biological molecules - water, carbohydrates and lipids Flashcards
polar definition (in regard to molecules)
molecules with regions of negativity and positivity
usually due to asymmetry, the distribution of electrons in a covalent bond or charge of particles
why can water form hydrogen bonds
water is a polar molecule
the positive and negative regions of the molecule attract each other and H atoms can interact with the lone pairs on O atoms to form hydrogen bonds
why is water a good solvent + reaction medium
due to water’s polarity, it can attract positive/negative regions of other molecules
these forces of attraction hold the molecules close together until the solute dissolves
it is also liquid at room temperature
this makes it a good reaction medium for ions or dissolved substances
why is water cohesive
due to water’s polarity, it can form hydrogen bonds meaning there are strong intermolecular forces of attraction between molecules that allow them to stick together
why is water adhesive
due to the polarity of water, the molecules are also attracted to other surfaces
why does water have high surface tension
water is more cohesive to itself than it is adhesive to air
this allows organisms to live on the surface of water e.g. pond skaters
why is water able to travel up plants
water is more cohesive to itself than it is adhesive to other surfaces e.g. the xylem
as water evaporates out of stomata, water molecules are pulled up through the xylem as they stick together - this is called capillary action, as it moves in opposition to gravity
why does water have an unusually high specific heat capacity/specific latent heat
hydrogen bonds between water molecules can absorb a lot of energy, therefore more energy needed to change temperature or state
why is water’s high specific heat capacity important for life
since a very large amount of energy is needed to change the temperature of water by 1 degree, it is a very stable habitat for living organisms as there will be less temperature fluctuations
this is good for living organisms who cannot thermoregulate, such as fish
why is water less dense as a solid/ice
hydrogen bonds between water molecules hold the molecules apart in open lattice structure when solid, so ice is less dense than water
why is it important for living organisms that ice is less dense than water - 2 reasons
- due to the open lattice structure of ice, it can act as a habitat for organisms in winter
- due to low density of ice, it is able to float in water, therefore it can act as insulation in ponds and other bodies of water in winter, protecting them against the extreme cold
what is a carbohydrate
a molecule made of just C, H and O, usually in the ratio CH2O
what is a single unit of sugar
a monosaccharide
2 monosaccharides form …
a disaccharide
glucose is composed of 6 carbons, making it a…
hexose sugar
what are the 2 types of glucose molecule and the differences between them
alpha glucose
- on carbon 1 H is above OH
(the OH groups on alpha do not alternate)
beta glucose
- on carbon 1 OH is above H
(so the OH groups on beta glucose alternate up-down-up-down)
what bonds do carbohydrates form
glycosidic bonds
C-O-C
formed in condensation reactions
broken in hydrolysis reactions
a-glucose + a-glucose =
maltose
a-glucose + fructose =
sucrose
used to transport sugars in plants
a-glucose + galactose =
lactose
found in mammal milk
deoxyribose/ribose are composed of 5 carbons, making them…
pentose sugars
what is a polysaccharide
a complex carbohydrate molecule, made of more than 2 monosaccharide sugars bonded together
4 examples of polysaccharides
- starch
- glycogen
- cellulose
- callose
what is the structure of starch
made of amylose and amylopectin - both made of a-glucose
amylose is unbranched and formed of 1-4 glycosidic bonds, it twists into a helix shape held together by hydrogen bonds
amylopectin is branched and formed of both 1-4 and 1-6 (1 in 25) glycosidic bonds
