Passive Transport

Passive Transport

Cells need to move substances in and out to maintain balance and function properly. Passive transport is a process that allows molecules to move across the cell membrane without requiring energy. Instead, it relies on the natural movement of molecules from an area of high concentration to an area of low concentration.

Examples of passive transport include diffusion, osmosis, and facilitated diffusion. Scientists can better understand how cells maintain homeostasis and regulate vital processes by studying passive transport.

Science and Engineering Practices (SEP): Developing and Using Models

Scientists create models to show how molecules move across the cell membrane without using energy, a process called passive transport. These models help us see how things like water and other substances move through the cell by diffusion and osmosis. They also show how different factors, like temperature or concentration, can affect how these molecules travel.

By improving these models, scientists can better understand how cells control what happens inside them and how they react to changes outside, like temperature or pressure. This helps them understand how cells stay healthy and balanced.

Activity Ideas:

• Investigating Osmosis Using Dialysis Tubing – Use dialysis tubing to simulate a cell membrane. Fill the tubing with a concentrated sugar solution and place it in a cup of water. Over time, observe how water moves into the tubing due to osmosis, demonstrating the movement of water across a semi-permeable membrane.
• Osmosis in a Raisin – Soak a raisin in water and observe how it gradually swells as it absorbs liquid. This simple activity demonstrates osmosis in a natural context, showing how water moves from an area of lower solute concentration (the surrounding water) into the raisin, which has a higher solute concentration.

Crosscutting Concept (CCC): Structure and Function

The function of passive transport depends on the structure of the cell membrane and its permeability. By studying these structures, scientists can figure out how molecules move naturally across membranes.

• Structure: The phospholipid bilayer allows selective permeability.
  Function: It controls which molecules pass through by diffusion and osmosis.
• Structure: Channel and carrier proteins assist in facilitated diffusion.
  Function: These proteins help transport larger molecules without using energy.
• Structure: The concentration gradient drives molecular movement.
  Function: Molecules move from high to low-concentration areas to maintain balance within cells.

By understanding how structure influences function in passive transport, scientists can improve medical treatments and enhance knowledge of cellular processes.