How do substances move across cell membranes?
substances are transported across cell membranes via passive, active and bulk transport process.
- passive transport occurs when substances can cross the semipermeable plasma and organelles membranes and move down the concentration gradient without using energy and happen through diffusion, facilitated diffusion and osmosis.
- active transport occurs when substances are transported up their concentration gradient from a lower to a higher concentration. sodium potassium pump is an active transport mechanism that maintains homeostasis to be electrolytes sodium and potassium.

Read the excerpt from the war of the worlds.beyond the pit stood the little wedge of people with the white flag at its apex, arrested by these phenomena, a little knot of small vertical black shapes upon the black ground. as the green smoke arose, their faces flashed out pallid green, and faded again as it vanished. then slowly the hissing passed into a humming, into a long, loud, droning noise. slowly a humped shape rose out of the pit, and the ghost of a beam of light seemed to flicker out from it.forthwith flashes of actual flame, a bright glare leaping from one to another, sprang from the scattered group of men. it was as if some invisible jet impinged upon them and flashed into white flame. it was as if each man were suddenly and momentarily turned to fire.then, by the light of their own destruction, i saw them staggering and falling, and their supporters turning to run.which options accurately describe how the author develops the plot in the excerpt? (select all that apply.)the war of the worldsthe narrator does not react at first as he watches the men with the flag and hears the sounds in the pit. his inaction decreases the tension in the plot because the narrator is simply standing by.the narrator does not react at first as he watches the men with the flag and hears the sounds in the pit. his inaction keeps the tension steadily increasing as the narrator comes to realize the men are being killed.the narrator is distracted by his own observations of the men with the white flag and the humming sound, so he doesn't react as quickly as he should when the men are killed, thus extending the tension in the plot.the narrator is attentive to the men with the white flag and the humming sound, so he immediately understands what has happened when the men are killed, increasing the tension in the plot.