A1.1: Water

Question 1

Water as medium of life

Answer 1

First cells -> watery environment (hydrothermal vents)

Water and solutes got trapped in membrane -> chemical reactions occur in the membrane bound structure -> evolution of cells

Water allows dissolved molecules to move around -> easily collide and react

Most life processes occur in water

Question 2

Examples of hydrogen bonds importance in biological molecules

Answer 2

Dissolving solutes in water

Cohesion + adhesion of water molecules
-> allow water to move up (transpiration)

Base-pairing between two strand of DNA

Structure
-> H bonds help form secondary/tertiary structure of protein
-> H bonds found between strand of cellulose/collagen -> tensile strength

Interactions between mRNA and tRNA during protein synthesis

Surface effects on membrane between polar phosphate groups and water

Question 3

Why is water so important?

Answer 3

Medium in which all metabolic reactions occur

70%-95% of the mass of a cell = water

So fundamental that:
71% of earths surface = water -> major habitat
Astronomers look for water as a sign of life

Question 4

What is the structure of water (+ polarity)?

Answer 4

Each H shares a pair of electrons with O

Electrically neutral but:
Oxygen atom attract electrons more strongly -> slight negatively charge region (δ-)
Hydrogen atoms have a slight positively charged region (δ+)

-> also result of asymmetric shape

-> different charged regions -> water is polar
-> 2 unevenly charged regions -> dipole
-> charge -> attract to other water molecules

H bonds cause many of the properties of water molecules -> very important

Question 5

Strength of H-bonds

Answer 5

Singular H bonds -> weak -> constantly breaking and reforming

Many H bonds -> stable structure, strong

Question 6

How do hydrogen bonds contribute to the cohesion of water molecules?

Answer 6

Water -> polar -> can form hydrogen bonds

Single H bond -> weak
Many H bonds (1 water ->bond to three other in tetrahedral) -> stronger

H bonds within water allow for strong cohesion:
Columns of water move under tenions (mass transport) through xylem

Enable surface tension -> body of water meet air -> H bonds occur on the top later -> ‘film’ created

Question 7

How do hydrogen bonds enable surface tension?

Answer 7

Caused by cohesive hydrogen bonding resisting an object trying to penetrate the surface

Near surface -> water form H bonds with each other but not air molecules
-> upwards force - acts like skin

Question 8

What is adhesion?

Answer 8

Water molecules tend to stick to other molecules that are charged/polar for similar reason as why they stick to each other

Large number of H bonds give adhesive forces strength

-> enables transpiration

-> enables water drawn up narrow channels (capillary tubes) in soil -> capillary action

-> spaces between cellulose fibers in plant cell wall -> draw water from xylem vessels -> allow water to flow through plant

Question 9

What is capillary action?

Answer 9

A combination of adhesion (water bond to a surface) and cohesion (water bond together)

Helpful in the movement of water during transpiration or drink water from straw

Question 10

How does polarity affect the ability of a molecule to form H bonds with water? What does this have to do with water=universal solvent?

Answer 10

Polar -> charged -> can from H bonds and dissolve
-> hydrophilic

Nonpolar -> no charge -> cannot from hydrogen bond
-> hydrophobic
-> tend to group together (hydrophobic interaction)
—> water bonds with other water but not nonpolar molecules

Most biological molecules -> hydrophilic
Water -> universal solvent

Question 11

What are the solvent properties of water?

Answer 11

Différent solute -> behave differently with water solvent

Water -> universal solvent
BUT different metabolites -> different solubilities in water

Different solutes -> different hydro-loving level -> affect solubility

Question 12

Water as a solvent:
Soluble and insoluble molecules

Answer 12

Soluble:
Ex: NaCl, urea
Easily transported in solution within organisms
-> salts, glucose, AA
(AA does have hydrophobic R group but is soluble enough)

Insoluble:
Ex: fats
Nonpolar, hydrophobic molecules -> no dissolve
Function of molecules determine hydrophobic/insolubility
-> phospholipids have hydrophobic tails to help form cell membrane

-> different transport mechanism exist for insoluble/less soluble molecules

Question 13

Water as a solvent:
Less soluble molecules

Answer 13

Low solubility molecules
Ex: oxygen -> require assistance -> combine with haemoglobin -> more/sufficient O can be transported

O less soluble at body temp than at 20°C

Oxygen -> sparingly soluble but soluble enough to allow it to be dissolved in oceans, rivers, etc. -> aquatic animals

Question 14

What is waters role in enzyme action?

Answer 14

Most enzymes -> need water to hold shape/improve stability

-> Enables them to catalyze reactions in aqueous solutions

H bonds -> facilitate the bind of enzymes active site to substrate molecule -> enzyme substrate complex

Question 15

What is specific heat capacity?

Answer 15

A measure of the energy required to raise the temperature of 1 kg of a substance by 1°C

Question 16

What is waters specific heat capacity? Why is it so?

Answer 16

Water -> 4200 J/Kg/°C or 42 KJ/Kg/°C

Much higher that air (1000 J/Kg/°C)
-> large amount of energy required to raise water temp

This is because of the MANY hydrogen bonds

Question 17

How does water specific heat capacity play a role in its stability as an environment?

Answer 17

Water resist temp changes (higher c than air) -> stable environment within cells and for aquatic organisms

Artic/subartic species (ex ringed seal) -> able to survive throughout the year due to stable sea temp

Density of ice lower than that of liquid water -> ice floats
Forms a habitat for seals -> on and below ice

Question 18

What is latent heat of vaporization?
What properties of water does it connect to?

Answer 18

The amount of heat that is needed to turn a substance into a gas without a change in temperature

Water -> high latent heat of evaporation
-> evaporation of water from surface of organisms -> significant cooling effect

Question 19

What is thermal conductivity?
How does the thermal conductivity of water effect aquatic animals?

Answer 19

Thermal conductivity -> the ability of a substance to conduct heat

Water -> x30 that of air
-> air = good insulator for organisms in cold climates
-> ex: black throated loon: diving bird -> feathers trap air -> insulation

Seals -> relies on blubber to insulate from cold temp
Ice -> form insulating later above water -> thermal conductivity of ice is lower than liquid water -> increase sea temp below the ice (thermal energy trapped)

Question 20

What is buoyancy?
How does buoyancy affect aquatic animals?

Answer 20

Buoyancy -> ability of an object to float in water

To overcome buoyancy -> black throated loon -> solid bones (bird usually hollow to help with float)
-> increased weight + air out of lungs/feathers during dive

Ringed seal -> blubber improve buoyancy of animal

Question 21

What is viscosity?
How does it affect aquatic animals?

Answer 21

Viscosity -> the resistance of a fluid to flow

Viscosity of water > viscosity of air

Black throated loon -> fly through air without much friction

Body shape of loon+seal -> easy through water

Both -> adapted to movement though water:
-> seals -> flippers to propel
-> loon -> webbed feet to push against water, lateral location of feet reduces drag

Question 22

What is a hypothesis for the origin of water on earth?

Answer 22

Water -> crucial for existence
BUT when earth formed -> too hot for water vapor to condense
-> led scientist to think -> water originated from elsewhere

one hypothesis:
Asteroids/meteorites may be origin
-> many contain ice/other organic materials

One of the oldest groups of meteorites in solar system -> carbonaceous chondrites
-> contain H isotope similar to that in seawater

Another group of ancient meteorites -> eucrite achondrites -> ratio of H isotopes that is similar to that on earth

Possible that during impact -> meteorites release water vapor -> trapped earths gravity -> temp on earth low enough to allow vapor to condense -> liquid water -> retained on surface by gravity

Question 23

How does water relate to the search of extraterrestrial life?

Answer 23

Living organism -> depends on water for existence -> requirement of any planet to support life

Water exist in liquid -> temp on planet need to be correct -> depend on distance to nearest star
-> Goldilocks zone

Search of extraterrestrial life -> look for exoplanet in Goldilocks zone

Question 24

How do scientist search for water?

Answer 24

Use technique called transit spectroscopy:
Analyzes light passing through the planets atmosphere as it passes in front of nearest star

Based on wavelength of light being absorbed/deflected -> analysis can be made about the elements and molecules in front of its nearest star
-> if water may be present -> exoplanet has ‘water signature’

Question 25

What characteristics have to be present for an exoplanet to support life?

Answer 25

For exoplanet to support life must have following characteristics:
-> water signature
-> in Goldilocks zone
-> large enough to support an atmosphere