Clue: Delightful chap on the radio provides penicillin, etc (5)
Answer: FUNGI
Explanation: Definition: provides penicillin, etc
Sounds like ('on the radio') FUN GUY ('delightful chap'). The definition is not precise: FUNGI is plural, 'provides' indicates singular; and things are no better if 'provides' is regarded as a link word – penicillin is an extract of Penecillium fungi.