Difference between Opportunity cost and marginal cost I understand that the marginal cost is the cost of producing one additional unit of a good or service.

Is it correct to say that the opportunity cost is part of the marginal cost (I'm trying to figure out what is meant by this picture below)? 



And secondly, is this statement correct "whatever a producer receive aboves its opportunity cost of providing the good/service is its producer surplus?" I read this online. Isn't it suggesting that the opportunity cost is the marginal benefit (because price received minus the points on the supply curve is producer surplus)?
Opportunity cost is the price of doing something in terms of something else. For example, cost of taking trip to Prague may be giving up new bike. In this broad sense marginal cost of producing one unit of q would be also it’s opportunity cost because you could use the same resources to produce something else. Opportunity cost of producing 1 widget at 5€ might be giving up possibility to produce 2 pins at 2,5€ each.

What the quote says is not that only time has opportunity cost but that you should not forget to add the opportunity cost of the persons time to the costs.

Also opportunity cost is not producer surplus. You don’t need to give up producer surplus to produce the particular good or service you are producing. You could include that in opportunity costs if you would be looking at it from a point of view of person deciding to leave the market to go to do some other business or retiring