When lead acts as a poison, it can do so by either replacing another ion (such as zinc) in the active site of an enzyme or reacting with cysteine side chains to form covalent bonds. which of these is irreversible and why?

an adaptation is a change or process by which an organism takes to be better suited for its environment. for example; migration is a behavioral adaptation, this is needed because birds are not built to last extremely cold climates. there are different adaptations because there are different species needing to adjust to different things, bears don't migrate; they hibernate.

helicase, i think thats it