Tag: Diffusion

Introduction

The fundamental building block of life, a cell is capable of carrying out every metabolic task required to maintain life. A cell must be able to permit the passage of various substances into and out of its boundaries in order to be able to perform the metabolism of various substances. A cell can take in and release substances out of the cell, through the process of diffusion and osmosis. This exchange is essential for the cell’s survival. The processes of molecules moving down a concentration gradient are diffusion and osmosis. Although they both aid in the movement of substances through the cell membrane, they differ slightly from one another.

Diffusion

• The spontaneous movement of a molecule down a concentration gradient is called diffusion. For example- diffusion is the spreading of a dye in water.
• It is referred to as a passive process because it doesn’t require any energy input.
• Concentration gradients and the random dynamic movement of the solute molecules are the only factors that influence diffusion.
• Diffusion keeps going until there is equilibrium i.e until there is an equal concentration of the solute on both sides.
• Diffusion happens through a plasma membrane in biological systems.

Types of diffusion

There are two types of diffusions which are explained below

• Simple Diffusion-
  • Simple Diffusion is also known as Independent Diffusion. 
  • This type diiffusion does not require the involvement of membrane proteins.
  • The relative concentration of the molecules inside the cell as compared to outside the cell determines the direction of the flow of the molecules.
  • Simple diffusion is non-selective and permits the passage of all non-polar molecules across a lipid bilayer.
• Facilitated Diffusion

• • Some molecules cannot move across the cell membrane due tu their hydrophilicity.
  • Thus, the movement of such molecules and charged ions is mediated by certain membrane proteins. This process is termed facilitated diffusion.
  • The channel proteins and the carrier proteins are the two different types of membrane transport proteins.
  • Polar and charged molecules can cross the cell membrane through the process of facilitated diffusion.

Factors affecting rate of diffusion

• Partition Coefficient-It represents the ratio of a solute’s concentration in two phases when both the phases are in equilibrium with one another. The greater the solubility of a solute, the greater will be its partition coefficient.  A substance can pass a biological membrane more readily if its partition coefficient is larger.
• The concentration of the solutes-Fast diffusion occurs when the concentration gradient is higher.
• Temperature- The molecules’ kinetic energy is increased by an increase in temperature, which causes them to travel more quickly across the membrane.
• Mass-Heavier solutes diffuse slowly as compared to lighter solutes.
• The density of the solvent- As solvent density rises, the rate of diffusion declines.
• Nature of the solutes- Lipophilic and non-polar compounds can easily cross the plasma membrane as compared to hydrophilic and polar compounds.

Osmosis 

• Osmosis is the process by which solvent molecules move down a concentration gradient and across a semipermeable membrane (i.e., higher to lower concentration). 
• It is the net movement of solvent molecules from a high water potential region to a low water potential region. 
• Osmosis results in equal solute concentrations on both sides of the membrane.
• The transfer of water from locations with high water potential to those with low water potential is also termed osmosis.

Tonicity

Pertaining to the proportional solute concentrations of a cell and its surroundings there are three different tonicities, they are-

• If a cell is placed in a hypertonic environment, that is, an environment in which the solute is present at a higher concentration than within the cell, the water travels out of the cell and into the surrounding environment.  This causes the cell to lose volume and become flaccid. Plasmolysis, a severe condition in which the cell membrane separates from the cell wall and ruptures.
• Water moves into the cell and causes it to swell if the external environment is hypotonic, that is, if the environment has a lower concentration of solute than the cell. Here, the cell gets turgid.
• There is no net change in the volume of the cell if the external environment is isotonic, or if it contains the same number of solutes per litre of solution as the interior of the cell.

Osmolarity 

• The number of solute molecules per litre of the solvent is referred to as osmolarity.
• Simply said, osmolarity is a measurement of the amount of solute in the solution.
• As a result, referring to a solution as having low osmolarity suggests that its solute concentration per liter of solution is lower. 
• In biology, a cell’s osmolarity is crucial in determining how easily water can move through a bilayer.
• If a semipermeable membrane is used to separate two solutions with differing osmolarities, water from the solution with the lower osmolarity will pass through the membrane and into the solution with the greater osmolarity.

Difference between Osmosis and Diffusion  

Summary 

• The spontaneous movement of molecules along a concentration gradient is known as diffusion.
• In biological systems, diffusion across the cell may be independent or facilitated by membrane proteins
• Osmosis is the transfer of solvent molecules across a semi-permeable membrane along a concentration gradient.
• Osmosis and diffusion vary primarily in that the former takes place through a semi-permeable membrane while the latter can happen in any medium.

 

Frequently Asked Questions

1. What is Osmotic Pressure?

Ans: Osmotic pressure is the amount of force required to stop solvent molecules from passing through a semipermeable membrane into a solution. Temperature and concentration both have an impact on osmotic pressure. Osmotic pressure rises as concentrations and temperatures rise.

2. What are channel proteins?

Ans: A channel protein is a type of transport protein that functions as a pore in the cell membrane to allow water molecules or small ions to pass through. Aquaporins, which are water channel proteins, enable rapid water diffusion across the membrane. Ions can diffuse across the membrane through ion channel proteins.

3. Give two examples of osmosis and diffusion each.

Ans: Red blood cells’ enlargement when exposed to freshwater, and absorption of water by plant root hairs are examples of osmosis

The fragrance of perfume spreading throughout a room and the passage of tiny molecules across a cell membrane are both examples of diffusion.

Introduction

Transport is a crucial component of plant physiology and involves moving organic nutrients and water throughout the plant body. Food is produced by photosynthesis in the leaves which is transported to other parts of the plant and water is absorbed from the soil through the roots and then to various aerial regions of the plant. In higher plants, the transport of food and water takes place through specialized structures known as the xylem and phloem. An elaborate root system helps these plants to absorb water from the soil.  However, primitive plants perform the function of absorption of water through simple structures such as pores, or the external body surface.

For more help, you can Refer to our video in Class 7 Science in Lesson no 11. Check out the video Lesson for a better understanding.

Transportation in plants-

The main 3 means of transport in plants are via diffusion, Facilitated diffusion, and Active transport. Vascular bundles assist in the movement of water and carbohydrates throughout the entire plant body.

Simple Diffusion- Diffusion is the process of movement of a molecule from a location of higher concentration to a lower concentration i.e. along the concentration gradient. It is a spontaneous process and doesn’t require any energy. Here no special membrane proteins are required and this method only allows the transportation of hydrophobic molecules as the cell membrane is made up of a lipid bilayer.

• Facilitated diffusion- Facilitated diffusion is a type of diffusion facilitated by some proteins which assist in the movement of various metabolites through the cell membranes. These are majorly used for the transportation of water, ions, and other hydrophilic molecules which cannot pass through the lipid bilayer. The channel proteins and the carrier proteins are the two different types of membrane transport proteins.
• Channel proteins- Pores in the plasma membrane are created by channel proteins. These proteins are highly selective and hence allow the transportation of specific molecules only. Eg-Aquaporins only permit water movement and Aquaglyceroporins facilitate only the movement of glycerol and water.
•  
• Carrier proteins- These are special types of proteins that undergo conformational changes after binding to a particular solute. Carrier proteins help in the transportation of ions eg- chloride-bicarbonate exchanger, also known as the anion exchange protein, which facilitates the simultaneous transit of HCO3- and Cl–. It also helps in the transport of glucose via the glucose transporter(GLUT).
• Active transport- Active transport facilitates uphill solute movement throughout the cell by functioning against a concentration gradient. Here the molecules move from an area of lower concentration to a higher concentration. Hence, some kind of energy is required. There are two ways to supply energy:

• The energy produced by ATP hydrolysis is known as primary or direct active transport. For instance, the energy is given through the Na+-K+ ATPase (electrogenic pumps). 

• The energy supplied through the electrochemical gradient is enabled by the Symport pumps (such as the Na+-Glucose symporter, lactose permeases, etc.) and Antiport pumps (such as the Na+-Ca2+ antiporter) These are often referred to as secondary or indirect active transport.

Transport of water from roots

Long-distance transportation of water and nutrients in plants takes place through the xylem and phloem. The soil-plant-atmosphere continuum (SPAC) is a pathway that discusses the movement of water from the soil, its transportation to plant parts, and 

the expulsion of water from the plant. Absorption of water in plants occurs through-Passive absorption- when water is absorbed from a higher water potential (in soil) to a lower water potential (in root cells). Active absorption-which occurs due to transpiration.

Ascent of sap

The term “ascent of sap” refers to the movement of water and minerals from the soil to aerial portions like leaves and stems. The cohesion-tension theory, also known as transpirational pull, explains this (Dixon and Jolly, 1894). According to this idea, water from locations with higher water potential (such as the roots) is drawn up, to areas with lower water potential (the leaves)  due to the tension (negative hydrostatic pressure) which is generated by the leaves. There is low water potential in the leaves because they lose water due to the process of transpiration. The water column is kept from collapsing by the cohesive forces of attraction between the water molecules. As a result, water absorption happens to make up for the transpirational loss.

Summary

Intricate transportation networks are needed by plants to enable the interchange of materials and nutrients. The passive process of moving molecules from higher to lower concentrations is known as diffusion. It could be simple (independent) or facilitated transport. Energy is spent during active transport, which is carried out by membrane proteins called transporters and channel proteins. The transpirational pull/cohesion-adhesion principle is used by the roots to absorb water. 

Frequently Asked Questions

1. What do you understand about water potential?
Ans: The potential energy of water per unit volume is referred to as water potential. It describes the amount of water in the atmosphere, plants, and soil.

It is shown as the sum of Osmotic potential, matrix potential, hydrostatic potential, and gravitational potential. 𝜳w = 𝜳𝛑 (osmotic potential)   + 𝜳m (matrix potential)  +𝜳p (hydrostatic potential)  +  𝜳g (gravitational potential).

2. What is the symplastic pathway of water absorption?
Ans: The continuous network of cell cytoplasms is known as the symplastic route.

Through the plasmodesmata connections present between two cells, this pathway allows absorbed water to flow from cell to cell.

3. Which method of water absorption is quick?
Ans: The apoplastic pathway will move more quickly since there won’t be as many obstacles in its path as there are in the symplastic pathway, which is obstructed by Casparian strips and must travel through the protoplasm, which slows down movement.

Introduction

The matter may be found on Earth in three different states: solid, liquid, or gaseous. Every matter is composed of incredibly tiny building components called atoms and molecules. These particles in a solid are strongly attracted to each other and vibrate in place without passing by each other. Despite not being as strong as it is in a solid, there is still an attraction between the particles in a liquid. The proximity and frequent movement of the particles in a liquid allow them to slip past one another. There is only a weak attraction between gaseous particles. They are continually moving and spread out compared to the particles in a solid or liquid. Here the particles do not interact when they collide; they just strike and bounce off of one another. This article provides a thorough understanding of the concept of matter of space between particles and attraction between the matter particles with specific instances.

Particles have Space between Them

Let’s observe a small activity to determine whether the particles are separated from one another; this is explained below.

Experiment

Take a beaker filled with 100 ml of water and then add 20 gm of sodium chloride (table salt) into it. Make sure to swirl the water with a glass stirring rod until all the salt has completely dissolved. The salt will dissolve, and then we will get a solution.

Observations

It has been observed that even after 20 gm of salt has been dissolved in 100 ml of water, the level of the water doesn’t actually rise. This displays how free and interparticle space-containing water atoms are. This area is known as the interparticle or intermolecular space. In this interparticle area, the salt granules that were scattered have settled.

Particles of Matter are Constantly Moving at Random

Diffusion and Brownian motion demonstrate that particles are moving.

Diffusion

A material will mix and disperse with another substance through a process called diffusion while its particles are in motion. To homogenize the mixture, this process is repeated. For instance, the ink diffuses in the water as a result of the random movement of water and ink particles. Ink migrates from areas of higher concentration to regions of lower concentration at a pace that is inversely associated with the liquid diffusion rate of the ink. Diffusion occurs in liquids, solids, and gases, however, it occurs more rapidly in gases and less efficiently in solids.

Brownian Motion

Brownian suspended several pollen grains in water and then examined them under a microscope. He saw that the pollen grains were moving in a zigzag pattern. The movement is significantly more evident when the water is warmed. Water is made up of randomly migrating atoms. As a result, the moving atoms frequently strike the pollen grains, causing them to migrate. As an example of Brownian motion, the pollen grains are travelling in this manner.

Particles of Matter Attract Each Other

A force acting on the particles of matter holds them together. Some substances crumble into powder, while others form tiny crystals, and still, others are challenging to separate. The strength of the force of attraction varies from one type of substance to another, depending on that substance. This is done so that the force of attraction between the particles can keep the particles inside them. This interparticle force of attraction exists in all substances that cause the attraction of particles. Therefore, to break objects, we must defeat the force of attraction. A varying amount of strength is necessary depending on the chemical.

Examples show that breaking a chalk is easier than breaking a nail. This illustrates how 

various material particles have varied levels of attraction. The attraction between particles of the same material is referred to as “cohesion.”

Summary

The particles are separated by a certain amount of space, in which the gaseous form of matter has the largest inter-particle space among the three states of matter. Interestingly, the interparticle gaps that exist in various types of matter are what give rise to the three states of matter, and therefore the density of different states of matter increases from a gas to a solid state (for example water vapor to water and then ice). 

Frequently Asked Questions

1. Define Matter.

Ans: A component that is made up of several types of particles, takes up space, and has motion is referred to as “matter.”

2. What Constitutes Matter?

Ans: Matter is made up of atoms, which are made up of electrons, protons, and neutrons.

3. How to Develop the Model of Particles of Gas and Liquid?

Ans: By compressing a flexible plastic container with a balloon on top, we can imitate the gas particles. We can also try to squeeze a water-filled container as part of their modelling of liquid particles.