water

Question 1

what are polar molecules?

Answer 1

molecules that have regions of negativity and regions of positivity

Question 2

what group in water molecules, makes them polar?

Answer 2

the hydroxyl group

Question 3

how strong are hydrogen bonds?

Answer 3

they’re weak interactions which break and reform between constantly moving water molecules

Question 4

even though hydrogen bonds are weak, what makes them strong sometimes?

Answer 4

the fact that they occur in high numbers

Question 5

what gives water its unique characteristics?

Answer 5

hydrogen bonding

Question 6

what type of intramolecular bonds are in water molecules?

Answer 6

polar covalent bonds

Question 7

what is water’s boiling point like?

Answer 7

it’s unusually high

Question 8

why is water’s boiling point the way it is and why is it liquid at room temperature, even if its a lighter molecule than oxygen?

Answer 8

• because of the hydrogen bonding between water molecules.

- lots of energy is needed to increase water temperature and cause it to evaporate

Question 9

what happens to water when it turns into ice in terms of weight?

Answer 9

it becomes less dense

Question 10

why does water have its unusual property as ice?

Answer 10

• because as water is cooled, the hydrogen bonds fix the positions of the water molecules further apart than in the liquid state
• this produces a giant, rigid but open structure, with every oxygen atom at the centre of a tetrahedral arrangement of hydrogen atoms, resulting in a solid that’s less dense than liquid water.
• so, ice floats

Question 11

what properties of water allow water to move as one mass? give an example of where this happens?

Answer 11

• cohesion and adhesion

- plants are able to draw water up their roots

Question 12

what are water molecules more strongly cohesive to? what does this result in?

Answer 12

• to each other rather than the air

- results in water having a ‘skin’ of surface tension

Question 13

since water is a polar molecule, what can it act as?

Answer 13

a solvent in which many solutes in an organism can be dissolved

Question 14

give an example in cells, where water is vital as a solvent?

Answer 14

• the cytosol of bacterial prokaryotes and eukaryotes is mainly water.
• many solutes are also polar
• water acts as a medium for chemical reactions and also helps transport dissolved compounds into and out of cells

Question 15

what does water’s adhesion and cohesion lead to? what does this make it?

Answer 15

• capillary action

- an efficient transport system in living things

Question 16

what is water’s role in living things in terms of temperature?

Answer 16

• water acts as a coolant helping to buffer temperature changes during chemical reactions in cells, because of the large amounts of energy needed to overcome hydrogen bonding

Question 17

why is it important to maintain constant temperatures in cellular environments?

Answer 17

because enzymes are only active in a narrow temperature range

Question 18

how is water important for fish as a habitat?

Answer 18

• water is a stable environment, it doesnt change temperature or vaporise easily = constant environment

Question 19

how does ice help fish in ponds?

Answer 19

• because ice floats, it forms an insulating layer on top of the water

Question 20

explain how hydrogen bonds form (3 marks)

Answer 20

• Oxygen and hydrogen share electrons unequally when they bond.
• Oxygen is more negative & Hydrogen is more positive
• The more negative oxygen atom on one molecule is attracted to the more positive hydrogen atom

Question 21

Why is water a polar molecule? (2 marks)

Answer 21

• In water the bonds between oxygen and hydrogen involve unequal sharing of electrons
• resulting in the oxygen atom being more negative and the hydrogen atoms being more positive.

Question 22

which properties of water make it an important component of blood and why? (3marks)

Answer 22

• water is a liquid = transport medium
• polar solvent and (many) biological molecules are polar , so better at dissolving them
• coolant = more resistant to temperature change

Question 23

Water forms the basis of Stroma in chloroplasts and the matrix in mitochondria. which properties of water make it an important component of these organelles?

Answer 23

• water is liquid = allows movement of substrates and enzymes
• movement of these is necessary for reactions to occur
• water is a polar solvent and substrates / enzymes are, polar.
• water is substrate for some reactions