Explanation

Physiological variation refers to differences in how body systems function internally. Blood pressure measures how hard blood pushes against artery walls. Different people have different blood pressure levels even when healthy, showing natural physiological variation.

These internal functional differences cannot be seen from outside the body. They involve chemistry, metabolism, and organ function. Blood pressure, heart rate, enzyme levels, and hormone amounts all vary between individuals physiologically.

Fur color, beak shape, and leaf shape are morphological variations affecting physical appearance and structure. These can be seen with eyes. Blood pressure is internal body function that must be measured with instruments, making it physiological variation.