PLEASE answer....Does each individual seed become a plant?

I planted Salad Bowl lettuce seeds and Evergreen Bunch onions by seed today outside and I put 1 seed every inch or so....will each seed become its own plant?

I planted Iceberg lettuce seeds about three weeks ago and it seems that every seed sprouted because I just sprinkled the seeds i the soil, so now it is hard to tell where one plant from another....I have alot of transplanting to do I guess....I'm new to gardening by seed.