12.1 Respiration

2026 Syllabus Objectives

  1. State the uses of energy in living organisms, including: muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature
  2. Investigate and describe the effect of temperature on respiration in yeast

What is Respiration? 🔬

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Respiration is a series of metabolic reactions that take place in cells to release energy from nutrient molecules, particularly glucose. Like all metabolic reactions, respiration is controlled by enzymes.

🔑 Key Point: Respiration is NOT the same as breathing! Respiration is a series of chemical reactions that occur inside cells to release energy from glucose.

Why Do Living Organisms Need Energy? ⚡

Every living cell requires energy to carry out essential life processes. In humans and other organisms, cells need energy for:

  • Muscle contraction – to move parts of the body
  • Protein synthesis – linking amino acids into long chains to make protein molecules
  • Cell division – to repair damaged tissues and enable growth
  • Active transport – moving substances across cell membranes against their concentration gradients
  • Growth – building new cells which can then divide to form more cells
  • Passage of nerve impulses – transferring information quickly from one part of the body to another
  • Maintenance of a constant body temperature – producing heat inside the body to keep warm even in cold environments

All of this energy comes from the food we eat. Food is digested (broken down into smaller molecules) and absorbed from the small intestine into the blood. The blood transports these nutrients to all cells in the body, where they are taken up and used.

The main nutrient used to provide energy in cells is glucose. Glucose contains a lot of chemical energy stored in its bonds. To make use of this energy, cells break down glucose molecules through respiration.

Types of Respiration

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There are two main types of respiration:

🔹 Aerobic Respiration

Aerobic respiration refers to chemical reactions that take place in mitochondria, which use oxygen to break down glucose and other nutrient molecules to release energy for the cell to use.

🔹 Anaerobic Respiration

Anaerobic respiration refers to chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.

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