I have 2010 motherboard with USB 2.0 ports. However I plan to buy a Dell monitor with in-built USB Hub which requires connecting USB 3.0 upstream cable to the motherboard. Does USB 3.0 upstream on monitor work with USB 2.0 downstream port from motherboard?
The USB 3.0 standard specifies it must be backwards compatible with USB 2.0. It will (should) work but only at 2.0 speeds. I would suggest purchasing a PCI or PCI-E 1x USB 3.0 card, they are relatively cheap and can be had for under $10 with a little due diligence, which will give you full USB 3.0 support.