7PhotosynthesisLight is absorbed – excites electrons in pigments = start of photosynthesisExplain why a leaf appears greenBecause it is absorbing most of the other wavelengths of light and reflecting green
11Lets Photosynthesize!Light reactions = first stage of photosynthesis – light energy is converted to chemical energy (energy from the sun ATP + NADPH)
12The Leaf What organelle in the leaf is responsible for photosynthesis? ChloroplastParts of a chloroplastThylakoids - Flattened sacs where photosynthesis occurs – surrounded by a membraneGrana –Stacks of thylakoidsStroma –Solution that surrounds the grana
15The Light-Dependent Reactions: Generating ATP and NADPH The light-dependent reactions encompass the steps of photosynthesis that directly involve sunlight.The light-dependent reactions occur in the thylakoids of chloroplasts.
16The Light-Dependent Reactions: Generating ATP and NADPH Thylakoids contain clusters of chlorophyll and proteins known as photosystems.Photosystems absorb sunlight and generate high-energy electrons that are then passed to a series of electron carriers embedded in the thylakoid membrane.
18Light Reactions Occurs on thylakoid membrane Chlorophyll absorbs light and electrons get excited – flow on electron transport chainEnergy in excited electrons is used to create NADPH and ATP These are temporary energy carrier moleculesWater – electron donor – releases O2ATP + NADPH are then used to create glucose in the Calvin Cycle18
19Chlorophyll absorbs light and electrons are excited Chlorophyll absorbs light and electrons are excited. These electrons flow on electron transport chain along the thylakoid membrane. As the electron is transported it loses some energy and is used create a H+ concentration gradient inside the thylakoid, which is later used to create ATP from ADP +P. The electron finally reaches the final electron acceptor and is combined with NADP+ and a H+ to form NADPH, which is an energy carrier molecule. Water is split to (2 H2O = 4H+ + 4e- + O2) to replace the lost electrons.
20Light Reactions 2 H2O = 4H+ + 4e- + O2 One of the most important steps (water molecules split):2 H2O = 4H+ + 4e- + O2protonsoxygenelectrons
21REVIEWDuring the light reactions ___ and ___ are used to make ___, ___, and ___.
26Announcement1-13Quiz up to and including the light reactions (notes pages 1-7) on Wednesday 1-19
27REVIEW How are heterotrophs and autotrophs different? 1-13How are heterotrophs and autotrophs different?2. Photosynthetic pigments …3. What colors does a plant primarily use for photosynthesis?How do you know?
28Review 4. Photosynthesis uses… Photosynthesis produces… 1-135. Where do the light reactions take place?6. Why is the splitting of water molecules important for photosynthesis?
29Review 7. The light rxns use… To produce… 1-138. What’s the electron transport chain?