▶️ Answer/Explanation
(i)
A mutation is a change in the DNA sequence of an organism.
It can involve a change in one or more bases (nucleotides) in a gene.
Sometimes mutations have no effect, but other times they can change the way a protein is made.
(ii)
- Mutations create genetic variation in a population — this means individuals are not all the same.
- Some of these changes might give an individual a better chance of surviving in their environment.
- The individuals with helpful mutations are more likely to survive, reproduce, and pass on those traits to their offspring.
- Over many generations, the helpful mutations become more common in the population.
- This process is called natural selection, and it’s how species evolve and adapt over time.
Markscheme
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/way of 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 make individuals better adapted
▶️ Answer/Explanation
(a)
- Starch is a carbohydrate made of carbon, hydrogen, and oxygen.
- It is a polysaccharide, which means it’s a large molecule made of many glucose units.
- The glucose units are joined together by condensation reactions.
- Starch is made up of two types of molecules:
- Amylose – a long, unbranched chain of glucose.
- Amylopectin – a branched chain of glucose.
Starch is how plants store energy, and we digest it to get glucose.
(b)
- Chewing breaks the food into smaller pieces in the mouth.
- The food mixes with saliva to form a soft ball called the bolus.
- The bolus moves down the esophagus to the stomach by peristalsis (muscle contractions).
- In the stomach, pepsin starts breaking casein (a protein) into smaller chains.
- In the small intestine, enzymes from the pancreas (like trypsin) continue breaking down proteins into amino acids.
- These amino acids are absorbed by the villi in the walls of the small intestine using active transport.
- The amino acids enter the bloodstream through capillaries.
Blood from the small intestine travels through the hepatic portal vein to the liver, where the amino acids are processed or stored.
(c)
- L = normal allele, l = lactose intolerance allele
- Parents are both carriers: genotype Ll × Ll
- Using a Punnett square:
| L (Parent 1) | l (Parent 1) | |
|---|---|---|
| L (Parent 2) | LL (normal) | Ll (carrier) |
| l (Parent 2) | Ll (carrier) | ll (affected) |
So, there is a 1 in 4 chance (25%) that the child will have congenital lactose intolerance.
Markscheme
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 via 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 (e.g., 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