The youngest defendant in an alleged fertiliser bomb plot was "used as a gofer" by his older brother, his barrister has told the Old Bailey.
The defendants deny all the charges against them
Baroness Helena Kennedy QC said Shujah Mahmood, 19, was "completely overshadowed" by Omar Khyam, 24.
She said he knew nothing of the alleged UK-wide bombing campaign plot he was accused of taking part in.
The brothers, from Crawley, West Sussex, deny conspiring to cause explosions along with five others.
The seven defendants were arrested after more than half a ton of fertiliser was found at a storage depot in Hanwell, west London in March, 2004.
The prosecution alleges the men were part of a cell linked to al-Qaeda which was targeting utilities, the Bluewater shopping centre in Kent, and the Ministry of Sound nightclub in London.
Baroness Kennedy told the court her client was "someone with learning problems, someone considered backward at school".
"He was a low achiever, not a learner - someone who lived in the shadow of his older brother," she said.
Mr Khyam had been asked to take his brother under his wing by their mother because she was worried he was falling under bad influences, she said.
She told the court her client, who was only 16 when he was alleged to have taken part in the plot, was "useful" to Mr Khyam but was "never part of the inner circle".
"Shujah was taken for granted but never taken on board," she said.
A tin containing aluminium powder, another component for explosives, was found near a shed at the brothers' family home in Crawley.
Mr Mahmood's fingerprints were found on a plastic bag in the tin.
Mr Mahmood told the jury one of the bags had contained a pair of trainer shoes he had bought.
He said: "There is a cupboard in mum's kitchen where she puts bags. It must have come from that."
The brothers deny conspiring to cause explosions likely to endanger life between January 1, 2003 and March 31, 2004, along with Waheed Mahmood, 34, and Jawad Akbar, 23, of Crawley; Salahuddin Amin, 31, from Luton, Bedfordshire; Anthony Garcia, 24, of Barkingside, east London; and Nabeel Hussain, 21, of Horley, Surrey.
Mr Khyam, Mr Garcia and Mr Hussain deny a further charge under the Terrorism Act of possessing 1,300lb (600kg) of ammonium nitrate fertiliser for terrorism.
The brothers also deny possessing aluminium powder for terrorism.