biological molecules and food tests 2.7, 2.8, 2.9 Flashcards
what is the test for reducing sugars (glucose)?
benedicts solution
what’s the method for reducing sugars test - benedicts solution?
- add benedicts solution to a sample of food (5cm3)
- place in a water bath at 80 degrees for 5 minutes
- if glucose is present the colour will change from blue to brick red
if it is yellow, green or orange it is a positive but lower concentration of sugar
what’s the colour change for a positive sugar-reducing test - benedicts solution?
blue to brick red
what’s the test for starch?
iodine
what’s the method for testing for starch - iodine?
- add a few drops of orange iodine solution to the food sample on a spotting tile
- a blue-black colour indicates the presence of starch
what’s the colour change for a positive starch test - iodine?
orange to blue-black
what’s the test for protein?
biuret
what’s the method for testing for proteins - biuret?
- add 2cm3 water to a food sample and shake (if not a liquid)
- add an equal volume of dilute sodium hydroxide and shake
- add two drops of 1% copper sulfate solution
- if protein is present a pale purple colour will appear
what’s the colour change for a positive test for proteins - biuret?
blue to pale purple
what’s the test for lipids?
emulsion
what’s the method for testing for lipids - emulsion?
- place the food sample in a tube
- add a small amount of ethanol and shake to dissolve any lipid in the alcohol
- add an equal amount of water
- a cloudy white colour indicates the presence of lipids
what’s the colour change for a positive lipids test - emulsion?
cloudy white
why do leaves store glucose as starch?
glucose is not a good storage molecule as it is soluble, meaning it can draw water through osmosis causing plants to swell
starch is insoluble molecule
what are carbohydrates made of?
carbon, hydrogen, oxygen
made up of simple sugars
what is the use of carbohydrates?
carbohydrates are broken down in a chemical reaction, respiration, to release energy in the form of ATP
this energy is used for other processes
what are the simple sugars of carbohydrates?
simple sugars - glucose and fructose - are the smallest units of carbohydrates
examples of complex carbohydrates:
many sugar molecules (1000s) are joined together to make complex carbohydrates:
- starch, used to store glucose in plants
- glycogen, used to store glucose in animals and fungi
these are better storage molecules as they are less soluble than simple sugar and so have less effect on water movement i n and out of cells
what are fats (lipids) made of?
carbon, hydrogen, oxygen
made of 3 fatty acids joined to glycerol molecules
what is the function of fats (lipids)?
- energy storage (can used in respiration)
- part of cell membranes
- thermal insulation
- electrical insulation (around nerve cells)
- buoyancy (helps marine animals such as whales to float)
what are proteins made of?
carbon, hydrogen, oxygen, nitrogen
made amino acids joined together
20 different amino acids which can be combined in any order
shape of a protein helps carry out its job
what are the functions of proteins?
- structural molecules
- controlling chemical reactions - these are enzymes
- messenger molecules - hormones
- combating disease - antibodies
- transport
what do you do before a food test (preparation)?
- break up food using a pestle and mortar
- transfer food into a beaker with distilled water
- stir mixture with a glass rod to dissolve some of the food
- filter solution with a lined filter paper funnel to get rid of any solid bits of food
