Marine Biology Lesson 3

1. Marine Biology Lesson 3 The Nature of Water

2. Water • Very important resource for anything living in our biosphere (land, water, atmosphere) • Makes up 99% of the biosphere • Oceans hold more life and diversity than any other place on earth • To understand marine life you must understand the water that they live in

3. The Water Cycle

4. Today's Plan • We will discuss the following • Unique properties of water • Salinity of sea water • Transport of molecules in water • Sound • Pressure

5. A) Unique Properties of Water • Water is a Polar Molecule • Chemical Formula: H2O • 3 atoms in total, 2 are hydrogen, 1 is oxygen • Hydrogen and oxygen are bonded together (held) by a covalent bond (sharing of electrons) • Oxygen atoms attracts the shared electrons close to its nucleus • Creates a lopsided molecule with two hydrogen atoms on one side and an oxygen atom on the other • Hydrogen is positively charged while oxygen is negatively charged so we end up with a molecule with a positive end and a negative end • A molecule with positively and negatively charged ends is said to be polar

6. Water is Polar • This polarity allows more water molecules to bond together • The negative end is attracted to the positive end • The bond between water molecules is called a hydrogen bond

7. Hydrogen Bonds • Weak compared to covalent bonds so they break easily but.... • As a group of bonds they have cumulative strength so they’re much stronger when there are lots of them • This leads to the following unique properties • Liquid state • Cohesion/adhesion • Viscosity • Surface tension

8. Liquid State • Without hydrogen bonds, water would be a gas (steam) • This is because the hydrogen bonds hold the water molecules together so more heat is required to turn it into a gas • That’s why water has such a high boiling point (100C)

9. Cohesion/Adhesion • Cohesion – ability for water molecules to stick to each other • Due to the hydrogen bonds formed between water molecules • Adhesion – ability for water molecules to stick to other things • Due to the polar nature of water • Think of water climbing up the stem of a plant to the leaf – water sticks to itself to help pull it up the stem and it sticks to the sides of the stem as it climbs up • Penny example!

10. Viscosity • The tendency for a fluid to resist flow • Oil in a pan – cold oil flows more slowly, once it’s heated it flows faster • Water is more viscous than many substances because hydrogen bonds hold the molecules together closely • As temperatures cool the water becomes more viscous because hydrogen bonds resist the tendency to be broken • Remember we have to put a lot of heat in to break those bonds • This affects the amount of energy a marine organism has to expend to move through water • Plankton expend less energy in cool water because they don’t sink as easily • Fish expend more energy in cool water because they have to swim through it

11. Surface Tension • Due to the strength of hydrogen bonds together it creates a skin-like surface to water • This surface tension is a resistance to objects trying to penetrate the surface • Also due to cohesion • Think of the water strider bug • In a marine environment – neuston are plankton that live on water’s surface

12. Ice floats! • Why?? • As substances cool they become dense, turn to solid and sink • Water becomes dense and turns to a solid when it cools too but it doesn’t sink • As water cools and turns from liquid to solid the molecules spread out into a crystal structure that takes up more room than liquid water • With more volume, ice is less dense than water so it floats • Super important because it allows for water to remain in liquid form under the ice • The ice actually insulates the water below • If ice sank, all the water would freeze and the marine organisms would freeze with it

13. Ice Floats

14. B) Salinity of Sea Water • Salt dissolves in water • Water is the solvent (more abundant) and salt is the solute (substance being dissolved) • Salt water is a solution which means you can’t see the different parts (it’s homogeneous) • Because water is polar, the water molecules pull apart the salt crystals (Na+ and Cl-) causing salt to dissolve

15. B) Salinity of Sea Water • There are other salts dissolved in sea water • NaCl (we just mentioned) • KCl is another example • The fact that sea water has a solute dissolved in it gives it special properties called colligative properties • Raised boiling point (need more heat to break bonds between oxygen, hydrogen and now sodium and chlorine) • Decreased freezing temperature (why we salt the roads) • Slower evaporation

16. How does salt affect sea life? • diffusion is the tendency for a liquid, gas or solid to move from areas of high concentration to low concentration • Semi-permeable membranes surrounds all living cells to allow wastes in and nutrients out • Oxygen can move into cells for cellular respiration if there is a low concentration on the inside • Water can move across a semi-permeable membrane via osmosis to the area of lower concentration • So if there is water with a different concentration of solute on opposite sides of a membrane, water will diffuse to the higher concentration

17. Osmosis • Movement of water across a semi-permeable membrane • The concentration of water inside a marine animal must be the same as the surrounding water (isotonic) • Otherwise, water will move in or out of the animal to balance this – pretty important in a salt water environment • If you put a marine fish into fresh water the fish cells have a higher salt concentration so they’re hypertonic and water will flow into the fish cells • If you took a fresh water fish and put it into the ocean the fish cells would have less salt in them and therefore they’d be hypotonic • ****** see page 6-31 figure 6-35

18. Osmosis • Osmosis is a form of passive transport because it just happens based on movement from high to low concentration • Active transport requires energy to move substances in a certain direction • Osmoregulators use active transport to adjust the water concentration in their cells • This allows them to adapt to changes in the salinity of their environment • Bony fish consume a lot of seawater to replace what is lost through osmosis and excrete only a small amount of urine. They have special glands in their gills to eliminate the salt they take in

19. In Conclusion • Marine Life is specialized to live in a marine environment and it’s not as easy to take a marine organism and pop it into a freshwater environment • All life is specialized for their habitat and adaptations allow organisms to move from one habitat to another and still survive • Sometimes this is done in a short period of time but most often it’s over long periods of time = evolution • Water is a very unique substance that supports all life, without it we wouldn’t survive for very long!