CourseCourseQ BankQuestion BankDocsDocuments

C1.1.12 (HL)—Heat generation

Exergonic metabolic reactions release some energy as heat, helping endotherms maintain body temperature in cold environments and small bodies during survival.

Syllabus
First assessment 2025
Objective
C1.1.12
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks2

Common command terms

  • Explain

Recent exam appearances

November 2025Paper2 ["HL"] · TZ11(g)[ 2 ]C1.1.12 (HL)—Heat generation
November 2025Paper2 ["HL"] · TZ11(f)[ 2 ]C1.1.12 (HL)—Heat generation
Practice this objective

Coverage 2025–2025 · Updated 15 Jul 2026

Metabolism Can Release Heat

HL only

Metabolic reactions transfer energy, and some of the released energy appears as heat rather than being captured in ATP or products.

Cells use coupled reactions and ATP to conserve part of the energy, but inefficiency and thermodynamic constraints produce heat. Heat generation can help endotherms maintain body temperature but must be regulated.

Trace energy allocation:

  • chemical energy in substrate
  • captured work or ATP
  • unavoidable heat release
  • heat loss or regulation

During respiration, not all glucose energy becomes ATP; some warms tissues and must be dissipated or used for thermoregulation.

Heat is an energy transfer, not a separate metabolic substance or proof that ATP production stopped.

Heat generation

HL only

Assessment in practice

2 marks
How it is assessed

This objective is assessed through structured response, commonly using Explain.

Command terms

Explain

What earns marks

Build the answer around this relationship: Metabolic reactions release some energy as heat.

Representative question

Question 1

[Maximum number: 2]

Above a body mass of 10 kg , there is little difference in BMR between desert and polar mammals. Suggest reasons for this.

Enzyme Regulation

HL only

Enzymes can act inside or outside cells, metabolic reactions release heat, pathways may be linear or cyclical, and pathway output is regulated by inhibition. Competitive inhibitors bind active sites and can be overcome by more substrate; non-competitive inhibitors bind allosteric sites; feedback inhibition uses end products to inhibit earlier enzymes; mechanism-based inhibitors trap enzymes after reaction begins.

  • Location: intracellular versus extracellular enzyme action.
  • Pathway shape: linear products move forward; cyclical pathways regenerate acceptors.
  • Inhibition: competitive active-site competition, non-competitive allosteric shape change, feedback end-product control, mechanism-based irreversible trapping.

Concept essentials

  • Metabolic reactions release some energy as heat.
  • Endotherms use metabolic heat to help maintain body temperature.
  • Cold environments increase heat loss and can raise metabolic demand.
  • Large mammals lose proportionally less heat because of lower surface area to volume ratio.