Movement through the Cell Membrane

When the movement of molecules occurs on its own, without any organized energy input from the cell, the movement is termed 1($). When the cell expends energy to move molecules from one location to another, the process is known as 2($)

In a system where diffusion occurs, a net movement of particles can be observed over time from regions of 1($) concentration of that substance to regions of 2($) concentration of that substance.

The particles moving from the area of greater concentration will produce a concentration gradient ranging from the point of highest concentration to the point farthest away, where the lowest concentration occurs

Arrange diffusion steps

When a semipermeable membrane separates two solutions of pure water, the two sides are at 1($) —that is, the osmotic pressure is equal on both sides.

When the osmotic pressure is the same on both sides of a semipermeable membrane, each solution is said to be isosmotic or 1($).

1. When a cell is in a medium with a higher concentration of osmotically active dissolved or colloidal particles, rendering a higher osmotic pressure.  In such a situation, water moves across the cell membrane into the medium that is 1($) (also called hypertonic) relative to the solution inside the cell.
2. When a cell is in a medium with a lower concentration of osmotically active dissolved or colloidal particles, and the solution thus has a lower osmotic pressure than that inside the cell, the cell is said to be in a medium that is 2($) (or hypotonic) relative to it, so water moves into the cell.

One of the two main types of transport that involve 1($), as opposed to passive, transport is known as 2($). Here, 3($) molecules move substances either in or out of a cell in a manner that 4($) the rate of diffusion across the membrane. The mechanism involved combines molecules that are to be 5($) across the membrane with the carrier molecules in the membrane. In such a manner, molecules are picked up on one side of the membrane and released on the other side.