PHOTOSYNTHESIS (LIGHT DEPENDENT AND LIGHT INDEPENDENT REACTIONS)

What is the order of the pathways

• Light dependent

• Light independent

What is the function of the light dependent pathway

• To transform sunlight that is captured by chlorophyll into the chemical energy of loaded coenzymes

What is the location of the light dependent pathway

• thylakoid membranes

How does the light dependent pathway occur

• Electron transport chain pathway

• A series of proteins that are embedded in the thylakoid membranes

What are the inputs and outputs of the light dependent pathway - unloaded to loaded

• H20 → O2

• ADP + Pi → ATP

• NADP+ → NADPH

• Sunlight

Briefly describe the electron transport chain pathway in the light dependent pathway

• Radiant energy from the Sun is absorbed by chlorophyll

• Water becomes ‘excited’ and splits, producing electrons, hydrogen ions (H+/protons) and oxygen

• Electrons and hydrogen ions load onto NADP+ to form NADPH

• Chemical Formula: (NADP+ + H+ + 2e - → NADPH)

• This energy is used to pump protons from the stroma to inside the thylakoid, creating a proton gradient

• Passive movement of protons down this gradient back into the stroma produces kinetic energy which is used by ATP synthase enzyme to produce ATP from ADP and Pi

What is the function of the light independent pathway

• To assemble simple inorganic carbon dioxide molecules into more complex organic glucose molecules

Where is the location of the light independent pathway

• Stroma of the chloroplasts

What is the main enzyme in C3 plants? What is it vital for?

• Rubisco

• Carbon fixation

What enzymes does the light independent stage use

• Preloaded coenzymes from light-dependent stage

What does NADPH do in the light dependent stage

• Donates hydrogens and electrons

• As molecules are reduced to higher energy levels

What is ATP used for in the light independent stage

• An energy source

• Supplies energy for the anabolic steps of this cycle

Inputs and outputs of the light independent stage - loaded to unloaded

• ATP → ADP + Pi

• NADPH → NADP+

• CO2 → glucose

What is inorganic CO2 converted to

• 3-carbon molecule (carbon fixation)

Some of the outputs of each stage become…

• inputs to the other stage

• the two stages depend on each other

Examples of how the two stages depend on each other

• Loaded coenzymes that are outputs from the first stage are the inputs to the second stage

• Unloaded coenzymes produced in the second stage are recycled back to the first stage for reloading

What occurs if the supply and recycling of either coenzyme is interrupted

• photosynthesis stops

Role of oxygen in electron transport chain

• Oxygen sucks out the leftover hydrogens to remake the hydrogen concentration gradient

• Creates water as a by-product