Biochemical Tests & Stomata: Starch, Sugars, Proteins

tests

presence of starch iodine solution turns from yellow brown to blue-black presence of reducing sugars benedict's solution turns from blue to orange red presence of proteins biuret solution turns from blue to purple/violet presence of lipids ethanol emulsion test mix the food with ethanol and shake add ethanol to distilled water milky white appearance presence of vitamin c DCPIP purple to colourless

hydrogen carbonate indicator red at normal co2 yellow at high, purple at low sodium hydrogen carbonate soln source of co2 sodium hydroxide used to absorb co2 buffer solution used to fix pH at a certain point

to determine no of stomata

• polish leaf with varnish

• leave to dry and remove the varnish layer

• put it on a microscopic slide and count

control tests

• adding water instead of the substance

• use boiled solution of substance to eliminate enzyme activity

• use glass bead to assess for non biological factors

to decrease humidity use a dehumidifier to increase humidity place hot water bowls around it use colorimeter or colour chart when experiment involves colour change(indicator) as it is difficult to identify endpoint with naked eyes any experiment involving drops of a liquid.

errors and their improvements

any experiment involving drops of a liquid error → volume of drops size is inconsistent or unknown or different improvement → use syringe/ burette/ graduated pipette

any experiment involving shaking or stirring a liquid. error → different degree of, shaking / mixing / stirring improvement → shake at a fixed speed or use a (mechanical) stirrer error → different time of, mixing or shaking improvement → shake or stir, for a fixed time ;

any experiment involving hot or cold water. error → temperature of the water not controlled / temperature changes improvement → thermostatically controlled water-bath / insulation / bunsen burner

any experiment involving unknown volume of a liquid. error → volume of starch not measured improvement → measuring cylinder / burette / pipette

investigation question:

• independent variable

• dependant variable

• constant/controlled variables (need at least 2 max 3)

• procedure of investigation (methods)

• safety precautions (goggles,mask,gloves)

• repeat experiment two or more times

how to calculate surface area with grid paper :