion and adhesion and why are they important for living things?

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Adhesion and cohesion are water properties that affect living and non-living things on earth through water molecules.

Cohesion: Water is attracted to water
Adhesion: Water is attracted to other things

Water is very cohesive in that it "sticks" to itself. Cohesion is what allows a water droplet to form, for example. When water molecules surround one another, they settle toward a low energy state. For water molecules, they are most stable when they form a ball surrounded by other water molecules. As the molecules "pull" together, the surface tension acts like a casing for the group of water molecules. If it weren't for cohesion, water molecules would behave very differently and we would not expect to see water droplets.

Although water likes to stick to itself, it sometimes prefers to adhere to other things. The adhesive property of water allows water allows water molecules to stick to non-water molecules, which results in some common water behaviors. For example, if you fill a glass tube with water, a meniscus will form. The meniscus is the result of water molecules being more attracted to the polarized glass rather than to their neighboring water molecules.

Cohesive and adhesive properties of water impact living things in many ways:

  • Water droplets form on plants, allowing the plants to soak up the water over time rather than all at once.
  • Water striders (insects) glide across water surfaces owing to the cohesive property of water.
  • Adhesion allows for water to move against gravity through plant cells.
  • Capillary action owing to adhesion allows blood to move through tiny vessels in some animal bodies.
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