What is happening during the plateau phase of
cardiacdepolarization?
a) sodium ions block voltage-gated calcium ion channels.
b) acetylcholine is hyperpolarizing the sa node
c) nothing - all ion gates and valves are closed.
d) voltage-gated potassium ion channels open to allowpotassium
ions to diffuse out.
e) calcium ions enter the cystol of cardiac myofibers
fromsarcoplasmic reticulum and through voltage-gated
slowchannels.

Option (3).

Explanation:

Heart contains the cardiac myocetes cells that are surrounded by the sarcolemma.  Heart has the ability to conduct the electrical impulse same as the muscle cell have.

The plateau phase is the second phase of the cardiac action potential. During this phase, the calcium ions moves out of the cell from the sarcoplasmic reticulum to the cytosol through voltage gated sodium calcium channels. Sodium ions will move inside the cell during this phase.

Thus, the correct answer is option (3).

answer-

the statement that f(x) = |x+a| + b has exactly one x-intercept is sometimes correct.

solution-

it solely depends on b, whether the function will have one or two or zero x intercept.

this plot of the given function, f(x) = |x+a| + b will be the basic absolute value graph i.e v shape, with vertex translated to (-a, b), instead of origin.

1-   if b is zero, the graph will have exactly one x-intercept, at x= -a

2- if b is positive, the whole graph will be above the x-axis, hence it will have no x-intercepts.

3- if b is negative, the graph will be below the x-axis, hence it will have two x-intercepts.

∴ the statement is sometimes true.