CHAPTER 9 NOTES : PHOTOSYNTHESIS AND RESPIRATION SECTION 1: Energy in Living Systems Cells need energy to: Move (some bacteria swim) Change their shape ( blood cells extend and retract when engulf invading bacteria cells) Manufacture new cellular components Maintain and repair cellular structures Transport food into the cell Expel wastes All organisms need chemical energy that comes from carbon compounds in food to carry out their life activities. Almost all of the energy in carbon compounds comes from the sun. The sun is the ultimate source of energy for all living things. Plants, algae, and some prokaryotes carry out Photosynthesis, the process during which sunlight’s energy is used to change CO₂ and H₂O into carbon compounds. Organisms that carry out photosynthesis are called Autotrophs or Producers . Heterotrophs or Consumers are other organisms , including all animals and fungi and most bacteria , that cannot perform photosynthesis and absorb energy by eating other organisms. The energy stored in food molecules in living cells is gradually (step-by-step)released in a series of chemical reactions. Metabolism involves either using energy to build carbon compounds or breaking down carbon compounds and releasing energy in them. Metabolism is part of Earth’s carbon cycle. The main organic compound that cells use is glucose which is produced during photosynthesis. 6 CO₂ + 6H₂O + energy → Glucose + 6O₂ In order to get energy from glucose organisms use Cellular Respiration Glucose +6 O₂ → 6CO₂ + 6H₂O + energy(ATP) ATP is not very useful for storing large amounts of energy over the long term. A single sugar molecule stores more than 90 times the chemical energy. This is why it is efficient for the cells to keep only small supply of ATP on hand. SECTION 2: PHOTOSYNTHESIS Chemical reaction: 6CO₂ +6H₂O+ light →C₆ H₁₂O₆ +6O₂ MUST REMEMBER! Inside a Chloroplast: Molecules that absorb light are called Pigments . The major lightabsorbing pigment in the plants is Chlorophyll which is found in the chloroplasts of plant cells. Chlorophyll molecules are contained within disk-like structures called Thylakoids. A stack of thylakoids is called a Granum. The region outside the thylakoid membrane in the chloroplast is called Stroma. Photosynthesis consists of three stages: Light-dependent reactions(stage 1 and stage 2): Stage1 – the capture of light energy The chlorophyll traps the light energy in the electrons of its atoms Stage 2- the conversion of light energy into chemical energy Converts ADP to ATP Produces oxygen gas Takes place within the thylakoid membranes of chloroplast ATP synthase is an enzyme that assists in production of ATP. ATP synthase allows H⁺ ions to pass through the thylakoid membrane. As the ions pass through, ATP synthase rotates, binding ADP and phosphate group together to produce ATP. Stage 3 Light-independent reaction (Calvin Cycle)(Dark Reaction) (Carbon fixation) Uses CO₂ from the atmosphere Uses ATP and NADPH from light-dependent reaction to produce high-energy sugars Factors Affecting Photosynthesis Availability of water Temperature Intensity of light Carbon dioxide concentration Concepts you must know: What are the reactants and the products of photosynthesis? Name and describe the stages of photosynthesis. What are the factors affecting the rate of photosynthesis? SECTION 3 CELLULAR RESPIRATION Cellular respiration is the process used by humans and most other organisms to release the energy stored in the food they consume. Step1 Glycolysis –does not require oxygen.(anaerobic) cytoplasm Takes place in the Breaks down glucose Produces NADH (electron carrier molecule) from NAD⁺ to be used later Produces two pyruvate molecules from one glucose molecule. This stage uses two ATP and makes 4 ATP= net gain of 2 ATP molecules. 90 % of chemical energy in the glucose is still left. Step2 The Krebs Cycle – aerobic respiration- needs oxygen. Takes place in the mitochondria. Pyruvic acid is broken down into carbon dioxide Produces 1 ATP molecule for each pyruvate molecule. Step 3 Electron Transport chain – series of proteins in the inner membrane of mitochondria Uses the electrons from NADH and FADH₂ to convert ADP into ATP Produces 34 ATP molecules 62 % of energy in the glucose is not used by cellular respiration and is released as heat. The waste products of cellular respiration are H₂O and CO₂.