National 5 Biology Course Notes Unit 1 : Cell Biology Part 8 : Respiration

Glucose + Oxygen Carbon dioxide + Water + Energy Respiration Respiration is a series of enzyme controlled reactions by which energy stored in glucose molecules is released. The word equation below summarises aerobic respiration (breakdown of glucose in the presence of oxygen). Glucose + Oxygen Carbon dioxide + Water + Energy ATP production The energy released from glucose is used to make ATP. ATP is produced when a molecule of ADP is joined to a molecule of Pi (inorganic phosphate). Energy is stored in ATP until it is needed for cell processes. When the energy is required for a cellular processes the ATP is broken down to for ADP and Pi releasing the stored energy. Respiration ADP + Pi ATP Glucose + Oxygen Amino Acids Protein Carbon Dioxide + Water Cellular Processes, e.g. protein synthesis

Processes in cells and organisms that require energy These are examples of processes in cells and organisms that require energy Protein synthesis Cell division Active transport Muscle contraction Transmission of nerve impulses Respiration reactions The first stage of respiration occurs in the cytoplasm of the cell. During this stage, glucose is broken down to form pyruvate (pyruvic acid). (This stage is called glycolysis) Glucose Pyruvate

Second stage of respiration in the mitochondria The second stage of respiration requires oxygen. It takes place in the mitochondria and only occurs in aerobic respiration. Carbon dioxide and water are produced from pyruvate by these reactions Pyruvate Carbon dioxide + Water Mitochondria The diagram shows a mitochondrion Cells that need to use a lot of energy, like muscle cells, sperm cells and neurones (nerve cells) have a lot of mitochondria.

Fermentation is the breakdown of glucose in the absence of oxygen. Fermentation in yeast cells and plant cells produces ethanol and carbon dioxide The summary equation for fermentation in yeast and plant cells is: glucose ethanol + carbon dioxide Fermentation in animal cells (including human muscle cells) produces lactic acid. The summary equation for fermentation in animal cells is: glucose lactic acid Production of ATP Aerobic respiration produces 38 molecules of ATP for each glucose molecule broken down. Fermentation produces 2 molecules of ATP for each glucose molecule broken down.

Comparison of aerobic respiration and fermentation Type of Respiration Fermentation in Animals Fermentation in Plants and Yeast Location(s) Cytoplasm and Mitochondria Cytoplasm Final Products Carbon Dioxide and Water Lactic Acid Ethanol and Carbon Dioxide ATP Yield 38 molecules 2 molecules