PRAC QUESTIONS Flashcards
desc how to carry out test for presence of lipids in a liquid sample of food (2)
- Add ethanol
- Then add water
- Shake
- white/milky emulsion forms
2/3
desc how a triglyceride is formed (3)
- it consists of 1 glycerol and 3 fatty acids. these molecules join together to form triglyceride via condensation reaction, which involves forming a bond between the molecules through the elimination of 3 molecules of water (for the 3 fatty acids)
- ester bonds are formed
desc how an ester bond is formed in a phospholipid molecule (2)
- condensation reaction
- between the glycerol and fatty acid
desc how you’d test a liquid sample for the presence of lipid and how you’d recognise a positive result (2)
- (Mix / shake sample) with ethanol, then water;
Sequence is important - White / milky (emulsion);
desc how you’d test a piece of food for the presence of lipid (2)
- dissolve in alcohol THEN add water
- white emulsion shows presence of lipid
the scientists expressed their results as percentage of lipid in plasma membrane by mass explain how they’d find these results (2)
- divide mass of each lipid by total mass of all lipids (in that type of cell)
- multiply answer by 100
a biochemical test to show that raffinose sol contains a non-red sugar (3)
- heat w acid
- heat w benedict’s sol
- red precipitate
other than using colorimeter how can student measure quanitity of red sugar in sol (2)
filter sol and then dry and nweigh it. the heavier it is the more concentrated it is
use of a colorimeter in this investigation would improve nrepeatability of results, why? (1)
quantitative –> standardises the method
1 similarity and 1 difference between strcuture is lactulose and lactose
SIMILAR - both contain galactose, a glycosididc bond
DIFFERENCE- lactulose contains fructose, whereas lactose contains glucose
desc 2 differences between the strcuture of cellulose molecule and glycogen molecule (2)
- cellulose= straight chain, glycogen is branched, only has 1,4 glycosidic bonds
- glycogen has 1,4 and 1,6 glycosidic bonds and
suggest how glycogen acts as a source of energy (2)
- hydrolysed to glucose
- glucose used in respiration
1 difference in strcuutre of starch and cellulose molecule
position of hydrogen hydroxyl groups on carbon atom 1 inverted
explain how cellulose molecules are adapted for their function in plant cells (3)
- long and straight chains
- become linked together by many hydrogen bonds to form fibrils
- provide strength to cell wall
desc the induced fit model of enzyme action AND how an enzyme acts as a catalyst (3)
- substrate binds to the active site therefore forming an enzyme-substrate complex
- active site chnages shape (slightly) so its complimnetary to substrate
- reduces activation energy