Zadanie 10, Paper 2, maj 2025, TZ3, Biologia IB HL

(a) ATP is a temporary transferable energy store, often termed the cell’s energy currency. ✔

Hydrolysis of ATP to ADP and phosphate releases usable free energy. ✔

The energy change can be coupled to many cellular tasks in manageable amounts. ✔

For example, ATP hydrolysis powers active transport or muscle contraction. ✔

ATP can be regenerated from ADP and phosphate. ✔

Different pathways, including aerobic and anaerobic processes, can supply energy for ATP formation. ✔

ATP is kinetically stable enough for release to be enzyme-controlled rather than immediate and uncontrolled. ✔

Its small size and water solubility permit movement within the cell. ✔

Its charge prevents free diffusion through the lipid bilayer, limiting loss from the cell. ✔

(b) Photophosphorylation occurs in chloroplasts. ✔

The thylakoid membrane contains photosystems, electron carriers and ATP synthase. ✔

Pigments absorb light. ✔

Light collection occurs in photosystem pigment arrays. ✔

Absorbed energy excites electrons. ✔

Electrons pass along electron carriers. ✔

Electron-transfer energy drives proton translocation. ✔

Protons are moved from the stroma into the thylakoid lumen. ✔

This creates a proton electrochemical gradient across the thylakoid membrane. ✔

Protons flow back towards the stroma through ATP synthase. ✔

ATP synthase couples this flow to phosphorylation of ADP. ✔

Cyclic electron flow uses photosystem I, whereas linear flow uses both photosystems. ✔

Water splitting supplies electrons to replace those lost from photosystem II. ✔

(c) All heterotrophs use organic compounds as respiratory fuel for ATP production. ✔

Those compounds ultimately come from other organisms rather than being fixed entirely from inorganic carbon by the heterotroph. ✔

Saprotrophs use dead organic matter. ✔

Saprotrophs release digestive enzymes externally and absorb soluble products. ✔

Consumers feed on other organisms. ✔

Primary consumers obtain food directly from producers, unlike consumers at higher trophic levels. ✔

Detritivores ingest fragments of dead organic matter. ✔

Digestion breaks large food molecules into absorbable products. ✔

Holozoic animals and detritivores digest internally, unlike external digestion by saprotrophs. ✔

Cellular respiration transfers energy from acquired compounds into ATP. ✔

Communication: the whole answer is clear, relevant and avoids needless repetition. ✔

(a) Any 3, maximum 3; small/soluble must be linked to mobility for that point. (b) Any 7, maximum 7; accept a valid account linking photosynthetic carbohydrate production to later mitochondrial ATP production, including the relevant inner-membrane machinery. (c) Any 5 distinct points, maximum 5; comparisons should include shared dependence on organic food and differences in acquisition/digestion. Add 1 holistic clarity mark. Total 16. In (b), photosynthesis/chloroplast location OR photosynthetic glucose production earns the introductory point; any relevant thylakoid component correctly located earns the membrane point; ADP phosphorylation alone earns the ATP-formation point. In (c), external enzyme secretion OR external digestion suffices for the saprotroph mechanism; internal digestion by holozoic animals OR detritivores suffices.