5.1 Photosynthesis Flashcards
Energy transfer and nutrient cycle
Photosynthesis and energy
The process where energy from light is used to make glucose from water and carbon dioxide. Photosynthesis an example of a metabolic pathway
ATP
ADP phosphorylated to ATP, ATP hydrolysed to ADP
ATP properties
Stores only a small, manageable amount of energy, no energy wasted as heat. Small, soluble molecule so easily transported. Easily broken down, energy released instantaneously. Quickly remade. Can phosphorylate molecules. Can’t pass out of cell, cell always has immediate supply of energy
Compensation point
Particular light intensity at which the rate of photosynthesis matches rate of respiration
Chloroplasts
Contain photosynthetic pigments (e.g. chlorophyll a/b, carotene) found in thylakoid membranes, create a photosystem when attached to protein
Stroma
Contains enzymes, sugars and organic acids. Starch grains store carbohydrates in stroma
Redox reactions
Reactions that involve reduction and oxidation. Oxidation is loss of electrons, reduction is gain of electrons
Coenzymes
A molecule that aids the function of an enzyme, transfer a chemical group from one molecule to another
NADP
NADP coenzyme transfers hydrogen from one molecule to another. Reduces by giving hydrogen, oxidises by taking hydrogen
Light-dependent reaction
Photophosphorylation of ADP to ATP, making reduced NADP from NADP, splitting water into protons. Photolysis splits water into protons, electrons and oxygen
Non-cyclic photophosphorylation (Light-dependent) Step 1
Light energy absorbed by PSII. Electrons move to higher energy level, they are released from chlorophyll and move down ETC to PSI
Electron carriers
Proteins that transfer electrons. Photosystems and electron carriers form an electron transport chain
Non-cyclic photophosphorylation (Light-dependent) Step 2
Photolysis replaces the electrons lost from PSII
Non-cyclic photophosphorylation (Light-dependent) Step 3
Electrons lose energy as they move down ETC, energy used to transport protons into thylakoid so proton gradient across thylakoid membrane. Protons move down ATP synthase into stroma, forming ATP
Non-cyclic photophosphorylation (Light-dependent) Step 4
Light energy absorbed by PSI, exciting electrons. Electrons transferred to NADP along with proton from stroma. Forms reduced NADP
Chemiosmotic theory
Process of electrons flowing down ETC and creating proton gradient to form ATP
Cyclic photophosphorylation (Light-dependent)
Produces ATP only using PSI. Electrons recycled to PSI via electron carriers. Only produces small amounts of ATP, no NADPH or oxygen
Calvin Cycle (Light-independent)
Takes place in stroma of chloroplasts. Makes triose phosphate which can be used to make glucose or other useful organic substances
Calvin Cycle Step 1
CO2 enters leaf through stomata and diffuses into stroma. Combined with RuBP and catalysed by rubisco. Unstable compound breaks down to glycerate 3-phosphate
Calvin Cycle Step 2
Hydrolysis of ATP reduces GP to triose phosphate with H ions from NADPH
Calvin Cycle Step 3
Five out of every 6 molecules of TP used to regenerate RuBP, which uses rest of ATP from light-dependent reaction
Hexose sugars
Used to make larger carbohydrates. Calvin cycle happens six times to make one hexose sugar from 2 TP. Requires 18 ATP and 12 reduced NADP
Light intensity optimum
Higher light intensity, more energy provided. Photosynthetic pigments only absorb red and blue wavelengths
Temperature optimum
Temperatures around 25 degrees Celsius optimum. At high temperatures enzymes denature and stomata close to prevent too much loss of water, so less CO2 enters leaf which slows down photosynthesis
