Why was it initially difficult for researchers to discover the existence of microtubules?

a. microtubules were too small to be seen by electron microscopy.
b. microtubules were initially thought to be the same protein fibers seen in the extracellular matrix and thus were not thought to be unique structures.

c. microtubules dissociate under the colder conditions initially used to fix tissues, and were thus disappearing during sample preparation.

d. researchers thought microtubules were appendages of the golgi apparatus. e. the marginal band obscured all visualization of the microtubules

c.

Explanation:

1) Microtubules are components of a various array of structures. They form the mitotic spindly of dividing cells and core of flagella.

2) Microtubules are strong enough to resist or oppose the forces that can bend or compress fiber. Microtubules provide mechanical support like the poles support the structure of a tent.

3)The placement of cytoplasmic microtubules in a cell, determines the  shape of that cell.

4) Microtubule are highly sensitive to various environmental effects.

For e.g. Very low levels of free calcium can destabilize microtubule.

This was the reason that researchers could not study microtubules in vitro.

Also Cold temperatures lead to rapid depolymerization of microtubules.

the correct answer is option b

behavioral response need communication and thus co-ordination at several levels such as interaction among cells, organ system and the entire organism.

behavioral response produces both internal and environmental stimulus.