What is the main function of spindle fibers?

a.) to condense chromatin into chromosomes.
b.) to replicate the chromosomes before cell division.
c.) to decondense chromosomes following mitosis.
d.) to separate chromosomes during mitosis.

The correct option is D. To separate chromosomes during mitosis.

Explanation:

All cells of the body replicate through the process of mitosis except the sex cells. The formation of the spindle fibres is a very important step in the mechanism of mitosis and meiosis both.

Spindle fibres are present on the opposite poles and pull the chromosomes to each side. As a result, the chromosomes get separated into two halves and gametes are formed. This process also ensures that equal division takes place.

the answer is: the „power stroke“ step.

muscle contraction can be divided into a few steps:

1. the release of ach (acetylcholine) in the synaptic cleft, binding of ach for its receptor and consequently opening of the ca channels.

2. the release of ca, binding of ca for the troponin

3. troponin shifting the tropomyosin, which was blocking the active site on the actin

4. myosin heads attaching to actin by breaking down atp to adp+ pi

5.   formation of the ‘cross-bridge’ on the active site of the actin filament by myosin head

6. “power stroke” -the cross bridge pulls actin, which slides over the myosin

9.     7. the release of adp completes the cross-bridge movement and atp attaches to myosin, breaking the actin-myosin cross bridge.