Evolution of Photosynthesis Flashcards
(15 cards)
What major impact did the evolution of photosynthesis have on Earth?
It provided organisms with a new energy source and released oxygen into the atmosphere.
What was likely the first step in the evolution of photosynthesis?
The evolution of UV-absorbing compounds to protect cells from harmful sunlight.
How might early UV-absorbing compounds have evolved into energy-capturing molecules?
Through random mutations creating variants capable of transferring electrons like modern reaction centers.
How was early light-driven ATP synthesis potentially achieved?
By coupling light-driven electron transport to proton movement across membranes without electron donors.
What was a likely first electron donor for early photosynthetic organisms?
Reduced iron (Fe²⁺), abundant in early oceans.
Why is it unlikely that early photosynthetic organisms used chlorophyll?
Chlorophyll synthesis requires at least 17 enzymatic steps, which is too complex for early life.
How might the chlorophyll biosynthetic pathway have evolved?
Gradually, with each step improving efficiency or expanding light absorption, selected through mutation.
What is unique about cyanobacteria’s photosynthetic capabilities?
They were the first to use water as an electron donor by incorporating two photosystems.
Why can’t organisms with only one photosystem use water as an electron donor?
One photosystem doesn’t provide enough energy to extract electrons from water and reduce CO₂.
What are two hypotheses for how cyanobacteria gained two photosystems?
1) Horizontal gene transfer between bacteria; 2) Duplication and divergence of one photosystem gene.
What was the result of cyanobacteria using water as an electron donor?
Global oxygen production and the ability to photosynthesize wherever sunlight and water are present.
How did eukaryotes acquire photosynthesis?
Through endosymbiosis with a photosynthetic cyanobacterium that became the chloroplast.
What does the inner chloroplast membrane correspond to?
The membrane of the ancestral cyanobacterium.
What structure in chloroplasts is analogous to the internal membrane of cyanobacteria?
The thylakoid membrane.
What is the endosymbiotic hypothesis?
The idea that chloroplasts and mitochondria originated from symbiotic bacteria inside ancestral eukaryotic cells.
