4. ¿Cuál es el orden correcto en que se incrementa la complejidad de los seres vivos? w
Dil
a) Célula
b) Órgano
c) Célula
d) Sistema
Órgano
Tejido - Sistema
Tejido
→ Sistema Célula
Tejido- - Organo Sistema
Organo Tejido - Célula
a)
b

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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.