A1.1 Water

Question 1

Why is water important?

Answer 1

It’s essential for life:
- Universal solvent
- Where biochemical reactions can take place
- Where most organisms live
- Most organisms have a high water content

Question 2

What gives water molecules special properties?

Answer 2

Their polarity:
- the oxygen in water has a bigger nucleus which attracts more electrons
- this causes an unequal distribution of charge within the molecule
- overall charge is zero but the molecule has ‘poles’

Question 3

What are the bonds formed in and between a water molecule?

Answer 3

In: Covalent bonds
Between: Hydrogen bonds (due to the polarity of water and the electromagnetic attraction between molecules)

Question 4

How many bonds can be formed between water molecules?

Answer 4

4 H-bonds per water molecule

Question 5

What special properties does water have due to its polarity? What do all of these special properties allow for?

Answer 5

• Cohesion
• Adhesion
• Solvency
• High specific heat
  These properties allow water to be the main medium for life

Question 6

Solvency:
what does/doesn’t water dissolve?
+ give some examples

Answer 6

Water is a universal solvent:
- it can dissolve polar molecules/ionic compounds (hydrophilic molecules) such as glucose and NaCl

• it can’t dissolve non-polar/non-charged molecules (hydrophobic molecules) such as cholesterol and fats

Question 7

Solvency:
how does water’s solvent properties benefit organisms?

Answer 7

• most organisms have a high water content
• allows for transport of essential materials (amino acids, carbohydrates, minerals) around the body
  - usually transported through blood
• allows for biochemical reactions to take place
  - cytoplasm is made of mostly water

Question 8

Cohesion:
What is cohesion?
Why does this happen?
What properties does it give water?

Answer 8

• water sticks to itself
• it forms h-bonds between water molecules
• resists the increase of surface area and can counteract/resist gravity

Question 9

Cohesion:
Why is cohesion beneficial to animals?

Answer 9

• allows animals to transport water through cells and tissue (transpiration)
• creates surface tension which is used by small insects to walk on the surface of water (pond skaters)
• allows for capillary action as they stick together and climb up against gravity

Question 10

Adhesion:
What is adhesion?
Why does this happen?
What properties does it give water?

Answer 10

• water sticks to other polar/charged molecules
• water is polar so it can form h-bonds with other molecules
• on their own, bonds are weak but the more bonds the stronger they are

Question 11

Adhesion:
Why is adhesion beneficial to animals?

Answer 11

• allows for capillary action as the water forms bonds with the xylem cell wall which pulls/sucks water up through the plant

Question 12

Why is ice less dense?
How does this help animals?

Answer 12

The hydrogen bonds spread the molecules farther apart
It forms an ice layer over bodies of water that insulates the water underneath

Question 13

Specific heat capacity
What is it?
Is it high or low for water?
What does this mean for animals?

Answer 13

Water has a high specific heat capacity
This means it takes a lot of energy to heat up water
This provides a stable environment for organisms, both in water habitats and inside their bodies
It allows for thermal regulation

Question 14

Latent heat of vaporisation
What is it?
Is it high or low for water?
What does this mean for animals?

Answer 14

Water has a high latent heat of vapourisation
This means it takes a lot of energy for water to change state from liquid to gas
This means that animals can sweat to lose heat as it draws away heat from the body

Question 15

Buoyancy
What is it?
What does this mean for animals?
Give specific examples

Answer 15

The ability for an object to stay afloat
or
the ability of a liquid to exert upward force on an object
things that are less dense than water will float
this helps animals minimise the energy expended trying to stay afloat
Loons trap air and oil in their feathers
Seals have a lot of blubber

Question 16

Viscousity
What is it?
Is it high or low for water? Compared to air?
What does this mean for animals? How do they adapt? Give specific examples

Answer 16

A liquids resistance to movement
Water is more viscous than air
Harder to move through it so being aerodynamic is important
loons and seals are torpedo shaped

Question 17

Thermal conductivity
What is it?
Is it high or low for water? Compared to air?
What does this mean for animals? How do they adapt? Give specific examples

Answer 17

ability to move heat across a temperarzre gradient
water is a good conductor
means you get colder in water and lose heat quickly
to prevent this:
- loon have oiled feathers that trap air and repel water which insulated them
- seals have thick layers of blubber that keep them insulated

Question 18

Origin of water
Where did water come from?
Why does it stay on earth? What conditions does the earth have to allow this?

Answer 18

Scientists believe that a comet carrying ice hit the earth and brought water to it
Once the water was able to exist in a majority liquid state, life could begin
This temp was reached because Earth exists in the habitable/goldilocks zone
Gravity is what keeps the water from escaping

Question 19

What properties do enzyme molecules have relating to water?

Answer 19

Enzymes are proteins and are carried in the blood, meaning they have to be hydrophilic and soluble.

Question 20

How are fats transported in the body? Explain the structure?

Answer 20

• They are carried in blood inside lipoprotein complexes (in the plasma)
• Outer layer consists of single layer of phospholipid molecules:
• Hydrophilic phosphate heads of the phospholipids face outwards and are in contact with water
• Hydrophobic hydrocarbon tails face inwards and are in contact with the fats
• Proteins are also embedded in the phospholipid layer

Question 21

State the property of water that causes water to be retained in soil by capillary action

Question 22

explain how the physical properties of water support life in aquatic environments (with specific examples)

Question 23

Outline the thermal, cohesive and solvent properties of water:

Answer 23

Thermal:
- water has a high specific heat capacity - takes a lot of energy to heat it up
- water has a high latent heat of vaporization - takes a lot of energy to vaporise it

Cohesive:
- hydrogen bonds between water molecules make them
cohesive/stick together;

- gives water a high surface tension
(explains how water rises
up xylem)

Solvent:
- water molecules are polar;
this makes water a good solvent;


Question 24

Explain, with reference to its properties, the significance of water as a coolant, a means of transport and as a habitat.

Answer 24

Coolant:
- High specific heat capacity and latent heat of vaporisation
- When water evaporates energy is used and cools down organism;

- eg sweating / panting / transpiration;

Transport:

- water is polar and a universal solvent

- dissolves many organic and inorganic substances;

- water is adhesive and cohesive
- can transport vital nutrients and substances through xylem, blood, plasma etc

Habitat:

- water is transparent and allows for light photosynthesis
- Surface tension creates a habitat for surface creatures to live on
- contains dissolved gases fo fish and aquatic organisms survive under ice at surface;
- ice is less dense than liquid water and insulates bodies of water in the winter

Question 25

Which physical property of water makes it an effective coolant?

Answer 25

High specific heat capacity