The argument
Animal advocates criticize the speciesism that ignores some of animals' interests just because they don't have all the interests humans have. Some biocentrists say: "You do the same to plants. They also have biological needs, like water, light, and nutrients. So they have interests too."
The answer
Beings who feel have an interest in eating, drinking, and resting. But that interest is instrumental: it matters because without those things, they suffer and can't have good experiences.
For a being that doesn't feel, meeting its biological needs has no value at all for it, because it has no point of view. There's nobody inside for whom it makes a difference.
"What about the interest in staying alive?"
Someone could say: "Eating and resting also serve to stay alive, which is a purely biological interest." But, as we've seen, staying alive matters because it lets you keep having experiences. Without experience, there's nobody for whom life matters.
In short
- Having biological needs isn't the same as having interests.
- For those who feel, needs matter because they affect their experiences.
- For those who don't feel, there's nobody for whom anything matters.