How might more extreme heat days and nights affect living things (including humans) ?

It'd be logical to say the effects vary, but most of it would be very negative.

In a cell, the heat would limit the temperatures that it'd normally have to maintain in order to survive.

In humans and most living organisms, it'd make it easier to become dehydrated than days and nights where it's much cooler. Heat strokes are highly possible alongside dehydration. Humans and a lot of other living organisms are not adapted to maintain survival in extremely high climates.

Water would evaporate from the heat, causing a drought - making the dehydration issue even more serious unless another water source is found.