Water

Question 1

What are the two structures of water?

Answer 1

Water is polar and water is hydrogen bonded.

Question 2

Explain water being polar

Answer 2

1. Each hydrogen atom is slightly positive as it shares electrons in a covalent bond with oxygen
2. The unshared negative electrons in oxygen give it a slightly negative charge
3. This makes a polar molecule as the charges are unequal

Question 3

Explain water being hydrogen bonded

Answer 3

1. Bonds between slightly positively charged hydrogen atoms and slightly negatively charged oxygen atoms
2. Occur as the slightly negatively charged oxygen atoms of water is attracted to the slightly positively charged hydrogen atoms of other water molecules
3. Hydrogen bonds are weak on its own and strong as a collective
4. Represented by dotted lines

Question 4

What are the 5 properties of water?

Answer 4

1. Important metabolite
2. Good solvent
3. High latent heat of vaporisation
4. High specific heat capacity (buffer)
5. Very cohesive

Question 5

Explain why water is an important metabolite?

Answer 5

1. Involved in many metabolic reactions which require hydrolysis and condensation reactions

Question 6

What is a condensation reaction?

Answer 6

A reaction that releases a molecule of water as a new bond is formed

Question 7

What is an example of a condensation reaction?

Answer 7

Amino acids joined together make polypeptides which are proteins

Question 8

What is a hydrolysis reaction?

Answer 8

A reaction that requires a molecule of water to break a bond

Question 9

What is released through a hydrolysis reaction?

Answer 9

Energy from ATP is released through a hydrolysis reaction

Question 10

Explain why water is a good solvent?

Answer 10

1. Lots of important substances in biological reactions are ionic (eg. Salt)
2. As water is polar, the slightly positively charged end of a water molecule is attracted to a negatively charged ion and the slightly negatively charged end of a water molecule is attracted to positively charged ion
3. So ions will be completely surrounded by water molecules and dissolve

Question 11

What is an example of water being a good solvent?

Answer 11

1.The transport of inorganic ions around the body in blood plasma
2. Dissolves monosaccharides and inorganic ions as water is dipolar

Question 12

Explain why water has a high latent heat of vaporisation?

Answer 12

1. Water vaporises when hydrogen bonds holding water molecules together are broken
2. This allows water molecules on the surface of water to escape into the air as gas
3. Takes a lot of heat energy to break hydrogen bonds between water molecules so water has a high latent heat of vaporisation
4. When water evaporates, it carries away the heat energy from the surface so cools and lowers the temperature

Question 13

What is an example of latent heat vaporisation?

Answer 13

Organisms use water loss through evaporation to cool down without losing excessive amounts of water

Question 14

Explain why water has a high specific heat capacity (can buffer temperature)?

Answer 14

1. Hydrogen bonds give water a high specific heat capacity (energy needed to raise the temperature of 1g of a substance by 1°c)
2. Large amount of energy needs to be lost before water freezes (large latent heat of fusion)
3. When water is heated, lots of energy to break hydrogen bonds are needed
4. Less heat energy is available to actually increase temperature of water

Question 15

What is specific heat capacity?

Answer 15

The energy needed to raise the temperature of 1g of a substance by 1°c

Question 16

What is latent heat of fusion?

Answer 16

Amount of energy needed to melt or freeze a substance at its melting point

Question 17

Why is high specific heat capacity in water useful?

Answer 17

1. Useful for living organisms in water as it doesn’t experience rapid temperature changes so the environment is stable for them to live in
2. Water inside organisms remains fairly stable temperature which helps maintain a constant internal body temperature for efficient enzyme activity

Question 18

Explain why water is cohesive

Answer 18

1. The attraction between the molecules of the same type
2. Strong cohesion helps water flow in columns making it great for transporting substances
3. Strong cohesion means water has a high surface tension when there is contact with air- when water molecules are more attracted to each other than the air

Question 19

Why is cohesive water molecules useful?

Answer 19

1. Transports water and minerals in columns in a xylem
2. Water tension is why sweat forms droplets which evaporates from skin to cool down
3. Water tension is why pond skaters can walk on the surface of a pond

Question 20

As water freezes it…

Answer 20

… Expands so frozen water is less dense than liquid so it floats

Question 21

Why does the water underneath the ice layer not freeze?

Answer 21

The frozen ice layer insulates the water below