Is this an older 3750 or a newer 3750-X? If this is a 3750-X you can select the type of uplink module you want to use which provides the options for 1GB or 10GB uplinks. If you decided to use either of those it is just the appropriate transceiver for the speed and type of fiber you want to use.
If this is an older 3750 and you have SFP ports available then you can use the appropriate transceiver for 1GB depending on the type of fiber you decide to use (MM or SM).
If you are using an older 3750 which does not have any SFP ports then you'll need to use copper to connect to the 5k at 1GB.
Regards,
Dave
