12.3.4: Active Transport - Biology

12.3.4: Active Transport - Biology

We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

Skills to Develop

  • Understand how electrochemical gradients affect ions
  • Distinguish between primary active transport and secondary active transport

Active transport mechanisms require the use of the cell’s energy, usually in the form of adenosine triphosphate (ATP). If a substance must move into the cell against its concentration gradient—that is, if the concentration of the substance inside the cell is greater than its concentration in the extracellular fluid (and vice versa)—the cell must use energy to move the substance. Some active transport mechanisms move small-molecular weight materials, such as ions, through the membrane. Other mechanisms transport much larger molecules.

Electrochemical Gradient

We have discussed simple concentration gradients—differential concentrations of a substance across a space or a membrane—but in living systems, gradients are more complex. Because ions move into and out of cells and because cells contain proteins that do not move across the membrane and are mostly negatively charged, there is also an electrical gradient, a difference of charge, across the plasma membrane. The interior of living cells is electrically negative with respect to the extracellular fluid in which they are bathed, and at the same time, cells have higher concentrations of potassium (K+) and lower concentrations of sodium (Na+) than does the extracellular fluid. So in a living cell, the concentration gradient of Na+ tends to drive it into the cell, and the electrical gradient of Na+ (a positive ion) also tends to drive it inward to the negatively charged interior. The situation is more complex, however, for other elements such as potassium. The electrical gradient of K+, a positive ion, also tends to drive it into the cell, but the concentration gradient of K+ tends to drive K+ out of the cell (Figure (PageIndex{1})). The combined gradient of concentration and electrical charge that affects an ion is called its electrochemical gradient.

Art Connection

Injection of a potassium solution into a person’s blood is lethal; this is used in capital punishment and euthanasia. Why do you think a potassium solution injection is lethal?

Moving Against a Gradient

To move substances against a concentration or electrochemical gradient, the cell must use energy. This energy is harvested from ATP generated through the cell’s metabolism. Active transport mechanisms, collectively called pumps, work against electrochemical gradients. Small substances constantly pass through plasma membranes. Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive movements. Much of a cell’s supply of metabolic energy may be spent maintaining these processes. (Most of a red blood cell’s metabolic energy is used to maintain the imbalance between exterior and interior sodium and potassium levels required by the cell.) Because active transport mechanisms depend on a cell’s metabolism for energy, they are sensitive to many metabolic poisons that interfere with the supply of ATP.

Two mechanisms exist for the transport of small-molecular weight material and small molecules. Primary active transport moves ions across a membrane and creates a difference in charge across that membrane, which is directly dependent on ATP. Secondary active transport describes the movement of material that is due to the electrochemical gradient established by primary active transport that does not directly require ATP.

Carrier Proteins for Active Transport

An important membrane adaption for active transport is the presence of specific carrier proteins or pumps to facilitate movement: there are three types of these proteins or transporters (Figure (PageIndex{2})). A uniporter carries one specific ion or molecule. A symporter carries two different ions or molecules, both in the same direction. An antiporter also carries two different ions or molecules, but in different directions. All of these transporters can also transport small, uncharged organic molecules like glucose. These three types of carrier proteins are also found in facilitated diffusion, but they do not require ATP to work in that process. Some examples of pumps for active transport are Na+-K+ ATPase, which carries sodium and potassium ions, and H+-K+ ATPase, which carries hydrogen and potassium ions. Both of these are antiporter carrier proteins. Two other carrier proteins are Ca2+ ATPase and H+ ATPase, which carry only calcium and only hydrogen ions, respectively. Both are pumps.

Primary Active Transport

The primary active transport that functions with the active transport of sodium and potassium allows secondary active transport to occur. The second transport method is still considered active because it depends on the use of energy as does primary transport (Figure (PageIndex{3})).

One of the most important pumps in animals cells is the sodium-potassium pump (Na+-K+ ATPase), which maintains the electrochemical gradient (and the correct concentrations of Na+ and K+) in living cells. The sodium-potassium pump moves K+ into the cell while moving Na+ out at the same time, at a ratio of three Na+ for every two K+ ions moved in. The Na+-K+ ATPase exists in two forms, depending on its orientation to the interior or exterior of the cell and its affinity for either sodium or potassium ions. The process consists of the following six steps.

  1. With the enzyme oriented towards the interior of the cell, the carrier has a high affinity for sodium ions. Three ions bind to the protein.
  2. ATP is hydrolyzed by the protein carrier and a low-energy phosphate group attaches to it.
  3. As a result, the carrier changes shape and re-orients itself towards the exterior of the membrane. The protein’s affinity for sodium decreases and the three sodium ions leave the carrier.
  4. The shape change increases the carrier’s affinity for potassium ions, and two such ions attach to the protein. Subsequently, the low-energy phosphate group detaches from the carrier.
  5. With the phosphate group removed and potassium ions attached, the carrier protein repositions itself towards the interior of the cell.
  6. The carrier protein, in its new configuration, has a decreased affinity for potassium, and the two ions are released into the cytoplasm. The protein now has a higher affinity for sodium ions, and the process starts again.

Several things have happened as a result of this process. At this point, there are more sodium ions outside of the cell than inside and more potassium ions inside than out. For every three ions of sodium that move out, two ions of potassium move in. This results in the interior being slightly more negative relative to the exterior. This difference in charge is important in creating the conditions necessary for the secondary process. The sodium-potassium pump is, therefore, an electrogenic pump (a pump that creates a charge imbalance), creating an electrical imbalance across the membrane and contributing to the membrane potential.

Link to Learning

Visit the site to see a simulation of active transport in a sodium-potassium ATPase.

Secondary Active Transport (Co-transport)

Secondary active transport brings sodium ions, and possibly other compounds, into the cell. As sodium ion concentrations build outside of the plasma membrane because of the action of the primary active transport process, an electrochemical gradient is created. If a channel protein exists and is open, the sodium ions will be pulled through the membrane. This movement is used to transport other substances that can attach themselves to the transport protein through the membrane (Figure (PageIndex{4})). Many amino acids, as well as glucose, enter a cell this way. This secondary process is also used to store high-energy hydrogen ions in the mitochondria of plant and animal cells for the production of ATP. The potential energy that accumulates in the stored hydrogen ions is translated into kinetic energy as the ions surge through the channel protein ATP synthase, and that energy is used to convert ADP into ATP.

Art Connection

If the pH outside the cell decreases, would you expect the amount of amino acids transported into the cell to increase or decrease?


The combined gradient that affects an ion includes its concentration gradient and its electrical gradient. A positive ion, for example, might tend to diffuse into a new area, down its concentration gradient, but if it is diffusing into an area of net positive charge, its diffusion will be hampered by its electrical gradient. When dealing with ions in aqueous solutions, a combination of the electrochemical and concentration gradients, rather than just the concentration gradient alone, must be considered. Living cells need certain substances that exist inside the cell in concentrations greater than they exist in the extracellular space. Moving substances up their electrochemical gradients requires energy from the cell. Active transport uses energy stored in ATP to fuel this transport. Active transport of small molecular-sized materials uses integral proteins in the cell membrane to move the materials: These proteins are analogous to pumps. Some pumps, which carry out primary active transport, couple directly with ATP to drive their action. In co-transport (or secondary active transport), energy from primary transport can be used to move another substance into the cell and up its concentration gradient.

Art Connections

[link] Injection of a potassium solution into a person’s blood is lethal; this is used in capital punishment and euthanasia. Why do you think a potassium solution injection is lethal?

[link] Cells typically have a high concentration of potassium in the cytoplasm and are bathed in a high concentration of sodium. Injection of potassium dissipates this electrochemical gradient. In heart muscle, the sodium/potassium potential is responsible for transmitting the signal that causes the muscle to contract. When this potential is dissipated, the signal can’t be transmitted, and the heart stops beating. Potassium injections are also used to stop the heart from beating during surgery.

[link] If the pH outside the cell decreases, would you expect the amount of amino acids transported into the cell to increase or decrease?

[link] A decrease in pH means an increase in positively charged H+ ions, and an increase in the electrical gradient across the membrane. The transport of amino acids into the cell will increase.

active transport
method of transporting material that requires energy
transporter that carries two ions or small molecules in different directions
electrochemical gradient
gradient produced by the combined forces of an electrical gradient and a chemical gradient
electrogenic pump
pump that creates a charge imbalance
primary active transport
active transport that moves ions or small molecules across a membrane and may create a difference in charge across that membrane
active transport mechanism that works against electrochemical gradients
secondary active transport
movement of material that is due to the electrochemical gradient established by primary active transport
transporter that carries two different ions or small molecules, both in the same direction
specific carrier proteins or pumps that facilitate movement
transporter that carries one specific ion or molecule

Hands-on Activity Active and Passive Transport: Red Rover Send Particles Over

Partial design process

NGSS Performance Expectations:

Curriculum in this Unit

Units serve as guides to a particular content or subject area. Nested under units are lessons (in purple) and hands-on activities (in blue).

Note that not all lessons and activities will exist under a unit, and instead may exist as "standalone" curriculum.

TE Newsletter


Students model active and passive transport in a cell.

Engineering Connection

Engineers use models to represent and better understand the world at various scales. To better understand cells, engineers construct and manipulate models. In this activity, students construct a cell membrane and provide areas for specific transport. A molecule's ability to permeate through a cell membrane is one of the main focuses of intracellular engineering. A great deal of research is being done in the field of biomedical engineering to learn about the inner-workings of cells in order to develop new forms of medical technology.

Learning Objectives

After this activity, students should be able to:

  • Act as a different particle or part of the cell membrane to model active and passive transport.
  • Explain how particles are transported from one side of the cell membrane to the other.
  • Explain why engineers use models.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (

In the ASN, standards are hierarchically structured: first by source e.g., by state within source by type e.g., science or mathematics within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

HS-LS1-2. Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. (Grades 9 - 12)

Do you agree with this alignment? Thanks for your feedback!

Alignment agreement: Thanks for your feedback!

Alignment agreement: Thanks for your feedback!

Alignment agreement: Thanks for your feedback!

International Technology and Engineering Educators Association - Technology
  • Refine a design by using prototypes and modeling to ensure quality, efficiency, and productivity of the final product. (Grades 9 - 12) More Details

Do you agree with this alignment? Thanks for your feedback!

Materials List

Materials needed for this activity include:

  • yarn (or string)
  • scissors
  • hole punch , one per student (use the hole punch and yarn to make these game cards into student role identification placards optional: laminate them so they are re-usable) , one per student

Worksheets and Attachments

More Curriculum Like This

Students explore the structure and function of cell membranes. As they study the ingress and egress of particles through membranes, students learn about quantum dots and biotechnology through the concept of intracellular engineering.

Students learn about the different structures that comprise cell membranes, fulfilling part of the Research and Revise stages of the legacy cycle. They view online animations of cell membrane dynamics (links provided).

Students learn that engineers develop different polymers to serve various functions and are introduced to selectively permeable membranes. In the main activity, student pairs test and compare the selective permeability of everyday polymer materials engineered for food storage (including plastic groc.


Today you are all going to participate in a cell membrane game called "Red Rover- Send Particles Over." This kinesthetic learning allows you to model and explore relationships within the cell involving the cell membrane. Active learning helps you to model what is happening on a molecular level so you can better understand processes that you are unable to visualize. You should have a chemical and biological understanding of the fluid mosaic model of the cell membrane and be familiar with the structure and polarity of molecules that will transport across the membrane. The act of modeling processes is a tool used by many engineers as they follow the steps of the design process in to solves problems and find good solutions.

Let's review passive and active transport:

Passive transport is the movement of substances across the membrane without any input of energy from the cell. Osmosis and diffusion (the focus of the previous lesson) are two examples of passive transport.

Active transport refers to movement of materials from an area of lower concentration to an area of higher concentration, against the concentration gradient. To do this, energy is required, usually from ATP. Cell membrane pumps, endocytosis and exocytosis (the focus of the previous lesson) all aid in active transport.

In the red rover game, you will physically "move" your body through a cell with either ease or constraints, depending on the type of transport specified.


Before starting the game, students review the activity sheet to familiarize themselves with the transport types and related topics. The teacher serves as the game facilitator, announcing the type of transport and summing up what has happened at the end of each session. During the activity, remind students about the concentration gradient and dynamic equilibrium.

  • Make copies of the Cell Membrane Quiz and Types of Transport Activity Sheet, one each per student.
  • Print out the game cards that illustrate ions, molecules and cell membrane members. Hole-punch the cards on the top two corners and tie yarn through each to make placards for each student to wear during the activity, illustrating their roles. Use the pink atoms as potassium or another ion and write the ion element and charge on each. Have students write the charges on the sodium and chlorine atoms. (Tip: To make these cards re-usable, copy them onto card stock and laminate before punching the holes. Dry erase marker wipes off the laminated surface so the blank atoms can be easily changed.)
  • Move aside desks and tables to clear a space to conduct the game. Or arrange to go outside or to the gym.
  • Give students the activity sheet prior to the activity so they may familiarize themselves with the various types of transport being studied. Also have students review shape and structure of molecules to determine their polarity and method of movement into and out of the cell membranes.
  1. Offer students the stack of game cards, face down, and have them randomly choose their roles in the game by choosing a card. Have them place the placards around their necks so everyone knows their roles in the game.
  2. Direct students who have drawn similar cards to group together to talk about their strategy for movement into the cell membrane. Suggest they look over the activity sheet to review what type of transport they are able to participate in each time. Likewise, have members of the lipid bilayer and the proteins discuss placement of their proteins within the membrane.
  3. Begin the game by announcing which transport type will be illustrated. Similar to playing "Red Rover," the particles try to enter the cell and still be aware of the dynamic equilibrium that takes place in conjunction with the concentration gradient. Have the cell membrane hold hands so as to be "fluid" enough for small particles such as water, carbon dioxide and oxygen gas to enter and exit the cell at will, while charged particles must enter and exit the cell only through their specific channel proteins. Have the channel proteins announce which specific ion they allow to enter and exit. Have the carrier proteins also announce their specific molecule, such as glucose or amino acids.
  4. Periodically stop to discuss what the students are modeling. Transition to new games by summarizing and discussing what happened. Restart new games, announcing different transport types. Periodically allow students to switch roles during the game so that they gain perspective for different parts of the process. Remind students about the concentration gradient and dynamic equilibrium.
  5. At activity end, administer the quiz.


active transport: The movement of substances through the cell membrane that requires energy.

passive transport: The movement of particles through the cell membrane that does not require energy.


Quiz: At activity end, administer the Cell Membrane Quiz. Review students' answers to gauge their comprehension of the concepts.



Supporting Program


The contents of this digital library curriculum were developed under National Science Foundation RET grant nos. 0338092 and 0742871. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.