Bellwork: What happens during the light independent reactions of photosynthesis

The process of photosynthesis Section 8.3

Photosynthesis Two parts of photosynthesis Light Dependent Occurs in thylakoid membrane Light independent Occurs in Stroma

Light dependent reactions Energy from the sun is used to produce oxygen and convert ADP to ATP and NADP+ to NADPH Occurs in thylakoid membranes Clusters of chlorophyll and proteins called photosystems Surrounded by accessory pigments Absorb sunlight Generate high energy electrons

Photosystem II Pigments in photosystem II absorb light Light energy absorbed by electrons in pigments Passed to the electron transport chain More light – more electrons Water molecule - source of electrons in chlorophyll Split into 2 H+ ion, 1 O atom and 2 electrons by enzymes on inner thylakoid surface Oxygen released H+ ions are released into thylakoid

Electron Transport Chain Energy from electrons used to pump H+ ions from stroma into thylakoid space Example of active transport Electrons end up at a second photosystem – Photosystem I

Photosystem I Electrons do not contain as much energy when they reach photosystem I It has been used up by pumping H+ ions into the thylakoid Light energy re-energizes the electrons Passed onto second electron transport chain before NADP+ molecules pick up electrons and H+ to form NADPH

Hydrogen Ion movement and ATP Formation Buildup of Hydrogen ions within thylakoid makes the Stroma negatively charged in comparison to stroma This gradient provides the energy to make ATP H+ ion can not cross the membrane directly ATP synthase – protein that spans the membrane Flow of H+ ions causes it to spin Acts like a turbine Binds phosphate and ADP to form ATP Causes Chemiosmosis

Summary

Light independent reactions NADPH and ATP formed during light dependent reactions contain lots of energy Not effective long term store In the Calvin Cycle this energy is used to create sugars

Carbon enters the cell Carbon dioxide enters the Calvin cycle from the atmosphere Enzyme in chlorophyll binds CO2 with 5 carbon compounds already in chloroplast 6CO2 molecules lead to 12 3 carbon molecules These 3 carbon molecules are converted to higher energy forms Comes from ATP and NADPH

Sugar production Halfway through the cycle 2 of the 3-C molecules are removed Used as building blocks to produce sugars or other compounds Can be used by the plant or passed on to organisms when plant is eaten Remaining carbon molecules are re-arranged into 6 5-C molecules ready to go around the cycle again

Factors affecting photosynthesis Temperature Enzymes function best between 0 and 35 degrees Celsius At very low temperatures photosynthesis can stop entirely Light Intensity More light = more photosynthesis until a point There is a maximum rate Water Raw material for photosynthesis No water, no photosynthesis Explain waxy coatings on plants in arid environments

Photosynthesis under extreme conditions Under bright hot conditions many plants will close small openings in their leaves that allows CO2 to enter Stops water leaving, but also stops CO2 from entering CO2 level drops, photosynthesis can stop Specific types of plants have adapated C4 CAM plants Water loss is minimized Photosynthesis can still take place

C4 photosynthesis and CAM plants C4 plants Specialized chemical pathway Low levels of COR can be captured and passed to the Calvin cycle Requires extra energy to function 4 carbon atoms in first compound formed Example – Corn, sugar cane CAM plants Carbon dioxide is incorporated into organic acids in cool darkness Carbon is trapped within the leaves Leaves are sealed during day time, but carbon has already been stockpiled Example – pineapple, cactus