A1.1: Water Flashcards
What is the structure of a water molecule?
A polar covalent molecule with a negative pole (oxygen) and two positive poles (hydrogen)
How do non-polar molecules differ from polar molecules?
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.
What is cohesion? Explain in the context of water.
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
What is surface tension?
- 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
What organisms benefit from the strong surface tension of water?
Basilisk lizards
Water striders
How is water able to move as a water column in the xylem?
- 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
What is adhesion? Give an example of this in nature
An attraction between two unlike molecules due to hydrogen bonding
E.g. between water molecules and cellulose molecules in the xylem
How do cohesion and adhesion work together in the xylem?
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
Give some examples of hydrophilic molecules in the cell.
What does hydrophilic mean?
Glucose, ions, amino acids, proteins, enzymes
It’s attracted to water
Give some examples of hydrophobic molecules in the cell.
What does hydrophobic mean?
Steroid hormones, some proteins with hydrophobic structures
It’s repelled from water
What is buoyancy?
An upwards force exerted on an object placed in a medium
What is viscosity?
The resistance to an object moving through a medium
What is thermal conductivity?
The ability of a substance to transfer heat energy
Rate at which heat flow through a substance
What is specific heat capacity?
Amount of energy needed to change the temperature of a medium by 1C
A medium’s ability to maintain a temperature
What are the important physical properties of water?
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
Compare the physical properties of air to those of water
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
What are the two animal case studies for the physical properties of water?
Black-throated loon
Ringed seal
How has the black-throated loon adapted to life in water?
- 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
How has the ringed seal adapted for life in the water?
- 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
What is the theory of how water came to Earth?
- 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
What evidence have scientists found that consolidates the asteroid theory?
The ratio of deuterium (heavy water) to “ordinary” water is the same in the ocean as it is on asteroids.
State the conditions necessary for a planet to be classified as in the Goldilocks zone.
- 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
