Topic 5

• Photosynthesis occurs in chloroplasts, which contain structures such as thylakoid stacks, thylakoid membrane, stroma, inner and outer membranes.
• Photosynthesis is a two-stage reaction consisting of the light dependent and light independent reactions.
• The light dependent reactions require light and water to create ATP and NADPH, which are then used in the light independent reactions.
• The light independent reactions involve the conversion of light energy into chemical energy, which is stored in the form of ATP.
• Photolysis is the process where light energy is used to split water into oxygen, electrons, and protons.
• The protons are picked up by NADP to form NADPH, which is then used in the light independent reaction.
• The electrons are passed along a chain of electron carriers and the oxygen is either used in respiration or diffuses out through the stomata.
• In chemiosmosis, the electrons gain energy from the chlorophyll and are released from the chlorophyll.
• Those electrons move along a series of proteins embedded within the thylakoid membrane, releasing energy as they move.
• Growers need to consider how they can remove limiting factors to maximize profits.
• Adding in artificial lighting, heating a greenhouse, and burning fuels to produce carbon dioxide can be cost effective if the additional cost is offset by the additional profit.
• Aerobic respiration consists of four key stages: glycolysis, the link reaction, Krebs cycle, and oxidative phosphorylation.
• Glycolysis produces some ATP but not a lot and it happens in anaerobic respiration because oxygen is not required.
• Glycolysis occurs in the cytoplasm, not inside of the mitochondria.
• Glycolysis begins with the phosphorylation of glucose to create glucose phosphate, which uses two molecules of ATP.
• Glucose phosphate is quickly converted into triose phosphate, which is then oxidized to form pyruvate, producing 4 ATP and reduced NAD.
• The link reaction involves the oxidation of pyruvate to acetate, with an NAD picking up a hydrogen to create another reduced NAD molecule.
• The acetate produced in the link reaction combines with coenzyme A to create acetyl-CoA, which can then enter the Krebs cycle.
• For every glucose molecule, the link reaction happens twice, creating two acetyl-CoA, two carbon dioxides, and two reduced NAD.
• The Krebs cycle generates even more reduced coenzymes, a small amount of ATP, and some carbon dioxide.
• The final coenzyme involved in respiration is FAD, which is regenerated in the Krebs cycle.
• The products per cycle are three reduced NAD, one reduced FAD, 180p, and two carbon dioxides.
• For every glucose, the cycle happens twice, doubling all of the values.
• Some of the energy from the released electrons is used to actively transport or pump those protons from the stroma across a protein and into the thylakoid lumen, resulting in a concentration gradient being built up.
• The electrochemical gradient enables the protons to move by facilitated diffusion back down their concentration gradient to the stroma.
• The only protein that the protons can attach to is ATP synthase, which enables the enzyme to phosphorylate the ADP into ATP.
• The ATP produced in the light reactions is used in the light independent reactions, also known as the Calvin cycle.
• The Calvin cycle uses carbon dioxide as well as the two products from the light dependent reaction to create a hexose sugar.
• The ATP needed for the Calvin cycle is hydrolyzed to provide energy for the reaction and the reduced NADP is used to donate the hydrogen to reduce the molecule Gp within the cycle.
• Carbon dioxide reacts with ribulose 1,5-bisphosphate (RibP) to form a five-carbon compound, which splits into two three-carbon compounds, forming glyceraldehyde 3-phosphate (Gp).
• One ATP molecule is used and the reduced NADP is reformed when glyceraldehyde 3-phosphate (Gp) picks up the hydrogen.
• The two carbons removed from the three-carbon compounds are used to create a hexose sugar.
• The Calvin cycle has to happen six times before a hexose sugar, which could be glucose, is made.
• The limiting factor in photosynthesis is anything that reduces the rate of photosynthesis, which could be light intensity, carbon dioxide concentration, or temperature.
• The rate of photosynthesis increases with light intensity until a certain point, after which the rate plateaus and level off, indicating that another factor, such as carbon dioxide concentration or temperature, is now limiting the rate of reaction.
• Carbon dioxide limits the rate of photosynthesis because it is a reactant in the Calvin cycle.
• Light intensity can limit the rate of photosynthesis because light energy is needed in the light dependent reactions for photolysis and photoionization.
• Kilojoules is the unit of energy but it is also recorded per unit area and per year to standardize the results and enable environments to be compared.
• Nitrogen is essential for the creation of proteins, ATP, and nucleic acids, which are essential for animals, plants, and microbes.
• The nitrogen cycle involves key processes such as ammonification, nitrification, nitrogen fixation, and denitrification.