Energy – Cells need energy to do work and to catalyse reactions Energy is also needed for growth, cell division, movement and to get rid of waste products. Energy comes in different forms but cells use chemical energy. Chemical energy is stored in bonds or the connections that join the atoms to molecules. Once a bond is broken energy is released. Things like sugars, fats and proteins which you will remember are all made of chains of smaller molecules contains lots of bonds and energy.

ATP……. Usable energy for cells. The molecule contains a bond which when broken releases lots of energy to be used by the cell. Once released, the energy is called adenosine di-phosphate (two) ADP can be recharged again and recycled. As always this conversion of energy means some is lost as heat

Where does ATP come from? Food is broken down by the digestive system into smaller molecules such as glucose. Tho body then breaks the glucose down further in the cells by a series of steps, controlled by enzymes to release ATP. This process occurs in the mitochondria and uses the oxygen we breathe in and is called AEROBIC RESPIRATION This allows energy to be used for movement contraction of muscles, nerve transmission of messages, transport, warmth, growth, cell division and moving molecules against the concentration gradient. Complete aerobic breakdown of glucose: Glucose + oxygen carbon dioxide + water + energy MUST MEMORISE ABOVE FORMULA!

Aerobic respiration Means there is always a complete breakdown of the glucose molecule. Occurs in 3 steps: Glycolysis, Krebs cycle, Electron Transport Chain The 36-38 units of ATP are produced from one molecule of glucose and six oxygen molecules. If there is no oxygen present then anaerobic respiration occurs – this happens in the cytoplasm not mitochondria and only produces about 2 molecules of ATP What happens: ~ glucose diffuses into the cytoplasm ~ about 7 different enzymes breakdown the glucose in small steps and produce a substance called pyruvic acid (if this doesn’t proceed to the mitochondria with oxygen then lactic acid is produced)

Aerobic respiration

Comparison Aerobic Anaerobic Occurs in the mitochondria Occurs in the cytoplasm Requires oxygen No oxygen required Complete breakdown of glucose molecules Incomplete breakdown of original glucose molecules Large amount of energy produced (36 ATP) Minimal amount of energy produced (2 ATP)

Anaerobic respiration- fermentation in animals When no oxygen is present. If this happens in the muscles (think of a marathon runner who after some time was running out of fuel- hadn’t eaten so had no more glucose…was tired and finding it difficult to get enough oxygen….) The marathon runners muscle cells would start burning stored fuel and only undergo the process of glycolysis. This produces lactic acid (the thing that gives you cramp..) Therefore, the pyruvate produced in glycolysis undergoes fermentation into lactic acid in most animals READ and note Page 42

Anaerobic respiration – fermentation in plants and microorganisms The pyruvate produced in glycolysis undergoes fermentation into carbon dioxide and alcohol in most plants, and in microorganisms such as yeast and bacteria. Yeast respires by converting the sugar to alcohol and carbon dioxide and when they have produced a lot the yeast does not survive. Alcohol is made with sugar, yeast and water. Need warm conditions for fermentation to occur Need to allow carbon dioxide to escape and prevent bacteria getting in (if bacteria gets in we may end up with vinegar). READ and note pg 43-44 Answer the key questions on pg 44