Bio

• Photosynthesis is the process by which green plants and certain other organisms transform light energy into chemical energy.
• The cells in a middle layer of leaf tissue called the mesophyll are the primary site of photosynthesis.
• Small pores called stomata — singular, stoma — are found on the surface of leaves in most plants, and they let carbon dioxide diffuse into the mesophyll layer and oxygen diffuse out.
• Each mesophyll cell contains organelles called chloroplasts, which are specialized to carry out the reactions of photosynthesis.
• Within each chloroplast, disc-like structures called thylakoids are arranged in piles like stacks of pancakes that are known as grana — singular, granum.
• The membrane of each thylakoid contains green-colored pigments called chlorophylls that absorb light.
• The fluid-filled space around the grana is called the stroma, and the space inside the thylakoid discs is known as the thylakoid space.
• Light-Dependent Reactions involve the excitation of photosystems by light energy, the production of ATP via an electron transport chain, and the reduction of NADP+ and the photolysis of water.
• Photosystem is a light collecting unit of the chloroplast.
• Photosystems are groups of photosynthetic pigments (including chlorophyll) embedded within the thylakoid membrane.
• The electrons lost from Photosystem II are replaced following the photolysis of water.
• The light dependent reactions occur within the intermembrane space of the thylakoids.
• Photosystems (PS) are classified according to their maximal absorption wavelengths, with Photosystem I (700 nm) and Photosystem II (680 nm) being the most common.
• As the electrons are passed through the chain, they lose energy, which is used to move H+ ions into the thylakoid.
• Chlorophyll in Photosystems I and II absorb light, which triggers the release of high energy electrons (photo activation).
• The protons are returned to the stroma via ATP synthase, which uses their passage (via chemiosmosis) to synthesize ATP.
• The products of the light dependent reactions (ATP and NADPH) are used in the light independent reactions.
• The electron transport chain transports H+ ions from the stroma to within the thylakoid, creating a proton gradient.
• The H+ ions return to the stroma (along the proton gradient) via the transmembrane enzyme ATP synthase (chemiosmosis).
• ATP synthase uses the passage of H+ ions to catalyze the synthesis of ATP (from ADP + Pi), a process known as photophosphorylation.
• The reactions of the Calvin cycle take place in the stroma, which is the inner space of chloroplasts.
• Some G3P molecules go to make glucose, while others must be recycled to regenerate the RuBP acceptor.
• In the second step of the Calvin cycle, each molecule of 3-PG receives a phosphate group from ATP, turning into a doubly phosphorylated molecule called 1,3-bisphosphoglycerate (and leaving behind ADP as a by-product).
• Regeneration of the RuBP acceptor in the Calvin cycle requires ATP and involves a complex network of reactions.
• In the first step of the Calvin cycle, an enzyme nicknamed rubisco (RuBP carboxylase-oxygenase) catalyzes CO2 to a five-carbon sugar called ribulose bisphosphate (RuBP).
• The Calvin cycle is fueled by ATP and NADPH from the light reactions.
• The Calvin cycle is a process that converts carbon dioxide into organic molecules and is used to build three-carbon sugars.
• The resulting 6-carbon molecule is unstable, however, and quickly splits into two molecules of a three-carbon compound called 3-phosphoglycerate (3-PG).
• This step of the Calvin cycle produces NADP+ as by-products.