IB DP Biology Topic 3: Genetics: 3.1 Genes SL Paper 2


(i) Define mutation.      [1]

(ii) Explain how evolution by natural selection depends on mutations. [4]



i. change in genetic makeup/DNA/nucleotide/base sequence


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;


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]




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   


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 


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/ \tfrac{1}{4} chances of inheritance of intolerance

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