A1.1: Water Flashcards
Water as medium of life
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
Examples of hydrogen bonds importance in biological molecules
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
Why is water so important?
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
What is the structure of water (+ polarity)?
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
Strength of H-bonds
Singular H bonds -> weak -> constantly breaking and reforming
Many H bonds -> stable structure, strong
How do hydrogen bonds contribute to the cohesion of water molecules?
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
How do hydrogen bonds enable surface tension?
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
What is adhesion?
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
What is capillary action?
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
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? (Group)
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
What are the solvent properties of water?
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
Water as a solvent:
Soluble and insoluble molecules
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
Water as a solvent:
Less soluble molecules
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
What is waters role in enzyme action?
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
What is specific heat capacity?
A measure of the energy required to raise the temperature of 1 kg of a substance by 1°C
What is waters specific heat capacity? Why is it so?
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
How does water specific heat capacity play a role in its stability as an environment?
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
What is latent heat of vaporization?
What properties of water does it connect to?
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
What is thermal conductivity?
How does the thermal conductivity of water effect aquatic animals?
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)
What is buoyancy?
How does buoyancy affect aquatic animals?
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
What is viscosity?
How does it affect aquatic animals?
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
What is a hypothesis for the origin of water on earth?
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
How does water relate to the search of extraterrestrial life?
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
How do scientist search for water?
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’
What characteristics have to be present for an exoplanet to support life?
For exoplanet to support life must have following characteristics:
-> water signature
-> in Goldilocks zone
-> large enough to support an atmosphere
