Energy travels through a food chain/web. When an organism eats another organism, the energy from the food is passed to the eater. For example, we humans eat food to give ourselves enough calories (energy) to function properly.
The membrane of an organelle or cell is comprised of proteins circulating in a phospholipid bilayer.
The proteins in membranes are the ones which can facilitate chemical reactions.
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Examples of protists that possibly evolving form endosymbiosis are Paramecium and amoeba.
As per the theory of endosymbiosis, it is likely that some non-photosynthetic organisms formed a symbiotic relationship with organisms that had the ability to photosynthesize using chloroplasts. These organisms then got the ability to photosynthesize due to the addition of chloroplasts into their cells, and this resulted in eukaryotic organisms with chloroplasts.
It is the first one. I just answered this.
