What is Diffusion in Biology?

Diffusion is the net or total movement of molecules from an area of higher concentration of molecules to a region of lower concentration of molecules. In diffusion, Molecules usually move down a concentration gradient, as a result of their random movement.


What do you mean by Dynamic Equilibrium in diffusion?

In liquids and gases, molecules possess kinetic energy and constantly move about.

As this movement is random, an equilibrium is reached when the molecules are evenly spread out, where there is no more net change – dynamic equilibrium reached.


What is Passive Transport in diffusion?

The steeper the gradient for a substance, the faster the rate of diffusion. No energy input is essential for diffusion because the particles already are in motion. Hence, it is known as passive transport.

What do you know about Facilitated diffusion in biology?

When we talk about, the principle of the movement down a concentration
gradient is the same, but there is one restriction.  Cell membrane which is a semi permeable membrane is present around the cell, and it does not allow the free movement of the molecules.  This membrane is made up of lipid and protein which permits some molecules to cross with easiness, but others with difficulty or not at all.Proteins in the cell membrane  act like as passages or bridge to help the movement of the molecules. There is an intermediate transport process where semi permeable membrane help very small molecules to cross.Sometimes, proteins are used as helper or supporter to move molecules more quickly. It is a process called facilitated diffusion. This is based on the size of the molecules.


Example of the Facilitated diffusion in biology?

Example of the facilitated diffusion can be bringing glucose molecule in the cell. As we know that the cell membrane does not allow glucose to cross the membrane by diffusion so some importers or helpers are required. First of all the cell notices some free glucose molecules outside the cell. The membrane proteins then take one molecule in and shift their position to bring the molecule into the cell. That is an easy situation of passive transport because the glucose is moving from higher to lower concentration. It is a movement of molecule down a Concentration Gradient. But if you need to remove the glucose molecule then the cell would require some energy.

How a Concentration Gradient can be defined?

A concentration gradient happens when the concentration of molecules is higher in one area than another. In passive transport, movement of particles will be down the concentration gradient, from an area of higher concentration gradient to an area of lower concentration gradient, until they are evenly spaced.

Why a concentration gradient is important for life? Explain with an example?

Organisms that want to move any substance in or out of their cells, they use the movement of the molecules down the concentration gradient.


Sometimes some cells are present in an area where there is a large concentration gradient difference. For example, in lungs oxygen molecule concentrations is very high inside the alveoli as compared to inside the blood vessels that are surrounded the alveoli.  Oxygen molecules are so minor and huge in numbers that they are easily exchange. There is no energy wanted in this procedure. Thus exchange of gases take place in lungs following this method.


What are the Factors affecting the rate of diffusion?

  • Concentration gradient: The greater the concentration difference, the faster the rate of diffusion.
  • Temperature: The greater the temperature, faster the rate of diffusion.
  •  Pressure: increasing the pressure increases the kinetic energy of the particles, thus increasing the rate of diffusion.
  •  Size of particles: Heavier the particles, slower the rate of diffusion because the particle will move slowly while smaller the particles, faster will be the rate of diffusion because they can move faster.
  •  Surface area to volume ratio:  Whenever the cell gets larger in size, the volume grows quicker than the surface area. Whenever there is large volume and less surface area, diffusion takes much time and is less effective.

What is the importance of the process of diffusion in living things?

Diffusion helps living organisms in many ways:

  • It help to obtain many of the necessities.
  • It helps to get rid of many waste products.
  • It helps in exchange of gases for the process of respiration.


  • Carbon dioxide is used up by the plants for the process of photosynthesis. During the process of diffusion, carbon dioxide from the air diffuses into the leaves, through small microscopic pores called stomata that are present at the surface of the leaves. There is a lower concentration of carbon dioxide inside the leaf, as the cells are using it up. Oxygen as a waste product of photosynthesis diffuses out in the same manner.


  • Flowering plants use the process of diffusion to attract pollinators like bees for the process of pollination.
  • In our digestive system some of the products of digestion are absorbed from the ileum of mammals by diffusion.


  • During Respiration  carbon dioxide is produced as a waste product and this causes the increase of carbon dioxide in the cell. This causes the concentration of carbon dioxide higher in the cell than in the blood present in the surrounding. So carbon dioxide diffuses out through the cell membrane into the blood. This method of gaseous exchange takes place in alveoli as well where carbon dioxide diffuses out and oxygen diffuses for blood purification.

  • In the same way water diffuses into plants through root hair cells. The movement of water molecules takes place from the soil (an area of high concentration) into the root hair cell (an area of lower concentration). This is because root hair cells are surrounded by partially permeable.



Osmos(Ancient greek word) means water and osmosis means diffusion of water molecules from higher concentration, or it refers to the movement of water molecules from a region of higher water potential to a region of lower water potential across a semi or partially permeable membrane.

What is a semi-permeable membrane?

A wall-like structure is present around each cell in our body that is the cell membrane that protects our cells . This membrane is very special because only water and very small molecules can pass through it.

We use the word semi-permeable to describe the ability only to let certain things pass through a membrane. It separates 2 solutions: cytoplasm and solution around the cell. If the solutions are of different concentrations, osmosis occurs.

Osmosis is a passive transport and no extra energy required and molecules move by their energy.

What do you mean by Hypotonic, Isotonic, and Hypertonic solutions?

A hypertonic solution contains a higher concentration of solutes compared to another solution.When we compare the hypotonic solution to another solution, then the hypotonic solution has low solute concentration.A solution is called an isotonic when it has the same concentration of solutes as another solution across a semi-permeable membrane.A solution cannot be hypotonic, isotonic or hypertonic without a solution for comparison.

What are the Effects of Osmosis on plant and animal cells?

What does happen when you place an animal cell in a hypotonic solution?

The animal cell will swell and may bust in a hypotonic solution because it does not have a cell wall as we know that water moves from a region of high water potential towards the low water potential.

Since the extracellular fluid has less osmolarity/high water potential, the water would enter into the cell and eventually the cell would then expand and eventually lyse or burst.

What does happen if we place any plant cell in Hypotonic?

The water moves from a region of extracellular fluid/high water potential to a region of high osmolarity inside the cell. The cell would then enlarge. But the plant cell does not burst like an animal cell. This is because the plant cells have a rigid and firm cell wall (made up of cellulose) around the plasma membrane. Upon swelling with water, they become turgid.



What does happen if an animal cell is placed in Hypertonic solution?

Water will leave the cell because the cell has a lower osmolarity / high water potential than the external environment of the cell. As a result of this, the cell would shrink, called plasmolysis.


What will happen if an animal cell is placed in hypertonic solution?

What would happen when you place an animal cell in an isotonic?

The osmolarity of both fluids is alike. Because of water diffusion in and out, there will be no net change in the volume of the cell.

What does happens when you place a plant cell in an isotonic?

The osmolarity of both fluids is the same. So, diffusion of water in and out will no produce a net change in the volume of the cell.


How do you define the Turgor in plants?

  • Turgor is very important in maintaining the shape of soft tissues in plants
  • Young stems and most leaves, especially those of herbaceous or non-woody plants, can remain steady and erect because of the turgor pressure created within the cells.
  • But when there is a fast rate of evaporation of water from the cells, they lose their turgidity and the plant wilts
  • The movement of certain plants is due to changes in turgor. For example, opening and closing of the stomata, folding of leaflets of the Mimosa plant etc.


What do you mean by Active Transport?

Active transport means that this the process of transferring substances into the cell, out of the cell, and between the cells but by using energy. In some cases, the movement of substances can be accomplished by passive transport, which uses no energy. However, the cell often needs to transport materials against their concentration gradient. In these cases, active transport is required.

Some important examples of active transport in plants include are as follows:

  • From soil, minerals and ions enter into the roots through this process.
  • This process also helps in the transportation of chloride and nitrate from the cytosol to the vacuole.
  • Movement of sugars synthesized after photosynthesis from leaves to fruit to store.
  • Between the cells, Calcium moves with the help of energy taken from ATP.
  • Minerals transported via a stem to various parts of plants.
  • Water moves from plant roots to other plant cells with the help of root pressure.




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