Active transport in cells is a necessary biological and genuine process that occurs in all biological systems, including plants, animals, and humans. This process is critical for maintaining life because it transports various essential materials in the eukaryotic cells, tissues, and organs.
Water, hormones, gases, mineral nutrition, organic material, and other important substances are just a few examples of the essential nutrients transported by the active transport process.
Table of Contents
Definition of active transport
Active transport is a type of cellular transport in which substances move in the opposite direction of a concentration gradient. This indicates that the flow is from a lower concentration area to a higher concentration area. This process will necessitate the expenditure of energy as well as the involvement of membrane proteins such as carrier proteins.
What is active transport in biology?
It is a form of cellular transfer in which materials (such as ions, glucose, and amino acids) are moved across a biological membrane to a region where there are already many of them. It also utilizes chemical energy (for example, ATP) to migrate substances across concentration gradients. For instance, root hair cells and the small intestinal wall villi are common active transport sites.
Does active transport require energy?
Yes, it does, because substances move against the concentration gradient during active transport, from a low concentration area to a high concentration area. Hence the process is considered “active” because it necessitates the use of energy (usually in the form of ATP).
Examples of active transport
- Pump for sodium and potassium
- Sodium-glucose transport protein
- Destruction of pathogens by white blood cells
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Pump for sodium and potassium
The sodium-potassium pump is one of the most significant active transport proteins in animals. As animals, we rely on a variation in ion concentrations between the inside and outside nerve cells to keep our nervous systems functioning. The body’s nerve cells ignite because of this gradient, causing muscular contraction, feelings, and even thoughts. Even our heart muscle contracts due to ion gradients.
The sodium-potassium pump’s capacity to transport potassium into cells while also carrying sodium out of cells is so crucial that some studies indicate we spend 20-25 percent of our total energy from food on just this one activity. The sodium-potassium pumps in neurons are said to consume the majority of the cell’s energy.
This may appear to be a large amount of energy, but it is necessary for us to walk, imagine, pump blood across all of our bodies, and experience the world around us.
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Sodium-glucose transport protein
The sodium-glucose transport protein is a well-known representation of a symport pump (a pump that simultaneously transports more than one substance at a time). This protein binds to 2 sodium ions that want to enter the cell and 1 glucose molecule that wants to remain outside. It is a crucial mode of sugar transfer in the body, as it is necessary to provide energy for cellular respiration.
The motion of glucose into the cell is aided by the natural diffusion of sodium ions within the cell. Glucose and sodium can be brought into the cell without ATP being expended by the transport protein, unlike the sodium-potassium pump that uses ATP to maintain the sodium gradient in cells.
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Destruction of pathogens by white blood cells
Another example of active transport occurs during the destruction of pathogens by white blood cells. The system whereby the white blood cells ingest pathogens is an interesting example of endocytosis (the engulfing of substances by the cell membrane into the cell). White blood cells wrap their cell membrane around a foreign object inside the body, such as a bacterium, to take it into their cytoplasm; this process involves the use of energy, hence it is an active transport process.
Enzymes then combine the invader-containing vesicle with a lysosome, a vesicle that contains powerful chemicals and enzymes that can digest and break down organic matter.
3 Types of active transport
Active transport can be divided into 3 categories:
- Primary active transport
- Secondary active transport
- Bulk transport
Primary active transport
The primary active transport is also referred to as direct transport entails the direct application of metabolic energy (e.g., ATP hydrolysis) in the transportation of materials in and out of the cell. Primary active transport is exemplified by the sodium-potassium pump, which is the most important pump in the animal cell because Na+, K+, Mg2+, and Ca2+ are the substances that are transported by it. The sodium-potassium pump is a transport system in a biological membrane that removes three Na+ ions while allowing two K+ ions to enter the cell against concentration gradients. Another case in point is the active transport of protons across the inner mitochondrial membrane against a concentration gradient, which is powered by NADH’s redox energy. Movement of protons across the thylakoid membrane a form of primary active transport that can be driven by photon energy results in the formation of a proton gradient, similar to that seen during photosynthesis
Secondary active transport
Secondary active transport is also known as indirect transport is a type of active transport that relies on electrochemical energy for its operation. This electrochemical energy is created by some membrane proteins that use active transport to establish an electrochemical gradient across the membrane of the cell. The electrochemical gradient created is a form of energy known as electrochemical energy and it is capable of moving ions across the membrane.
In secondary active transport, the electrochemical gradient created can be released when the cell membrane is triggered, this causes the movement of one ion against its concentration gradient while also causing the movement of another ion down the electrochemical gradient. For instance, the transport of H+ ions against their concentration gradient is boosted during the process of Na+ ions moving down their electrochemical gradient across the plasma membrane. In this case, the hydrogen ions are indirectly transported against their concentration gradient as the Sodium ions move down their electrochemical gradient using the electrochemical energy that was created initially by some proteins involved in primary active transport.
There are 2 types of secondary active transporters and they are as follows;
- Counter transporters
- Cotransporters.
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Counter transporters or antiporters
Counter transporters are also known as antiporters. These are proteins that act as transmembrane co-transporters because they move one substance in one direction while pumping another component in the other direction. Since many of these pumps can fuel both of these tasks with just 1 ATP molecule, they are incredibly effective. Some examples of these types of transporters in action are mentioned below;
- The sodium-calcium counter-transport occurs when sodium ions binds to the transport carrier protein on the membrane’s exterior side while calcium ions binds to the same protein on the interior side. When both ions are bound, a conformational change occurs, releasing energy and transporting the sodium ion to the interior and the calcium ion to the exterior. Almost all cell membranes contain this transporter. In this case, Sodium ions are transported down their electrochemical gradient whereas calcium ions are transported against their concentration gradient.
- Counter-transport of Na+ and H+. This is another example of counter transport and occurs commonly in the proximal tubules of the kidneys.
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Cotransporters or symporters
Cotransporters are also known as symporters and they use diffusion gradients to transport materials. Diffusion gradients are concentration variations that induce substances to naturally migrate from high to low concentration areas. In the situation of a symport pump, a substance that wishes to travel from a high concentration area to a low concentration area down the concentration gradient is employed to carry some other substance against their concentration gradients. An example of this type of transporter is the sodium-amino cotransport in which some amino acids absorption in the intestines depends on sodium for their uptake. As the sodium is transported into the intestinal cells down their concentration gradient, the amino acids bind to the same protein in order to be transported against their concentration gradient together with the sodium into the cells.
Bulk transport
Bulk transport is a form of active transport that deals with the movement of larger materials or molecules in and out of the cells. It is divided into 2 namely;
- Endocytosis
- Exocytosis
Endocytosis
Endocytosis is the process by which a cell takes in substances by wrapping its membrane around the substances; these wrapped substances are then pinched off into the cell for further digestion. The process requires the use of energy, hence it is a type of active transport.
Bulk items or enormous amounts of extracellular fluid are often transported by this process of endocytosis.
The folding of the cell membrane is actually achieved through a mechanism similar to that of potassium and sodium ion antiport transport. Adenosine triphosphate (ATP) molecules bind to proteins in the cell membrane, inducing them to change shape and triggering the endocytotic process.
Endocytosis is further divided into 3 categories namely;
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
Phagocytosis
Phagocytosis, or cell eating, is a type of endocytosis in which large particles are moved into the cell, such as cells or cellular debris. Amoebas, which are single-celled eukaryotes, utilize phagocytosis to search and eat their prey. When a cell effectively swallows an intended particle, the pocket carrying the particle pinches away from the membrane, developing a membrane-bound compartment known as a food vacuole. Afterward, the food vacuole will merge with a lysosome for further digestion.
Pinocytosis
Pinocytosis also known as cell drinking, is a type of endocytosis in which a cell takes in small amounts of extracellular fluid. Pinocytosis is a consistent process that occurs in several cell types, with the cell sampling and re-sampling the surrounding fluid to obtain whatever nutrients and other molecules that are present. Pinocytosed substance is held in small vesicles, far smaller than the large phagocytosed food vacuole.
Receptor-mediated endocytosis
Receptor-mediated endocytosis is a type of endocytosis in which an identified target molecule is captured by receptor proteins on the cell surface. The receptors, which are transmembrane proteins, congregate in coated pits on the plasma membrane. Endocytosis is then triggered when the receptors bind to their particular target molecule, and the receptors and their affixed molecules are carried into the cell in a vesicle.
The coated proteins aid in this process by giving the vesicle its rounded shape and assisting in its separation from the membrane. Endocytosis mediated by receptors enables cells to take up huge quantities of molecules in the extracellular fluid that are relatively rare (present in low concentrations).
Exocytosis
Exocytosis is the process by which a cell moves large amounts of material outside of itself by wrapping it in a membrane called a vesicle and spitting it out of the cell by attaching the vesicle to the membrane.
Cells should indeed take in some molecules, such as nutrients, but they should also release others, such as signaling proteins and waste products, into the environment. Exocytosis (Exo = external, cytosis = transport mechanism) is a type of bulk transport during which substances are moved from within the cell to the outside in membrane-bound vesicles that merge with the plasma membrane.
A few of these vesicles are produced by the Golgi apparatus and contain proteins created especially for discharge outside the cell, such as signaling molecules. Certain vesicles contain trash that the cell needs to get rid of, like the leftovers from phagocytosing and digesting a particle.
Such vesicles are carried to the cell’s periphery, where they combine with the plasma membrane and release their material into the extracellular space. A few vesicles entirely combine with the membrane and become fully integrated into it, while others touch and pass, fusing just enough with the membrane to discharge their material (touching the membrane) before pinching off and reverting to the cell interior.
Passive Vs Active Transport
Criterion |
Active transport |
Passive transport |
Definition |
Active transport is the movement of molecules across the cell membrane while pumping them against a concentration gradient using ATP (energy). |
Passive transport is the movement of molecules within and across the cell membrane, carrying them via a concentration gradient without the use of ATP (energy). |
Concentration gradient |
Particles migrate from a low concentration to a high concentration, which signifies they move in the opposite direction of the concentration gradient. |
Particles migrate from a high concentration to a low concentration, which is referred to as a concentration gradient. |
Energy requirements |
In active transport, energy in the form of ATP is needed. |
There is no requirement for energy. |
Carrier proteins |
Carrier proteins are needed for active transport. |
Passive transport does not use carrier proteins. Nevertheless, in facilitated diffusion, there are some channels that do not use any energy. |
Direction of molecules |
The molecules are pumped upwards with the help of ATP. |
The molecules are moved downwards. |
The principle behind their function |
It permits molecules to pass through the cell membrane, distorting the diffusion balance. |
Passive transport between the cytosol and the extracellular environment maintains a dynamic balance of water, nutrients, gases, and wastes. |
Matrix or permease participation |
The membrane’s matrix or permeases are not engaged. |
It occurs through the use of a matrix, channels, and permeases. |
The efficiency of the procedure |
It’s a quick procedure. |
It is a relatively slow procedure. |
Directionality of the process |
It only happens in one direction. |
The process is bidirectional. |
Type of procedure |
It is a necessary process. |
The process of passive transport is a physical one. |
Selectivity |
It is extremely picky. |
It is non-selective in part. |
Influence of temperature |
Temperature affects it. |
The temperature has no influence. |
The Influence of Oxygen Levels |
As the amount of oxygen in the air decreases, this process slows or stops. |
The amount of oxygen in the air has no effect on this process. |
Metabolic inhibitors’ impact |
Active transport is stopped or halted by metabolic inhibitors. |
Passive transport is unaffected by metabolic inhibitors. |
Transported Molecules |
Proteins, carbohydrates (sugars), lipids, and large cells are just a few of the macromolecules that are transported this way. |
Only a few soluble materials are transported this way: oxygen, monosaccharides, water, carbon dioxide, and lipids. |
Types |
Primary active transport and secondary active transport are the two types of active transportation.
Exocytosis, endocytosis, and cell membrane/sodium-potassium pump |
Osmosis, diffusion, facilitated diffusion, and filtration is four different types of passive transport. |
Functions |
Even if both forms of transport carry ions and molecules via the cell membrane, active transport has always been doing so quite separately. |
It’s used to keep nutrients, water, and gases, among other things, in balance both inside and outside the cell. |
Examples |
Active transport can be illustrated in the following ways;
Sodium pump, glucose selection in the intestines, and mineral ion uptake by plant roots. |
Passive transport happens when oxygen and carbon dioxide are exchanged in the kidneys and liver, as well as in the alveoli of the lungs. |
Active transport process
In way of comparison to the process of osmosis, active transport necessitates the use of energy to transfer substances from a low concentration to a high concentration. Active transport is most frequently achieved by a transport protein that changes shape when it binds to the cell’s fuel (ATP).
For instance, another form of active transport platform in the cell membrane will attach to the molecule it’s supposed to transport like sodium ions and hang on to it until a molecule of ATP arrives by and binds to the protein. The sodium ion is then spat out on the opposite side of the cell membrane, thanks to the energy stored in ATP. This sort of active transport utilizes ATP directly and is referred to as primary active transport.
Another sort of active transport utilizes electrochemical gradient instead of ATP, and this is found in secondary active transport.
The electrochemical gradient is a combination of voltage across the membrane and a concentration gradient that allows ions to move freely. Whenever there is a net difference in charges, an electrochemical gradient is created.
Active transport in plants
Plants, like humans and animals, need transportation systems to transport materials such as water, minerals, and essential nutrients to all parts of the plant in order to survive. Active transport is a type of transport used by plants to move particles against a concentration gradient by utilizing stored energy. It happens in the root cells of a plant and is used for absorbing water and minerals.
Biological importance of active transport
Active transport is required for a variety of biological processes.
- It is used in chemosynthesis – the release of chemical substances such as hormones in the body.
- Volatile organic compounds are secreted by plants through the process of active transport; these secretions are important for plants because pollinators and seed-dispersal organisms are attracted to the volatile organic compounds.
- When plants absorb nutrients (such as chlorine and nitrates) from the soil into the vacuole, they use active transport.
- Active transport is often used in metabolic activities in humans and animals, such as glucose absorption.
FAQs
What is the difference between passive and active transport?
Passive transport moves molecules and ions from a higher to a lower concentration without using any energy while active transport moves molecules and ions from a lower concentration to a higher concentration.
What is active transport in biology?
A cell must use energy to move substances against a concentration or electrochemical gradient. Active transport mechanisms do just that, expending energy (often in the form of ATP) to keep ions and molecules in living cells at the proper concentrations.
What are the three types of active transport?
The 3 types of active transport include primary active transport, secondary active transport, and bulk transport.