How would life on earth be different if earth’s axis were not tilted with respect to its orbit?

a.
there would be no seasons.

b.
there would be no day and night.

c.
all places would have the same climate.

d.
the seasons would be much shorter.

If Earth's axis was "straight up and down" instead of tilted, then ...

-- There would be no seasons.

-- The climate at any one place would be the same all year around. 

-- The days would be the same length, everywhere,
    and all year around.

-- So would the nights.

-- The sun would be up a little more than 12 hours every day.
    It would be down a little less than 12 hours every day.

-- At the middle of the day, the sun would be at the same height
   in the sky all year around, not higher in some months and lower
   in others.

-- The equator would be the only place on Earth where the sun
    could ever be directly over your head.

-- If you were at the north pole or the south pole, the sun would be
   down on the horizon, and it would just go around and around you
   every day.  It would never rise or set, and it would never get any
   higher or lower.