Chapter 5 Metabolism

Chapter 5 : Metabolism Producers and consumers : a chemical process that uses light energy and produces carbohydrates. Photosynthesis is carried out by plants, algae and some bacteria. Anything which carries out photosynthesis is called a producer. Photosynthesis Consumers, like animals (including humans) and fungi, get their food by eating plants. They cannot make organic molecules from scratch, like producers. Photosynthesis is a series of reactions that form glucose and other carbohydrates. Photosynthesis 6 CO2 + 12 H2O ----------> C6H12O6 + 6 H2O + 6 O2 Leaf structure Water comes into the leaf through veins from the roots. CO2 enters the leaf through small holes called stomata. Chloroplasts are mainly on the top surface of the leaf. Calvin cycle This takes place in the stroma of the chloroplast. It takes in CO2 and produces carbohydrate ( glyceraldehyde phosphate or GA3P ). Fig 10.10. The Calvin cycle uses the ATP and NADPH that were produced in the light reactions. Fig 10.12 1) C3 plants : typical plants that open their stomata during the day, and close their stomata at night. Common plants in cool areas eg Canada. Three different types of plants: : open their stomata only briefly during the day. They store CO2 as a 4 carbon sugar. Mainly tropical plants eg sugarcane. 2) C4 plants : only open their stomata at night. These are desert plants like cactus. 3) CAM plants Respiration is a chemical reaction that releases energy from food. Animals, plants and fungi all carry out respiration. In respiration, oxygen is used to break apart food molecules. The energy released by this reaction is stored as the chemical ATP. When the cell needs energy, it breaks down ATP (adenosine tri-phosphate) to ADP (adenosine di-phosphate). Cellular respiration respiration : uses oxygen. does not use oxygen. Aerobic Anaerobic respiration : Aerobic respiration Glucose + Oxygen produces Carbon dioxide + Water + Energy C6H12O6 + 6 O2 produces 6 CO2 + 6 H2O. Energy is stored in the cell as ATP or NADH. Aerobic respiration is divided into three main stages: Glycolysis, Citric acid cycle and Electron transport chain. Fig 10.14 Glycolysis: Glucose ( 6 carbon atoms) is split into 2 molecules of pyruvic acid (3 carbons each). This produces 2 ATP and 2 NADH. Glycolysis takes place in the cytoplasm. Citric acid cycle This breaks down the pyruvic acid to carbon dioxide. This produces 2 ATP and 6 NADH , for every glucose molecule entering glycolysis. The citric acid cycle takes place inside the mitochondria. The citric acid cycle produces the CO2 that you breath out. Electron transport chain This stage produces most of the energy ( 32 - 34 ATP molecules, compared to only 2 ATP for glycolysis and 2 ATP for Krebs cycle). Table 10.1. This stage converts the NADH into ATP. The electron transport chain works as a proton pump: it pumps hydrogen ions (protons) through the membrane, and only allows them back through a protein (ATP synthase) which makes ATP. The electron transport chain uses oxygen to accept electrons at the end of the chain (the electrons combine with hydrogen ions and oxygen to produce water molecules). The electron transport chain takes place in the mitochondria. Anaerobic respiration ( or fermentation) Anaerobic respiration does not use oxygen. Only glycolysis can occur. Single celled organisms eg bacteria and yeast can survive anaerobically. Large animals (eg humans) build up an oxygen debt when anaerobic. During anaerobic respiration, pyruvate builds up and is converted to : lactic acid in animals. ethanol ( alcohol ) in plants.