A1.1 Flashcards
Water
How much of our planets surface is water?
71%
How much time has water existed on earth?
3.8 Billion years
Where and how did the first cells originate?
The first cells originated in water, where the oceans blocked harmful ultraviolet radiation from the Sun, allowing the first life to evolve.
What is the medium in which most life processes occur?
water
What portion of a living organism does water form?
between 65-95%, 80% in human cells
What does a water molecule consist of?
The water molecule consists of one atom of oxygen and two atoms of hydrogen combined by sharing pairs of electrons (covalent bonding).
What is a polar molecule?
An unequal distribution of electrical charge within a molecule ( net negative charge oxygen atom and net positive on the hydrogen atom)
What is a hydrogen bond?
When a positively charged hydrogen atom is attracted to a negatively charged oxygen atom of a nearby water molecule. (weaker than covalent bonds but enough to hold water molecules together)
What is Cohesion?
Cohesion is the force by which individual molecules of the same type attract and associate (stick together).
Why do water molecules stick together
Hydrogen bonding
What does cohesion do in a plant?
Helps water be drawn up the xylem vessels in plants
What is surface tension in water?
The outermost molecules of water form hydrogen bonds with the water molecules below and next to them causing an inward net force that allows the molecules on the surface to contract and resist being stretched or broken
Why is waters surface tension high?
The water molecules on the surface have no neighbouring water molecules so they exhibit stronger forces of attraction to the molecules on the surface and beneath them.
What does surface tension do in water?
allows it to form perfectly spherical droplets
What is adhesion?
Adhesion is the force by which molecules cling to surrounding material surfaces
What does hydrophilic mean?
Materials and substances with an affinity for water as described as hydrophilic
What is capillary action?
When adhesion between the walls of the capillary tubes and the water draws water up the tube
What is water a powerful solvent for ?
Polar substances
What does hydrophobic mean?
Materials and substances that are repelled by water
Are non polar substances hydrophobic or hydrophilic?
Hydrophobic
What is thermal conductivity in water?
Water has a high thermal conductivity (28 times that of air) allowing it to conduct heat well
What is buoyancy?
The ability of any fluid (liquid or gas) to provide a vertical upwards force on an object placed on it
What is viscosity?
The resistance to flow (one can move easier through air than through water)
What is specific heat capacity in water?
the large amount of heat needed to raise the temperature of water because a lot of energy is needed to break the hydrogen bonds
Where do scientists hypothesise water came from?
extra planetary asteroids
The relationship between life and water
life on other planets needs water and water can only exist at the right distance from a star (goldilocks zone).
What is transit spectroscopy?
A method scientists use to see if a planet has water
