Photosynthesis

• Oxygen is released as a by-product of the light reaction.
• Energy carriers: ATP and NADPH are the products of light reaction.
• The major features and chemical events in photosynthesis include the conversion of light energy into chemical energy, the reduction of carbon dioxide, and the regeneration of NADP+.
• The pigments present in the leaves of a plant include chlorophyll and carotenoids.
• Chlorophyll and other pigments are important for photosynthesis.
• Photosynthesis in plants happens within an enclosed double-membrane structure known as chloroplasts contained within leaf cells.
• The chloroplast contains a semi-fluid medium, the stroma, which is made up of a mixture of enzymes and water.
• The stroma is embedded by a complex network of stacked sacs known as granum.
• Granum consists of disk-shaped, interconnected membranous sacs known as thylakoids.
• Photosynthetic pigments are unique pigments found in all photosynthetic organisms.
• Chlorophyll absorbs certain wavelengths of light within the visible light spectrum.
• Chlorophyll a is present in all photosynthetic plants including red, brown, and blue-green algae except in photosynthetic bacteria.
• Chlorophyll b is an accessory pigment and acts indirectly in photosynthesis by transferring light it absorbs to chlorophyll a.
• Chlorophyll c is found in certain marine algae, including the photosynthetic chromista (e.g., Diatoms, brown algae) and dinoflagellates.
• Carotenoids or tetraterpenoids are plant pigments responsible for bright red, yellow, and orange colors in many fruits and vegetables.
• Carotenoids also protect chlorophyll from photodamage.
• Xanthophylls contain oxygen.
• Carotene are purely hydrocarbons and contain no oxygen, giving carrots their color.
• The process of photosynthesis is aided by the different pigment molecules that form clusters known as photosystems.
• While the electron moves from one carrier to the next, its energy is being depleted.
• The net process of photosynthesis is summarized by the formula: LIGHT-DEPENDENT REACTIONS.
• The light reactions start when photosystem II absorbs light which excites the electrons in the reaction center chlorophyll then captured by the primary electron acceptor.
• The excited electron is passed to the primary electron acceptor of photosystem I and along the electron transport chain of PS I until they reach nicotinamide dinucleotide phosphate (NADP+), also an electron carrier.
• Together with the electron, NADP+ picks up hydrogen ion from water to become NADPH.
• An enzyme associated with PS II splits water molecules that allow electrons to escape and serve as replacement electrons in the reaction center.
• Photosynthesis is the process where light energy is converted into a form of chemical energy that can be stored and used later on.
• Phycobilins occur only in Cyanobacteris and Rhodophyta.
• Some of this energy is released and is used to pump hydrogen ions from stroma to thylakoid compartment, where they will be utilized to generate ATP, in a process called chemiosmosis.
• Two photosystems: photosystem I (PS I) or also known as PS 700 because it is more reactive to 700 nm wavelength of light and photosystem II (PS II) or PS 680 which reacts most in 680 nm light wavelength are termed PS I and PS II based on the order of their discovery, but the sequence when they proceed in light reactions is from PS II to PS I.
• Photosynthesis is a major process in synthesizing ATP.
• Phycobilins are photosynthetic pigments efficient at absorbing red, orange, yellow, and green light, wavelengths that are not well absorbed by chlorophyll a.
• The process of photosynthesis is divided into two main groups: light reactions which require light energy to operate and light-independent reactions, also known as the Calvin cycle, which do not require sunlight to complete the process.
• The sun is the ultimate source of energy to the earth.
• Light energy is trapped and converted into chemical energy by the thylakoids.
• Electron carriers such as NADP+ and ATP are produced during this process.
• Photosystem II is located on the outer surface of the thylakoid membrane, where it absorbs photons from sunlight to generate electrons that are transferred through an electron transport chain.
• The light-dependent reactions occur in the thylakoid membranes, while the Calvin cycle occurs in the stroma.
• In the light dependent reactions, water molecules are split into oxygen gas and hydrogen ions.
• Light-dependent reactions involve two photosystems, photosystem I (PS I) and photosystem II (PS II).
• Light energy absorbed by chlorophyll causes electrons to move up the electron transport chain, generating ATP and reducing power (NADPH).