5&6 Processes Flashcards
Light dependent stage of photosynthesis
STEP 1
Light hits photosystem II. A water molecule is split forming H+ and O2. The light excites an electron that moves through the membrane to photosystem I
As the electrons moves through the protein complexes on the thylakoid membrane more H+ ions go through ATP-synthase and make ATP. The H+ are pumped into the lumen
STEP 2
02 used in cellular respiration by the plant or diffuses out of the stomata in the plant leaf
· The highly energised electron from photosystem I is transferred to NADP+ reductase.
NADP+ + 2e- + 2H+ —> NADPH + H+
STEP 3
H+ are loaded to the coenzyme NADP+ to form NADPH. The movement of H+ help load energy onto ADP forming ATP.
STEP 4:
ATP and NADPH are moved to the light independent stage of photosynthesis.
Calvin Cycle
- 𝐶𝑂2 enters the Calvin Cycle and is converted into two 3-carbon molecules.
- NADPH donates hydrogen and ATP donates energy to the carbon molecules.
- Carbon molecules continue to cycle until 6 𝐶𝑂2 molecules in order for glucose to be formed
- Leftover oxygen molecules bind to hydrogen ions to form water.
Rubisco responsibility
- Carbon fixation: 3 CO2 and 5 RuBP molecules form 6 3-PGA molecules.
- Reduction: energy and hydrogen is donated from ATP and NADPH to convert 3-PGA into G3P. One G3P molecule is removed to form glucose.
- Regeneration: ATP is used to convert 5G3P molecules into 3 RuBP molecules to restart the cycle.
C4 Plants
Separate the light independent stage into two separate cells; Corn, sugarcane
¡ Carbon fixation in mesophyll cells (like C3 plants)
¡ Calvin Cycle in bundle-sheath cells
This process occurs through;
o CO2 is fixed by the enzyme PEP carboxylase, (which has no chemical affinity to oxygen), to form oxaloacetate.
o Oxaloacetate is converted to malate which is transported to a bundle-sheath cell.
o Malate breaks down into CO2,which enters the calvin cyle and follows the 3C process
o Pyruvate is also formed from malate breakdown. This is transported to the mesophyll cells and converted to PEP with the help of ATP.
o PEP then helps in the production of oxaloacetate
This process allows for a higher concentration of 𝐂𝐎𝟐 than oxygen for rubisco.
More ATP is used in this process.
Crassulacean Acid Metabolism (CAM) plants
Typically found in warm or drought prone environments. Eg. pineapples, cacti or orchids
- Light dependent stage is the same at C3 & C4 plants
- At night stomata, open so CO2 to diffuses in.
- CO2 is fixed into oxaloacetate by the enzyme PEP carboxylase,
- oxaloacetate is converted to malate (or another organic molecule) and stored in the vacuole.
- During daylight, they shut their stomata to prevent water loss,
- Stored malate or like molecules leaves the vacuole and breaks down to release CO2 for use in the Calvin Cycle as in C3 plants.
This controlled release of molecules from the vacuole ensures high concentration of CO2 o reduce photorespiration.
More ATP is need and Water is conserved.
Electron transport chain
Protons (𝐻+) are released from NADH and 〖𝑭𝑨𝑫𝑯〗𝟐 and moved along the membranes forming a high concentration gradient.
From here the protons move across a protein channel called ATP synthase, an enzyme that uses this energy to form ATP from ADP + 𝑃_𝑖, the protons then bind to 𝑂_2 forming 𝐻_2 𝑂.
The coenzymes 〖𝑵𝑨𝑫〗+ and 〖𝑭𝑨𝑫〗+ are recycled in the Krebs cycle.
Lactic acid fermentation
- After glycolysis, pyruvate is fermented into lactic acid to recycle NADH to 〖𝑵𝑨𝑫〗+.
- Lactic acid lowers the pH of tissue, causing damage to cells and toxicity in high levels.
- Once oxygen becomes available, lactic acid is converted back to pyruvate for aerobic respiration.
Ethanol Fermentation
Occurs in fungi, like yeast
- Following glycolysis, pyruvate is fermented into ethanol and a 〖𝑪𝑶〗𝟐 molecule. This recycles NADH to 〖𝑵𝑨𝑫〗+.
- Ethanol is then diffused out of the cell. Ethanol is highly toxic and will build up in the environment.
