Zadanie 6, Paper 2, maj 2024, TZ2, Biologia IB SL

(a)

Proteins are built from amino acids. ✔

Peptide bonds connect the amino acids. ✔

These bonds form through condensation reactions. ✔

Linked amino acids make polypeptide chains. ✔

The amino-acid sequence influences the protein’s three-dimensional shape. ✔

(b)

The hormones involved are insulin and glucagon. ✔

Regulation uses negative feedback. ✔

Raised blood glucose stimulates insulin release from pancreatic beta cells. ✔

Insulin promotes glucose uptake by target cells. ✔

Low blood glucose stimulates glucagon release from pancreatic alpha cells. ✔

Glucagon promotes conversion of liver glycogen into glucose OR glucose release from liver glycogen. ✔

(c)

A diploid nucleus undergoes meiosis to produce haploid nuclei; four is acceptable but not required. ✔

The chromosome number is halved. ✔

Each chromosome initially has two sister chromatids. ✔

Homologous chromosomes pair. ✔

Crossing over exchanges material between homologous chromosomes. ✔

Crossing over generates new combinations of alleles. ✔

Homologous pairs orient randomly in the first division, or chromatids assort randomly during the second division. ✔

The first division separates homologous chromosomes. ✔

Random orientation generates different combinations of chromosomes or alleles. ✔

Meiosis produces haploid gametes; restoration of the full chromosome complement by fertilization is an optional explanation. ✔

Fusion of gametes from different parents further contributes to variation. ✔

Quality of communication: clear on first reading, concise and without unnecessary repetition or irrelevant material. ✔

Part (a): any 4 points, maximum 4. Part (b): any 4 points, maximum 4. Part (c): any 7 points, maximum 7. Award 1 independent communication mark. Maximum 16. Accept equivalent wording and relevant diagrams. Part (b): full 4 requires at least one insulin-specific point and at least one glucagon-specific point; otherwise maximum 3.