Can I connect AirPort Extreme to iMac as well as router?

I have just bought an AirPort Extreme, which I have connected to my router/modem with the ethernet cable which used to be connected to my iMac (21.5 inch, Mid 2010 with Yosemite 10.10.2). I also have an AirPort Express in another area of the house to extend the wifi network. Although the wifi on our iPhone 4S devices is now much improved, the speed of the iMac is slower - presumably because it is now using the wifi network instead of the wired connection.

Is it possible to connect another ethernet cable from the iMac into one of the <...> ports on the back of the AirPort Extreme to restore the wired connection to the iMac?

Thank you.