Pb is a line segment on a number line. it has endpoints at -2 and 12. what is the coordinate of its midpoint

The midpoint is halfway between the two ends. That means it is the average of the two values:

(-2+12)/2 = 5

5 is 7 above -2, and 7 below 12

plants store their excess carbohydrate in the form of starch so that it could be used as energy source later on. the excess carbohydrate is converted into starch in the plastid i.e. chloroplast & this process occurs in the presence of sunlight. it is an insoluble polymer of glucose which gets stored in cell organelles named as amyloplasts. in some plants, starch is also stored in roots and embryos.