MEMBRANES + FUNCTIONS Flashcards
why is water considered the medium of life?
the first cells originated in water and water remains the medium in which most life processes occur
formation of hydrogen bonds
- 1 oxygen atom binds to 2 hydrogen atoms by sharing a pair of electrons (covalent bonds).
- The oxygen nucleus draws electrons away from the hydrogen nucleus
- The water molecule carries an unequal distribution of electrical charge. It is polar.
- The electrostatic attraction between the oppositely charged regions of 2 neighbouring molecules, gives rise to weak intermolecular forces called hydrogen bonds.
hydrogen bonds occur between water molecules, not within
Draw two water molecules and the hydrogen bond between them.
hydrogen bonds
a weak intermolecular force that exists when electronegativity creates a polar covalent bond (in water molecules)
electronegativity
measures how strongly the nucleus of an atom attracts the electrons it shares with another
factors affecting electronegativity
- no. of protons
- no. of orbital levels in the atom - more orbitals -> decreases the pull on shared electrons <- are further away from the nucleus + more shielding
polar molecule
has an unequal distribution of electrical charge
cohesion
attraction between 2 of the same substances
adhesion
attraction between molecules of 2 different substances
example of cohesion in trees
during transpiration, water is drawn up a tree trunk through xylem vessels: cohesive forces stop the water column from breaking and help draw water up the tree
strength of hydrogen bonds
- not strong
- are weak intermolecular interactions
(large cohesive forces in water arise from the fact there are many of them)
what causes surface tension
when the molecules on the surface of the water have no other water molecules above them and so establish stronger attractive forces upon their immediate neighbouring molecules. (this results in the formation of spherical droplets)
how do animals use surface tension to create a habitat
give an example
pond skaters - their waxy cuticle keeps them waterproof and their mass is not large enough to break the surface tension
an example of adhesion
capillary action
the process by which water molecules are drawn up capillaries without suction. this is the result of water molecules adhering to the walls of those thin walls.
when does capillary action occur
when adhesion is greater than cohesion
how is capillary action used in plants
to move water from the soil into root hair cells. because plant root hair cells are made of porous cellulose that can act as a wick, water can be drawn in by capillary action. When water evaporates from the cell walls of the mesophyll and then leaves the plant through the stomata water is transported up the plant through adhesion & cohesion.
solvent properties of water
- polar substances (e.g. Na+, Cl-) are very soluble in water -> the anions and cations become surrounded by a layer of water molecules
- non-polar substances (O2, N) are not very soluble -> do not form hydrogen bonds with water
when are enzymes able to catalyse reactions
in aqueous solution
state the properties of water
- buoyancy
- viscosity
- thermal conductivity
- specific heat capacity
buoyancy
the ability of a fluid to exert an upward force on an object
viscosity
a fluid’s resistance to objects passing through it
thermal conductivity
a material’s ability to conduct heat
specific heat capacity
the energy needed to raise one kilogram of a material by 1degree C
state the adaptations of the ringed seal
- have low-density blubber to increase their buoyancy
- have a stream-lined shape to reduce drag against viscosity
- have insulating blubber with low thermal condictivity to reduce heat loss
- pups survive in lairs insulated by trapped air
