Diffusion Means Of Transport, Direction, Factors and Importance

Plants need water, mineral nutrients, organic nutrients, and plant growth regulators for their growth and development. The transport of these substances occurs by different methods. 

Small-distance transport occurs in the cell, across the membrane, or from one cell to another in a tissue. It occurs by diffusion, facilitated diffusion, or by active transport.

Long-distance transport occurs via the vascular system, that is, the xylem and phloem, and is known as translocation.

Direction of Transport

• Xylem helps in unidirectional transport from roots to stem.
• Transport of organic and mineral nutrients occurs multi-directionally. Photosynthetic leaves synthesise organic compounds and are exported to all other plant parts, including storage organs.
• From the storage organs, they are later re-exported. The roots absorb the mineral nutrients, which are then transferred upward into the stem, leaves, and growth areas. When any plant part undergoes senescence, nutrients may be drawn from such regions and moved to the growing parts.
• In very minute amounts, hormones, plant growth regulators, and other chemical stimuli are transported.

Short distance transport

• It is a type of transport within or from one cell to another. Short-distance transport can occur by passive transport or active transport.

Simple diffusion and facilitated diffusion are two types of Passive transport.

Simple diffusion 

• Simple diffusion is a type of transport in which molecules move from a region of high concentration to a region of low concentration. For example, the diffusion of the fragrance of perfume and the diffusion of potassium permanganate in water.
• Diffusion occurs till the dynamic equilibrium is obtained. At equilibrium, molecules are equal in both directions. 
• Diffusion is a slow process and is used for short-distance transport. A movement across a plant cell takes 2.5 seconds for diffusion to occur.
• The rate of diffusion is Gas>Liquid>Solid.
• Diffusion of one substance is independent of other substances. For example, diffusion of carbon dioxide and oxygen can occur simultaneously.

Factors affecting the rate of diffusion

• Diffusion pressure gradient-The rate of diffusion is determined by the difference in the diffusion pressure. The difference in molecule concentration between the two regions directly correlates with the diffusion rate.
• Temperature- Diffusion increases with increase in temperature.
• Density- The square root of the gas’s density is inverse to the diffusion rate.

Importance of diffusion in plants

• Using the diffusion process, gasses are exchanged through stomata.
• Diffusion theory is what causes transpiration.
• Ions are taken up through diffusion.
• Translocation occurs via diffusion.
• The walls of the plant’s internal tissues are kept moist by this mechanism.
• It is in charge of dispersing the molecules and ions throughout the protoplast.
• The fragrance of flowers results from the release of aromatic molecules that serve as insect lures.

Facilitated diffusion

• Diffusion depends on a substance’s solubility in a membrane. Substances that are lipid soluble diffuse rapidly across the membrane.
• Hydrophilic substances find difficulty in crossing the membrane. So membrane proteins help with the transfer of such molecules. This is what is known as facilitated diffusion.
• Specific proteins help in transfer of substances across a membrane without the expenditure of energy. For facilitated diffusion, gradients should be created even if transport occurs via proteins. 
• Transport rate reaches saturation when all protein transporters are saturated.
• This type of diffusion is very specific and only allows selective molecules to be transported.
• Facilitated diffusion is sensitive towards the inhibitors.
• The protein forms channels in the membrane for molecules to pass through it. Some channels remain open, and some are closed.
• Facilitated diffusion also occurs via porin proteins in the outer membrane of mitochondria, chloroplast, and some bacteria.
• Aquaporins are proteins that form water channels. 8 different types of aquaporins form the water channels.

Types of transmembrane proteins

Proteins present in the cell membrane that allows the movement of certain molecules are known as transmembrane proteins. They are of two types- carrier proteins and channel proteins.

• Channel proteins help enter and exit molecules in the cell. Open channel proteins and gated channel proteins are two types of channel proteins. Open channel proteins function by creating a pore inside the cell membrane. Gated channel proteins are regulated channel proteins that open and close in response to entry or exit of substances.
• Carrier molecules transport the substances by changing their conformation and releasing them in and out of the cell.

Factors affecting facilitated diffusion

• Temperature: As the temperature rises, the molecules move more quickly because more energy is available.
• Concentration: Molecules travel from an area of higher concentration to an area of lower concentration.
• Diffusion Distance: Rate of diffusion is faster in shorter distances. For instance, gas diffuses through a thin wall much more quickly than through a large wall.

Significance of facilitated diffusion 

• The cell membranes are impermeable to some molecules. To pass across the membrane, the molecules should be tiny and non-polar. 
• Nucleic and polar amino acids are too big and polar to get through the cell membrane. Additionally, it can sometimes be challenging for water to travel bulk through the membrane.
• Certain integral membrane proteins or transmembrane proteins are necessary to transfer molecules across the membrane. They are carrier and channel proteins.

Active transport 

Active transport is characterised as a process in which molecules are moved using external energy from an area of lower concentration to a region of greater concentration, that is, against the concentration gradient. This type of transport is known as uphill transport. A protein pump uses ATP, a form of stored energy, to move molecules during active transport.

FAQs Diffusion Means Of Transport

What is diffusion?

Simple diffusion is a type of transport in which atoms or ions move from a region of high concentration to a region of low concentration. 

What is facilitated diffusion?

The passive transport of molecules down the concentration gradient is facilitated diffusion. It is a selective process, meaning only specific molecules and ions can pass through the membrane. 

What are transmembrane proteins?

Proteins in the cell membrane that allow movement of certain molecules are known as transmembrane proteins. They are of two types- carrier proteins and channel proteins.

What is active transport?

Active transport is characterised as a process in which molecules are moved using external energy from an area of lower concentration to a region of greater concentration, that is, against the concentration gradient.