IGCSE Biology Topic 12: Respiration

Vocabulary flashcards covering key terms and definitions from the IGCSE Biology lecture on Topic 12: Respiration.

Respiration

Chemical process in cells where glucose is broken down to release energy, controlled by enzymes.

Breathing

Physical act of inhaling oxygen and exhaling carbon dioxide from the lungs.

Aerobic Respiration

Breakdown of glucose using oxygen to release a large amount of energy, producing carbon dioxide and water.

Anaerobic Respiration

Breakdown of glucose without oxygen, releasing little energy; products differ by organism (lactic acid in muscles, ethanol + CO₂ in yeast).

Glucose

Six-carbon sugar (C₆H₁₂O₆) that serves as the main fuel molecule for respiration.

Enzymes

Biological catalysts that speed up and control the reactions of respiration.

Yeast

Single-celled fungus used to investigate respiration and for bread-making and brewing.

Methylene Blue

Indicator dye that turns colorless when oxygen is removed, used to monitor respiration rate in yeast.

Rate of Respiration

Speed at which respiration occurs; often calculated as 1 ÷ time taken for an indicator to change.

Independent Variable

Factor deliberately changed in an experiment (e.g., temperature in the yeast respiration investigation).

Dependent Variable

Factor measured in an experiment (e.g., rate of respiration).

Controlled Variables

Factors kept constant to ensure a fair test, such as yeast volume, glucose concentration, pH, or dye amount.

Water Bath

Equipment that maintains a set temperature for test tubes during experiments.

Denaturation

Permanent loss of enzyme shape (and function) at high temperatures, reducing respiration rate.

Temperature Optimum

Approx. 40 °C for yeast respiration, where enzyme activity and respiration rate are highest before denaturation starts.

Oxygen Debt

Temporary shortage of oxygen during vigorous exercise that must be ‘repaid’ post-exercise to oxidise lactic acid.

Lactic Acid

Toxic product of anaerobic respiration in muscle cells; causes cramps and fatigue.

Ethanol (Alcohol)

Alcohol produced, along with CO₂, during anaerobic respiration in yeast.

Active Transport

Energy-requiring movement of substances against a concentration gradient across membranes.

Muscle Contraction

Shortening of muscle fibers; an energy-dependent process supplied by ATP from respiration.

Protein Synthesis

Cell process of building proteins from amino acids; requires energy from respiration.

Cell Division

Process of one cell splitting into two; energy-dependent and powered by respiration.

Enzyme–Substrate Collisions

Interactions between enzymes and their substrates; frequency increases with temperature up to the optimum.

Energy Yield (per Glucose)

High in aerobic respiration and low in anaerobic respiration.

Carbon Dioxide (CO₂)

Gas produced in both aerobic respiration and anaerobic respiration in yeast, expelled during breathing.