Transcript notes
Photosynthesis • Takes place only in autotrophs (make their own food) • (e.g. plants, Archaea, also some Protists and Bacteria) • Basically, light energy is used to make CO2 and H2O into sugars (chemical energy). O2 and H2O are waste products. • Happens in the chloroplast of the plant cell Others… • Chemosynthesis…getting energy from chemicals • Bacteria by hydrothermal vents at bottom of ocean take chemicals out of water, break them down and get energy from them. • Some called heterotrophs have to eat other things for food. • (e.g. animals, fungi, also some Protists and Bacteria) Chemosynthesis 2 steps • Light Dependent Reactions – Also just called Light Reactions – Must have light to take place • Light Independent Reactions – Also called Dark Reactions or Calvin Cycle – Can happen in light or dark Light Dependent Reactions • Happens in the thylakoid (inside membranes) of the chloroplast • Chlorophyll (green chemical) traps sunlight • Energy is used to split water into O2 (waste product) and H2 • Energy from H2 is stored as ATP and NADPH ATP & NADPH • ATP is the molecule all cells use as energy • It has an amino acid (adenine) a sugar (ribose) and 3 phosphates. • Energy stored in the phosphates’ bonds • Break bond…use energy…become ADP + P • ADP + P + energy = ATP • NADP+ carries 2 electrons and a hydrogen atom ATP and NADPH • The energy from light is passed from protein to protein in the thylakoid membrane as part of an electron transport chain. • As H+ ions and electrons are moved into/out of the thylakoid membrane, energy is stored in ATP and NADPH used in the light independent reactions. Electron Transport Chain Summary of Photosynthesis https://www.youtube.com/watch?v=2IygaV0_-B0 Light Independent Reactions • CO2 is made into 3-carbon sugars in a process called carbon fixation • Uses the ATP and NADPH from the light reactions • Water is a waste product, but is reused by the cell and not given off • These sugars are the end product of photosynthesis. They are used by the plant as energy and stored for later use. • Happens in the stroma (open areas) of the chloroplast Summary of Photosynthesis https://www.youtube.com/watch?v=m8v7prlscM0 Summary of Photosynthesis • In the chloroplast… • 6 CO2 + 6 H2O and light energy makes sugars (CH2O) + O2 (waste) • (Actually it takes 12 H2O, but there’re 6 H2O left over, so they cancel out) • CH2O is a generic formula for a carbohydrate (sugars). You could also write C6H12O6 • ATP and NADPH are energy carriers from light dependent reactions to light independent reactions Technically… • Photosynthesis does not make glucose (C6H12O6) • It makes a 3-carbon sugar called G3P which is used to make other organic compounds, like cellulose (many sugars linked together) used in the cell wall. • The sugars can be used for energy by the plant (in the mitochondria) or to build structures So why… • Have you been taught that the end product is glucose? • Scientists (and teachers) often say that it makes glucose, because it is one of the things photosynthesis can make, and it helps show the relationship between photosynthesis and cell respiration (next unit). Factors Affecting Photosynthesis • Temperature: – between 0oC and 35oC is best. • Light: – “perfect” amount – More is good, up to a certain point • Water – “perfect amount” – More is good up to a certain point