Help novice with question about cell concentration in batch culture - (Nov/26/2018 )

Hi,

I am a 30 year old guy from Sweden studying pharmaceutical manufacturing at a pretty basic level - or, mostly basic, because the course I have now (cell culture; fed batch, continuous batch...) exceeds my knowledge so much that I've been given a completion (I don't know the English word) since I didn't make the big exam. If I pass the completion questions, they'll approve me.

I will try to translate the task that I want help for. It's about cell growth in a chemostat. I hardly know what a chemostat does.

"In continuous cultivation, but also in feedbatch and perfeusion cultivation, you can have a (cell) culture that grows with lower speed than the maximum speed. You have equilibrium between limiting substrate and cell-concentration. Even if there's too many or too few cells, the culture still will have the same cell-concentration after a while. Why? Describe what happens and draw a diagram if you want."

How would you answer that question in the most easy way possible? Why will the culture have the same cell-concentration after a while?

I'm very grateful if some of you can help me!

Moved to homework...

As this is homework for you and you should understand the concepts involved in the process... think about the system. 

What are the limiting factor(s) to the growth of the cells? Hint - it's part of a continuous system - what's going in?

Because biproducts are washed away?

That's the wrong end of the fermenter/chemostat... think about continuous input(s) and how this might affect growth curves in the long run.