A.1: Water

Question 1

State what water is the medium of: (1)

Answer 1

• Life (1)

Question 2

State the type of bond between hydrogen and oxygen atoms in a water molecule: (1)

Answer 2

• Polar covalent bonds (1)

Question 3

Define the term polar molecule: (2)

Answer 3

A molecule that contains an uneven distribution of charges . (1), causing one side of the molecule to be partially negative and the other side to be partially positive.

Question 4

Explain why electrons are pulled closer to the oxygen in a water molecule: (4)

Answer 4

• It is more electronegative (1)
• Because oxygen has a partial negative charge (1)
• So the oxygen side become more negative
• So the hydrogen side has a less negative but more positive charge.

Question 5

State the bond that forms between hydrogen and oxygen atoms between different molecules: (1)

Answer 5

• Weak hydrogen bond (1)

Question 6

Define the term cohesion: (1)

Answer 6

The ability of water molecules to attract and stick to other water molecules.

Question 7

Describe how water molecules are kept together: (2)

Answer 7

• Through the weak hydrogen bonds (1)
• Between hydrogen and oxygen atoms (1)

Question 8

Define the term xylem: (1)

Answer 8

Special pathway that is used to transport water and nutrients up the plant.

Question 9

Explain how cohesion allows water to be moved up the xylem: (4)

Answer 9

• Hydrogen bonds between water molecules hold each other together (1)
• So they are cohesive and help to pull each other up.
• Transpiration allows water to be lost.
• So another water molecule is pulled up to replace it.

Question 10

Define the term transpiration: (1)

Answer 10

• The process of water movement through a plant (1)
• And its evaporation from aerial parts, like leaves, stems and flowers.

Question 11

Explain why water striders can ‘walk’ on water

Answer 11

• There are cohesive forces between molecules which creates surface tension
• The cohesive force (weak hydrogen bonds) takes more energy to break than the strider exerts
• So the surface of the water is maintained.

Question 12

Define the term surface tension: (1)

Answer 12

When cohesive forces between liquid molecules allow the liquid to resist an external force. (1)

Question 13

Define the term adhesion: (1)

Answer 13

The ability of water molecules to stick to other surfaces and molecules

Question 14

Explain how adhesion occurs in soil: (5)

Answer 14

• Some materials in soil have polar properties.
• This allows water to form hydrogen bonds and stick to the soil
• This allows capillary action to occur
• Where water moves through spaces of a porous material.
• Which allows water to be absorbed by plant roots

Question 15

Define the term capillary action: (2)

Answer 15

• The movement of water within spaces of a porous material. (1)
• Due to the forces of adhesion, cohesion and surface tension.

Question 16

Explain how adhesion allows water to move up the plant:

Answer 16

• The xylem walls are made of lignin and are polar.
• Allows the xylem wall and water molecules to attract
• Creates tension which supports upward movement vs gravity.

Question 17

Define the term hydrophilic: (1)

Answer 17

Substances that have a tendency to be attracted to water.

Question 18

Explain why sodium chloride (salt) dissolves in water:

Answer 18

• Ionic bonds between sodium and chlorine atoms break apart into 2 charged ions. (1)
• Positively charged sodium will be attracted to the partially negative oxygen (1)
• The negatively charged chloride will be attracted to the partially positively charged hydrogen (1)
• Water molecules wrap around and encloses the ions. (1)

Question 19

State what water can be described as: (1)

Answer 19

• A universal solvent (1)

Question 20

Define the term metabolism: (1)

Answer 20

The sum of chemical reactions in the body that change food into energy.

Question 21

Explain why phospholipids can make up the cell membrane: (1)

Answer 21

• They contain structures which are hydrophobic (1)
• These structures are more attracted to each other than the surrounding water
• This creates a barrier because they cannot dissolve in water. (1)

Question 22

Define the term specific heat: (1)

Answer 22

The amount of energy needed to rise the temperature of a substance by 1 degrees celcious. (1)

Question 23

Explain why water has a high specific heat:

Answer 23

• Due to hydrogen bonds that hold water molecules together (1)
• It takes a lot of energy to break these bonds and get water molecules to move. (1)

Question 24

Explain why the specific heat capacity of water is a benefit to aquatic organisms: (3)

Answer 24

• Water can withstand large fluctuations in temperature (1)
• Which keeps things constant, such as body temperature. (1)
• This is because chemical reactions occur in the body. (1)

Question 25

Define the term thermal conductivity: (1)

Answer 25

The rate at which heat can move through a material

Question 26

Define the term buoyancy: (1)

Answer 26

The ability to float on water.

Question 27

Explain how viscosity in water works: (1)

Answer 27

When molecules move, they tend to stick together due to the friction between them. (1)

Question 28

Explain how the physical properties of water allow the Pusa hispida (Ringed seal) to survive: (6)

• Buoyancy (2)
• Viscosity (1)
• Thermal Conductivity (3)

Answer 28

• The seal is buoyant enough to keep its snout over the water. (1)
• This allows an easy supply of air. (1)
• The seal has a streamlined shape and paddle-life feet to overcome the viscosity of water. (1)
• Water has a high thermal conductivity. (1)
• They minimize heat loss by having a thick blubber under their skin. (1)
• This reduces heat loss from the seals internal organs. (1)

Question 29

Explain how the physical properties of water allow the Gavia artica (Black-Throated Loon) to survive: (5)

• Buoyancy (1)
• Viscocity (2)
• Thermal conductivity: (2)

Answer 29

• The buoyancy of water allow it to keep afloat. (1)
• Webbed feet and streamlined body shape allows the loon to dive for fish and other food sources in the water. (1)
• It also allows the bird to overcome the viscosity of water and move along the surface. (1)
• They have an oil gland near the tail and rubs this on their feathers. (1)
• This makes them waterproof. (1)

Question 30

Describe the temperature of water in the early times of Earth: (2)

Answer 30

• Exceeded 100 degrees celcious. (1)
• So it would have been boiled into gas and lost into space. (1)

Question 31

Explain a theory how water was obtained on Earth: (1)

Answer 31

• Water was delivered from large, colliding asteroids. (1)
• Due to its position from the sun, water could be housed on the planet and exist in a liquid state. (1)
• The gravitational pull holds the water on earth. (1)

Question 32

Explain why there is no water on Mars: (2)

Answer 32

• Due to the chemistry of the sediment that reacts with water. (1)
• Through hydration reactions (1)

Question 33

Explain what will happen if a planet is: (5)

• Too close to a star (2)
• Too far from a star (2)
• Just right from the star (1)

Answer 33

• The temperature will be too great for water to exist. (1)
• So it will vapourise into a gas. (1)
• Water will exist as a solid. (1)
• By freezing into ice. (1)
• The liquid state of water can exist. (1)