What is Active and Passive Transport?
Active transport is the movement of molecules across cell membranes in a direction against their concentration gradient, that is, moving from low concentration to high concentration. Active transport is usually associated with the accumulation of high concentrations of molecules needed by cells, such as ions, glucose, and amino acids.
If the process uses chemical energy, such as from adenosine triphosphate (ATP), it is called primary active transport. Secondary active transport involves the use of electrochemical gradients. Active transport uses cellular energy, such as passive transportation, which does not use cellular energy.
Active transport is a good example of the process of cells that need energy. Examples of active transport include absorption of glucose in the intestine in humans and the absorption of mineral ions into the hair cells of plant roots. Passive transport is the biochemical movement and substances of atoms or other molecules in cell membranes.
Unlike active transport, it does not require chemical energy input, which is driven by the growth of system entropy.
The amount of passive transport depends on the permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the lipid membrane and protein. The four main types of passive transportation are diffusion, facilitated diffusion, filtration, and osmosis.
The following terms are used to describe the movement of substances in, out, and between cells:
- The movement of substances can occur through selectively permeable membranes (such as plasma membranes).
- Selective permeable membranes only pass certain substances.
- Substances, whose movements are being described, may be water (solvents) or substances that are soluble in water (solutes).
- The movement of substances can occur from high concentrations to low concentrations (down the concentration slope) or the opposite direction (up or against the concentration slope).
- The concentration of solutions varies. The solution can be hypertonic (has a higher concentration of solute), hypotonic (has a lower concentration of solute) or isotonic (has the same concentration of solutes) compared to other regions.
The movement of substances can be active or passive. Active movement usually opposes the concentration slope and requires the release of energy.
- Examples of primary active transport, where energy from ATP hydrolysis is directly combined with the movement of a particular substance across an independent membrane
- Examples of primary active transport, where energy from ATP hydrolysis is directly combined with the movement of a particular substance across an independent membrane.
- Diffusion is an example of passive transport
Active Transport Process
Active transport is the movement of solutes against the concentration slope and requires the release of energy (usually ATP). Active transport is usually achieved through one of the following two mechanisms:
The transport proteins in the plasma membrane remove solutes such as small ions (Na +, K +, Cl-, H +), amino acids, and monosaccharides.
Vesicles or other bodies in the cytoplasm move macromolecules or large particles through the plasma membrane. Types of vesicle transport include:
- Exocytosis, describes the process of vesicles joining the plasma membrane and releasing its contents to the outside of the cell. This process is common when cells produce substances to be taken out of cells.
- Endocytosis describes the capture of substances outside the cell when the plasma membrane joins to swallow it. These substances enter the cytoplasm sequentially wrapped in vesicles. There are three types of endocytosis:
- Phagocytosis (“eating cells”) occurs when insoluble material enters the cell. Plasma membranes ingest solid material, forming phagocytic vesicles.
- Pinocytosis (“drinking cells”) occurs when cell membranes bend inward to form tunnels that allow solutes to enter cells. When this tunnel closes, the liquid circulates inside the pinocytic vesicles.
- Endocytosis that is receptor-mediated endocytosis occurs when certain molecules in the fluid around the cell are bound to certain receptors in the plasma membrane. As with pinocytosis, the plasma membrane bends inward and vesicles are formed. Certain hormones are able to select specific target cells with receptor-mediated endocytosis.
Passive Transport Process
Passive transport describes the movement of substances down the slope of concentration and does not require energy consumption.
Simple diffusion or diffusion is the net movement of substances from areas of high concentration to areas of low concentration. This movement occurs as a result of the random and continuous motion characteristics of all molecules (atoms or ions), which are free from the movements of other molecules.
Because at some time, some molecules can move against the concentration plane and some other molecules move down the concentration plane (remember that this movement is random). If there is a difference in concentration, then the molecule (which is always moving) will eventually be distributed evenly (reaching a balance point).
Osmosis is the diffusion of water molecules across selective permeable membranes. When water enters a body through osmosis, hydrostatic pressure (osmotic pressure) can accumulate in the body.
Dialysis is the diffusion of solutes through selective permeable membranes.
Simplified diffusion is the diffusion of solutes through channel proteins in the plasma membrane. Note that water can pass through the plasma membrane freely without the help of certain proteins.
Difference Between Active and Passive Transport
Active Transport: Active transport pumps molecules through cell membranes against the concentration gradient.
Passive transport: Passive transport allows molecules to pass through cell membranes through concentration gradients.
Use of Cell Energy
Active transport: Active transport uses cellular energy in the form of ATP.
Passive transport: Passive transport doesn’t need cellular energy.
Type of transport
Active transport: Endocytosis, exocytosis, secretion of substances into the bloodstream, and sodium/potassium pumps are types of active transport.
Passive transport: Diffusion, facilitated diffusion, and osmosis are types of passive transport.
Role of active and passive transport
Active transport: Active transport allows molecules to pass through cell membranes, disturbing the equilibrium determined by diffusion.
Passive transport: Dynamic water, nutrition, gas and waste balance is maintained by passive transport between the cytosol and the extracellular environment.
Active transport: Ions, large proteins, complex sugars and cells are transported by active transport.
Passive transport: Water-soluble molecules such as small monosaccharides, lipids, sex hormones, carbon dioxide, oxygen, and water are transported by passive transport.
The benefits of active and passive transport
Active transport: Active transport is required for the entry of large insoluble molecules into the cell.
Passive transport: Passive transport allows the maintenance of fine homeostasis between the cytosol and extracellular fluid.
Summary – Active and Passive Transport
Active and passive transport are two methods of transporting molecules across cell membranes. Active transport pumps molecules against concentration gradients using cellular energy. In primary active transport, ATP is used as energy. In secondary active transport, electrochemical gradients are used to move molecules across the membrane. Nutrients are concentrated into cells using active transport.
Passive diffusion allows non-polar small molecules to move across the membrane. It only happens through concentration gradients. Therefore, there is no energy utilized by the process. Osmosis and filtration are also passive diffusion methods. However, the main difference between active transport and passive transport is their mechanism of transporting molecules across a membrane.