1. Living Cells Respiration

2. Energy release There are 3 main food groups; CarbohydratesFatsProteins Carbohydrates are energy-rich compounds, often referred to as ‘fuel foods’ ‘fuel foods’ To get energy from our food, we need to chemically break it down (See sheets pg 26) Complex carbohydrates are built up from repeating units of simpler ones i.e.. Glucose units, which must be broken down into the simpler form before they can be used by the body….. (See top of sheets pg 27) Glucose Maltose Starch Glucose Maltose Starch

3. Glucose as a source of energy Glucose from food diffuses into cells The chemical energy stored in glucose is a source of energy for cells This energy is released gradually in stages, in a series of enzyme controlled reactions called Respiration Some energy is released as heat from cells during respiration while the rest is used to drive chemical reactions. (See sheets pg 27 bottom expt.)

4. Role of ATP Energy released when glucose is broken down in living cells is not used directly but is used to synthesise the chemical adenosine triphosphate (ATP) Adenosine Pi Pi Pi Adenosine Pi Pi Pi ATP can provide energy for cell processes such as contraction of muscle cells, (ie. When energy is needed immediately) The energy stored in the ATP molecule is released when the bond attached to the terminal (last) phosphate is broken by enzyme action This gives ADP (Adenosine diphosphate) and Pi (inorganic phosphate) Adenosine Pi Pi Adenosine Pi Pi (See sheets pg 28)

5. Chemistry of respiration Respiration is the process by which chemical energy is released during the breakdown of foodstuff such as glucose It occurs in every living cell, and involves the regeneration of the high energy compound ATP by a complex series of biochemical reactions Respiration occurs in 2 stages. Stage 1 = Glycolysis (Occurs in the cell cytoplasm) Stage 2 = Krebs cycle (Occurs in the matrix of the mitochondria)

6. The Mitochondrion Mitochondrion (sl) Mitochondria (pl) Living cells contain mitochondria The more energy a cell requires the more mitochondria are present Ie. Sperm cells (tails), muscle cells See diagram – Highly folded inner membrane to create a larger surface area, each fold is called a crista (sl), or cristae (pl) All cristae contain stalked particles which are the site of ATP production.

7. Glycolysis Glycolysis ‘glucose splitting’, is the first stage of respiration which involves each molecule of glucose being broken down to form 2 molecules of pyruvic acid Glycolysis also results in the production of 2 ATP per molecule of glucose. (See sheets pg 29)

8. The Krebs Cycle Pyruvic acid is needed for stage 2 which involves a series of enzyme controlled reactions, which requires oxygen During this stage oxygen is used to break down pyruvic acid to carbon dioxide and water (in animal cells) Enough energy is released to make 36 more ATP molecules Hydrogen is removed from the glucose molecule and the carbon and oxygen are released as carbon dioxide The hydrogen then joins with the raw material oxygen (from the air) to produce water The energy released is used to build up ATP

9. Comparison of energy yield in aerobic and anaerobic respiration The complete breakdown of glucose in the presence of oxygen releases a great deal of energy which is used to produce 38 ATP molecules The breakdown of glucose in the presence of oxygen is called aerobic respiration When oxygen is absent from cells, glucose can only be partly broken down and releases only enough energy to produce 2 ATP molecules This breakdown of glucose in the absence of oxygen is called anaerobic respiration.

10. Aerobic respiration Glucose is a carbohydrate Formula C 6 H 12 O 6 In aerobic respiration glucose is broken down by living cells, using up oxygen (O 2 ) This process releases energy (ATP), carbon dioxide (CO 2 ), and water (H 2 O) (See sheets pgs 29/30) This can be summarised; Glucose + Oxygen Energy + ATP + Water C 6 H 12 O 6 + 6 O 2 38 ATP + 6 CO 2 + 6 H 2 0

11. Anaerobic respiration If not enough oxygen is available, glucose can still be broken down partially to release some energy Glycolysis proceeds and produces pyruvic acid which is then converted into lactic acid (in animal cells), and ethanol and carbon dioxide (in plant cells) Animal cells Lactic acid is a poison which causes muscle ache This anaerobic conversion of pyruvic acid is reversible (See sheets pgs 30/31) When oxygen does become available again, the lactic acid is converted back to pyruvic acid which can be completely broken down to release the rest of the energy in aerobic respiration Plant cells In plant (and yeast) cells anaerobic respiration proceeds but the pyruvic acid is irreversibly converted to ethanol and carbon dioxide (See sheets pg 31)

12. Comparing aerobic and anaerobic respiration (See sheets pg 32) AerobicAnaerobic AerobicAnaerobic Need for Oxygen AlwaysNever Energy Yield 38 ATP2 ATP per moleculeper molecule per moleculeper molecule of glucoseof glucose of glucoseof glucose Degree CompletelyPartially Of glucose Breakdown End CO 2 + H 2 OLactic acid (animals) Products Ethanol + co 2 (plants)