Question

List and compare different forms of passive transport and active transport.

Answer 1

Passive Transport:

“Passive transport is the fundamental movements of ions and other molecular substances within the cells along the concentration gradient, without any external energy.”

There are four types of passive transport:

1. Simple Diffusion
2. Facilitated Diffusion
3. Filtration
4. Osmosis

Simple diffusion

Diffusion is the movement of substances from a region of higher concentration to lower concentration. The difference in the concentration of the two areas is termed as concentration gradient and the process of diffusion continues until this gradient neutralizes. Diffusion occurs in liquid and gases because their particles move randomly from one place to another. It is an important process in living things required for different life processes. The substances move in and out of the cells by simple diffusion.

Facilitated Diffusion

Facilitated diffusion is the passive transportation of ions or molecules across the cell membrane through specific-transmembrane integral proteins. The molecules, which are large and insoluble require a carrier substance for their transportation through the plasma membrane. This process does not require any cellular or external energy.

Glucose transporter, ion channels and aquaporins are some of the examples of facilitated diffusion. The cell membrane is permeable only to a few molecules that are smaller in size and non-polar. Therefore, facilitated diffusion with the help of transmembrane proteins is important.

Filtration

Filtration is the process of separating solids from liquids and gases. The selective absorption of nutrients in the body is an example of filtration. This process does not require any energy and takes place along the concentration gradient. The kidneys are an example of a biological filter. The blood is filtered by the glomerulus and the necessary molecules are reabsorbed.

In the process of filtration, the cell membrane permits only those substances which are soluble and could easily pass through its pores.

Osmosis

In the process of osmosis, water and other molecules pass through a selectively permeable membrane in order to balance the concentration of other substances.

Osmosis is affected by the concentration gradient and temperature. The greater the concentration gradient, the faster is the rate of osmosis. Also, the rate of osmosis increases with the increase in temperature.

There is a theory of conflict about the process of osmosis. Few biologists suggest that osmosis is an active transport and not passive transport.

Active transport:

“Active Transport is defined as a process that involves the movement of molecules from a region of lower concentration to a region of higher concentration against a gradient or an obstacle with the use of external energy.”

During the process of active transport, a protein pump makes use of stored energy in the form of ATP, to move molecules

The below diagram shows the process of active transport, which uses an external energy ATP for the movement of the molecules.

The uptake of glucose in the intestine of the human body and also the uptake of minerals or ions into the root hair cells of the plants are some of the examples of active transport.

Types of Active transport

There are two types of active transport namely – Primary active transport and secondary active transport.

Primary active transport

In this process of transportation, the energy is utilized by the breakdown of the ATP – Adenosine triphosphate to transport molecules across the membrane against a concentration gradient. Therefore, all the groups of ATP powered pumps contain one or more binding sites for the ATP molecules, which are present on the cytosolic face of the membrane. Basically, the primary active transport uses external chemical energy such as the ATP.

Sodium-potassium pump, the most important pump in the animal cell is considered as an example of primary active transport. In this process of transportation, the sodium ions are moved to the outside of the cell and potassium ions are moved to the inside of the cell.

Secondary active transport

Secondary active transport is a kind of active transport that uses electrochemical energy. It takes place across a biological membrane where a transporter protein couples the movement of an electrochemical ion (typically Na+ or H+) down its electrochemical gradient to the upward movement of another molecule or an ion against a concentration or electrochemical gradient.

Active Transport in Plants

Like humans and animals, plants also require transport systems which are mainly involved in the transport of materials, such as water, minerals, and necessary nutrients to all parts of the plant for its survival.

Active Transport is a mode of transportation in plants, which uses stored energy to move the particles against the concentration gradient. In a plant cell, it takes place in the root cells by absorbing water and minerals. Active transport always leads to accumulation of molecules are ions towards one side of the membrane. This mode of transportation in plants is carried out by membrane proteins and transports the substance from the lower concentration to higher concentration.