# Chapter 7: Water: A Physically Unique Molecule

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Chapter 7: Water: A Physically Unique Molecule

Soda and Density Differences DEMO
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 m 2) 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 Life
1) 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
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
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. Sound Pressure Light Density Temperature