Molecules a and b come in contact with the cell membrane of the same cell. molecule a passes through the membrane readily, but molecule b does not. which statement could describe molecules a and b?

Molecule A is a simple sugar or amino acid, while molecule B is a starch or protein.

Explanation:

Molecule A, as a simple sugar or amino acid, consists of small molecules which can readily pass through the cell membrane, while Molecule B, as a starch or protein, consists of large molecules, thus, can't pass across the cell membrane.

This is the reason why the cell membrane is considered to be selectively permeable.

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.