Like rubidium, caesium tends to substitute potassium in the body, but is significantly larger and is therefore a poorer substitute.
lˈaɪk ɹuːbˈɪdiəm, sˈiːsiəm tˈɛndz tə sˈʌbstɪtˌuːt pətˈæsiəm ɪnðə bˈɑːdi, bˌʌt ɪz sɪɡnˈɪfɪkəntli lˈɑːɹdʒɚ ænd ɪz ðˈɛɹfoːɹ ɐ pˈʊɹɹɚ sˈʌbstɪtˌuːt.