Basic concept of transportation in plant - diffusion, Facilitated diffusion ,Active transport

Overview of transportation in plants 

In a flowering plant the substances or material like water, mineral nutrients, organic nutrients and plant growth regulators are transported. 

In plants, basically we can  consider that there are some types of transportation in terms of distance - transport of small distance, transport of long distance. The transportation of material over small distances is facilitated by diffusion and cytoplasmic streaming supported by the active transport. 

Transport of water -minerals  and food in long distances is done by the xylem and the phloem respectively. such transportation is called translocation. In plants, transport of water and minerals by the  xylem  is  unidirectional, that is  from roots to the stems. Organic and mineral nutrients are transported in every direction according to the needs of plants hence it is  multidirectional.

The organic compounds like glucose are synthesized  by the photosynthesis in the  leaves and transported to  other parts of the plant including storage organs. From the storage organs they are later re transported as per the requirement.

The mineral nutrients are absorbed by the roots from the soil  and transported towards the stem, leaves and the growing regions. If any parts of a plant are old or facing senescence, then  nutrients may be withdrawn from such  parts and transported to the growing parts. Hormones or plant growth regulators and other chemical stimuli are also transported  in very small amounts  from where they are synthesized .

Methods  used in transportations in plant 

There are various methods that are  used by the plants for the transportation of  various materials through the different routes. These methods include diffusion, Facilitated Diffusion, Active transport etc.

Transportation of materials by the diffusion in plants 

Diffusion is the process by which the transportation of material takes place  from higher concentration to lower concentration. The process of diffusion is passive because it does not require the energy for the transportation of materials. Plant uses the diffusion process for the transportation of material from one part of the cell to the other part of the cell, or from cell to cell and from the intercellular spaces of the leaf to the outside.

Diffusion is slow,  but it is quite fast in gases followed by the  liquid and gases. Diffusion is the only means for gaseous movement within the plant body.  The rate of diffusion is affected by the gradient of concentration, the permeability of the membrane,  temperature and pressure. The examples of diffusion in plant are as - The exchange of gases  and transpiration by stomata, absorption of ions in plants,etc.

Transportation of materials by the Facilitated diffusion in plants

Facilitated diffusion is the process by which any material is transported across the plasma membrane with the help of protein but without any use of energy. The transportation of material through the facilitated diffusion should have concentration gradient.

If any substance has a small size, this substance diffuses at faster rate.This signifies that the diffusion rate depends on the size of the substances.

The diffusion of any substance across a membrane also depends on its solubility in lipids. the major constituent of the membrane. Substances that are soluble in lipids, they diffuse through the membrane at a faster rate.

Substances that  are water loving or dissolve in water or have a hydrophilic moiety, those water can not pass through the cell membrane therefore their transportation needs some assistance or  their movement has to be facilitated. To facilitate their transportation, cell membranes have some proteins. These proteins have some  sites  through which such molecules may  cross the membrane. This protein does not help to set up a concentration gradient for crossing whereas  the concentration gradient remains present in substances that need to be  diffused  by the  help of proteins. This process is called facilitated diffusion. In facilitated diffusion special proteins help move substances across membranes without expenditure of ATP energy. 

Facilitated diffusion allows  the cell to choose the  substances that will move inside the cell.  If any substance makes a reaction with protein side chains then it inhibits the entry of that substance.  These  proteins also form  a channel in the cell  membrane for the entry  of substances. These protein channels sometimes open and sometimes can control the movement of substances.

The porins are proteins that form huge pores  in the form of a protein channel  in the outer membranes of the plastids, mitochondria and in  some bacteria. These channels allow the movement of substances that have size up to   small proteins. For example - water channels that are present in cell membranes made up of eight types of aquaporins. 

Symports, antiports and uniport mode of transportation  

Generally carrier proteins  transport the material by the facilitated diffusion But  if two types of molecules move together, these carrier or transport proteins transport the material by the  diffusion.

If both molecules cross the membrane in the same direction, it is called symport transportation. In  an antiport, they move in opposite directions but in an uniport, the movement of one material  is independent of other molecules. 

👌👌Remember - Energy is required in only Active transport whereas  diffusion and facilitated diffusion transport material without the expenditure of energy.

Transportation of materials by the Active transport in plants

Active transport  requires the energy to transport the  Molecule against  the concentration gradient. This type of  transport is carried out by carrier proteins present in cell membranes. 

All kinds of  Pumps  worked in plants , used proteins and energy to transport the substances across the cell membrane. These pumps can transport substances from a low concentration to a high concentration. Such  transport is related to uphill transport.