biological molecules year 1 mistakes

Describe the hydrolysis reactions involved in the digestion of triglycerides.

• Breaking of ester bonds;

• By addition of water;

Explain why phospholipids can form a bilayer but triglycerides cannot.

• Phospholipid both hydrophobic and hydrophilic

• OR

• Phospholipid polar

•  Triglycerides only hydrophobic

• Hydrophilic/phosphate group attracts water (to either side of

• bilayer);

A student has an apple with a mass of 180 g. The ratio of flesh tissue to core tissue in this apple is 5:1

8% of the whole apple is sugar. Calculate the mass of sugar in the flesh tissue.

12

A student carried out the benedict’s test. Suggest a method other than using a colorimeter that this student could use to measure the quantity of sugar in a solution

• Filter and dry the precipitate 

• measure/find mass

What term is used to describe the different structures of alpha and beta glucose

isomers

Explain the difference in the structure of starch and cellulose molecule shown in diagram above

• Starch is a polymer of alpha glucose, cellulose formed from beta glucose 

• Position of hydrogen and hydroxyl groups on carbon 1 inverted

Explain how cellulose molecules are adapted for their function in plant cells

• Long and straight chains

• Become linked by many hydrogen bonds  to form fibrils

• Provide strength to cell wall

• To resist turgor pressure

Describe how to test for reducing sugar

• Heat in Benedict's solution in a water bath 

• Brick-red precipitate

How to test for enzymes 

• ENZYMES ARE PROTEINS

• Add biuret 

• Turns lilac

Describe how the results from the colorimeter determine which solution contains higher concentration of reducing sugar

Lower transmission has more sugar

Describe how the structure of glycogen is related to its function

• Glycogen is insoluble so does not affect osmosis or water potential 

• Glycogen is branched and more ends means faster hydrolysis 

• Coiled into a helix so more compact for storage 

• Its a polymer of glucose so provides respiratory substrate for energy

Explain why triglycerides are not considered polymers

Not made up of monomers

what chemical group is OH

hydroxyl

Suggest one reason why a data logger is used

to increase accuracy because it reduces human error

to increase accuracy because measurements are small

Describe a chemical test for lipids

add ethanol and shake 

then add water and shake 

produces a milky white emulsion 

How many molecules are produced when a triglyceride molecule is hydrolysed

4

Describe a chemical test to show a solution contains sucrose

• Boil in acid 

• Add alkali to neutralise acid 

• Heat with Benedict’s in a water bath

• Brick red precipitate

A drop of phospholipid was put into a large dish of water. The drop had a volume of 1mm^3. It spread out to form a film on the surface of the water with an area of 400,000mm^2. Calculate the length of a single phospholipid molecule.

2.5x10^-6

Give two differences between the structures of disaccharide and polysaccharide.

• Lactose is a disaccharide and GOS is a polysaccharide;

• Lactose has one glycosidic bond and GOS has many glycosidic

• bonds

Explain why amylase produced in the human digestive system does not

digest GOS.

• Active site (only) complementary to starch OR Active site not complementary to GOS;

• (Due to) tertiary structure;

Prebiotics are foods used to promote good health in humans.

Prebiotics stimulate the growth of ‘healthy’ bacterial populations in the

human digestive system. The bacteria in these ‘healthy’ populations produce enzymes that

hydrolyse GOS.

Suggest how GOS (polysaccharide) can work as a prebiotic.

• Provides galactose/sugar/monosaccharide;

• (Bacteria use the galactose/sugar) for respiration;

(Bacteria use the galactose/sugar) for binary fission/ cell division /replication/reproduction

Iodine solution stains fresh apple tissue black. When iodine solution is

added to apples stored for a week, the stain is less black.

The water potential of apple juice decreases when apples are stored.

Suggest why the water potential of apple juice decreases when apples are

stored.

• Starch hydrolyzed 

• Maltose is soluble so decreases water potential

Compare and contrast structure of cellulose and starch

• Both polysaccharides;

• OR

• Both are glucose polymers

• Both contain glycosidic bonds (between monomers);

• Both contain carbon, hydrogen and oxygen/C, H and O;

• Starch made of α-glucose and cellulose made of β-glucose;

• Starch (molecule) is helical/coiled and cellulose (molecule) is

straight;

Starch (molecule) is branched and cellulose is not/unbranched;

Describe the complete digestion of starch in animals

• Hydrolysis;

• (Of) glycosidic bonds;

• Starch to maltose by amylase;

• Maltose to glucose by disaccharidase/maltase;

explain how 2 enzymes with different amino acid sequences can catalyse the same reaction

both the active sites have very similar/identical tertiary structure

they form enzyme substrate complexes with the same substrate