Cellular Respiration

• Cellular respiration is the process by which the cell breaks down nutrients to produce ATP and heat energy as a by-product
• ATP is used to power many processes in the cell, including:

  • The active transport of molecules across membranes
  • The synthesis of macromolecules, e.g. synthesizing proteins from amino acids
  • Movement, e.g. phagocytosis, beating cilia, and the action of myosin and actin in muscle contraction
  • Bioluminescence, e.g. glow worms, fireflies, and angler fish
  • Other metabolic reactions
• Breathing introduces air containing oxygen into the lungs, which then diffuses into the bloodstream during gas exchange
• Red blood cells carry oxygen from the bloodstream to every cell in the body for respiration
• Carbon dioxide is a waste product of respiration that diffuses out of the cell and back into the bloodstream, then returned to the lungs to be exhaled
• The purpose of cellular respiration is to release the chemical energy stored in food molecules by breaking down the chemical bonds in the food
• The raw materials for cellular respiration are glucose, amino acids, or lipid molecules from food, and oxygen from the respiratory system
• Cellular respiration is a catabolic reaction that oxidizes organic molecules by removing hydrogen atoms and reduces the oxygen molecule by adding these hydrogen atoms to form water
• Results in the production of water, carbon dioxide, and energy in the form of ATP
• Cellular respiration and photosynthesis are complementary metabolic reactions. This is because the products generated in photosynthesis (glucose and oxygen) are the raw materials needed for cellular respiration, while the products of cellular respiration (carbon dioxide and water) are used in photosynthesis. This interdependence between the two processes allows for the cycling of energy and nutrients within ecosystems.
• Anaerobic respiration occurs when there is a lack of oxygen or in low quantities
• In anaerobic respiration, only glycolysis takes place, producing 2 ATP molecules instead of 38 in aerobic respiration
• Anaerobic respiration is also known as fermentation and requires specific enzymes
• In animals, anaerobic respiration happens when oxygen is scarce, like in muscles during intense exercise
• During anaerobic respiration in animals, pyruvate from glycolysis forms lactic acid, causing muscle fatigue
• In yeast and bacteria, anaerobic respiration is a common process
• In yeast, pyruvate is broken down into ethanol and carbon dioxide
• Respiration rate is measured by the amount of oxygen consumed or carbon dioxide produced in a given time
• Factors affecting respiration rate include temperature and energy demands
• Increasing temperature initially increases respiration rate up to an optimum, beyond which enzymes denature and respiration declines rapidly
• Energy demands affect respiration rate, with higher demands leading to increased respiration
• During intense exercise, a combination of aerobic and anaerobic respiration is used to generate ATP when oxygen supply cannot meet demand
• Excess post-exercise oxygen consumption (EPOC) occurs after exercise to repay oxygen debt and remove lactic acid from anaerobic respiration