carbs and lipids Flashcards
What is a monomer?
. A monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made
A starch molecule has a spiral shape. Explain why this shape is important to its function in cells.
. Compact/occupies small space/tightly packed;
The structure of cellulose is related to its role in plant cell walls. Explain how. (3)
. Long, straight, unbranched chains of Beta glucose;
. (Joined by) many WEAK hydrogen bonds;
. Form microfibrils / macrofibrils;
. Provide rigidity/strength/support;
Give one feature of starch and explain how this feature enables it to act as a storage
substance.
. Helical / spiral So compact / tightly packed / can fit (lots) into a small space;
. Insoluble So no osmotic effect / does not leave cell / does not affect water potential;
. Large molecule / long chain (So) does not leave cell / contains large number of glucose units;
. Branched chains (So) rapid hydrolysis to remove glucose for respiration;
Hydrogen bonds are important in cellulose molecules. Explain why.
. Holds chains/cellulose molecules together/forms cross links between chains/cellulose molecules/forms microfibrils;
. Providing strength/rigidity (to cellulose/cell wall);
. Weak Hydrogen bonds provide strength in large numbers;
Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein
. Glucose and galactose
. Joined by condensation
. Joined by glycosidic bond
. Added to polypeptide in Golgi
Describe how the student would show that reducing sugars were present in a solution.
. Add Benedict’s;
. Heat to 95°C;
. Red/orange/yellow/green precipitate (shows reducing sugar present);
Describe how you would test a sample of food for the presence of starch.
. Add potassium iodide (KI) solution to the food sample;
. Blue/black/purple indicates starch is present;
Describe how you would test a liquid sample for the presence of lipid box and how you would recognise a positive result.
. (Mix / shake sample) with ethanol, then water and shake;
. Cloudy White / milky (emulsion);
. Add ethanol and shake
. Then add water and shake again
. Cloudy white emulsion forms if lipid present
Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?
. Double bond(s);
. (Bonds) between carbon atoms within the hydrocarbon chain;
Describe how an ester bond is formed in a phospholipid molecule.
. Condensation (reaction) OR Loss of water;
. Between of glycerol and fatty acid;
Some seeds contain lipids. Describe how you could use the emulsion test to show that a seed contains lipids. (3)
. Crush/grind;
. With ethanol/ alcohol, to dissolve the lipid;
. Then add water then shake;
. Forms a white emulsion / goes white;
What are the differences between a triglyceride and a phospholipid?
. Fatty acid removed;
. Replaced with a phosphate group;
Compare and contrast the structure and properties of triglycerides and phospholipids
. Both contain ester bonds
. Both contain glycerol
. Fatty acids on both may be saturated or unsaturated
. Both are insoluble in water
. Both contain C, H and O but phospholipids are also contain P
. Triglyceride has three fatty acids and phospholipids have two fatty acids plus phosphate group
. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region
. Phospholipids form monolayer/micelle/bilayer but triglycerides don’t.
Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.
Lipid
1. Add ethanol/alcohol then add water and shake/mix OR Add ethanol/alcohol and shake/mix then pour into/add water;
2. White/milky emulsion OR emulsion test turns white/milky;
Non-reducing sugar
3. Do Benedict’s test and stays blue/negative;
4. Boil with acid then neutralise with alkali;
5. Heat with Benedict’s and becomes red/orange (precipitate);
Amylase
6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;
7. Add starch, (leave for a time), test for reducing sugar/absence of starch;
