Answer:
Transport Across a Cell Membrane
The cell membrane is one of the great multi-taskers of biology. It provides structure for the cell, protects cytosolic contents from the environment, and allows cells to act as specialized units. A membrane is the cell’s interface with the rest of the world - it’s gatekeeper, if you will. This phospholipid bilayer determines what molecules can move into or out of the cell, and so is in large part responsible for maintaining the delicate homeostasis of each cell.
Semi-Permeability
Some cells function best at a pH of 5, while others are better at pH 7. The steroid hormone aldosterone is made in the adrenal gland, but affects mostly the kidney. Sodium is more than ten times more concentrated outside of cells rather than inside. If our cells couldn’t control what crossed their membranes, either no molecules would make it across, or they’d be traveling willy-nilly and the internal environment would always be in flux. It’d be like taking every item on a menu and blending it together before serving (not the tastiest idea).
So how do cells maintain different concentrations of proteins and molecules despite the pressures on them to be homogenous? Cell membranes are semipermeable, meaning they have control over what molecules can or cannot pass through. Some molecules can just drift in and out, others require special structures to get in and out of a cell, while some molecules even need an energy boost to get across a cell membrane. Each cell’s membrane contains the right mix of these structures to help that cell keep its internal environment just right.
Important Speech:
I just watch the 100 Awesome Minutes to Help Fix the Planet from youtube.
And I realize that the Ozone layer is getting thinner and thinner each year, and the scientist said that we can not live any longer in our world,(why?).because the pollution is getting higher and higher every each day and also that the green life and the environment is losing every day. So that's why we need your help to help our World to come back to it's own shape, because the World we know now is endanger. We need you to help us by your own way to help.
The Link I watch:
youtube.com/watch?v=NJ-juLXoFxM&t=5116s
#Save the Green Life
#Plastic must die
# Stop the Pollution
