Diffusion
“Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration down the concentration gradient.”
What is Diffusion?
Diffusion is the process of movement of molecules under a concentration gradient. It is an important process occurring in all living beings. Diffusion helps in the movement of substances in and out of the cells. The molecules move from a region of higher concentration to a region of lower concentration until the concentration becomes equal throughout.
Liquid and gases undergo diffusion as the molecules are able to move randomly.
Example:
Take water in a beaker. Add a few copper sulfate crystals in one place and leave it as it is for some time without disturbing it. After some time we can see that the beaker contains a uniformly coloured solution. Here, both water and copper sulfate diffuse independently. With this experiment, we can infer that solutes move from a higher concentration to a lower concentration in a solution.
Types of Diffusion
Diffusion is widely used in various fields such as biology, physics, chemistry, etc. Diffusion can be classified into two main types: Simple diffusion and facilitated diffusion.
Simple diffusion
A process in which the substance moves through a semipermeable membrane or in a solution without any help from transport proteins. For example, bacteria deliver small nutrients, water and oxygen into the cytoplasm through simple diffusion.
Facilitated diffusion is a passive movement of molecules across the cell membrane from the region of higher concentration to the region of lower concentration by means of a carrier molecule.
Dialysis: It is the diffusion of solutes across a selectively permeable membrane. A selectively permeable membrane is one that allows only specific ions and molecules to pass through, while it obstructs the movement of others.
Factors affecting Diffusion
There are a few factors that affect the process of diffusion, which individually and collectively alters the rate and extent of diffusion. These factors include:
- Temperature.
- Area of Interaction.
- Size of the Particle.
- The steepness of the concentration gradient.
Examples of Diffusion
- A tea bag immersed in a cup of hot water will diffuse into the water and change its colour.
- A spray of perfume or room freshener will get diffused into the air by which we can sense the odour.
- Sugar gets dissolved evenly and sweetens the water without having to stir it.
- As we light the incense stick, its smoke gets diffused into the air and spreads throughout the room.
- By adding boiling water to the dried noodles, the water diffuses causing rehydration and making dried noodles plumper and saturated.
Causes of Diffusion
Diffusion is a natural and physical process, which happens on its own, without stirring or shaking the solutions. Liquid and gases undergo diffusion as the molecules are able to move randomly. The molecules collide with each other and change their direction.
Significance of Diffusion
Diffusion is an important process, which is involved in the different life processes. As mentioned above, it is the net movement of particles, ions, molecules, solution, etc. In all living species, diffusion plays an important role in the movement of the molecules during the metabolic process in the cells.
Diffusion is important for the following reasons:
- During the process of respiration, this process helps in diffusing the carbon dioxide gas out through the cell membrane into the blood.
- Diffusion also occurs in plant cells. In all green plants, water present in the soil diffuses into plants through their root hair cells.
- The movement of ions across the neurons that generates electrical charge is due to diffusion.
Factors that influence Diffusion:
- Difference in concentration affects the rate of diffusion. The greater the concentration gradient, the quicker diffusion takes place. …
- The temperature affects the rate of diffusion. …
- The surface area of the membrane affects the rate of diffusion. …
Why is water called the ‘universal solvent’?
Solution
- Water is called a ‘universal solvent’ because water can dissolve much more substances than any other liquid found in nature but water cannot dissolve every substance.
- For example- water cannot dissolve fats, waxes, and hydroxides due to the low solubility of oppositely charged particles.
Reasons for the solvency of water are:
- Water molecules consist of a polar arrangement of hydrogen and oxygen atom.
- Hydrogen present on one side has a positive charge while the oxygen atom carries a negative charge.
- These charges help the water molecule to bind to different types of molecules.
Osmosis
It is the movement of water molecules (solvent) from a region of higher water potential to a region of lower water potential. This movement is by a partially permeable membrane, down the water potential gradient. It is a living feature.
| Concentrated -> Hypertonic
Dilute -> Hypotonic |
Significance of Water Potential Gradient &
the Effect of Osmosis on Animal and Plant Tissues
osmosis in plant
- When a plant cell is placed in a solution of high water potential, water moves inside the cell due to the process of osmosis. There is a cell wall is present to sustain the water pressure, so the cell does not burst. It becomes turgid.
- If a plant cell is placed in a solution of lower water potential, water moves out of the cell. Thus, the cytoplasm of the cell shrinks, and the cell becomes flaccid. If the water loss continues, the cell will get plasmolyzed.
Osmosis in animal
- When an animal cell is placed in a solution of higher water potential, the cell will expand. If excess water enters the cell, the cell will burst as there is no cell wall present in animal cells to maintain water pressure.
- When an animal cell is placed in a concentrated solution, water will move out of the cell. The cell becomes wrinkled and crenated.
Active Transport
It is the movement of ions inside or outside of a cell through the cell membrane, from an area of lower concentration to an area of higher concentration against the gradient, using the energy released during respiration. Carrier proteins present on the cell membrane allow these charged particles to pass through.
Importance of Active Transport
The energy-consuming process has several important uses, as in ion uptake by root hairs and glucose uptake by cells in the villi. The root hair cells contain carrier proteins in their plasma membranes which move the mineral ions across them into the cell through the process of active transport. The mineral ions are necessary for the growth of plants. Nitrate ions are required for producing amino acids, which are used to form proteins. Magnesium ions are needed for chlorophyll production in plants. Active transport is also used in the process of glucose uptake by epithelial cells in the villi of the small intestine. Epithelial cells have numerous mitochondria in which cellular respiration takes place. The chemical energy produced by this is converted into kinetic energy which is used for the movement of glucose molecules. This ensures that glucose gets transported into the bloodstream.
