Ineed with this homework:
trace the path of energy from the sun to mechanical energy in an organism
does anyone have any idea what it's about? : d

Yes. You do.  Try thinking about it in reverse:

One obvious form of mechanical energy in an organism is the energy
that you have in you to make your muscles work, to move you around,
to throw a ball, to pick stuff up, etc.y

Where does the energy come from to make your muscles work ?
It comes from the food you eat.

Where does the energy in the food you eat come from ?
It comes either from the plants you eat, or else from the plants that
the animals you eat eat.  (Or possibly from the plants eaten by an
animal before that animal is eaten by an animal that you eat.)

Where does the energy come from that's stored in the plants ?
It comes from the sun.

So there. You've traced the path backward, from the mechanical energy
in the organism, back to the sun.  Can you turn it around now, and trace
it forward ?

That is true tge cactus as a structural adaptation to its envirinment has it leaves reduced to spines. but this doesnt mean it cant produce food it produces food because of the presence of chlorophyll in its stem