active transport experiments

FREE K-12 standards-aligned STEM

curriculum for educators everywhere!

Find more at TeachEngineering.org .

• TeachEngineering
• Active and Passive Transport: Red Rover Send Particles Over

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

Grade Level: 9 (9-12)

Time Required: 45 minutes

Expendable Cost/Group: US $0.00

Group Size: 1

Activity Dependency: Keepers of the Gate

Subject Areas: Algebra, Biology, Chemistry, Data Analysis and Probability, Life Science, Measurement, Problem Solving, Reasoning and Proof, Science and Technology

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.

• Grand Challenge Journaling and Brainstorming
• Cell Membrane Color Sheet and Build a Cell Membrane
• Quantum Dots and the Harkess Method of Critical Reading
• Cell Membrane Experimental Design

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Engineering connection, learning objectives, materials list, worksheets and attachments, more curriculum like this, introduction/motivation, vocabulary/definitions, user comments & tips.

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.

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 (www.achievementstandards.org). 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, state standards, tennessee - science.

View aligned curriculum

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

Materials needed for this activity include:

• yarn (or string)
• Types of Transport Activity Page , one per student
• Red Rover Game Pieces (use the hole punch and yarn to make these game cards into student role identification placards; optional: laminate them so they are re-usable)
• Cell Membrane Quiz , one per student

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.

Before the Activity

• 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.

With the Students

• 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.
• 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.
• 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.
• 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.
• 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.

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 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 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...

Students learn about the basics of molecules and how they interact with each other. They learn about the idea of polar and non-polar molecules and how they act with other fluids and surfaces. Students acquire a conceptual understanding of surfactant molecules and how they work on a molecular level. ...

Contributors

Supporting program, acknowledgements.

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.

Last modified: September 3, 2021

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Osmosis, diffusion and active transport

The movement of molecules is quite abstract and difficult to imagine. This list gives a range of practical demonstrations and investigatiosn for students to carry out.

It is worth remembering that activities need to help students develop an understanding of the processes. The analysis, interpretation and discussion of observations should not be rushed. Time for reflection and checking that learning has taken place should be built into the topic.

These are fundamental concepts in biology and can be revisited and reinforced when they are encountered in other topics.

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.

Visking Tubing

Quality Assured Category: Science Publisher: Gatsby Charitable Foundation

This video is for teachers and shows how to set up an experiment in which Visking tubing acts as a model gut. It illustrates diffusion and the action of a semi-permeable, partially permeable, or differentially permeable membrane. Take care to note what term your specifications use.

When setting up the experiment it is not necessary to be particularly accurate with measuring concentrations of glucose and starch solutions. Solutions can readily be put into the Visking tubing using a pipette.

In the video, the Visking tubing is kept open using a cut-off syringe barrel. This aids in access to the internal contents of the tube when being sampled. If this is not required, it is just as effective to take a sample from inside the tubing at the start of the experiment and then tie off the top.

Instead of using Benedict’s reagent, the presence of glucose can be indicated using glucose test strips.

Students can draw diagrams to illustrate why glucose can escape the model gut whilst starch is retained within the gut. Relate this to the digestion of starch in the diet. Remind students that the cell surface membrane is also semi-permeable and will act in the same manner to control substances getting into and out of cells.

Students can be challenged to assess the validity of using Visking tubing to model absorption in the small intestine. It could also be used to investigate factors such as the effect of temperature, or initial solute concentrations on the speed of diffusion.

Membrane Channels

This is a brilliant simulation although it does need some setting up. Firstly, Java needs to be installed on the computers being used. The simulation can though be downloaded and used off-line.

It looks at the movement across a membrane through membrane channels. In this way it is a model for diffusion across a semi-permeable membrane.

Open the simulation and drag some green leakage channels into the cell membrane. These will allow green circles through but will not allow blue diamond molecules to pass through. Describe this as being the same as the semi-permeable cell membrane or the Visking tubing used in the previous experiment.

Introduce green molecules above the membrane by selecting them and pressing the large red button on the dispenser. Note how they cross through the channels to the other side of the membrane.

Select the blue diamond molecules and introduce them above the membrane. Note how these are unable to pass through the membrane.

This is a powerful simulation. Set students the task of investigating the movement of molecules across a membrane. • Explain how the simulation relates to movement in and out of a cell. • What is the effect of differing concentrations of molecules and rate at which they get from one side of the membrane to the other? • How does the number of channels (permeability) of the membrane effect movement? • Do molecules move only in one direction through the channels or do they move back-and-forth? What is the overall effect? How does this relate to the definition of diffusion. • What happens if molecules are introduced on both sides of the membrane?

Water Potential During Ripening and Storage

Quality Assured Category: Science Publisher: Science & Plants for Schools (SAPS)

This activity is designed for post-16 students. However, the first practical described is suitable for 14-16 students.

This practical sees cylinders of a vegetable (potato is the easiest to use) placed in different sucrose solutions. Depending on the concentration of the solution, the potato cylinder either gains or loses weight due to the movement of water in or out of the potato cells.

It is best to calculate the % change in weight for each potato cylinder. Plot this data on a graph. Loss in weight (negative change) is below the x-axis and a gain in weight above it.

Similar results can be obtained by measuring the change in length of the potato cylinder. This is then related to the cells either shrinking or expanding depending on water movements.

Students may need to be prompted to realise that any change in weight is due to the movement of water in or out of cells. Looking at the graph, challenge students to think about the overall direction of water movement in relation to the concentration of the sugar solution. Notes can be added to the graph. What would they suggest is happening when there is overall no change in weight (where the line crosses the x-axis)?

Using these observations, it is possible to challenge students to come up with a definition of osmosis. You may need to prompt them into including that osmosis requires the presence of a differentially permeable membrane.

Students tend to have a good understanding of the idea of a concentrated or a weak solution. Only once students have understood the process, consider introducing terms such as water potential, that may be required by your specification.

Gaseous exchange in the lungs

This video looks at gas exchange and it can be used to illustrate an instance where diffusion takes place in the body. Students do not need to have prior knowledge of the lungs and breathing but if they do, it will also serve as a reminder of this topic.

Near the start of the video, the presenters talk about the concentration of carbon dioxide and oxygen in air inhaled and exhaled. Draw students’ attention to the difference. This will be needed when thinking about how diffusion happens at the alveoli.

It is worth stressing that there is some carbon dioxide in inhaled air and also oxygen in exhaled air. This is to avoid giving the impression that we breath in oxygen and breath out carbon dioxide.

You may also remind students that nitrogen makes up around 78% of air.

The animation of the alveolus is slightly confusing as the deoxygenated blood is represented as red and the oxygenated blood as blue. Pause the video and point this out.

Remind students about the concentrations of gases in the inhaled and exhaled air that they noted earlier in the video.

If students consider the carbon dioxide first. Where is it at its highest concentration (in the deoxygenated blood) and where is it at its lowest (the air space in the alveolus). Which direction should the carbon dioxide diffuse?

Repeat this line of questioning with the oxygen before continuing the video to see what happens.

The video goes on to look at surface area. Stress this is an important feature of areas where exchange happens. Ask students for any other examples where they have come across a large surface area being important.

Diffusion, osmosis and active transport

This is an animation showing active transport, diffusion and osmosis. It can be found by scrolling to the bottom of the page.

Active transport can be looked at first by reminding students that diffusion sees molecules move down a concentrations gradient. Suggest that there are times when cells need to move molecules up a concentration gradient.

What is moving up a gradient likely to need? The process is called active transport as it requires energy.

The animation can be used to point out how the transport protein carries the molecule into the cell where there is already a high concentration present. Stress that this carrier protein needs energy to do this. Without energy, the process will stop. Students can be reminded about the process of cellular respiration and that this is the process that provides the energy for active transport.

The processes of diffusion, active transport and osmosis can be summarised by having students produce a revision table that contains the similarities and differences of each process. This page is also useful in reminding students of the key features when they construct their table.

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Very simple diffusion and osmosis experiment.

5 comments:

Good blog. Very easy to understand the point of each piece of text.

How do you make your starch solution and glucose solution?

Since no quantitative data is being collected, there is no need to make solutions of a specific concentration. I put some corn starch in a beaker of water and boil it until it clears up a bit. I put several teaspoons of Karo syrup in a beaker of water and stir until throughly mixed.

where can i find these dialysis tubing??

We order them with our lab supplies. You can also use a plastic sandwich bag.

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4.8 Active Transport

Created by: CK-12/Adapted by Christine Miller

Like Pushing a Humvee Uphill

You can tell by their faces that these airmen (Figure 4.8.1) are expending a lot of energy trying to push this Humvee up a slope. The men are participating in a competition that tests their brute strength against that of other teams. The Humvee weighs about 13 thousand pounds (about 5,897 kilograms), so it takes every ounce of energy they can muster to move it uphill against the force of gravity. Transport of some substances across a plasma membrane is a little like pushing a Humvee uphill — it can’t be done without adding energy.

What Is Active Transport?

Some substances can pass into or out of a cell across the  plasma membrane  without any  energy  required because they are moving from an area of higher concentration to an area of lower concentration. This type of transport is called  passive transport . Other substances require energy to cross a plasma membrane, often because they are moving from an area of lower concentration to an area of higher concentration, against the concentration gradient. This type of transport is called  active transport . The energy for active transport comes from the energy-carrying molecule called ATP (adenosine triphosphate). Active transport may also require proteins called pumps, which are embedded in the plasma membrane. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.

The Sodium-Potassium Pump

The  sodium-potassium pump is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cells — in all the trillions of cells in the body! Both ions are moved from areas of lower to higher concentration, so energy is needed for this “uphill” process. The energy is provided by ATP . The sodium-potassium pump also requires carrier proteins . Carrier proteins bind with specific ions or molecules, and in doing so, they change shape. As carrier proteins change shape, they carry the ions or molecules across the membrane. Figure 4.8.2 shows in greater detail how the sodium-potassium pump works, as well as the specific roles played by carrier proteins in this process.

To appreciate the importance of the sodium-potassium pump, you need to know more about the roles of sodium and potassium in the body. Both are essential dietary minerals. You need to get them from the foods you eat. Both sodium and potassium are also electrolytes, which means they dissociate into ions (charged particles) in solution, allowing them to conduct electricity. Normal body functions require a very narrow range of concentrations of sodium and potassium ions in body fluids, both inside and outside of cells.

• Sodium is the principal ion in the fluid outside of cells. Normal sodium concentrations are about ten times higher outside of cells than inside of cells.  To move sodium out of the cell is moving it against the concentration gradient
• Potassium is the principal ion in the fluid inside of cells. Normal potassium concentrations are about 30 times higher inside of cells than outside of cells. To move potassium into the cell is moving it against the concentration gradient.

These differences in concentration create an electrical and chemical gradient across the  cell membrane , called the  membrane potential . Tightly controlling the membrane potential is critical for vital body functions, including the transmission of nerve impulses and contraction of muscles. A large percentage of the body’s energy goes to maintaining this potential across the membranes of its trillions of cells with the sodium-potassium pump .

Vesicle Transport

Some molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called  vesicle transport . Vesicle transport requires energy input from the cell, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure 4.8.3.

Endocytosis

Endocytosis  is a type of vesicle transport that moves a substance into the cell. The plasma membrane completely engulfs the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell. When an entire cell or other solid particle is engulfed, the process is called  phagocytosis .  When fluid is engulfed, the process is called  pinocytosis .

Exocytosis  is a type of vesicle transport that moves a substance out of the cell (exo-, like “exit”). A vesicle containing the substance moves through the cytoplasm to the  cell membrane . Because the vesicle membrane is a  phospholipid bilayer  like the plasma membrane, the vesicle membrane fuses with the cell membrane, and the substance is released outside the cell.

Feature: My Human Body

Maintaining the proper balance of sodium and potassium in body fluids by active transport is necessary for life itself, so it’s no surprise that getting the right balance of sodium and potassium in the diet is important for good health. Imbalances may increase the risk of high blood pressure ,  heart disease ,  diabetes , and other disorders.

If you are like the majority of North Americans, sodium and potassium are out of balance in your diet. You are likely to consume too much sodium and too little potassium. Follow these guidelines to help ensure that these minerals are balanced in the foods you eat:

• Total sodium intake should be less than 2,300 mg/day. Most salt in the diet is found in processed foods, or added with a salt shaker. Stop adding salt and start checking food labels for sodium content. Foods considered low in sodium have less than 140 mg/serving (or 5 per cent daily value).
• Total potassium intake should be 4,700 mg/day. It’s easy to add potassium to the diet by choosing the right foods — and there are plenty of choices! Most fruits and vegetables are high in potassium. Potatoes, bananas, oranges, apricots, plums, leafy greens, tomatoes, lima beans, and avocado are especially good sources. Other foods with substantial amounts of potassium are fish, meat, poultry, and whole grains. The collage below shows some of these potassium-rich foods.

Figure 4.8.5 Potassium power! 

4.8 Summary

• Active transport requires energy to move substances across a plasma membrane , often because the substances are moving from an area of lower concentration to an area of higher concentration, or because of their large size. Two types of active transport are membrane pumps (such as the sodium-potassium pump) and vesicle transport.
• The sodium-potassium pump is a mechanism of active transport that moves sodium ions out of the cell and potassium ions into the cell against a concentration gradient, in order to maintain the proper concentrations of ions, both inside and outside the cell, and to thereby control membrane potential.
• Vesicle transport is a type of active transport that uses vesicles  to move large molecules into or out of cells.

4.8 Review Questions

• Define active transport.
• What is the sodium-potassium pump? Why is it so important?
• What are the similarities and differences between phagocytosis and pinocytosis?
• What is the functional significance of the shape change of the carrier protein in the sodium-potassium pump after the sodium ions bind?
• A potentially deadly poison derived from plants called ouabain blocks the sodium-potassium pump and prevents it from working. What do you think this does to the sodium and potassium balance in cells? Explain your answer.

4.8 Explore More

Neutrophil Phagocytosis – White Blood Cell Eats Staphylococcus Aureus Bacteria, ImmiflexImmuneSystem, 2013.

Cell Transport, The Amoeba Sisters, 2016.

Attributions

Figure 4.8.1

Humvee challenge by Airman 1st Class Collin Schmidt on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

Figure 4.8.2

Sodium Potassium Pump by Christine Miller is used under a  CC BY 4.0   ( https://creativecommons.org/licenses/by/4.0/) license.

Figure 4.8.3

Cytosis by Manu5  on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 4.8.4 

Endocytosis and Exocytosis by Christine Miller is used under a  CC BY 4.0   ( https://creativecommons.org/licenses/by/4.0/) license.

Figure 4.8.5

• Canteloupes. Image Number K7355-11 by Scott Bauer/ USDA on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
• Spinach by chiara conti on Unsplash is used under the Unsplash license (https://unsplash.com/license).
• Eleven long purple eggplants by JVRKPRASAD on Wikimedia commons is used under a  CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
• Bananas by Marco Antonio Victorino on Pexels is used under the Pexels license (https://www.pexels.com/license/).
• Potato picking by Nic D on Unsplash is used under the Unsplash license (https://unsplash.com/license).
• Maldives by Sebastian Pena Lambarri on Unsplash is used under the Unsplash license (https://unsplash.com/license).

Figure 4.8.6

Active Transport by Christine Miller is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

Amoeba Sisters. (2016, June 24). Cell transport [digital image]. YouTube. https://www.youtube.com/watch?v=Ptmlvtei8hw&feature=youtu.be

ImmiflexImmuneSystem. (2013). Neutrophil phagocytosis – White blood cell eats staphylococcus aureus bacteria. YouTube. https://www.youtube.com/watch?v=Z_mXDvZQ6dU

Mayo Clinic Staff. (n.d.). Diabetes [online]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/diabetes/symptoms-causes/syc-20371444

Mayo Clinic Staff. (n.d.). High blood pressure (hypertension) [online]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/high-blood-pressure/symptoms-causes/syc-20373410

Mayo Clinic Staff. (n.d.). Heart disease [online]. MayoClinic.org.  https://www.mayoclinic.org/diseases-conditions/heart-disease/symptoms-causes/syc-20353118

Wikipedia contributors. (2020, June 19). Ouabain. In  Wikipedia.  https://en.wikipedia.org/w/index.php?title=Ouabain&oldid=963440756

The ability to do work.

A semi-permeable lipid bilayer that separates the interior of all cells from their surroundings.

a type of movement of substances across the cell membrane which does not require energy because the substances are moving with the concentration gradient (from high to low concentration).

The movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.

A complex organic chemical that provides energy to drive many processes in living cells, e.g. muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all forms of life, ATP is often referred to as the "molecular unit of currency" of intracellular energy transfer.

A solute pump that pumps potassium into cells while pumping sodium out of cells, both against their concentration gradients. This pumping is active and occurs at the ratio of 2 potassium for every 3 calcium.

The smallest unit of life, consisting of at least a membrane, cytoplasm, and genetic material.

Proteins that carry substances from one side of a biological membrane to the other. Many carrier proteins are found in a cell's membrane, though they may also be found in the membranes of internal organelles such as the mitochondria, chloroplasts, nucleolus, and others.

The semipermeable membrane surrounding the cytoplasm of a cell.

The difference in electric potential between the interior and the exterior of a cell due to differences in the concentrations of ions on opposite sides of a cellular membrane.

A signal transmitted along a nerve fiber.

A form of active transport in which substances cross the plasma membrane with the help of a vesicle.

Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. Endocytosis includes pinocytosis and phagocytosis.

The process by which a cell uses its plasma membrane to engulf a large particle, giving rise to an internal compartment called the phagosome.

The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.

An important process of plant and animal cells as it performs the opposite function of endocytosis. In exocytosis, membrane-bound vesicles containing cellular molecules are transported to the cell membrane and released into the area surrounding the cell.

A thin polar membrane made of two layers of phospholipid molecules. These membranes are flat sheets that form a continuous barrier around all cells.

A structure within a cell, consisting of lipid bilayer. Vesicles form naturally during the processes of secretion, uptake and transport of materials within the plasma membrane.

Human Biology Copyright © 2020 by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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Microbe Notes

Active Transport- Definition, Types, Process, Examples

The cellular membrane of biological organisms is semi-permeable in nature, meaning they allow only a fraction of ions, molecules, and water across a membrane. The permeability of these molecules varies based on the structural pattern of lipid bilayer among different types of cells and organisms. The lipid bilayer, in accordance with macromolecules such as proteins, carbohydrates, and lipids, facilitates the transport of molecules. The ability of any membrane to control the transportation of molecules across a membrane is considered as one of the essential life processes in an organism.

The membranes apply two modes of transport for molecular movement, this includes: 

Passive Transport – This transport mechanism involves the movement of substances across the membrane down the concentration gradient from high to low without employing any energy expenditure. 

Examples include: 

• The diffusion of neurotransmitters like acetylcholine across synaptical junctions in neurons.
• Diffusion of gases in the lungs across alveolar membranes.
• Movement of water molecules by osmosis.

Active Transport – A transport mechanism that involves the movement of molecules across the membrane against the concentration gradient, meaning the transport of substances from low to high concentration. This movement is achieved by the energy expenditure from ATP (adenosine triphosphate). 

Examples include:

• Movement of Ca 2+ ions out of the cardiac muscle cells.
• Transportation of glucose molecules across membranes.
• Movement of amino acids in the human gut across the intestinal lining.

Read Also- Active vs passive transport- Definition, 18 Differences, Examples

Any mutational changes in the transportation system or the membrane transporters involved may lead to severe health conditions like depression, cystic fibrosis, drug abuse, migraine, and epilepsy.

Table of Contents

Interesting Science Videos

Lipid Bilayers and Membrane Proteins

• Most biological membranes are composed of a phospholipid bilayer, with the hydrophilic side exposed outwards and the hydrophobic side facing inwards, and transmembrane proteins spanning the bilayer.
• The integrated proteins present in the membrane form the transport channel, pumps, and carriers that are required for the translocation of ions and macromolecules across biological membranes.

• Channel proteins form pores in the membrane to allow free passage of inorganic ions like Na+, Cl-, K+, H+, etc, and molecules of appropriate size.
• The channel proteins are strictly regulated by extracellular signals to control the movement of ions and solutes across the membrane.
• Carrier proteins act like an enzyme that selectively binds to and transports specific small molecules such as glucose to facilitate the translocation across the membrane.
• The composition of the phospholipid-to-protein ratio varies depending on the type of cell it is present in. For example, the mitochondrial inner membrane has 75% protein suggesting the presence of protein complexes involved in oxidative phosphorylation and the electron transport system.

What is Active Transport?

Active transport is the energy-driven transportation of ions, small molecules, and solutes across the biological membrane against an electrochemical gradient (for ions) or concentration gradient i.e., from lower to higher concentration.

Since this mode of cellular transportation requires energy, a significant amount of cellular energy is spent on regulating the homeostasis of molecules and ions in a cell. Active transport is further divided into two types – Primary and Secondary active transport.

Active Transport Types

Classification of Active Transport is based on how energy is employed to bring about the movement of substances. Primary active transport is seen to use ATP as an energy source to translocate solutes against a concentration gradient, whereas in Secondary active transport, an electrochemical gradient is applied.

Primary Active Transport

This category of active transport directly employs the use of metabolic energy to translocate substances across the membrane, hence also called as ‘ Direct Active Transport. ’ The transportation of molecules uses energy released from ATP, where Adenosine triphosphate (ATP) is broken down to ADP (adenosine diphosphate). This transport mode is used to move metal ions like K+, Na+, Cl-, H+, Mg2+, and Ca2+. The enzymes utilized for the primary active transport of ions are ATPases that facilitate the movement of charged ions across ion channels or pumps. 

Types of Primary Active Transport

P-type atpases.

They are also referred to as E1-E2 (enzyme1-enzyme2) ATPases due to their ability to interchange between two conformations. 

• In humans, the pumps with P-type ATPases show diverse roles in nerve impulses, absorption of nutrients and solutes in the intestine and kidney, and in relaxation of muscles.
• Eukaryotes and bacteria have ion channels with P-type ATPases.
• The ‘P-type’ refers to the autophosphorylation among components present in the pumps, such as ATP and aspartate, present in the enzyme structural composition.
• The enzyme structure typically contains four significant functional domains to carry out the transportation process, which include 
• P-domain (Phosphorylation) containing amino acids like aspartate.
• N-domain – Used for nucleotide binding.
• A-domain – Actuator domain which contains a phosphatase domain for dephosphorylation of the phosphorylated element.
• R-domain – Regulatory domain.

Examples of P-type ATPases involved in ions pumps include Na+-K+ (sodium-potassium ) ion channel, Calcium ATPase (Ca2+ pump), Hydrogen ATPase (H+ pump), and H+/K+ ATPase in proton-potassium pump, in fungi, bacteria, humans, and plants.

Mechanism of Sodium-Potassium (Na+/K+ ATPase) Pump

This pump employs a direct utilization of ATP to bring about the conformational changes to the protein and allow passage of three Na+ ions out of cells while bringing two K+ ions into the cell.

• The transmembrane carrier protein is opened towards the cell interior with a high affinity for sodium ions.
• The binding of sodium ions to the carrier protein induces phosphorylation of the transmembrane protein by ATP hydrolysis.
• The phosphorylation of protein modifies the structural conformation making it open to the cell exterior, leading to a lower affinity for sodium ions, hence releasing the three bound sodium to the extracellular space.
• The outward-facing carrier protein conformation shows a higher affinity for potassium ions.
• As the potassium ions bind to the carrier protein, it releases the phosphate group attached to the protein.
• The detachment of the phosphate group from the protein causes it to change to its original conformation facing to the cell interior.
• The change in conformation loses the affinity for potassium ions, hence releasing it into the cell, and again sodium ions can bind to the protein, and the cycle repeats continuously.
• A cardiac glycoside called ‘Ouabain’ blocks the influx of potassium ions into the cell by binding to the protein surface and inhibiting the dephosphorylation of carrier protein.

They are mainly found in the mitochondrial inner membranes and chloroplast’s thylakoid membrane. 

• They are sometimes also referred to as ATP phosphohydrolase that transports H+ ions, or as ATP synthase.
• The enzyme uses rotating machinery to pump Na+ or H+ ions which are powered by energy derived from ATP hydrolysis.
• F-type ATPase contains two main domains – F1 and F0 .
• F1 Domain – It is a Hydrophilic catalytic globular domain made of an asymmetric hexameric ring and a central stalk at the center of the ring. This domain contains catalytic sites for ATP hydrolysis and synthesis.
• F0 Domain – Responsible for the translocation of ions across a membrane. It is hydrophobic in nature and is embedded in the membrane.
• The energy obtained from the movement of protons across the membrane is used to drive ATP synthesis, which helps in releasing newly formed ATP from F-ATPase’s active site.
• ATP hydrolysis is done at conditions of a lower driving force. Hence ATPase functions as ATP synthase that generates a transmembrane electrochemical gradient. 

V-ATPase  

The V denotes vacuolar ATPases, which are proton-translocating pumps present in the tonoplast of cells. They are responsible for making the organelle more acidic than the cytoplasm around them.

• This enzyme employs the energy obtained from ATP hydrolysis to drive the transport of protons across biological membranes.
• It is a multimeric protein that uses rotatory machinery to allow the passage of ions and has two distinct domains – V1 and V0.
• V1 Domain – Contains catalytic site for ATP hydrolysis and comprises eight subunits.
• V0 Domain –  This domain is responsible for the movement of protons across a membrane.
• They are considered an important molecular switch that toggles between anabolic and catabolic metabolism, and any disruption to their structure can lead to diseases like cancer.

ATP Binding Cassette (ABC) Transporters

They are significantly found in chloroplasts, mitochondria, and plasma membranes and are seen to play a vital role in detoxification, phytohormone transport, and in pathogen response. They utilize the energy released from the hydrolysis of ATP to allow the passage of solutes across a membrane.

• They have four significant domains, two of which are transmembrane integral domains spanning the membrane six times, and the other two domains are responsible for ATP hydrolysis.
• They are actively seen to export antimicrobial metabolites and volatile compounds such as benzene, 1,3-butadiene, etc.
• Approximately 48 genes are identified in humans, and most of these genes are part of diseases like Dubin-Johnson Syndrome, Cystic Fibrosis, Ataxia, Anemia, adrenoleukodystrophy, and many more.
• They participate in processes like drug/antibiotic resistance, signal transduction, antigen presentation, bacterial pathogenesis, etc.

Secondary Active Transport

Also called as Coupled Transport or Cotransport, as there is a movement of ions along with large molecules like glucose. First, the ions are pumped down the electrochemical gradient but against a concentration gradient, as a result of which energy is released. Then the solute is translocated across a membrane down the concentration gradient.

• The functions performed by this mode of transport include the generation of an electrochemical gradient due to the movement of ions at the expense of energy across a membrane.
• The ion gradient difference leads to a movement of solute in either the opposite direction, referred to as Antiport, or in the same direction, referred to as Symport.
• In yeast and bacteria, hydrogen (H+) ions are the commonly cotransported ion, whereas, in humans, sodium (Na+) ions are widely used for coupled transportation.

Secondary Active Transport Types

There are basically two modes of secondary active transport based on the direction of solute along with ions across a membrane: Antiport (opposite direction) and Symport (same direction) . The level of effective movement of substances can be measured by the concentration capacity of the transporters to translocate ions/solutes in the process per cycle. The higher the ion/substrate coupling ratio, the higher the concentration capacity of the transporter. For instance, the coupling of sodium (Na+) ions to glucose results in the movement of two sodium ions to one glucose molecule per transport cycle with a ratio of 2:1.

Also referred to as Counter transport or Exchanger as solutes and ions are allowed to move in the opposite direction. Examples include the Na+/Ca2+ transporter via calcium ATPase, Cl-/HCO3- transporter, and Na+/H+ transporter.

• Na+/Ca2+ Antiporter – This antiporter is necessary to regulate low calcium concentration in the cardiac muscle cells. This exchanger allows three Na+ ions down the electrochemical gradient and one Ca2+ ions against the electrochemical gradient from low to high solute concentration with a stoichiometric coupling ratio of antiporter 3:1.
• Cl-/HCO3- Antiporter – Results in electroneutral exchange as one Cl- ion down its electrochemical gradient per bicarbonate (HCO3-) ion against the electrochemical gradient with a stoichiometric coupling ratio of antiporter 1:1.
• Na+/H+ Antiporter – Electroneutral mechanism and very useful in maintaining the cytoplasmic pH as one Na+ ion is transported down its electrochemical gradient per H+ ion against its gradient with a stoichiometric coupling ratio of antiporter 1:1.

The solutes and ions are transported in the same direction , with one substance being translocated down its concentration gradient while the other substance is moved against its gradient from low to high solute concentration. Examples include glucose symporter (SGLT1), GABA symporter (GAT), oligopeptide symporter (PepT), and more.

• Glucose symporter (SGLT1) – It can be found in the cells of the intestinal epithelium, nephrons of the kidney, brain, and in heart. Two molecules of Na+ ions are imported down its concentration gradient into the cell per glucose (or galactose) molecule against the gradient.
• GAT Symporter – Responsible for regulating the concentration of GABA (gamma-aminobutyric acid), an inhibitory neurotransmitter in the synaptic cleft of the nervous system. The symporter is coupled with Na+ or Cl- ions for solute movement across a membrane.
• Oligopeptide symporter (PepT) – Serves as a crucial entry route for drugs like beta-lactam antibiotics and helps in the reabsorption of nitrogen in the intestine and kidney. In this symporter, one H+ ion is transported from high to low concentration per dipeptide or tripeptide molecule against its concentration gradient.

Active transport is a crucial transport mechanism opted by cells to maintain ionic homeostasis in the cytoplasm and regulate the uptake/removal of drugs,  nutrients, and waste products. This is an energy-driven process of translocating substances across a membrane down or against their electrochemical and concentration gradient. Active transport is categorized into two modes which include primary active transport (directly employs ATP’s energy to drive ions across the membrane) and secondary active transport (using energy from electrochemical gradient to couple movement of solutes and ions). It is a highly specific and regulated process with multiple proteins and transporter working together to allow efficient passage of molecules. Any anomalies in the structure of a transporter affect its efficacy in delivering molecules across the membrane, which leads to diseases like cancer, cystic fibrosis, renal tubular acidosis, Barter syndrome, and many more.

• Physiology, Active Transport – https://www.ncbi.nlm.nih.gov/books/NBK547718/
• Active transport – https://en.wikipedia.org/wiki/Active_transport
• Active Transport: Definition, Types, and Examples – https://conductscience.com/active-transport-definition-types-and-examples/
• Active transport – https://www.biologyonline.com/dictionary/active-transport
• Active Transport – https://www.sciencedirect.com/topics/immunology-and-microbiology/active-transport
• Cell Membranes – https://www.ncbi.nlm.nih.gov/books/NBK9928/
• The Lipid Bilayer – https://www.ncbi.nlm.nih.gov/books/NBK26871/
• P-Type ATPase – https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/p-type-atpase
• https://www.frontiersin.org/articles/10.3389/fphys.2019.00358/full

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Nidhi Dewangan

1 thought on “Active Transport- Definition, Types, Process, Examples”

Thanks for this awesome answer

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