Crossword Genius

Biological material sent out to Mars (6)

Ross

I believe the answer is:

stroma

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'biological material' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'sent out to mars' is the wordplay.
'sent out' is an anagram indicator (I've seen 'sending out' mean this).
'to'+'mars'='tomars'
'tomars' with letters rearranged gives 'STROMA'.

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I've seen this clue in The Times and The Sunday Times.
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