Active and passive transport

Introduction

The word transportation is widely used in different facets of life. Transportation is a process of moving items from one area to another. However,  biological means of transport is essential to maintain various bodily process such as metabolism, excretion, hormonal secretions etc. It is equally important in both plants and animals but a slight difference exists in the way it takes place in animals and plants. In human beings, in particular, an individual organ cannot produce all the necessary molecules by itself, rather they are derived from other parts of within our body. For example, growth hormones essential for the development of bones are synthesized in the pituitary and the bones receive the hormones through the blood. In this case, blood is used as a medium of transportation, however, let`s be precise about the modes of transportation;  active and passive.

Importance of biological transportation

Imagine if there is no movement of materials through different parts of the body, tonnes of wastes would have accumulated in the body. Consequently, the effects toxins that lie in the surface of membranes and organs would deeply seeped into vital organs. Furthermore, the nutrients, hormones and enzymes necessary for bodily functions could have failed to reach the target areas. Let us understand some basic concepts of biological transportation in this section.

Transportation in Animals

Transportation takes many forms of our body, in fact in the bodies of every animal. Though there are many systems involved in transportation, the most predominant role is played by the circulatory system and the excretory system. Moreover, almost every process in our body relies upon transportation. Some of the ways different materials transported in our body are as follows:

  1. Water and food that we consume start travelling from the mouth into all parts of the GI system, however, this is a type of mechanical transportation fall under active mode.

  2. Blood moves in and out of the heart is a type of transportation. Additionally, it travels to the whole body with the help of the pumping action of the heart in addition to the arterial and venous pressure exerted by the blood vessels. It also helps in transporting various nutrients. The nutrients are absorbed from the villus of the small intestine.

  3. The hallmark of the movement of gases in the lungs is gaseous transportation. Blood assist in the gaseous exchange by allowing carbon dioxide out and the oxygen into the lungs,  the process is assisted by arterial and venous circulation within the lungs.

  4.  Our circulatory system is made up of 2 types of blood vessels- arteries and veins. The arteries carry oxygenated blood from the heart to other parts of the body while veins drain the wastes from different parts of the body into the heart. 

  5. Transportation of wastes is called excretion, a process of removal of wastes from the cells after the cellular metabolism.

  6. Our kidney actively participates in the absorption, secretion and excretion of urine. One of the primary processes that drive urine out is transportation. 

  7. The lower organisms such as amoeba, hydra, and paramecium excrete the nitrogenous waste with the help of diffusion.

  8. Many hormones, toxins, drugs, enzymes, cellular wastes are carried through the blood. 

Active and Passive Transport

 

“Active transport is the movement of substances through biological membranes from lower concentration areas to higher concentration areas. During the process, molecules move against the concentration gradient.”  Conversely, “passive transport is the movement of molecules through the membranes without using energy" . Therefore, it is understood that the molecules are spontaneously pushed from the regions of higher concentration to the lower ones.

Active transport

During the active transport, the molecules are pumped against gravity in an upward direction. It is not a spontaneous process as it needs some energy. The process is sponsored by the energy systems in our body. The energy required for active transport is supplied in the form of  ATP ( Adenosine triphosphate). The molecules such as proteins, lipids, sugars, use active transport mode. They move through the cell membranes with the help of membrane potential . Membrane potential helps positive ions attracted by the negative side of the membrane while the negative ions by the positive ones. The cell membrane is very selective while doing this as it allows only the necessary materials while leaving behind others. Active transport is classified into 2 types- primary active transport and the secondary active transport.

Types of active transport

In the primary active transport, the proteins present in trans-membrane at first identify the substance that needs to be transported, followed by this, the membrane potential is initiated to move the materials.  Ion pumping such as sodium/potassium pump (Na+/K+ ATPase), happens in this way. On the other hand, secondary active transport occurs through the pore-forming proteins. The substances are moved with the help of the secondary channels found in the cell membrane.  Furthermore, it requires the help of the electromagnetic gradient in the presence of mediators called cotransporters. The 2 types of cotransporters: symporters and antiporters play a major role during secondary transport. Symportes help when the solutes and ions move in the same direction through the cell membrane, while antiporters require the solutes and ions to move opposite to each other.

Passive Transport

In a passive transport system, the materials are carried from higher concentration areas to the lower concentration areas against the concentration gradient.  Passive transport is again classified into 4 subtypes; osmosis, diffusion, facilitated diffusion, and filtration. Osmosis takes place when the movement of molecules happens through a selectively permeable membrane conversely, the diffusion does not necessarily need the help of a medium such as a membrane. It is simply the movement of molecules from the more concentrated area to the less concentrated area in a free manner which is comparable to the ink that spreads through clean water. The facilitated diffusion requires the help of proteins to move the molecules. Lastly, the filtration is the movement of molecules between the 2 or more regions due to concentration gradients. It is favourable if the size of the molecules is relatively smaller in addition to the presence of some hydrostatic pressure.

Differences between Active and Passive Transport

Active Transport    

Passive Transport

Requires some energy in the form of ATP

Doesn’t  require  cellular energy

Molecules move from the area of lower concentration to the area of higher concentration

Molecules move from higher concentration region to lower concentration regions.

This is the most common method used in the transportation of major biomolecules like proteins, ions, and sugars.

It is seen in the transportation of tiny soluble molecules such as oxygen, water, carbon dioxide, lipids, some hormones, and glucose.

It may not assist in maintaining cellular homeostasis (equilibrium) because molecules move randomly within the cell.

It involves in the maintenance of the balance or equilibrium inside cell.

Active transport is not a spontaneous process

Passive Transport is a spontaneous process

It involves  selective absorption by the target cells  

It is partly non-selective

It occurs in a unidirectional fashion irrespective of a concentration gradient.

It occurs in 2 directions.

The intensity of the process depends upon the amount of cellular temperature.

The temperature levels don’t affect the process in any way.

 Active transport is assisted by  carrier proteins

Passive transport doesn't require carrier proteins.

The oxygen levels of the molecules can hinder the process.

This process is not affected by the level of oxygen.

Metabolic inhibitors can influence and stop the active transport.

Passive transportation is not influenced by metabolic inhibitors.

Various types of active Transport includes
Exocytosis, endocytosis,  sodium-potassium pump

Different types of Passive Transport includes  Osmosis, diffusion, and facilitated diffusion

  

Matrix or permeases of the membrane are not involved.

 

It takes place through matrix/channels/permeases.

Questions

  1. Explain the importance of biological transportation.

  2. define active and passive transportation.

  3. List 10 differences between active and passive transport.

  4. What are symporters and antiporters? Explain.

  5. What is the difference between osmosis and diffusion?

  6. Briefly explain the 2 types of active transport.

  7. Explain the importance of transportation in animals.

 

 



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