Unit 3: Topic 5 - Photosynthesis Flashcards
What was the first classification of cells to start photosynthesis, and what were their effects on the atmosphere?
The first cells to start photosynthesis were prokaryotic cells. These cells, namely cyanobacteria, are stated to have helped oxygenate the early atmosphere of the Earth.
What is the general equation for photosynthesis?
6(CO2)+6(H20)–>C6H12O6+6(O2)
How did eukaryotic photosynthesis first take place?
Eukaryotic photosynthesis is theorized to have started after a process called endosymbiosis. This is a process in which a protist cell is engulfed by a cyanobacteria, which combines both aspects of these cells into one.
How do light-dependent reactions work in photosystem II?
When a photosystem/chlorophyll absorbs light, electrons inside the system become excited. These excited electrons then get transferred to the thylakoid membrane. Once this electron is removed, a water molecule has to be split, which releases an electron, an O2 molecule, and hydrogen ions in the thylakoid space. The replacement of this electron allows the cycle to be restarted, and the products of the breakdown of water can be used elsewhere. Once this happens again, photosystem II can send the electrons into the electron transport chain. The chain helps the membranes pump hydrogen ions against their concentration gradient. The pumping from the stoma to the thylakoid space creates an electrochemical gradient. The electron used in this system is then used in the pigments in photosystem I.
How is ATP generated after photosystem II releases electrons?
The previously produced hydrogen ions in the photosystem II can now be transferred back down their concentration gradient through the use of a protein complex called ATP synthase. This complex uses the energy generated to attach an additional phosphate to ADP, forming ATP in the process of photophosphorylation. This process is called chemiosmosis, as the ions move from a high to a low concentration through a semi-permeable protein.
How is NADPH generated in light-dependent reactions?
NADPH is created in photosystem I. The electron that was previously transferred over from photosystem II is re-excited with a photon absorbed by chlorophyll. This energy is then used to create NADPH from NADP+, finishing the production of these precursor molecules (ATP and NADPH) which will be used in the Calvin cycle.
How does chlorophyll excite electrons?
When chlorophyll and other pigments reflect sunlight, this excites an electron. When an electron is excited, it means that it has been transferred to a higher energy state, which takes the sunlight’s energy and converts it to potential energy.
What is an electrochemical gradient?
An electrochemical gradient is a difference in solute concentration and charge across a membrane.
How does an electrochemical gradient important to photosynthesis?
As electron carriers are carried down the electrochemical gradient ADP(adenosine diphosphate) gets an extra phosphate to make ATP(adenosine triphosphate).
Where does the Calvin cycle(dark reactions) take place?
The stroma, which is located in the chloroplast.
