Pluto was once classified as a planet. however, scientists no longer classify pluto as a planet. which is a likely reason for this change?
the original hypothesis about pluto was supported.
no observations of pluto were made in the past.
several planets in outer space were found to be similar to pluto.
there were significant changes in scientific knowledge about planets.

There were significant changes in scientific knowledge about planets.

Explanation:

The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System, a planet is a celestial body which:

1. Is in orbit around the Sun.

2. Has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).

3. Has "cleared the neighborhood" around its orbit.

Among other things, this definition caused Pluto to no longer be a planet, a change from how it had been widely considered until that point.

the correct answer is 2 and 4

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.