Nucleic Acids are the largest molecule
The stem has more things to transport that's why it has more vascular bundles. The roots only get water from the ground and moving nutrients from the soil to transfer it to the stem. Having more vascular bundles helps the stems to transfer things to leaves and other parts of the plants.
The new population that experienced natural selection is now better fit or more adapted to the environment than the old population
Well, ask yourself, "Do I try hard enough?" "Was it the best I could do?" And well if the answer is yes, then you have nothing to stress out about too much. Maybe talk to your teacher and ask for extra credit. Get tutoring. Talk to a guidance counselor. If none of that helps, well then you're just not the best at the subject, but just try your best. In the future, you won't even remember about all those grades! Coming from a 6th grader, the beginning of the year was super hard. I'm not the best at math, but I'm very good at Language Arts. Everyone has their own weaknesses and strengths. Don't worry about it.
