Facilitated Diffusion – Definition, Principle, Examples

What is Facilitated Diffusion?

• Facilitated diffusion, a fundamental biological transport mechanism, involves the selective interaction of specific membrane structures with certain solutes or solute classes. This interaction significantly accelerates the rate at which these solutes traverse the membrane.
• Unlike simple diffusion, facilitated diffusion is characterized by the reliance on molecular binding between the transported substance and specific transmembrane integral proteins. These proteins serve as channels or carriers, ensuring the selective and efficient movement of molecules or ions across the biological membrane.
• This process is passive in nature, meaning it operates without the direct expenditure of chemical energy or ATP. Instead, molecules or ions move in accordance with their concentration gradient, transitioning from areas of higher concentration to those of lower concentration.
• Notably, facilitated diffusion is distinct from free diffusion in its saturable rate concerning the concentration difference and its unique temperature dependence due to the activated binding event.
• The lipid-based membranes in living systems compartmentalize and regulate the transport of water-soluble substances. Such membranes present a barrier to hydrophilic, polar, or charged molecules, which cannot easily traverse them. Only small, non-polar entities, like oxygen and carbon dioxide, can diffuse effortlessly across these membranes.
• Consequently, larger polar molecules and ions require specialized transport proteins. These proteins, which can be gated, control the flow of ions or small polar molecules, sometimes even against their osmotic gradient. Larger entities, on the other hand, are shuttled by transmembrane carrier proteins, such as permeases, which undergo conformational changes during the transport process.
• Facilitated diffusion plays a pivotal role in the transport of vital molecules like glucose, sodium ions, and chloride ions, which cannot permeate the lipid bilayer of the membrane unaided.
• Proteins, such as glucose transporters and organic cation transport proteins, mediate this facilitated transport, providing an efficient bypass mechanism. This process is crucial for cellular function, dictating the selective intake and expulsion of substances. The plasma membrane, the cell’s gatekeeper, oversees these selective movements, ensuring cellular homeostasis.
• In summary, facilitated diffusion is a passive transport mechanism that enables the selective movement of molecules across biological membranes via specific transmembrane proteins. This process, essential for cellular function and homeostasis, operates without direct energy expenditure, relying instead on concentration gradients.

Facilitated diffusion Definition

Facilitated diffusion is a passive transport process in which specific molecules move across a biological membrane with the aid of specialized transmembrane proteins, following their concentration gradient without the direct use of energy.

Principle of Facilitated diffusion – How does facilitated diffusion work?

The principle of facilitated diffusion revolves around the selective permeability of the plasma membrane’s lipid bilayer. Due to its hydrophobic nature, the membrane inherently restricts the passage of hydrophilic and certain highly polar molecules. While some small hydrophilic molecules can traverse the membrane based on their concentration gradient, larger non-polar entities necessitate assistance from transport mediators, namely membrane carriers and channels.

Two primary mechanisms underlie facilitated diffusion: one involving channel proteins and the other utilizing carrier proteins. Channel proteins are transmembrane entities that form pores or channels in the membrane, enabling specific molecules to pass through. These channels span the plasma membrane, bridging the external environment with the cytosol, and can also extend across the biological membranes of various cellular organelles. Notably, charged ions predominantly utilize these transmembrane channels, which are constituted by protein complexes, for their transport.

Conversely, carrier proteins, also known as transporters, are embedded within the biological membrane and exhibit a distinct affinity for specific molecules present in the extracellular matrix. Upon binding to these molecules, carrier proteins undergo conformational changes, which in turn facilitate the molecule’s movement into the cytosol. This carrier-mediated mechanism is especially crucial for the transport of larger entities, such as enzymes.

In essence, facilitated diffusion is a passive transport mechanism that relies on specialized proteins to assist in the movement of specific molecules across the plasma membrane, ensuring selective permeability and cellular homeostasis.

Does Facilitated Diffusion Require Energy?

No, facilitated diffusion does not require energy in the form of ATP or other energy molecules. Instead, it relies on the inherent kinetic energy of molecules and their natural tendency to move from areas of higher concentration to areas of lower concentration.

Explanation: Facilitated diffusion is a type of passive transport, meaning it does not consume cellular energy. It involves the use of specific transport proteins embedded in the cell membrane to aid in the movement of molecules that cannot easily pass through the lipid bilayer on their own. There are two main types of transport proteins involved in facilitated diffusion:

1. Channel Proteins: These form pores or channels in the membrane, allowing specific ions or molecules to pass through. For instance, ion channels permit the movement of ions like sodium, potassium, and calcium across the membrane.
2. Carrier Proteins: These bind to specific molecules, undergo a conformational change, and then release the molecule on the opposite side of the membrane. An example is the glucose transporter, which facilitates the transport of glucose into cells.

In both cases, the movement of molecules is driven by a concentration gradient, where molecules move from an area of high concentration to an area of low concentration. Since this process harnesses the natural tendency of molecules to spread out or diffuse, it does not require an external energy input.

In contrast, active transport mechanisms, which move molecules against their concentration gradient, do require energy, typically derived from ATP.

Is Facilitated Diffusion Active or Passive?

Facilitated diffusion is a form of passive transport.

Explanation:

1. Nature of Movement: In facilitated diffusion, molecules move from an area of higher concentration to an area of lower concentration. This movement aligns with the natural concentration gradient of the molecules, meaning they move in the direction they would naturally tend to go.
2. Energy Requirement: Facilitated diffusion does not require the cell to expend energy in the form of ATP or other energy molecules. Instead, it relies on the inherent kinetic energy of the molecules themselves.
3. Role of Transport Proteins: While facilitated diffusion utilizes specific transport proteins (either channel proteins or carrier proteins) to aid in the movement of molecules across the cell membrane, these proteins merely facilitate the process without consuming energy. They provide a pathway or mechanism for specific molecules or ions to cross the membrane more efficiently than they would by simple diffusion.
4. Contrast with Active Transport: Active transport, on the other hand, involves the movement of molecules against their concentration gradient, from an area of lower concentration to an area of higher concentration. This process requires energy, typically in the form of ATP, because it works against the natural tendency of molecules.

In summary, facilitated diffusion is passive because it allows molecules to move according to their natural concentration gradient without the need for cellular energy expenditure.

Transmembrane Proteins

Transmembrane protein are the cells’ proteins that are found within the membrane that aid in the flow of certain cells across the membrane. There are specific protein channels and carriers that speed up the transport process.

Channel proteins

• Channel proteins are specialized integral proteins embedded within biological membranes, facilitating the transport of specific molecules, predominantly ions, across these membranes. These proteins, often referred to as transmembrane proteins due to their spanning nature across membranes, create channels that serve as pathways for ion movement.
• A hallmark feature of many channel proteins is their selectivity. They can discriminate between ions, allowing certain ions to pass through while restricting others. This selectivity is attributed to the channel’s structural attributes, with diameters typically ranging from 4 to 5 Å, mirroring the widths of prevalent biological ions. As a result, some channels may preferentially permit the passage of cations over anions or may exhibit differential permeabilities to ions bearing identical charges.
• The architecture of channel proteins is such that they possess hydrophilic domains exposed to both the extracellular and intracellular environments. Central to their structure is a hydrophilic core, offering a hydrated conduit through the membrane’s lipid layers. An exemplar of channel proteins is the aquaporin family, which specializes in rapidly transporting water molecules across the plasma membrane.
• The ion selectivity of channels is primarily determined by interactions between the ions and the channel’s pore regions, either at its entrance or along its walls. This design ensures that ions can traverse the channel, bypassing the plasma membrane’s non-polar central layer.
• Furthermore, channel proteins are often equipped with gating mechanisms, enabling them to open or close in response to specific signals. These signals can be as varied as electrical impulses or the binding of specific molecules, ensuring regulated and controlled ion movement across the membrane.
• In summary, channel proteins play a pivotal role in cellular homeostasis, providing selective pathways for ion transport across biological membranes, governed by intricate structural and functional attributes.

Carrier proteins

• Carrier proteins are specialized membrane proteins that play a crucial role in facilitated diffusion within cellular membranes. Unlike channel proteins that form open pathways, carrier proteins operate by binding to specific molecules, undergoing conformational changes, and subsequently transporting these molecules across the membrane.
• The fundamental mechanism of carrier proteins involves recognizing and binding to specific regions of target molecules. This binding induces a change in the protein’s conformation, allowing the bound molecule to be shuttled from one side of the membrane to the other, typically following its concentration gradient. Given the substantial size of carrier proteins, it is improbable that they achieve transport by simply diffusing across the membrane. Instead, their function is primarily driven by conformational shifts. While the exact mechanism underlying these shifts remains a subject of study, it is postulated that alterations in hydrogen bonding patterns may lead to the observed changes in molecular shape.
• A defining characteristic of carrier proteins is their selectivity. Their binding sites are meticulously tailored to recognize specific substrates. For instance, carriers responsible for sugar transport can discern between different isomeric forms of sugars, such as d- and l-sugars. This specificity arises from the unique configuration or charge distribution of the binding site, which must complement a particular segment of the intended substrate. Such selectivity enhances the overall discriminative nature of the plasma membrane.
• The efficiency of carrier proteins is also influenced by the presence of other solutes. There exists a saturation point, beyond which all carrier proteins are occupied with their respective ligands, leading to maximal transport rates.
• In addition to their role in passive transport, carrier proteins are instrumental in active transport processes. Here, they facilitate the movement of molecules against their concentration gradient, necessitating the expenditure of energy, typically in the form of ATP.
• In essence, carrier proteins are pivotal in ensuring selective and regulated transport of molecules across cellular membranes, either passively following concentration gradients or actively against them, with energy investment.

Facilitated Diffusion Requires

Facilitated diffusion is a type of passive transport that allows substances to cross cell membranes with the assistance of special transport proteins. The requirements for facilitated diffusion include:

1. Transport Proteins: These are specific proteins embedded in the cell membrane that assist in the movement of substances. They can be channel proteins, which provide a pore for substances to pass through, or carrier proteins, which bind to a substance and change shape to move it across the membrane.
2. Concentration Gradient: Facilitated diffusion moves substances from an area of higher concentration to an area of lower concentration. It does not require energy because it moves substances down their concentration gradient.
3. Specificity: Transport proteins are specific for the substances they transport. This means that a transport protein that moves glucose will not move amino acids.
4. Saturation: There is a limit to how fast substances can be transported by facilitated diffusion. When all the transport proteins are occupied, the rate of transport reaches a maximum.
5. No Energy Requirement: Unlike active transport, facilitated diffusion does not require energy from ATP. It relies on the inherent kinetic energy of molecules.
6. Regulation: The activity of transport proteins can be regulated by the cell. For instance, the presence of certain molecules or changes in the cellular environment can increase or decrease the activity of transport proteins.
7. Temperature Dependence: The rate of facilitated diffusion can be influenced by temperature. As temperature increases, the rate of diffusion typically increases until a certain point, after which it may decrease due to denaturation of transport proteins.
8. Presence of Specific Molecules: Some transport proteins require the presence of specific molecules to function. For example, the glucose transporter GLUT4 is activated in the presence of insulin.

In summary, facilitated diffusion is a passive transport mechanism that relies on transport proteins to move specific substances across cell membranes. It is driven by concentration gradients and does not require energy input from the cell.

Different Factors affecting on facilitated diffusion

Facilitated diffusion is a passive transport mechanism that relies on specific carrier proteins to move substances across cell membranes. Several factors influence the efficiency and rate of this process:

1. Concentration Gradient: One of the primary drivers of facilitated diffusion is the concentration gradient. Molecules tend to move from areas of higher concentration to areas of lower concentration. The potential energy created by this gradient intensifies as the difference in concentration increases, leading to accelerated diffusion rates.
2. Temperature: Temperature plays a significant role in determining the rate of facilitated diffusion. The energy barrier associated with the conformational changes in carrier proteins is typically higher than the activation energy required for diffusion via channel proteins. As the temperature rises, the interaction rate between carrier proteins and their ligands also increases, leading to enhanced transport rates. Essentially, higher temperatures boost the kinetic energy of molecules, making them move more rapidly.
3. Saturation: Carrier proteins can become saturated when all available binding sites are occupied by molecules. Once saturation is reached, the diffusion rate plateaus, meaning that even if there’s an increase in the concentration gradient, the rate of diffusion remains constant. This is because the number of carrier proteins is finite, and once they are all engaged, no additional molecules can be transported until some of the binding sites become available again.
4. Selectivity: Facilitated diffusion is a selective process. Carrier proteins have specific binding sites that can discriminate among available solutes. While this selectivity ensures that only specific molecules are transported, it can also slow down the transport rate. Generally, there’s an inverse relationship between transport rate and selectivity: the more selective the process, the slower the rate of diffusion.
5. Brownian Motion: This random movement of particles in a fluid medium, driven by their kinetic energy, is a foundational force behind diffusion. Factors like temperature, concentration, diffusion distance, and molecular size can influence the rate of diffusion due to Brownian motion. For instance, smaller molecules, being lighter, diffuse faster than larger ones. Similarly, gases diffuse more rapidly through thin walls compared to thick ones due to the shorter diffusion distance.

In summary, facilitated diffusion is a complex process influenced by various environmental and molecular factors. Understanding these factors is crucial for comprehending the intricacies of cellular transport and the conditions under which it operates most efficiently.

Aids in facilitated diffusion and active transport

Facilitated diffusion and active transport are two mechanisms that cells use to transport substances across their membranes. Both mechanisms involve specific proteins to aid in the movement of substances, but they operate under different principles and energy requirements. Here’s a breakdown of the aids involved in each process:

Facilitated Diffusion:

1. Transport Proteins: These proteins facilitate the movement of specific molecules across the cell membrane without the use of energy. They include:
   • Channel Proteins: These form pores or channels in the membrane, allowing specific ions or molecules to pass through. Examples include ion channels and aquaporins (for water transport).
   • Carrier Proteins: These bind to specific molecules, undergo a conformational change, and release the molecule on the other side of the membrane.
2. Concentration Gradient: This process relies on the natural tendency of molecules to move from an area of higher concentration to an area of lower concentration.
3. Specificity: Each transport protein is specific to a particular molecule or ion, ensuring selective transport.

Active Transport:

1. Transport Proteins: These proteins actively pump substances against their concentration gradient, requiring energy. They include:
   • Primary Active Transporters: These directly use energy, usually from the hydrolysis of ATP, to transport molecules. An example is the sodium-potassium pump (Na+/K+ pump), which maintains the electrochemical gradient in cells.
   • Secondary Active Transporters (Cotransporters): These use the energy stored in the concentration gradient of one molecule to transport another molecule. This can be further divided into:
     • Symporters: Transport two or more ions or molecules in the same direction.
     • Antiporters: Transport two or more ions or molecules in opposite directions.
2. Energy Source: Active transport requires energy, which is typically derived from ATP. In some cases, the energy from the electrochemical gradient can also drive transport.
3. Specificity: Like facilitated diffusion, active transport proteins are specific to the substances they transport.
4. Regulation: The activity of active transport proteins can be regulated by the cell in response to various signals or needs. For instance, the activity of the sodium-potassium pump can be influenced by the intracellular levels of sodium and potassium.

In summary, while both facilitated diffusion and active transport utilize transport proteins to move substances across the cell membrane, facilitated diffusion does so passively (without energy), relying on concentration gradients, whereas active transport requires energy to move substances against their concentration gradient.

Transport Mechanisms

The plasma membrane, characterized by its lipid bilayer structure, serves as a selective barrier that regulates the entry and exit of molecules. This selectivity arises from the hydrophobic region of the membrane, which impedes the passage of polar (hydrophilic) molecules. However, the cell has evolved various mechanisms to ensure the efficient transport of essential molecules.

1. Simple Diffusion:
   • Small nonpolar (hydrophobic) molecules can traverse the membrane by simple diffusion, moving spontaneously from an area of higher concentration to one of lower concentration. This process is driven by the molecule’s inherent kinetic energy and concentration gradient.
2. Facilitated Diffusion:
   • This mechanism involves specific membrane proteins that aid in the transport of molecules that cannot easily diffuse across the membrane.
   • Channel Proteins: These are protein complexes that form pores in the lipid bilayer, allowing specific molecules or ions to pass through. For instance, charged ions utilize transmembrane channels, as their transport is hindered by the hydrophobic nature of the lipid bilayer. Another example is aquaporins, which, despite being pore-forming proteins, specifically facilitate the transport of water molecules.
   • Carrier Proteins: These are transporters embedded within the membrane that bind to specific molecules on one side (e.g., the extracellular space) and undergo a conformational change to transport the molecule to the opposite side (e.g., the cytosol). Larger molecules, unable to pass through channels, often rely on carrier proteins for transport. These proteins can function in both passive and active transport mechanisms.
3. Active Transport:
   • While facilitated diffusion is a passive process, not requiring energy, active transport involves the use of energy to move molecules against their concentration gradient. Carrier proteins play a pivotal role in this process, undergoing conformational changes powered by energy, typically derived from ATP, to transport molecules.

In summary, the cell employs a combination of passive and active transport mechanisms, utilizing specialized proteins, to maintain its internal environment and ensure the efficient exchange of molecules with its surroundings.

Example of Facilitated Diffusion

Facilitated diffusion is a passive transport mechanism that relies on specific proteins to aid in the movement of substances across cell membranes. Several examples illustrate the significance and specificity of this process:

1. Glucose and Amino Acid Transport:
   • Glucose and amino acids are vital nutrients required by cells for energy and protein synthesis. However, due to their size and polarity, they cannot easily diffuse across the lipid bilayer of cell membranes.
   • To overcome this barrier, cells employ specialized carrier proteins. For glucose, these proteins are known as glucose transporters, while amino acids utilize amino acid permeases.
   • Once absorbed in the small intestine through active transport, glucose and amino acids enter the bloodstream. Their subsequent uptake by cells is facilitated by these carrier proteins, ensuring efficient nutrient delivery to where it’s needed.
2. Gas Transport:
   • Gases like oxygen, carbon dioxide, and carbon monoxide play crucial roles in cellular respiration and metabolic processes.
   • Hemoglobin, a protein found in red blood cells, binds to oxygen and facilitates its transport throughout the body. In muscles, myoglobin serves a similar function, storing and releasing oxygen as needed.
   • The movement of these gases is driven by pressure differences across membranes. For instance, oxygen diffuses from areas of high concentration in the lungs to areas of lower concentration in tissues, while carbon dioxide follows the opposite gradient.
3. Ion Transport:
   • Ions, being charged particles, face challenges when trying to cross the hydrophobic core of cell membranes.
   • To address this, cells have developed ion channels, which are transmembrane proteins specifically designed to allow the passage of certain ions.
   • These channels are highly selective. For example, potassium channels allow only potassium ions to pass through, while sodium and calcium channels are specific for their respective ions.
   • The specificity ensures that the right ions are transported to maintain cellular homeostasis and electrical neutrality.

In essence, facilitated diffusion is a finely-tuned process that ensures the efficient and selective transport of vital molecules and ions across cell membranes, underpinning many of the essential functions of living organisms.

Applications/Importance of Facilitated diffusion

Facilitated diffusion is a fundamental biological process that holds paramount importance in the functioning of cells and the maintenance of life. Its applications and significance can be elucidated as follows:

1. Maintenance of Cellular Equilibrium:
   • One of the primary roles of facilitated diffusion is to balance the concentrations of various substances inside and outside the cell. By allowing specific molecules to move down their concentration gradients, facilitated diffusion ensures that cells maintain an internal environment that is conducive to their survival and functioning.
2. Selective Permeability of Biological Membranes:
   • Biological membranes, such as the plasma membrane, are selectively permeable barriers. This selectivity is largely attributed to the presence of specific transport proteins that mediate facilitated diffusion.
   • These proteins ensure that only certain molecules can pass through the membrane, thereby regulating the entry and exit of substances and protecting the cell from potentially harmful agents.
3. Support of Vital Cellular Functions:
   • Facilitated diffusion is instrumental in the transport of essential molecules like oxygen, nutrients, and ions. For instance, glucose transporters enable cells to uptake glucose, a primary energy source, from the bloodstream.
   • Similarly, ion channels allow the movement of ions like sodium, potassium, and calcium, which are crucial for processes such as nerve impulse transmission and muscle contraction.
   • The transport of oxygen, facilitated by proteins like hemoglobin, ensures that cells receive the necessary oxygen for cellular respiration, a process vital for energy production.

In summary, facilitated diffusion is not just a passive transport mechanism but a critical process that underpins various cellular functions. It ensures that cells have access to the nutrients they need, maintains the internal balance of substances, and upholds the selective nature of biological membranes, all of which are essential for the optimal functioning and survival of cells.

Difference Between Facilitated diffusion and simple diffusion – Simple Diffusion vs Facilitated diffusion

Facilitated diffusion and simple diffusion are both passive transport mechanisms that allow substances to move across cell membranes without the direct expenditure of cellular energy. However, they differ in several key aspects:

1. Mechanism of Transport:
   • Facilitated Diffusion: This process requires the assistance of specialized transport proteins embedded in the cell membrane. These proteins facilitate the movement of specific molecules across the membrane.
   • Simple Diffusion: In this process, molecules move directly through the lipid bilayer of the cell membrane without the need for any transport proteins.
2. Rate of Diffusion:
   • Facilitated Diffusion: The rate of diffusion is generally faster and can be influenced by various factors, including temperature and the types of membrane proteins involved. The presence of membrane protein inhibitors can also affect the rate.
   • Simple Diffusion: The rate is typically slower and more consistent, as it is not influenced by the binding capacity of membrane proteins.
3. Molecules Involved:
   • Facilitated Diffusion: Polar molecules such as glucose and amino acids, larger ions like sodium and chloride, and certain large nonpolar molecules like retinol utilize facilitated diffusion. They require specific transport proteins to move across the plasma membrane.
   • Simple Diffusion: Small nonpolar molecules, including oxygen and carbon dioxide, can easily diffuse across the plasma membrane without the need for any proteins.
4. Requirement of Transport Proteins:
   • Facilitated Diffusion: Transport proteins are essential for this process. These proteins can be either carrier proteins, which undergo conformational changes to transport molecules, or channel proteins, which form pores for molecules to pass through.
   • Simple Diffusion: No transport proteins are required. Molecules move freely based on their concentration gradients.
5. Energy Requirement:
   • Both facilitated and simple diffusion are passive processes, meaning they do not directly require chemical energy such as ATP or GTP.

In summary, while both facilitated and simple diffusion are passive transport mechanisms that move substances from areas of higher concentration to areas of lower concentration, they differ in their reliance on transport proteins, the rate of diffusion, and the types of molecules they transport.

Criteria	Facilitated Diffusion	Simple Diffusion
Mechanism of Transport	Requires transport proteins for assistance.	Molecules move directly through the lipid bilayer.
Rate of Diffusion	Generally faster; influenced by temperature, types of membrane proteins, and presence of membrane protein inhibitors.	Typically slower; consistent rate not influenced by membrane proteins.
Molecules Involved	Polar molecules, larger ions, and certain large nonpolar molecules.	Small nonpolar molecules.
Requirement of Transport Proteins	Essential; can be carrier or channel proteins.	Not required.
Energy Requirement	Passive process; does not directly require ATP or GTP.	Passive process; does not directly require ATP or GTP.

Difference Between Facilitated diffusion and active transport – Facilitated diffusion vs. active transport

Criteria	Facilitated Diffusion	Active Transport
Energy Requirement	Does not require or expend ATP. The process is driven by the kinetic or natural entropy of molecules.	Requires and expends chemical energy, typically in the form of ATP.
Direction of Transport	Moves substances from an area of higher concentration to an area of lower concentration (down the concentration gradient).	Moves substances from an area of lower concentration to an area of higher concentration (against the concentration gradient).
Role of Membrane Proteins	Uses permeases as transport vehicles.	Uses membrane protein pumps, such as sodium-potassium pumps.
Types of Molecules Transported	Capable of transporting ions, sugars, and salts.	Capable of transporting ions, sugars, and salts.
Concentration Gradient	Requires a concentration gradient for the process to occur.	Requires a concentration gradient for the process to occur.

Quiz

What type of transport is facilitated diffusion?
a) Active transport
b) Osmosis
c) Passive transport
d) Endocytosis

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Which of the following molecules typically require facilitated diffusion to cross the cell membrane?
a) Oxygen
b) Carbon dioxide
c) Glucose
d) Nitrogen

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Which type of protein is primarily involved in facilitated diffusion?
a) Enzymes
b) Hormones
c) Transport proteins
d) Receptor proteins

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What drives the movement of molecules in facilitated diffusion?
a) ATP energy
b) Concentration gradient
c) Light energy
d) Mechanical energy

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Which of the following is NOT a characteristic of facilitated diffusion?
a) Requires energy
b) Utilizes transport proteins
c) Moves molecules from high to low concentration
d) Is a type of passive transport

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Aquaporins facilitate the diffusion of which molecule?
a) Sodium ions
b) Glucose
c) Water
d) Amino acids

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Carrier proteins change their __ to transport molecules across the cell membrane.
a) Size
b) Charge
c) Conformation (shape)
d) Composition

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In facilitated diffusion, molecules move __ their concentration gradient.
a) Against
b) With
c) Perpendicular to
d) Independent of

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Which of the following can affect the rate of facilitated diffusion?
a) Temperature
b) Light intensity
c) Sound waves
d) Magnetic fields

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When all transport proteins are occupied and cannot bind more molecules, the process is said to be:
a) Inactive
b) Saturated
c) Deactivated
d) Neutralized

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FAQ

References

1. https://www.britannica.com/science/facilitated-diffusion
2. https://www.biologyonline.com/dictionary/facilitated-diffusion
3. https://en.wikipedia.org/wiki/Facilitated_diffusion
4. https://byjus.com/biology/facilitated-diffusion/
5. https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/14-membrane-transport/facilitated-diffusion.html
6. https://biologydictionary.net/facilitated-diffusion/
7. https://www.thoughtco.com/diffusion-and-passive-transport-373399