Photosynthesis 🌱

• Photosynthesis is a reaction in which light energy is used to split apart the strong bonds in water molecules in a process of photolysis in order to combine hydrogen with carbon dioxide to produce a fuel in the form of glucose.
• Oxygen is a waste product of this reaction and is released into the atmosphere.
• The rate of photosynthesis is determined by carbon dioxide concentration, light intensity and well as temperature.
• It contains stacks of thylakoid membranes called grana which contain the photosynthetic pigments such as chlorophyll arranged as photosystems.
• It contains stroma which is the fluid surrounding the grana, stroma contains all the enzymes required for the light independent stage of photosynthesis.
• There are two stages of photosynthesis: Light-dependent reaction in which electrons are excited to a higher energy level by the energy trapped by chlorophyll molecules in the thylakoid membranes and Light-independent reaction also known as the Calvin cycle which uses ATP (source of energy) and reduced NADP (reducing power) to produce glucose.
• Light-dependent reaction occurs as follows: Electrons are excited to a higher energy level by the energy trapped by chlorophyll molecules in the thylakoid membranes.
• Electrons are then passed down the electron transport chain from one electron carrier to the next and this process generates ATP from ADP and inorganic phosphate in a process called photophosphorylation.
• Reduced NADP is also generated in the light-dependent stage as the electrons are transferred to NADP (NADPH) along with a proton.
• Both ATP and reduced NADP are then used in the light-independent stage of photosynthesis.
• Light-independent reaction, also known as the Calvin cycle, is the final stage of photosynthesis which uses ATP (source of energy) and reduced NADP (reducing power) to produce glucose.
• In the light-independent reaction, RuBP is combined with carbon dioxide in a reaction called carbon fixation catalysed by the enzyme RUBISCO.
• RuBP is converted into two glycerate 3-phosphate (GP) molecules in the light-independent reaction.
• Reduced NADP and ATP are used to convert GP to triose phosphate (TP) in the light-independent reaction.
• Some of TP molecules are used to make glucose which is then converted to essential organic compounds such as polysaccharides, lipids, amino acids and nucleic acids.
• Remaining TP molecules are used to reform RuBP with the help of ATP in the light-independent reaction.
• Photosynthesis is affected by many factors, the factor in lowest supply and therefore limiting the rate of the reaction is known as the limiting factor.
• Limiting factors in photosynthesis include light intensity, CO2 concentration, and temperature.
• If light intensity is in short supply, the light dependent reaction will slow, resulting in lower amounts of ATP and NADPH created.
• The level of GP will rise and TP will fall, causing RuBP levels to fall.
• If CO2 concentration is in short supply, the light independent reaction will slow.
• If temperature is low, Rubisco and other molecules will have lower levels of kinetic energy, affecting the enzyme-controlled reactions.
• L-Alanine is a starting point for the synthesis of amino acids.
• The light-dependent stage of photosynthesis is to generate products which will power the light-independent stage, also known as the Calvin Cycle.
• Light energy absorbed during the light-dependent stage of photosynthesis enables ATP production.
• During the light-dependent stage of photosynthesis, hydrogen from water is used to reduce NADP.
• Electrons from the reaction centre of photosystem II are excited during the light-dependent stage of photosynthesis.
• Excited electrons from photosystem II pass along the electron transport chain and ATP is produced during the light-dependent stage of photosynthesis.
• Photolysis produces electrons to replace the lost electrons from photosystem II during the light-dependent stage of photosynthesis.
• Electrons from the reaction centre of photosystem I are excited during the light-dependent stage of photosynthesis.
• ATP is produced via the second electron transport train during the light-dependent stage of photosynthesis.
• One TP molecule can convert into glycerol.
• ATP and NADH reduce GP to 3-carbon TP (triose phosphate).
• TP can be converted into many useful products: essential six-carbon sugars such as glucose and fructose, glucose and fructose can react to form sucrose, and glucose molecules can react together to form key polysaccharides such as amylose or cellulose.
• An enzyme called RuBisCo catalyses a reaction between RuBP and CO2 to form two molecules of 3-carbon GP (glycerate-3-phosphate).
• The chain of events taking place in the Calvin Cycle is described below:
• The energy required for these reactions is supplied by ATP produced in the light-dependent stage.
• More ATP is required to power this, and this is obtained through the light-dependent stage.
• Most of TP used to regenerate RuBP which allows the cycle to continue.
• The Calvin Cycle utilises hydrogen from reduced NADP and carbon dioxide to synthesise glucose and other useful organic molecules.