Water

Question 1

Why is water of great biological importance?

Answer 1

It is the medium in which all metabolic reactions take place in cells.

Question 2

Water is composed of which atoms?

Answer 2

Hydrogen and oxygen

Question 3

In water, how are the atoms bonded?

Answer 3

Covalent bonding by sharing electrons

Question 4

Is the sharing of electrons even or uneven between oxygen and hydrogen atoms?

Answer 4

Uneven, although water as a whole is electrically neutral

Question 5

Does oxygen or hydrogen attract electrons more strongly?

Answer 5

Oxygen

Question 6

What does oxygen attracting electrons more strong than hydrogen atoms result in?

Answer 6

A weak negatively charged region on the oxygen atom and a weak positively charged region on the hydrogen atoms, this also results in the asymmetrical shape

Question 7

What is the separation of charge due to the electrons in the covalent bonds being unevenly shared called?

Answer 7

A dipole

Question 8

What is the name of a molecule which has one end that is negatively charged and one end that is positively charged?

Answer 8

A polar molecule

Question 9

Is water a polar molecule?

Answer 9

Yes

Question 10

What bonds form between water molecules?

Answer 10

Hydrogen bonds

Question 11

How does the polarity of water affect how hydrogen bonds form?

Answer 11

Hydrogen bonds form between the positive and negatively charged regions of adjacent water molecules

Question 12

Are hydrogen bonds weak or strong when there are few?

Answer 12

Weak

Question 13

What are hydrogen bonds constantly doing because they are weak?

Answer 13

Breaking and reforming

Question 14

What properties do water molecules have which hydrogen bonds contribute to?

Answer 14

• an excellent solvent
• a relatively high specific heat capacity
• a relatively high specific latent heat of vapourisation
• water is less dense when a solid
• water has high surface tension and cohesion
• it acts as a reagent

Question 15

As water is a polar molecule, many ___ and ____ will dissolve in it?

Answer 15

Ions and covalently bonded polar substances (eg glucose)

Question 16

What does the dissolving of ions and covalently bonded polar substances allow for within cells?

Answer 16

Chemical reactions to occur within human cells as the dissolved solutes are more chemically reactive when they are free to move about

Question 17

What does water being a good solvent allow for in terms of metabolites?

Answer 17

They can be transported efficiently (except non polar molecules which are hydrophobic)

Question 18

Why does water have a high specific heat capacity?

Answer 18

Due to the many hydrogen bonds present in water. It takes a lot of thermal energy to break these bonds and a lot of energy to build them, thus the temperature of water does not fluctuate greatly

Question 19

What is the advantage of water having a high SHC on living organisms?

Answer 19

• provides suitable habitats
• able to maintain a constant temperature as water can absorb a lot of heat without big temperature fluctuations. This is vital in maintaining temperatures that are optimal for enzyme activity.

Question 20

What is water in blood plasma vital for?

Answer 20

Transferring heat around the body, helping to maintain a fairly constant temperature

Question 21

Why does water have a high latent heat of vapourisation?

Answer 21

In order to change state (liquid to gas) a large amount of thermal energy must be absorbed by water to break the hydrogen bonds and evaporate.

Question 22

Why is a high LHoV an advantage for living organisms?

Answer 22

Only a little water is required to evaporate for the organism to lose a great amount of heat.
This provides a cooling effect for living organisms, for example the transpiration from leaves or evaporation of water in sweat on the skin.

Question 23

What allows for strong cohesion between water molecules?

Answer 23

Hydrogen bonds between water molecules

Question 24

What does strong cohesions allow for in plants and animals?

Answer 24

Allows columns of water to move through the xylem of plants and through blood vessels in animals

Question 25

What is adhesion with water?

Answer 25

Water is able to hydrogen bond to other molecules such as cellulose, this is adhesion. This also enables water to move up the xylem due to transpiration.