from a proteobacterial lineage that were ingested by a eukaryotic organism. Somehow, the ingested proteobacteria managed to survive inside of the cell rather than
being digested. That survival would have been an example of primordial success at
evolutionary cheating. Mitochondria have a double membrane and part of the
mitochondrial genome has been transferred to the host cell genome. The adoption
of mitochondria as endosymbionts began a path of evolution that has left a trail from
simple forms such as amoeba upward through both the ‘animal’ and ‘plant’ sides of
our planets tree of life. Figure 26.5 shows the mitochondria inside of human cells.
Understanding the development of eukaryotic biology has in itself proven to be
an interesting topic. Gould et al. (2016) have suggested that the eukaryotic
endomembrane system might have originated from bacterial membrane vesicles
released by the mitochondrial ancestor within the cytosol of its archaeal host at the
time of eukaryotic origin. Hendrickson and Poole (2018) have presented their
philosophical efforts at trying to understand evolutionary development of the
eukaryotic cell nucleus.
It is not necessary that all of the cell types within an organism will contain
mitochondria. An example of this would be the fact that mature mammalian erythrocytes lack mitochondria, because those cells eject their mitochondria during
erythropoiesis after which the erythrocytes derive their energy via anaerobic fermentation. Interestingly, there are instances when mitochondrial functioning seems
to no longer have been retained by organisms (Yahalomi et al. 2020) and mitochondria have even been lost (Karnkowska et al. 2016). These abandonments of a
committment to mitochondria may be ways of trying to alter the competitive balance
by not expending unnecessary energy to maintain metabolic capabilities that have
become unnecessary.
26.4 Photosynthesis and the Evolution of Chloroplasts
Oxygenic photosynthesis, which I will simply refer to as photosynthesis for the
remainder of this essay, uses water as its terminal reductant and generates molecular
oxygen as a product. Bacterial anoxygenic photosynthesis is a different process and
it oxidizes hydrogen sulfide to generate elemental sulfur. The chlorophyll to which I
refer in this essay is that originated by cyanobacteria.
The development of oxygenic photosynthesis by cyanobacteria occurred perhaps
2.3 billion years ago, it was a major event in evolution and represented a cheating
against the idea of purely existing by chemoautrophy. Cyanobacteria, which are
prokaryotes, probably were the first photosynthesizers. When a eukaryotic organism
ingested some cyanobacteria, but did not digest those cyanobacteria, the pathway
which led to what we now call eukaryotic algae began to unfold (Fields 2020;
Sibbald and Archibald 2020). Constantly being in close proximity to one another
can lead to interesting encounters. Eating your neighbors would be a form of
competitive cheating! Causing indigestion after you have been eaten could lead
552
C. J. Hurst
being digested. That survival would have been an example of primordial success at
evolutionary cheating. Mitochondria have a double membrane and part of the
mitochondrial genome has been transferred to the host cell genome. The adoption
of mitochondria as endosymbionts began a path of evolution that has left a trail from
simple forms such as amoeba upward through both the ‘animal’ and ‘plant’ sides of
our planets tree of life. Figure 26.5 shows the mitochondria inside of human cells.
Understanding the development of eukaryotic biology has in itself proven to be
an interesting topic. Gould et al. (2016) have suggested that the eukaryotic
endomembrane system might have originated from bacterial membrane vesicles
released by the mitochondrial ancestor within the cytosol of its archaeal host at the
time of eukaryotic origin. Hendrickson and Poole (2018) have presented their
philosophical efforts at trying to understand evolutionary development of the
eukaryotic cell nucleus.
It is not necessary that all of the cell types within an organism will contain
mitochondria. An example of this would be the fact that mature mammalian erythrocytes lack mitochondria, because those cells eject their mitochondria during
erythropoiesis after which the erythrocytes derive their energy via anaerobic fermentation. Interestingly, there are instances when mitochondrial functioning seems
to no longer have been retained by organisms (Yahalomi et al. 2020) and mitochondria have even been lost (Karnkowska et al. 2016). These abandonments of a
committment to mitochondria may be ways of trying to alter the competitive balance
by not expending unnecessary energy to maintain metabolic capabilities that have
become unnecessary.
26.4 Photosynthesis and the Evolution of Chloroplasts
Oxygenic photosynthesis, which I will simply refer to as photosynthesis for the
remainder of this essay, uses water as its terminal reductant and generates molecular
oxygen as a product. Bacterial anoxygenic photosynthesis is a different process and
it oxidizes hydrogen sulfide to generate elemental sulfur. The chlorophyll to which I
refer in this essay is that originated by cyanobacteria.
The development of oxygenic photosynthesis by cyanobacteria occurred perhaps
2.3 billion years ago, it was a major event in evolution and represented a cheating
against the idea of purely existing by chemoautrophy. Cyanobacteria, which are
prokaryotes, probably were the first photosynthesizers. When a eukaryotic organism
ingested some cyanobacteria, but did not digest those cyanobacteria, the pathway
which led to what we now call eukaryotic algae began to unfold (Fields 2020;
Sibbald and Archibald 2020). Constantly being in close proximity to one another
can lead to interesting encounters. Eating your neighbors would be a form of
competitive cheating! Causing indigestion after you have been eaten could lead
552
C. J. Hurst