Diffusion In Plants : Definition, Meaning, Functions, Types, Topics, Example

What is Diffusion?

Diffusion in plants is the net movement of molecules from an area of higher concentration to an area of lower concentration through the cell membrane. The processes in plants, such as photosynthesis and respiration and uptake of nutrients, all occur to enable plants to grow and survive. Hence, they highly rely on diffusion.

Diffusion is one of the most important passive transport mechanisms for interchanging gases like oxygen and carbon dioxide, water and nutrient absorption, waste removal, and helping plants maintain homeostasis in other vital physiological activities.

Basic Physical Principles

The basic principle of the diffusion process includes:

Brownian Motion: The constant and random movement of molecules is called Brownian motion. This random motion leads to the slow, progressive dispersion of particles from higher to lower concentration areas.

Concentration Gradient: It is the difference in the concentration of particles in two regions. It is the driving force behind diffusion, with movement from areas of high to low concentrations to equate the concentration.

Dynamic Equilibrium: The rate of movement in one direction becomes equal to the rate of movement in the other direction and is called dynamic equilibrium—no net movement but continued molecular motion.

Types of Diffusion

Diffusion in biological systems can broadly be categorised into two types :

Simple Diffusion

Simple diffusion refers to the movement of molecules without the aid of transport proteins. The molecules move down their concentration gradient.

Examples: Oxygen and carbon dioxide diffusion.

Facilitated Diffusion

Facilitated diffusion refers to the movement of molecules with the help of transport proteins. The molecules still move down their concentration gradient but require protein channels or carriers

Examples: Glucose and ion transport

Osmosis — Diffusion of Water

Osmosis is a diffusion in which water molecules move through a semi-permeable membrane from an area with a low concentration of solutes to an area with a high concentration. It is central to the maintenance of cellular homeostasis.

Solutions are categorized by their relative concentrations of solutes.

• An isotonic solution has equal concentrations of solutes inside and outside the cell, so no net movement of water occurs.

• A hypertonic solution has a higher concentration of solutes outside the cell than inside, resulting in possible shrinkage of the cell as water leaves it.

• A hypotonic solution has a lower concentration of solutes outside the cell than inside it and water enters the cell with the result of possible swelling or bursting of cells.

Diffusion In Plant Cells and Tissues

Diffusion occurs in several plant tissues that have important functions.

Leaf diffusion — stomata, mesophyll adaptations

• Mesophyll cells enable the exchange of gases needed for photosynthesis and respiration.

• Mesophyll cells are adapted to increase surface area for diffusion.

Root diffusion — root hairs, soil to xylem pathway

• Roots absorb water and dissolved minerals from the soil.

• Root hairs increase surface area to allow for a more efficient intake.

Factors Affecting Diffusion

Various factors affect the diffusion process in plants.

Concentration Gradient

Concentration gradient is the difference in concentration of substance in two different regions. The greater the difference in concentration, the steeper the gradient and hence the faster the molecules will move.

Temperature

The temperature increases the kinetic energy of molecules. Hence, raising the temperature increases the speed of the molecules. While the molecular speed increases, so does the rate of diffusion.

Molecule Size

Smaller molecules diffuse faster than larger ones since of their smaller size as they have less resistance while diffusing across the medium. The larger the molecules, the less is the ability to pass through the medium, hence a slower diffusion rate.

Nature of Medium

The nature of the medium through which diffusion takes place affects the rate as well. In gases, the rate is higher because their density is lower and the movement of their molecules is more as compared to liquids and solids. In liquids, the rate is slow because the molecules are more closely packed and thus face more resistance.

Significance of Diffusion In Plants

Diffusion has several critical significance in plants.

Nutrient Uptake

Diffusion helps essential minerals and nutrients diffuse into plant cells. Proper nutrient diffusion is vital for healthy growth and development.

Waste Removal

Diffusion helps to maintain cellular homeostasis by removing metabolic wastes.

Environmental Interactions

Plants adjust to these different conditions to promote optimum diffusion. For example, Halophytes control their salt through specialised diffusion mechanisms.

Diffusion in Plants NEET MCQs (With Answers & Explanations)

Important topics for NEET exam are:

• Types of Diffusion

• Factors Affecting Diffusion

Practice Questions for NEET

Q1. Diffusion is the result of concentration gradient which refers to

1. Change of concentration with respect to time

2. Change of concentration with respect to space

3. Change of concentration with respect to temperature

4. Change of concentration with respect to gravity

Correct answer: 2) Change of concentration with respect to space

Explanation:

Movement of all substances from the area of their higher free energy to the area of their lower free energy along the concentration gradient. Neutral solutes move across the membranes by diffusion. The net direction of diffusion of particles depends on their concentration in a particular region or space.

Hence, the correct answer is option 2) Change of concentration with respect to space.

Q2. Why does an increase in temperature increase the rate of diffusion?

1. The increased thermal energy of the medium reduces the kinetic energy of particles

2. The decreased thermal energy of the medium increases the kinetic energy of particles

3. The increased thermal energy of the medium does not change the kinetic energy of particles

4. The increased thermal energy of the medium increases the kinetic energy of particles

Correct answer: 4) The increased thermal energy of the medium increases the kinetic energy of particles

Explanation:

Higher the thermal energy in a medium: this raises the kinetic energy of its particles resulting in faster diffusion. The more heat there is, the more violent motion the particles perform the more collisions they experience, and the better the diffusion becomes as particles spread out and mix with others. Such a process plays a very significant role in biological and chemical systems, for example, in the transport of molecules, gases, and ions that determine the rate of chemical reactions and dynamics of systems.

Hence, the correct answer is option 4) The increased thermal energy of the medium increases the kinetic energy of particles.

Q3. Which of the following has the maximum diffusion pressure?

1. Cell sap

2. Rainwater

3. Ice caps

4. All of these

Correct answer: 2) Rainwater

Explanation:

Pure water has a maximum diffusion pressure of 1236 atm, meaning it has the highest tendency to diffuse and move freely. When solutes are added, the diffusion pressure decreases, leading to a reduction in water potential. This works on the principle that during osmosis, the water moves from a region of higher diffusion pressure (pure water) to a region of lower diffusion pressure (solution).

Hence, the answer is option 2) Rainwater

Also Read:

• MCQs on Diffusion

• Transport in Plants

• Reverse Osmosis

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