exam Q's

Question 1

describe how a method that uses benedict’s reagent and a colorimeter could be calibrated to measure the concentration of lactose in an unknown sample/

Answer 1

1 zero the colorimeter / set to zero
2 using blank
3 use red filter
4 use known concentrations (of lactose) 5 (produce) serial / series, dilutions
6 construct calibration curve
7 test unknown sample (using the same method)
8 use / read from, graph / calibration curve, to determine (unknown) concentration

Question 2

explain how the properties of water are related to the transport role of water in a stem?

Answer 2

cohesion, attracts / holds, water molecules together ✓
allows chain of water molecules to be pulled up xylem ✓
adhesion allows water molecules, to stick / AW, to xylem vessel walls ✓

(water as) a solvent to dissolve ions for transport in the, xylem / transpiration stream

Question 3

suggest how hydrogen and sodium may help the cut flowers to last longer?

Answer 3

hydrogen regulates pH
Sodium used to regulate water potential

Question 4

explain how the structure of phospholipids allows them o form the bilayer of plasma membrane

Answer 4

hydrophilic head and hydrophobic tails (1)

hydrophobic part / tails, repelled / AW, by water (1)

head / hydrophilic part, forms H bonds with water (1)

idea that medium outside / inside plasma membrane is aqueous

Question 5

describe how the structure of llama haemoglobin is likely to be different from that of a camel haemoglobin with reference to the four levels of protein structure

Answer 5

· difference in primary structure
· different amino acid / polypeptide sequence
· amino acid change could cause change to secondary structure
· amino acid change could cause change to tertiary structure
· amino acid change has not changed quaternary structure
· alpha and beta subunits still able to form haemoglobin in both camel and llama.

Question 6

state three properties of a fibrous protein that re different from those of a globular protein

Answer 6

-insoluble
-strong
-unreactive

Question 7

explain how fig 21 shows that insulin has a quaternary structure

Answer 7

there are two polypeptides chained together with disulphide links between cysteine.

Question 8

plan a method to compare the amino acids present in the urine of a person who has been following one of these diets with that of a person who has not

Answer 8

-use chromatography
-place two spots of the urine samples
-separate with solvent
-use ninhydrin to visualise spots
-compare the pattern of the separated components.

Question 9

describe the role of cholesterol in cell surface membranes in the human body

Answer 9

cholesterol binds to phospholipid fatty acid tails increasing the packing of the membrane therefore reducing fluidity of the membrane.

Question 10

what are the differences in the structure of lactose and maltose

Answer 10

lactose
-one glucose one galactose
-beta glucose
-beta glycosidic bond
-sugars flipped

maltose
-both monomers are glucose
-alpha glucose
-alpha glycosidic bond
-monomers in same direction

Question 11

Describe and explain why collagen is a fibrous protein.

Answer 11

1- is long chain
2- insoluble
3- has a structural function / provides strength

a small range of amino acids

Question 12

Outline the method of chromatography that will separate the main amino acids in collagen.

Answer 12

1 digest / hydrolyse / break down, collagen into amino acids
and
2 place, sample / AW, on, chromatography paper /
chromatography plate / stationary phase
3place, (chromatography) paper / (chromatography) plate/
stationary phase, in solvent

additional detail
-place sample on pencil line
-use stain to make amino acids visible (ninhydrin)

Question 13

what is the order of the most to least soluble carbohydrates

Answer 13

glucose-ribose-amylose-amylopectin

Question 14

why do unsaturated fats have a lower melting point

Answer 14

have a c=c which causes kinks causing them to be less uniformly packed and so less energy required to melt it.