2.1.2 Biological Molecules - Water

Question 1

What kind of bonds hold atoms in water molecules together

Answer 1

Covalent

Question 2

What kind of bond hold water molecules together?

Answer 2

Hydrogen bonds

Question 3

Structure of a water molecule

Answer 3

• Covalent molecule
• Oxygen is slightly negative due to the electrons spending more time to the oxygen atom
• Hydrogen is slightly positive
• Water is a polar molecule due to these differing regions of slight charge

Question 4

How des water form hydrogen bonds?

Answer 4

The slightly positive and negative regions of the molecules attract each other

Question 5

What are the characteristics of water?

Answer 5

• High boiling point
• Cohesive and adhesive
• Good solvent
• Good transport medium
• Coolant

Question 6

Why does water have a high boiling point and why is this a good thing?

Answer 6

• Takes a lot of energy to raise temperature as more energy put into breaking hydrogen bonds between molecules
• High boiling point means water is a stable environment for organisms

Question 7

What does cohesion mean in terms of water, why is this a good thing?

Answer 7

Cohesion is when water molecules are attracted to other water molecules - creates surface tension on water which animals can sit on
- surface tension - unlike a molecule in the bulk of the liquid experiences cohesion in all directions this only occurs inward for the top layer of the surface of the liquid

Question 8

What is adhesion in terms of water?

Answer 8

Water molecules attracted to other different molecules

Question 9

What do cohesion and adhesion in water result in?

Answer 9

Capillary action - the process by which water can rise up a narrow tube against the force of gravity

Question 10

What is a solvent and why does water make an affective solvent?

Answer 10

Solutes can be dissolved in a solvent. This means water acts as a medium for chemical reactions and helps transport dissolved compounds in and out of cells

Question 11

Water as a coolant

Answer 11

• Water helps buffer temperature changes during chemical reactions in prokaryotic and eukaryotic cells because of large amounts of energy that are required to overcome hydrogen bonding
• Important to keep constant temp in cellular environment as enzymes are often only active in small temperature ranges

Question 12

Water’s density?

Answer 12

Water is the densest at 4 degrees, meaning ice is less dense than liquid water. As water is cooled below 4 degrees the hydrogen bonds fix the positions of the polar molecules slightly further apart producing a giant, rigid but open structure with every oxygen at the centre of a tetrahedral arrangement.

Question 13

What makes water a good environment for organisms?

Answer 13

• Density - ice floats creating an insulating layer for water underneath, water underneath can move and travel organisms, ions and molecules.
• Transparency - plants can photosynthesise
  -High BP - stable, does not evaporate easily
• Surface tension - good for insects floating on water
• water is a coolant - cools organisms that sweat due to high specific latent heat of vaporisation
• water is polar - other polar molecules can dissolve and move in water