Chapter 7: Water: A Physically Unique Molecule

Soda and Density DifferencesDEMO

• Will the diet soda sink or float? Will the regular soda sink or float?

• WHY!?!?

The Physics of water

• Seawater’s chemical reactions affect how life functions in the oceans.

• Water properties not only affect life processes of marine organisms and their survival, but also humans in the ocean as well (divers)

1) Heat and Heat Capacity

• Heat: kinetic energy in random movement, or vibration, of atoms and molecules in a substance

• Faster molecules = more heat

• Based on the speed of vibration and quantity of these molecules (total heat energy)

• Temperature: measures how fast the molecules vibrate

- Two most common temperature systems are Celsius and Fahrenheit.

- Celsius most used in science because it measures water’s physical properties

• Heat Capacity: amount of heat energy required to raise a given amount of substance by a given temperature.

-Measure by: 1 gram substance to raise 1⁰C-expressed by the number of calories needed-Water has highest heat capacity; takes longer; water can absorb more or less heat with little temperature change• This effects Earth’s climate

and weather.

2) Water Temperature and Density• Water cools, becomes denser. 39.8⁰C

= max density• Below this, water freezes where it

becomes less dense• Ice does not form all at once at the

freezing point; continuously crystallizes until all liquid is solid which produces:

- Non-sensible heat: change in heat energy that cannot be sensed with a thermometer.

- Latent heat of fusion: non-sensible heat lost when water goes from liquid to solid state

- Sensible heat: can actually sense in a thermometer

3) Latent Heat of Vaporization

• The heat required to vaporize a substance- It takes more heat to vaporize water than to

freeze it WHY?- Because when water freezes only some of the

hydrogen bonds break.- When it vaporizes, all the hydrogen bonds

must break, which requires more energy

4) Thermal Inertia• Tendency of water to resist

temperature change• Thermal equilibrium: water cools

at about the same rate as it heats• Important to life because:- Seawater is the global thermostat;

prevents major temperature swings (drastic in night and day summer and winter)

- Without thermal inertia, many of the organisms on Earth could not be able to survive the drastic temp changes that occur each night.

5) Ocean Water Density

• Seawater density varies with salinity and temperature-causes seawater to stratify: form layers• Dense water is heavy and sinks below less dense layers. 3

density layers:1) Surface zone: 2% of the oceans volume; Extends from top

to about 100 m2) Thermocline: separates surface zone from the deep zone.

Only temperature or salinity to exist. 18% of the oceans volume.3) Deep zones: lies below the thermocline. Very stable region

of cold water starting deeper than 1,000 m; shallower in polar regions; zone makes up about 80% of ocean’s volume.

How water Physics Affect Marine Life1) Light- Water scatters and absorbs light. When light

reaches the water’s surface, some light penetrates, but, depending on the sun’s angle, much may simply reflect back out of the water.

- Light reflects off light-colored suspended particles.- Dark colored particles and algae absorb some light- Water molecules absorb the energy, converting light

into heat- Water absorbs colors at the red end of the spectrum

more easily than at the blue end

Two zones with respect to light penetration

1) Photic Zone: where light reaches. Has two subzones:

- Euphotic Zone: upper shallow portion where most biological production occurs.

- Dysphotic Zone: where light reaches, but not enough for photosynthetic life

2) Aphotic Zone: makes up the vast majority of oceans. Light does not reach and only fraction of organisms live here

2) Temperature:-Marine organisms live in a much less challenging environment with respect to temperature range

ectotherm: organism’s internal temp changes with seawater temp (cold-blooded)

endotherm: organisms internal temp varies, but remains warmer then the surrounding water

Homeotherm: internal temp relatively stable. (warm-blooded) (marine mammals and birds)-Temperature affects metabolism: high temp= more energy releasing chemical processes-Metabolic rate remains the same regardless of external temperature allowing them to live in a variety of habitats

3) Sound- Travels through warm water faster than cool,

but travels faster in deep water due to pressure.

- Sound bounces off suspended particles, water layers, the bottom and other obstacles.

- Sound travels much farther thru water than light does.

- Sound is eventually absorbed by water as heat- Marine animals use echolocation: enables

them to sense an object’s size, density, distance, and position underwater.

4) Pressure-Hydrostatic pressure: pressure exerted by water; i.e. the weight of water.

- at 10 m hydrostatic pressure is equal to atmospheric pressure

- at 10 meters: total pressure is 2 bar- 1 bar atmospheric pressure and 1 bar from hydrostatic pressure

- A marine organism living at 10 m experiences twice the pressure present at sea level. Pressure increases 1 bar for each additional 10 m- HYDROSTATIC PRESSURE DOESN’T AFFECT MARINE ORGANISMS BECAUSE IT IS THE SAME INSIDE THE ORGANISM AS IT IS OUTSIDE. (pressure does not crush or harm marine organisms!)

5) Size and Volume:- Increase size=Increase volume- High surface to volume ratio is important for cell

function. - Bigger cell= lower surface to volume ratio, which

means that there is less relative area through which to exchange gases, nutrients, and waste.

6) Buoyancy- Archimedes' Principle: an object immersed in a

gas or liquid is buoyed up by a force equal to the weight of the gas or liquid displaced.

- This means that marine organisms don’t have to spend a lot of energy balancing their own weight.

- Allows some organisms to exist simply by drifting and never coming in contact with the bottom

7) Movement and Drag-Marine organisms avoid sinking by hairs, spines, etc. increasing their drag and help them resist sinking. Some have buoyancy adaptations .-Some organisms need to overcome drag. To do this: move or swim slowly, excrete mucus so they can “slip” through water, or have a shape that reduces drag (streamlining)8) Currents-Drifting provides several advantages:

-Disperses organisms into new habitats, ensuring survival

-Take organisms into nutrient rich areas, reducing competition for resources.

Daily Quiz #2

Explain three (3) physical properties of water and how they affect marine life.a. Soundb. Pressurec. Lightd. Densitye. Temperature