Question
(i) Define mutation. [1]
(ii) Explain how evolution by natural selection depends on mutations. [4]
▶️Answer/Explanation
Ans
i. change in genetic makeup/DNA/nucleotide/base sequence
ii.
a.mutations cause variation among organisms of same species/population;
b.some variations/mutations make individual more suited to its environment/wayof life;
c.individuals that are better adapted survive and produce offspring;
d.individuals pass on genetic characteristics/mutation/variation to offspring;
e.natural selection increases frequency of characteristics/alleles that makeindividuals better adapted;
Question
Pastry cream or confectioners’ custard is made with a combination of milk (rich in casein and lactose), egg yolks, sugar, starch and a flavouring such as vanilla.
(a) Describe the structure of starch. [5]
(b) Explain how amino acids in casein could reach the liver, starting from the moment when the person takes a bite of pastry cream pie. [7]
(c) Congenital lactase deficiency is a type of lactose intolerance that occurs in infants. It is inherited in an autosomal recessive pattern. Calculate the chance of congenital lactose intolerance in a child whose parents are both carriers for the disorder, showing fully how you reached your answer. [3]
▶️Answer/Explanation
Ans:
a
a. starch is a carbohydrate
b. starch is formed by carbon, hydrogen and oxygen
c. it is a polymer/chain/polysaccharide
d. formed from monosaccharides/simple sugars/glucose
e. linked together by condensation/dehydration
f. consists of amylose and amylopectin
g. amylose is a long chain/unbranched
h. amylopectin is branched
b
a. food is mechanically/physically digested in the mouth through mastication/chewing
b. mixed with saliva (to form the bolus) in mouth
c. moved through esophagus/peristalsis
d. proteins digested in the stomach (pepsin)
e. pancreas secretes enzymes into lumen of small intestine OR (endo)peptidases/trypsin) are secreted by pancreas
f. enzymes digest macromolecules to monomers OR endopeptidases digest polypeptides to peptides/amino acids
g. villi of small intestine absorb amino acids
h. amino acids carried to blood capillaries
i. blood (capillaries) carry amino acids to (hepatic portal) vein/blood vessel going to liver
j. amino acids absorbed by active transport/protein pumps in the villi
c
a. gametes of both parents shown as a capital and small letter (eg L and l)
b. possible F1 genotypes
c. 25% lactose intolerant, 50% carriers, 25% lactose tolerant OR 75% tolerant and 25% intolerant OR child has 25%/1:4/ chances of inheritance of intolerance