Final answer:
The phonemes /z/ and /s/ differ primarily in voicing; /z/ is voiced, causing vocal cord vibration, whereas /s/ is voiceless, produced without vocal cord vibration.
Step-by-step explanation:
The phonemes /z/ and /s/ differ in one major aspect, which is voicing. Voicing refers to whether the vocal cords vibrate or not during the production of a sound. Both phonemes have the same place of articulation, being alveolar sounds, and they share the same manner of articulation, being fricatives. However, /z/ is voiced, meaning the vocal cords vibrate when producing this sound, whereas /s/ is voiceless and produced without the vibration of the vocal cords.
For example, the difference in voicing can be clearly heard by placing your hand on your throat and pronouncing the words 'zoo' (with the /z/ sound) and 'soon' (with the /s/ sound). You will feel the vibration when you pronounce the /z/ sound, but not when pronouncing the /s/ sound. This distinction is fundamental in the English language and can change the meaning of words such as 'breeze' (voiced /z/) and 'breeze' (voiceless /s/).