Countable nouns are nouns that can be counted; e.g. dog, person, child, dollar, etc. If you have more than one of these, you can line them up and count them. If you have more of them than you require, you can say you have too many of them.
Uncountable nouns are nouns that cannot be counted; e.g. water, air, power, money, etc. You cannot line these up and count them. If you have more of them than you need you have to say you have too much of them.
The word apoptosis is both a countable and an uncountable noun. As the general term for 'programmed cell death' it is uncountable. The cell is either totally and permanently dead and unable to be revived, or it is not. Confusingly, a pathway that causes apoptosis is also called an 'apoptosis'; these pathways are countable. There are many apoptosis pathways by which the apoptosis state can be brought about, and those pathways can and have been counted, but there is only one state of total and permanent cell death.
Like all uncountable nouns, we can talk about 'too much apoptosis' (ie too many cells within an organism have entered the apoptotic state), but we cannot talk about 'too many apoptosis'. Note: we can talk about 'too many apoptoses', meaning too many pathways by which a cell can become apoptotic but, as discussed, the pathway and the final state are two different things.
The word 'photosynthesis' is an uncountable noun as well, so the above discussion applies to this word as well.
I have never heard the expression 'too close a contact', which is not to say that it does not exist, so I cannot assist with this.
I cannot think of a way of using 'too many a something' that would be regarded as acceptable, standard English. I could imagine it being used informally in regional areas, or in rustic expressions such as:
There's been too many a good soldier lost to incompetent leadership.
There's too many a young lad a'courtin' the lasses, 'n not enough bringin' in the harvest.
Hopefully, someone else on the forum may be able to assist youwith those other matters.