A1.1: Water

Question 1

What is the structure of a water molecule?

Answer 1

A polar covalent molecule with a negative pole (oxygen) and two positive poles (hydrogen)

Question 2

How do non-polar molecules differ from polar molecules?

Answer 2

In non-polar covalent bonds, electrons are shared equally.
In polar covalent bonds, electrons are not shared equally and one of the atoms has a greater electron affinity than the other.

Question 3

What is cohesion? Explain in the context of water.

Answer 3

When molecules of the same type are attracted to each other.

When two water molecules are close together, the positive Hydrogen end attracts the negative Oxygen eng. This forms a hydrogen bond

Question 4

What is surface tension?

Answer 4

• The layer of molecules at the surface do not have molecules of water above it.
• The water molecules therefore show a strong cohesive force to the molecules below and around them, as there are no molecules pulling upwards

Question 5

What organisms benefit from the strong surface tension of water?

Answer 5

Basilisk lizards
Water striders

Question 6

How is water able to move as a water column in the xylem?

Answer 6

• Water is transpired from a leaf’s surface
• The water that evaporates has cohesion to water still in the xylem tube
• The evaporation with cohesion creates a low pressure area (tension)
• This pulls on the other water molecules in the xylem so they all move upwards as a column

Question 7

What is adhesion? Give an example of this in nature

Answer 7

An attraction between two unlike molecules due to hydrogen bonding
E.g. between water molecules and cellulose molecules in the xylem

Question 8

How do cohesion and adhesion work together in the xylem?

Answer 8

Cohesion: moves the molecules as the column of water is pulled up
Adhesion: Prevents the column from dropping down when it is not being pulled up

Question 9

Give some examples of hydrophilic molecules in the cell.

What does hydrophilic mean?

Answer 9

Glucose, ions, amino acids, proteins, enzymes

It’s attracted to water

Question 10

Give some examples of hydrophobic molecules in the cell.

What does hydrophobic mean?

Answer 10

Steroid hormones, some proteins with hydrophobic structures

It’s repelled from water

Question 11

What is buoyancy?

Answer 11

An upwards force exerted on an object placed in a medium

Question 12

What is viscosity?

Answer 12

The resistance to an object moving through a medium

Question 13

What is thermal conductivity?

Answer 13

The ability of a substance to transfer heat energy

Rate at which heat flow through a substance

Question 14

What is specific heat capacity?

Answer 14

Amount of energy needed to change the temperature of a medium by 1C

A medium’s ability to maintain a temperature

Question 15

What are the important physical properties of water?

Answer 15

Buoyancy
* Buoyant force equals the weight of the water displaced by the object
* More pressure from below (water) than above (air)

Viscosity
* Water is dense, therefore it is harder to move through it

Thermal conductivity
* Water is extremely thermally conductive, meaning organisms will lose a lot of heat energy to it

Specific heat capacity
* Water can absorb or give off a great deal of energy without chaning temperature very much
* Takes a lot longer for water temperature to change

Question 16

Compare the physical properties of air to those of water

Answer 16

Buoyancy
* Almost insignificant compared to water

Viscosity
* Air is less dense than water, therefore air is less viscous to move through

** Thermal conductivity**
* Very low compared to water

Specific heat capacity
* Very low compared to water
* Temperature of the air changes easily and rapidly due to the weather

Question 17

What are the two animal case studies for the physical properties of water?

Answer 17

Black-throated loon
Ringed seal

Question 18

How has the black-throated loon adapted to life in water?

Answer 18

• Spends most of its time on the surface, relying on buoyant force
• Webbed feet and streamlined shape aid it for moving in the viscous water
• Oil glands near the tail allow the feathers to become waterproof. This helps prevent heat loss due to the high thermal conductivity of water
• Protected from the low temperatures of the arctic air by the relatively high temperatures of the arctic water, due to the high specific heat capacity of water

Question 19

How has the ringed seal adapted for life in the water?

Answer 19

• Buoyant enough to keep its snout above the water (easy access to air)
• Streamlined and has paddle-like feet to aid in moving through the viscous water
• Thick blubber under the skin helps prevent heat loss due to water’s high thermal conductivity
• Protected from the low temperatures of the arctic air by the relatively high temperatures of the arctic water, due to the high specific heat capacity of water

Question 20

What is the theory of how water came to Earth?

Answer 20

• Earth’s surface in the early stages was entirely magma; hot, molten rock that could not retain or form water.
• As the Earth cooled, numerous asteroid’s struck the Earth, bringing hydrated crystals that released water

Question 21

What evidence have scientists found that consolidates the asteroid theory?

Answer 21

The ratio of deuterium (heavy water) to “ordinary” water is the same in the ocean as it is on asteroids.

Question 22

State the conditions necessary for a planet to be classified as in the Goldilocks zone.

Answer 22

• Presence of liquid water
• Surface temperatures that allow water to exist in its liquid form
• Suitable gravity to prevent water from escaping
• An atmosphere to shield the planet’s surface from ionizing radiation