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

Interpret the model. a three-part model with black right-arrows between the parts. left part: a large green apple-shaped component with a w-shaped indentation centered on top. a small blue apple-slice shape sits above the left indentation and an arrow points from the shape to the indentation. a small purple apple-slice shape and arrow sit above the right indentation and an arrow points from the shape to the indentation. middle part: a large green apple-shaped component with a square indentation centered on top. sitting in the left side of the indentation is a blue apple-slice shape with a flat bottom, fused to a purple apple-slice shape with a flat bottom on the right side of the indentation. right part: a large green apple-shaped component with a w-shaped indentation centered on top. an up-arrow is centered above the indentation pointing to a fused blue and purple apple-slice-shaped flat-bottom component sitting above the indentation. assigne "true" or "false" to the end of each statement. the model shows a shape change occurring in the enzyme after the substrate is bound in the active site. t/fthere are two products in this model. t? f there are three substrates in this model. t/f the model shows two different enzymes. t/f

The mammal pictured below is a silvery mole rat. which statement is an inference based on the picture? the animal is ugly. the animal has hairless feet with sharp claws. the animal has prominent upper and lower incisor teeth. the animal likely has poor vision since its eyes are so small.

Which of the following was not a major animal on land during the carboniferous period? amphibians insects both a and b none of the above