2.1.2 - Biologial Molecules (set A - Water)

Question 1

Explain what a polar molecule is and why it becomes polar?

Answer 1

When atoms form a covalent bond the electrons are not shared equally, therefore the electrons will spend more time closer to one of the atoms which leads to the atom becoming slightly negative compared to the other atom which becomes slightly positive

Question 2

Explain why water is a polar molecule?

Answer 2

Oxygen and hydrogen do not share electrons equally in a covalent bond - oxygen has a greater share of the electrons which leads to it being more negative, while hydrogen is slightly positive

Question 3

Explain how hydrogen bonds are formed in water?

Answer 3

Positive and negative regions of the molecule attract each other and form relatively weak hydrogen bonds which break and reform between the constantly moving water molecules

Question 4

Why are hydrogen bonds important for water?

Answer 4

Despite them being weak interactions they occur in high number - gives water its unique characteristics for example high specific heat capacity, very cohesive and less dense when solid

Question 5

Explain why water has a high specific heat capacity?

Answer 5

The hydrogen bonds in the water can absorb lots of energy - which means there is less energy left to heat water up

Question 6

Explain the importance of water having a high specific heat capacity?

Answer 6

Means water doesn’t experience rapid temperature change - allows water to be a good habitat as it is more stable then land

Question 7

Explain why water has a high latent heat of evaporation?

Answer 7

It takes a lot of energy to break the hydrogen bonds between water molecules - means a lot of energy is used up when water evaporates

Question 8

Explain the importance of water having a high latent heat of evaporation?

Answer 8

Mammals able to regulate temperatures by sweating - when sweat evaporates it cools the surface of the skin

Question 9

Explain why water is very cohesive?

Answer 9

Cohesion is the attraction between molecules of the same type - water molecules stick together because they are polar

Question 10

Explain why water being cohesive is important?

Answer 10

• helps water flow, makes it useful for transporting substances
• helps water to be transported up plant stems in transpiration stream

Question 11

Explain why water is a good solvent?

Answer 11

Lots of important substances in reactions are ionic (made from one positively charged atom and one negatively charged atom) - water is polar so slightly positive end is attracted to negative ion and the same with the slightly negative end being attracted to the positive ion
- substance is completely surrounded by water (dissolved)

Question 12

Explain the importance of water being a good solvent?

Answer 12

Water is called a ‘universal solvent’ as it is capable of dissolving more substances than any other liquid - means ions will get totally surrounded by water molecules (dissolved)

Question 13

explain why water is less dense when solid?

Answer 13

In ice (solid) the water molecules are held further apart - because each water molecule forms 4 hydrogen bonds which makes a lattice shape and prevents the water molecules from moving around and becoming ‘tightly knit’, makes it less dense

Question 14

Explain the importance of water being less dense when solid?

Answer 14

In cold temperatures, ice forms an insulating layer on top of water which prevents the water below from freezing - essential for the survival of aquatic life

Question 15

Why is water an important solvent for organisms?

Answer 15

Polar universal solvent dissolves and transports charged particles involved in intra and extra cellular respiration

Question 16

State 5 biologically important properties of water?

Answer 16

• cohesion between molecules
• high surface tension
• solvent
• high latent heat of vaporisation
• high specific heat capacity