Content Writer-SME | Updated On - Nov 5, 2024
Passive transport across the cell membrane occurs primarily through osmosis and diffusion. The major difference between osmosis and diffusion arise in the terms of the nature of substance that are transported. These two processes play major roles in nutrition uptake, removal of waste, cell signaling, and other biological processes.
Osmosis is the movement of water or other solvent particles, whereas in diffusion, the movement of any substance can take place. This article covers complete definitions and differences between osmosis and diffusion for a clear understanding of the mechanisms of how substances are transported across cell membranes.
What is Osmosis?
[Click Here for Sample Questions]
Osmosis is the spontaneous movement of solvent molecules through a semipermeable membrane from a low-solute concentration (dilute solution) region to a high-solute concentration (concentrated solution) region. The primary distinction between osmosis and diffusion can be easily done by two ways: type of medium used and particles involved.
- This process occurs to equalize the concentrations on both sides of the membrane.
- It is a passive process that does not require energy expenditure.
- For example, plant roots absorb water from the soil through osmosis which is essential for their growth and survival.
- Another example is the swelling of erythrocytes when exposed to water.
What is Diffusion?
[Click Here for Sample Questions]
Diffusion is the movement of particles from a higher concentration region to a lower concentration region until equilibrium is achieved. It is a process that occurs in all life forms and is further divided into two groups: simple diffusion and facilitated diffusion.
- In simple diffusion, the substances move to and fro the semipermeable membrane without the need for energy and transport proteins.
- As the name suggests, facilitated diffusion requires a carrier molecule to facilitate the movement of molecules.
- An example of facilitated diffusion is dialysis.
- Diffusion is vital for transporting substances like oxygen, carbon dioxide, and nutrients in and out of cells.
Difference between Osmosis and Diffusion
[Click Here for Sample Questions]
Osmosis and diffusion are passive transportation systems, which means they do not require any additional energy to operate (however, facilitated diffusion requires ATP). However, they differ in various parameters like type of molecule, membrane, functions, liquid medium, etc. The table below shows the difference between osmosis and diffusion.
| Basis of Comparison | Osmosis | Diffusion |
|---|---|---|
| Definition | Movement of solvent molecules through a semipermeable membrane from a low-solute concentration region to a high-solute concentration region. | Movement of particles from higher to lower concentration. |
| Molecule Type | Involves only liquid molecules. | Involves all types of molecules (solids, gases, liquids). |
| Membrane | Requires a semi-permeable membrane. | Does not require a semi-permeable membrane. |
| Functions | Maintains cell turgor, helps in nutrient absorption in plants, etc. | Helps in gas exchange, nutrient absorption, etc. |
| Effect of solute | Depends on the potential of the solute. | Does not depend on the potential of solute. |
| Diffusivity | Only the solvent molecules diffuse. | Solute and solvent molecules both diffuse. |
| Solvent | Water is the main solvent that moves from one region to another. | Water is not necessary for movement. |
| Types | Simple and facilitated. | Simple, facilitated, active. |
In conclusion, the controlled movement of solute and solvent particles across cell membranes is achieved by osmosis and diffusion which in turn keeps the cells functioning properly. The requirement of semi-permeable membrane is one of the main distinctions between osmosis and diffusion.
Things to Remember
- Osmosis and diffusion involves the transport of molecules from higher to lower concentrations.
- Diffusion functions in solid, liquid, and gaseous mediums, unlike osmosis.
- Diffusion is a physical process that describes the net migration of molecules from a high-concentration region to a lower-concentration region.
- These two systems are passive transportation systems in the sense that they do not require any additional energy to operate.
- The movement of molecules through a membrane against the concentration gradient is called active transport.
Sample Questions
Ques. Give a brief explanation of the differences between osmosis and diffusion. (2 marks)
Ans. One distinction between osmosis and diffusion can be seen in the type of medium used. Diffusion can occur in any medium, including solids, liquids, and gases. Osmosis, on the other hand, occurs only in a liquid medium.
Ques. What exactly is active transportation? (2 marks)
Ans. The term "active transport" refers to a mechanism in which molecules and ions move against a concentration gradient while expending energy.
Ques. State two conditions required for osmosis. (2 marks)
Ans. (i) The difference in the concentration of water, one should have a higher concentration than the other.
(ii) Semi-permeable membrane is also required through which water will flow.
Ques. What is plasmolysis? (2 marks)
Ans. When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.
Ques. How do fungi and bacteria can withstand much greater changes in the surrounding medium than animal cells? (2 marks)
Ans. The cell wall present in fungi and bacteria permits these cells to withstand a very dilute external medium without bursting.
The cells take up water by osmosis, swells, and builds pressure against the cell wall. The wall exerts equal pressure against the swollen cell. It is because of the cell wall, such cells can withstand much greater changes in the surrounding medium than animal cells.
Ques. When we put raisins in water, why do they swell? (2 marks)
Ans. Raisins are dry with less water inside, when they are kept in water, osmosis takes place, water flows through the cell wall, cell membrane of the raisins and therefore it swells.
Ques. What is osmosis? (2 marks)
Ans. Osmosis is the process of movement of water molecules from a region of higher water concentration through a semi-permeable membrane to a region of lower water concentration.
Ques. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans? (2 marks)
Ans. In multicellular organisms like humans, all the body cells are not in direct contact with the surrounding environment. Therefore, every cell of the body will not get oxygen as per need by the process of diffusion from the environment. Therefore diffusion is insufficient to meet the oxygen requirements of multicellular organisms.
Ques. How are water and minerals transport in plants? (CBSE 2015) (4 marks)
Ans. The roots of a plant have hair called root hair. The root hair is directly in contact with the film of water in between the soil particles. Water and dissolved minerals get into the root hair by the process of diffusion. The water and minerals absorbed by the root hair from the soil pass from cell to cell by osmosis through the epidermis, root cortex, endodermis and reach the root xylem.
Water Transportation
The xylem vessels of the root of the plant are connected to the xylem vessels of its stem.
Therefore the water containing dissolved minerals enters the root xylem vessels into stem xylem vessels. The xylem vessels of the stem branch into the leaves of the plants. So, the water and minerals carried by the xylem vessels in the stem reach the leaves through the branched xylem vessels which enter from the petiole (stalk of the leaf) into each and every part of the leaf. Thus the water and minerals from the soil reach through the root and stem to the leaves of the plants. Evaporation of water molecules from the cells of a leaf creates a suction that pulls water from the xylem cells of roots. The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration.
Ques. How do plants exchange gases? (2 marks)
Ans. Exchange of gases takes place through stomata by simple diffusion. Large inter-cellular spaces ensure that all cells are in contact with air. The direction of diffusion depends upon the environmental conditions and the requirements of the plant. For e.g., CO2 elimination majorly takes place at night while oxygen release is the major event of the daytime.
Ques. What are the components of the transport system in highly organised plants? (3 marks)
Ans. In highly organised plants there are two conducting tissues xylem and phloem.
The xylem consists of vessels, tracheids and other xylem tissues. The interconnected vessels and tracheids form a continuous system of water-conducting channels reaching all parts of the plant. Xylem carries water and minerals.
Phloem conducts soluble products of photosynthesis from leaves to different parts of the plant body.
Ques. Where do plants get each of the raw materials required for photosynthesis? (3 marks)
Ans. (i) Carbon dioxide: Plants get carbon dioxide from the environment/atmosphere through stomata.
(ii) Water: Plants absorb water from the soil through roots and transport it to leaves by the process of osmosis.
(iii) Sunlight: Plants get sunlight from the sun.
(iv) Chlorophyll: It is present in chloroplast found in green leaves and green parts of plants.
Comments