To Lynn Margulis we owe the theory of endosymbiosis, a theory that explains the appearance of eukaryotic cells from primitive prokaryotic organisms. The following diagram summarizes the theory:

Figure 1: Taken from: https://mmegias.webs.uvigo.es/5-celulas/1-endosimbiosis.php 

Look at the figure and answer: 
1. How many endosymbioses gave rise to animal cells?  
2. How many endosymbioses were necessary to originate plant cells?  
3. According to the above, where do mitochondria come from, and where do chloroplasts come from? 
4. Will plant cells have mitochondria?