Zadanie 7, Paper 2, listopad 2024, Biologia IB HL

(a)

mRNA binds a ribosome OR initiation assembles ribosome, mRNA and tRNA. ✔

The ribosome moves along mRNA OR translation proceeds through repeated cycles. ✔

An aminoacyl-tRNA binds at the ribosome. ✔

The tRNA anticodon pairs with an mRNA codon. ✔

Complementary base pairing ensures the appropriate amino-acid sequence is specified. ✔

A peptide bond joins the incoming amino acid to the growing chain OR links amino acids at the ribosomal P and A sites. ✔

The polypeptide is released at a stop codon. ✔

(b)

Amino-acid sequences of corresponding proteins are compared. ✔

Sequence differences accumulate over time. ✔

Mutation produces these differences. ✔

More differences generally indicate a longer time since divergence OR fewer differences suggest more recent shared ancestry. ✔

A cladogram can represent the inferred branching history. ✔

Sequence change can be used as a molecular clock to estimate divergence time. ✔

(c)

Actin and myosin form protein filaments. ✔

These filaments form sarcomeres within myofibrils. ✔

Actin forms thin filaments and myosin thick filaments. ✔

Actin is anchored to Z-lines OR a diagram correctly shows overlapping actin and myosin. ✔

Actin provides sites to which myosin can bind. ✔

Myosin heads attach to actin, forming cross-bridges. ✔

ATP changes the myosin-head state, supplies energy for its cycle or permits detachment. ✔

Head movement shifts actin towards the sarcomere centre OR the filaments slide past one another. ✔

Greater overlap shortens the sarcomere, producing contraction. ✔

Quality of communication: clear on first reading, concise and free from unnecessary repetition or irrelevant material. ✔

Part (a): any 4 distinct points, maximum 4. Part (b): any 4 distinct points, maximum 4. Part (c): any 7 distinct points, maximum 7. Award 1 independent communication mark. Maximum 16.