Osmosis, Diffusion, and Cellular Transport: Tutorial
Directions
Read the instructions for this self-checked activity. Type in your response to each question, and check your answers. At the end of the activity, write a
brief evaluation of your work.
Method of transportation
across cell membranes
Activity
The mechanisms of transport across cell membranes are summarized in this table. Using the information from the table, draw a diagram of any
one of the transport mechanisms.
passive transport or facilitated
diffusion
simple diffusion
osmosis
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active transport
Description
Passive transport is the transport of substances across a membrane by a trans-membrane protein molecule.
Simple diffusion is the movement of molecules from a region of higher concentration to a region of lower
concentration. It does not require any transport protein.
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Osmosis is the movement of water molecules from higher concentration to lower concentration of water, that is,
from lower concentration of solute to higher concentration of solute across a semipermeable membrane.
It is the movement of molecules from a region of higher concentration to that of a lower concentration. Since the
movement is against the concentration gradient, energy is required for the process. ATP provides the energy in most
cases.
Smaller molecules like charged ions are transferred with the help of carrier proteins called pumps.
Larger molecules and aggregates are ingested by the cell by endocytosis. In this process, the cell membrane extends
and engulfs the material to be ingested.
When the molecule is particulate, the process is called phagocytosis and when it is liquid it is called pinocytosis.
Unwanted material can be thrown out of the cell by exocytosis.