Zadanie 9, Paper 2, specimen 2025, Biologia IB HL

(a) Maximum 4:

The chemical persists because it degrades slowly. ✔

It enters food chains at producers or other low trophic levels. ✔

Feeding transfers the chemical to higher trophic levels. ✔

Excretion may be difficult or slow. ✔

It accumulates in fatty tissues. ✔

Higher trophic levels can have higher concentrations. ✔

Bioaccumulation within organisms OR biomagnification along food chains occurs. ✔

(b) Maximum 7:

Both types reduce enzyme-catalysed reaction rates. ✔

Both involve interactions with the enzyme, including amino-acid side chains. ✔

Competitive inhibitors bind at the active site whereas non-competitive inhibitors bind elsewhere. ✔

Competitive inhibitors do not bind at the allosteric site, whereas non-competitive inhibitors bind at an allosteric site. ✔

Competitive binding blocks substrate access, whereas non-competitive binding changes enzyme function through a separate site. ✔

Competitive inhibitors often resemble the substrate, whereas such resemblance is not required for non-competitive inhibition. ✔

Increasing substrate concentration can overcome reversible competitive inhibition but does not restore the uninhibited maximum rate in pure non-competitive inhibition. ✔

Both types can be reversible; non-competitive inhibition is not necessarily permanent. ✔

A valid competitive example is malonate inhibiting succinate dehydrogenase; an appropriate allosteric example is isoleucine feedback inhibition of threonine deaminase. ✔

(c) Maximum 4:

Aerobic respiration slows. ✔

Reduced NAD accumulates when its oxidation is inhibited. ✔

Electron transfer through the affected pathway declines. ✔

Less energy is available to pump protons across the inner membrane. ✔

The proton gradient diminishes. ✔

Proton flow through ATP synthase decreases. ✔

Oxidative ATP production falls. ✔

Oxygen accepts fewer or no electrons OR less or no water is formed. ✔

Construction: 1 mark for clear, concise communication across the response.

Award any N listed points within each part, where N is its cap. Part caps: 4, 7, 4. Maximum 15 content marks plus 1 independent construction mark, total 16. In (b), at least one similarity is required for 7 marks. Accept accurate examples without requiring a particular named inhibitor. Do not credit the false universal statement that non-competitive inhibition is permanent. In (c), glycolytic ATP production may continue and the effect depends on the inhibited site.