Energy Photosynthesis Cellular Respiration EXAM UNIT III Energy Photosynthesis Cellular Respiration

Energy Energy is the ability to do work. All living things must have energy to survive. Energy is necessary for intracellular and extracellular movement, chemical reactions, and other vital processes. The vast amount of energy ultimately comes from the sun and flows through the biological system.

Forms of Energy There are various forms of energy. For example, kinetic energy,heat energy, potential energy, etc. Potential energy is stored energy. A common form of potential energy is the energy stored in chemical bonds. Hydrogen bonds in particular are an important source of stored energy that many organisms rely on.

The Laws of Thermodynamics 1st Law: Energy is neither created nor destroyed, it simply changes form. 2nd Law: When energy changes form there is a large energy loss.

Energy Pyramid The flow of energy through the biological system is often illustrated with an energy pyramid. Producers (plants & algae) capture the solar energy through photosynthesis and are eaten by primary consumers (herbivores), which are then eaten by secondary consumers (carnivores). All of these are broken down by decomposers (fungi & bacteria)

Types of Energy Transfer Reactions Endergonic reactions are reactions in which energy is stored. For example when a plant goes through photosynthesis to make carbohydrates. The making (synthesis) of organic molecules is known as “anabolism”. Exergonic reactions are reactions in which energy is released. For example when your body breaks down carbohydrates, or when a match burns. The breakdown of organic molecules is known as “catabolism”.

Anabolism and Catabolism

ATP: Adenosine Triphosphate ATP is a molecule that transfers energy in biological systems. It is a nucleotide comprised of the sugar ribose, the nitrogen-containing base adenine and 3 phosphates. The phosphates are arranged in a chain with the last phosphate attached by a high-energy bond. When this bond is broken energy is released. When this bond forms, energy is stored.

ATP CYCLE

Enzymes Enzymes are specialized proteins that act as biochemical catalysts. Enzymes speed up chemical reactions, make them more efficient, and control the rate of reaction. Enzymes are necessary for both anabolism and catabolism. Enzymes typically end in “ase”. For example, lactase is the enzyme that breaks down lactose.

Biochemical Reactions Chemical reactions in living systems are known as biochemical reactions. Biochemical reactions involve a reactant (or reactants) binding to an enzyme at a specific location known as the active site. A reaction occurs at the active site and a product (or products) is produced. Coenzymes often bind to enzymes and help them carry out chemical reactions.

Biochemical Reactions

Metabolic Pathways Biochemical reactions typically occur in a series of reactions known as a metabolic pathway. Metabolic pathways involve numerous reactants, enzymes, and products. A + B  C + D  E + F  G + H  I

Photosynthesis Photosynthesis is a series of biochemical reactions that captures solar energy and stores it in the bonds of a carbohydrate. Photosynthesis is a anabolic reaction. Photosynthesis is carried out by plants, algae, and some bacteria. In eukaryotic cells, photosynthesis occurs in the chloroplast. Photosynthesis involves 2 reactions: The Light Dependent Reaction The Light Independent Reaction

Chloroplast Structure

Light Dependent Reaction The Light Dependent Reaction is dependent on light. The purpose of this reaction is to harvest energy from sunlight. It occurs in the thylakoid within the chloroplast. In this reaction, water is split, oxygen is released as a waste product, and NADPH2 and ATP are produced.

Light Independent reaction The Light Independent Reaction is dependent on temperature. The purpose of this reaction is to store enrgy in the hydrogen bonds of a carbohydrate. It occurs in the stroma within the chloroplast. In this reaction, NADPH2 and ATP are used to reduce carbon dioxide (CO2) to glucose (C6H12O6). This reaction is also known as the Calvin Cycle.

Cellular Respiration Cellular respiration is the breakdown of glucose to harvest the energy it contains. There are two types of cellular respiration: aerobic cellular respiration and anaerobic cellular respiration. Both of these are catabolic reactions. In aerobic cellular respiration, glucose is broken down with oxygen. In anaerobic cellular respiration, glucose is broken down without oxygen.

Aerobic Cellular Respiration Aerobic cellular respiration is the braekdown of glucose with oxygen. All advanced cells use aerobic cellular respiration to harvest energy. This process involves 4 phases: Glycolysis Transition Reaction Kreb’s Cycle Oxidative Phosphorylation

Glycolysis Glycolysis is the breakdown of 1 molecule of glucose to form 2 molecules of pyruvate. This process occurs in the cytoplasm. During glycolysis, 2 pyruvate, 2 NADH, and 4 ATP are formed. It takes 2 ATP to get this process going (this is called the energy of activation). Therefore, your reactants are 1 glucose molecule and 2 ATP; your products are 2 pyruvate, 2 NADH, and 4 ATP molecules.

Transition Reaction The transition Reaction involves the convertion of pyruvate to Acetyl Co A. This process occurs in the mitochondria. During the transition reaction, 2 pyruvates are converted to 2 Acetyl Co A, and 2NADH, and 2 CO2 are produced. Therefore, your reactants are 2 pyruvates, and your products are 2 Acetyl Co A, 2 NADH, and 2 CO2 molecules.

Kreb’s Cycle The Kreb’s Cycle occurs when Acetyl Co A is converted to citrate and is then completely broken down. This occurs in the mitochondria. During the Kreb’s Cycle, citrate is broken down and 2 FADH, 6 NADH, 4 CO2 , and 2 ATP are released. Therefore, your reactants are 2 citrate molecules, and your products are 2 FADH, 6 NADH, 4 CO2 , and 2 ATP molecules.

Oxidative Phosphorylation Oxidative phosphorylation involves the oxidation of all of the NADH and FADH previously produced. The energy harvested during this process is used to produce ATP (by phosphorylating ADP). Oxygen is the final electron acceptor for this process and is reduced to water. This process occurs in the mitochondria. Therefore, your reactants are 2 FADH, 10 NADH, and 6 O2 , your products are 32 ATP and 6 H2O.

Anaerobic Respiration Anaerobic Respiration is the incomplete breakdown of glucose without oxygen. It is also known as fermentation. In this process, glycolysis occurs but then pyruvate is reduced by the NADH. In animal cells and most bacteria, the pyruvate is reduced to lactic acid and only 2 ATP are produced. In yeast cells and some bacteria, the pyruvate is reduced to ethyl alcohol, and CO2 , and only 2 ATP are produced.

Products of Fermentation

Comparison between Photosynthesis and Aerobic Cellular Respiration Photosynthesis is an anabolic reaction during which energy is stored in a carbohydrate. Energy + 6 CO2 + 6 H2O  C6H12O6 + 6 O2 Aerobic Cellular Respiration is a catabolic process during which carbohydrate is broken down to release its stored energy. C6H12O6 + 6 O2  Energy + 6 CO2 + 6 H2O