Zadanie 7, Paper 2, maj 2022, TZ2, Biologia IB HL

(a) Enzyme active sites bind particular substrates. ✔

Enzymes catalyse reactions OR lower activation energy. ✔

Activity rises with temperature below the optimum. ✔

There is an optimum temperature. ✔

Above the optimum, activity falls sharply; a graph should show an asymmetric temperature response. ✔

Activity falls on either side of an optimum pH. ✔

Activity initially rises as substrate concentration increases. ✔

At high substrate concentration activity approaches a plateau. ✔

Competitive inhibition shifts the substrate response so that more substrate is needed to approach the same maximum. ✔

Non-competitive inhibition lowers activity at given non-zero substrate concentrations OR lowers the maximum rate; failure of extra substrate to reverse it is optional. ✔

(b) Helicase separates the DNA strands. ✔

Topoisomerase/gyrase relieves supercoiling strain. ✔

Primase synthesizes an RNA primer. ✔

DNA polymerase I removes RNA primers and/or replaces them with DNA. ✔

DNA polymerase III synthesizes daughter DNA or joins DNA nucleotides. ✔

DNA ligase seals nicks between adjacent fragments. ✔

(c) A biological species comprises organisms able to interbreed and produce fertile offspring under natural conditions. ✔

Populations contain variation. ✔

Some heritable traits improve survival to reproduction. ✔

Alleles for favourable traits can increase in frequency or be inherited by descendants. ✔

Speciation creates new species. ✔

Populations become reproductively isolated OR experience different selection pressures. ✔

Behavioural isolation involves different courtship or mating behaviour. ✔

Temporal isolation involves different reproductive timing. ✔

Geographical barriers can prevent interbreeding, producing allopatric isolation. ✔

Polyploidy can cause reproductive isolation. ✔

Stabilizing selection favours intermediate phenotypes. ✔

Directional selection favours one extreme over the other. ✔

Disruptive selection favours both extremes relative to intermediates. ✔

Quality: the response is clear on first reading, concise and contains little repetition or irrelevant material. ✔

Part (a):any 5,maximum 5; without graphs maximum 3. Graphs need correctly labelled axes and appropriate shapes; clear annotations can earn the points. Part (b):mark only the first 3 named enzymes;1 per correct name/function,maximum 3. Polymerase I/III numbers are required for those respective functions. Part (c):any 7,maximum 7. Award 1 independent quality mark. Total 16.