Not so far as I am aware. they may be 'woody' in the centre and therefore not very palatable.

Agree with Sbg. Try cooking them for longer than usual.

Don't think so. You can eat the young leaves in salad/ steamed/stir fried or raw, they have a peppery taste.

Not poisonous, but tough, mustardy, and sometimes bitter.

Come to think of it Seaburn, I've never had a woody turnip, but have had woody parsnips.

yes that can happen to parsnips too.

Oh.....