Fill in the blanks : (a) ___ consists of membranous sacs and secretes 40 types of digestive enzymes. (b) ___ is surrounded by microtubules, located near the nucleus. (c) Very thin flexible, living membrane which is differentially permeable, is called ___ (d) More than 1000 chromosomes are found in the nucleus of certain ___ (e) ___ are hereditary units. (f) ___ is a plastid which stores starch.