Very urgent!! regarding bank account

AO can add that amount as your undisclosed income and can be taxed at 30%

But if your income is already below exemption limit and including this your income is below taxable limit then i dont think that you will be having problem.

THERE ARE RARE CHANCES OF DETECTION, BUT IF YOU ARE HAVING BIG TURNOVER IN YOUR BANK ACCOUNT THEN EVEN YOU DONT HAVE PAN CARD, INCOME TAX INVESTIGATION DEPARTMENT CAN TRACK YOU THROUGH INFORMATION FROM BANK, 

BUT AS IN YOUR CASE AMOUNT IS LESS , SO CHANCES ARE RARE.

Agree with @ raghavan but let me warn you that, since most accounts have Pan mentioned in the client details, ITD can ask the info. from bank without you even knowing it.

Remember, also that any transaction involving amount above Rs.50000 is considered high value transaction and may lead to a notice and thus keep proper accounting.

Accounts with small amounts are not the concern of ITD currently as they have bigger fish to fry but due to increase in technology access by ITD, they can track down hidden income and in future it would be better to show all your bank accounts in return or in your accounts.

ITD has much more resources available with it and it will have excess workforce, which might be utilized to harasse tax evaders so take care...

but currently, do not worry.