Water

Question 1

Properties of water

Answer 1

• high boiling point (100°C)
• polar molecule
• hydrogen bond
• good solvent
• cohesive
• adhesive

Question 2

Is water a polar or non-polar molecule

Answer 2

Polar

Question 3

How does hydrogen bonding occur between water molecules

Answer 3

2 H atoms covalently bonded to 1 O atom
-> oxygen = greater number of electrons therefore δ- whereas hydrogen δ+
—> all water molecules are like this so they attract each other; the negative O in one molecule attracts a positive H in another, allowing hydrogen bonding to occur

Question 4

Water is […] dense when it freezes

Answer 4

Less

Question 5

Why is ice less dense than water

Answer 5

When water starts to freeze, the H bonds that form fix the water molecules further apart than the liquid state

-> this produces a giant rigid open tetrahedral structure, with an O atom at the centre

Question 6

Water has cohesive properties… this means?

Answer 6

They stick together because they’re attracted to one another
-> therefore, it has a strong surface tension

Question 7

Example of water’s cohesive property in an organism

Answer 7

Plants drawing up water through the roots and stem

Question 8

Water is also adhesive… this means that

Answer 8

Water molecules are attracted to other molecules

-> this helps water act as a solvent, as it allows substances to dissolve in it

Question 9

How does water act as an important solvent for plants and animals

Answer 9

For plants:
-> they absorb nitrate and phosphate ions

For animals:
-> they take in sodium and chloride ions + removal of urea in urine (other metabolic waste) + makes up cytosol

Question 10

How does water act as a coolant

Answer 10

It helps buffer temperature changes during chemical reactions, as the H bonds can absorb a lot of energy before breaking

Question 11

Why is water acting as a coolant important

Answer 11

For homeostasis: maintaining a constant internal environment, which is important for molecules like enzymes

Question 12

Why is water a good transport medium

Answer 12

Because it’s a good solvent
It can carry polar molecules, nucleic acids, amino acids and proteins

Question 13

How are properties of water good for habitats

Answer 13

• when it freezes, it creates an insulating layer for the water below, so organisms can still survive
• transparent so photosynthesis can still occur
  High surface tension means organisms (e.g pond skaters) can inhabit the surface of the water

Question 14

Describe the ways in which the physical properties of water allow organisms to survive over a range of temperatures

Answer 14

1) High latent heart of vaporisation, so evaporation acts as an efficient cooling mechanism e.g. sweating, panting etc

2) Large amount of energy needed to change the temperature, so it’s a thermally stable environment for organisms, so they can use less energy on temperature control and biological reactions can function correctly

3) ice is less dense, so the surface provided habitat for organisms e.g polar bears