Interesting question. While researching the source of your claim, I believe I stumbled upon the answer:
Take a look at this Daily Mail article on a survey of British teens' food knowledge. Then look at the right-sidebar articles and count the number of times you see the word "Kardashian." There's your answer.
That said, I was actually surprised that only 10 percent thought eggs came from wheat. Perhaps I'm a bit cynical, but I expected worse, considering that only half of adults here in the U.S. know how long it takes for the Earth to go around the Sun.
We live in a very segmented society and most suburbanites have very little exposure to our agricultural roots. Food comes from the supermarket, and we don't spend much time thinking about how it got there.