What exactly is a portion?

I’m endeavouring to eat the statutory “five a day” of fruit and veg at the moment in an attempt to be healthy consistently but there are some things that are puzzling me.

Generally, on Tesco’s food at least they say that 100 grams is a portion.. that’s on most fresh fruit and veg. But what about salad? has anyone ever tried to eat 100 grams of lettuce at one sitting…?? I mean..it’s a lot of lettuce! Can’t i just shove a load of different salad things on a plate and make sure it adds up to say… 200 grams and then that could be classed as 2 portions?

ANd what about dried fruit? Gogi Berries for instance? and Raisins… You can’t eat 100 grams of those to be considered a portion surely?? I think there would be serious toilet consequences!!!

Your thoughts will be much appreciated thank you x