- Last updated
- Save as PDF
- Page ID
- 58825
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)
Learning Outcomes
- Define osmosis and diffusion.
- Distinguish among hypotonic, hypertonic, and isotonic solutions.
- Describe a semipermeable membrane.
- Predict behavior of blood cells in different solution types.
- Describe flow of solvent molecules across a membrane.
- Identify the polar and nonpolar regions of a cell membrane.
- Explain the components present in a phospholipid.
Fish cells, like all cells, have semipermeable membranes. Eventually, the concentration of "stuff" on either side of them will even out. A fish that lives in salt water will have somewhat salty water inside itself. Put it in freshwater, and the freshwater will, through osmosis, enter the fish, causing its cells to swell, and the fish will die. What will happen to a freshwater fish in the ocean?
Osmosis
Imagine you have a cup that has \(100 \: \text{mL}\) water, and you add \(15 \: \text{g}\) of table sugar to the water. The sugar dissolves and the mixture that is now in the cup is made up of a solute (the sugar) that is dissolved in the solvent (the water). The mixture of a solute in a solvent is called a solution.
Imagine now that you have a second cup with \(100 \: \text{mL}\) of water, and you add \(45 \: \text{g}\) of table sugar to the water. Just like the first cup, the sugar is the solute, and the water is the solvent. But now you have two mixtures of different solute concentrations. In comparing two solutions of unequal solute concentration, the solution with the higher solute concentration is hypertonic, and the solution with the lower solute concentration is hypotonic. Solutions of equal solute concentration are isotonic. The first sugar solution is hypotonic to the second solution. The second sugar solution is hypertonic to the first.
You now add the two solutions to a beaker that has been divided by a semipermeable membrane, with pores that are too small for the sugar molecules to pass through, but are big enough for the water molecules to pass through. The hypertonic solution is one one side of the membrane and the hypotonic solution on the other. The hypertonic solution has a lower water concentration than the hypotonic solution, so a concentration gradient of water now exists across the membrane. Water molecules will move from the side of higher water concentration to the side of lower concentration until both solutions are isotonic. At this point, equilibrium is reached.
Red blood cells behave the same way (see figure below). When red blood cells are in a hypertonic (higher concentration) solution, water flows out of the cell faster than it comes in. This results in crenation (shriveling) of the blood cell. On the other extreme, a red blood cell that is hypotonic (lower concentration outside the cell) will result in more water flowing into the cell than out. This results in swelling of the cell and potential hemolysis (bursting) of the cell. In an isotonic solution, the flow of water in and out of the cell is happening at the same rate.
Osmosis is the diffusion of water molecules across a semipermeable membrane from an area of lower concentration solution (i.e., higher concentration of water) to an area of higher concentration solution (i.e., lower concentration of water). Water moves into and out of cells by osmosis.
- If a cell is in a hypertonic solution, the solution has a lower water concentration than the cell cytosol, and water moves out of the cell until both solutions are isotonic.
- Cells placed in a hypotonic solution will take in water across their membranes until both the external solution and the cytosol are isotonic.
A red blood cell will swell and undergo hemolysis (burst) when placed in a hypotonic solution. When placed in a hypertonic solution, a red blood cell will lose water and undergo crenation (shrivel). Animal cells tend to do best in an isotonic environment, where the flow of water in and out of the cell is occurring at equal rates.
Diffusion
Passive transport is a way that small molecules or ions move across the cell membrane without input of energy by the cell. The three main kinds of passive transport are diffusion (or simple diffusion), osmosis, and facilitated diffusion. Simple diffusion and osmosis do not involve transport proteins. Facilitated diffusion requires the assistance of proteins.
Diffusion is the movement of molecules from an area of high concentration of the molecules to an area with a lower concentration. For cell transport, diffusion is the movement of small molecules across the cell membrane. The difference in the concentrations of the molecules in the two areas is called the concentration gradient. The kinetic energy of the molecules results in random motion, causing diffusion. In simple diffusion, this process proceeds without the aid of a transport protein. It is the random motion of the molecules that causes them to move from an area of high concentration to an area with a lower concentration.
Diffusion will continue until the concentration gradient has been eliminated. Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes "down the concentration gradient". The end result is an equal concentration, or equilibrium, of molecules on both sides of the membrane. At equilibrium, movement of molecules does not stop. At equilibrium, there is equal movement of materials in both directions.
Not everything can make it into your cells. Your cells have a plasma membrane that helps to guard your cells from unwanted intruders.
The Plasma Membrane and Cytosol
If the outside environment of a cell is water-based, and the inside of the cell is also mostly water, something has to make sure the cell stays intact in this environment. What would happen if a cell dissolved in water, like sugar does? Obviously, the cell could not survive in such an environment. So something must protect the cell and allow it to survive in its water-based environment. All cells have a barrier around them that separates them from the environment and from other cells. This barrier is called the plasma membrane, or cell membrane.
The Plasma Membrane
The plasma membrane (see figure below) is made of a double layer of special lipids, known as phospholipids. The phospholipid is a lipid molecule with a hydrophilic ("water-loving") head and two hydrophobic ("water-hating") tails. Because of the hydrophilic and hydrophobic nature of the phospholipid, the molecule must be arranged in a specific pattern as only certain parts of the molecule can physically be in contact with water. Remember that there is water outside the cell, and the cytoplasm inside the cell is mostly water as well. So the phospholipids are arranged in a double layer (a bilayer) to keep the cell separate from its environment. Lipids do not mix with water (recall that oil is a lipid), so the phospholipid bilayer of the cell membrane acts as a barrier, keeping water out of the cell, and keeping the cytoplasm inside the cell. The cell membrane allows the cell to stay structurally intact in its water-based environment.
The function of the plasma membrane is to control what goes in and out of the cell. Some molecules can go through the cell membrane to enter and leave the cell, but some cannot. The cell is therefore not completely permeable. "Permeable" means that anything can cross a barrier. An open door is completely permeable to anything that wants to enter or exit through the door. The plasma membrane is semipermeable, meaning that some things can enter the cell, and some things cannot.
Molecules that cannot easily pass through the bilayer include ions and small hydrophilic molecules, such as glucose, and macromolecules, including proteins and RNA. Examples of molecules that can easily diffuse across the plasma membrane include carbon dioxide and oxygen gas. These molecules diffuse freely in and out of the cell, along their concentration gradient. Though water is a polar molecule, it can also diffuse through the plasma membrane.
Cytosol
The inside of all cells also contain a jelly-like substance called cytosol. Cytosol is composed of water and other molecules, including enzymes, which are proteins that speed up the cell's chemical reactions. Everything in the cell sits in the cytosol, like fruit in a Jell-o mold. The term cytoplasm refers to the cytosol and all of the organelles, the specialized compartments of the cell. The cytoplasm does not include the nucleus. As a prokaryotic cell does not have a nucleus, the DNA is in the cytoplasm.
Supplemental Resources
- The Plasma Membrane: http://www.youtube.com/watch?v=moPJkCbKjBs
Contributors and Attributions
Allison Soult, Ph.D. (Department of Chemistry, University of Kentucky)
FAQs
What is 8 diffusion how it is different from osmosis? ›
Hint: Diffusion is the movement of any substance from a region of its higher concentration to a region of lower concentration. It occurs in all directions. Osmosis is the movement of water or any other solvent from a region of low solute concentration to a region of high solute concentration.
What is difference between osmosis and diffusion? ›Osmosis can only function in a liquid medium, but diffusion can occur in all three mediums (solid, liquid and gas). Furthermore, osmosis requires a semi-permeable membrane, while diffusion does not. The intake of water in plants is an example of osmosis.
What is osmosis high to low or low to high? ›Osmosis happens when molecules move from higher to lower concentrations, but diffusion happens when it is reversed.
What is the process of osmosis and diffusion? ›Osmosis is the result of diffusion across a semipermeable membrane. If two solutions of different concentration are separated by a semipermeable membrane, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. This process is called osmosis.
What is osmosis and diffusion and why is it important? ›Osmosis is the diffusion of water molecules, and diffusion is the diffusion of all other molecules. It is more important to living organisms because it is responsible for transporting water into and out of cells. Diffusion is important for transporting nutrients and other molecules into and out of cells.
What is the main difference between osmosis and diffusion quizlet? ›The main difference between the two is osmosis is the diffusion of water and has to do with water and diffusion is the process of movement. Diffusion can be air and osmosis is water.
What is a simple definition of osmosis? ›Here's the definition of osmosis that you will see in most textbooks: In biology, osmosis is the movement of water molecules from a solution with a high concentration of water molecules to a solution with a lower concentration of water molecules, through a cell's partially permeable membrane.
What is the example of diffusion? ›diffusion, process resulting from random motion of molecules by which there is a net flow of matter from a region of high concentration to a region of low concentration. A familiar example is the perfume of a flower that quickly permeates the still air of a room.
Is osmosis simple diffusion? ›Osmosis is a type of simple diffusion in which water molecules diffuse through a selectively permeable membrane from areas of high water concentration to areas of lower water concentration.
Is diffusion low to high? ›In the process of diffusion, a substance tends to move from an area of high concentration to an area of low concentration until its concentration becomes equal throughout a space.
What is a high concentration in osmosis? ›
A hypertonic solution is any external solution that has a high solute concentration and low water concentration compared to body fluids. In a hypertonic solution, the net movement of water will be out of the body and into the solution.
Does higher concentration mean faster osmosis? ›Concentration gradient - The movement of osmosis is affected by the concentration gradient; the lower the concentration of the solute within a solvent, the faster osmosis will occur in that solvent.
What are the 3 types of osmosis? ›What are the three types of osmotic conditions that affect living cells? The three types of osmotic conditions include- hypertonic, isotonic, and hypotonic.
What affects diffusion and osmosis? ›The greater the difference in concentration, the quicker the rate of diffusion. The higher the temperature, the more kinetic energy the particles will have, so they will move and mix more quickly. The greater the surface area, the faster the rate of diffusion.
What is the conclusion diffusion and osmosis? ›Answer and Explanation: Conclusion for Osmosis and Diffusion: In diffusion, molecules, whether identified as solute or solvent, move from an area with a higher concentration to a lower concentration to achieve equilibrium and this occurs in all types of solutions.
What is the purpose of diffusion? ›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.
How does osmosis work? ›Osmosis is the transport of a solvent through a semipermeable membrane that separates two solutions of differing solute concentration. During osmosis, the solvent moves from the solution that is lower in solute concentration to the solution that is higher in solute concentration.
Which of the following best summarizes the differences between osmosis and diffusion? ›Answer and Explanation: The answer is c. osmosis refers specifically to the movement of water, whereas diffusion refers to the movement of any molecules.
What is the main difference between osmosis diffusion and active transport? ›Diffusion can happen with or without passing through a semi-permeable membrane (cell plasma membrane is semi-permeable). Osmosis is the diffusion of water molecules down a concentration gradient through a semi-permeable membrane. Active transport is the movement of a substance against a concentration gradient.
How is diffusion defined? ›Diffusion is defined as the movement of individual molecules of a substance through a semipermeable barrier from an area of higher concentration to an area of lower concentration [34].
What is a good example of osmosis? ›
A slug's damp skin acts as a semipermeable barrier. The high concentration of salt on the slug's skin causes osmosis, which sucks water out of its cells. The water comes out as a result of the slug's skin's salt concentration.
Does osmosis only mean water? ›Osmosis is the movement of a solvent across a semipermeable membrane toward a higher concentration of solute. In biological systems, the solvent is typically water, but osmosis can occur in other liquids, supercritical liquids, and even gases.
Why does osmosis happen? ›Osmosis and Osmotic Pressure
In microporous membranes, osmosis is caused by a momentum deficit within the pores due to the reflection of solute molecules by the membrane. This reduces the pressure on the solution side of the pore by π for a semipermeable membrane.
Diffusion happens because gases and liquids move from place to place in quick random motions. When this happens, the particles collide, which in turn makes them change directions. The process of diffusion occurs on its own without any help from shaking or stirring.
Where does diffusion occur? ›Diffusion is a type of transport that simply occurs when there is a concentration difference where the molecules move from a region of higher concentration to a region of lower concentration. When particles in liquids and gases randomly collide and disperse, diffusion takes place.
Why is osmosis important? ›Osmosis plays an important role in the human body, especially in the gastro-intestinal system and the kidneys. Osmosis helps you get nutrients out of food. It also gets waste products out of your blood.
What type of diffusion is osmosis? ›Osmosis is a special type of diffusion, namely the diffusion of water across a semipermeable membrane. Water readily crosses a membrane down its potential gradient from high to low potential (Fig.
Is water diffusion or osmosis? ›Water moves across cell membranes by diffusion, in a process known as osmosis. Osmosis refers specifically to the movement of water across a semipermeable membrane, with the solvent (water, for example) moving from an area of low solute (dissolved material) concentration to an area of high solute concentration.
Why osmosis is called diffusion? ›Osmosis is a special kind of diffusion because in both cases there is a movement of particles from a higher concentration region to a lower concentration region. The only difference is that osmosis is referred onlyto the movement of the solvent (water) across a semi-permeable membrane.
What is a high diffusion rate? ›The higher the diffusivity (of one substance with respect to another), the faster they diffuse into each other. Typically, a compound's diffusion coefficient is ~10,000× as great in air as in water. Carbon dioxide in air has a diffusion coefficient of 16 mm2/s, and in water its diffusion coefficient is 0.0016 mm2/s.
What happens when diffusion increases? ›
When temperature increases, the kinetic energy of the particles has increased. The increased motion of the particles causes them to diffuse faster. Therefore, at higher temperatures, the rate at which fluid particles will diffuse is faster than at lower temperatures.
Why does diffusion increase? ›Temperature: Higher temperatures increase the energy and therefore the movement of the molecules, increasing the rate of diffusion. Lower temperatures decrease the energy of the molecules, thus decreasing the rate of diffusion.
What does low concentration mean in osmosis? ›Osmosis is the diffusion of water molecules across a semipermeable membrane from an area of lower concentration solution (i.e., higher concentration of water) to an area of higher concentration solution (i.e., lower concentration of water). Water moves into and out of cells by osmosis.
Does water move from low to high concentration? ›Water, like other substances, moves from an area of high concentration to one of low concentration.
How do you calculate osmosis a level? ›In order to calculate this, you must take the mass at the end, then subtract it from the original mass. Then divide this value by the original mass. To get the percentage, you must then multiply it by 100.
What are the 4 factors that affect the rate of osmosis? ›For example, temperature, particle size, and the size of the concentration gradient can all affect the rate of osmosis. A higher temperature can cause osmosis to occur at a faster rate, compared to a lower temperature due to the molecules' higher energy.
What are the factors that affect the rate of diffusion? ›The rate of diffusion in cells is affected by factors such as temperature, concentration gradient, size of the molecule, and the presence of a membrane.
Which is faster diffusion or osmosis? ›Answer 1: Diffusion is a fast process whereas osmosis is a slower one.
Does diffusion require energy? ›Simple diffusion does not require energy: facilitated diffusion requires a source of ATP. B. Simple diffusion can only move material in the direction of a concentration gradient; facilitated diffusion moves materials with and against a concentration gradient.
What type of transport is diffusion? ›Passive transport, most commonly by diffusion, occurs along a concentration gradient from high to low concentration. No energy is necessary for this mode of transport.
What are 3 facts about osmosis? ›
The misconception is that osmosis requires an attractive force. (3) Osmosis can drive solvent from a lower to a higher solvent concentration compartment. The misconception is that osmosis always happens down a concentration gradient. (4) The osmotic pressure cannot be interpreted as the partial pressure of the solute.
What are the stages of osmosis? ›What does each stage of a Reverse Osmosis Filtration system do? A standard RO system is equipped with 3 separate filter stages. Sediment, carbon, and reverse osmosis. Each filtration stage plays an important role on their own and also complement one another to achieve the best water filtration possible.
Is osmosis water or oxygen? ›Osmosis is the movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration. Osmosis helps regulate the flow of water in and out of cells, which is crucial to their function.
What is diffusion in biology? ›Diffusion is defined as the movement of individual molecules of a substance through a semipermeable barrier from an area of higher concentration to an area of lower concentration [34].
What is diffusion in science grade 8? ›Diffusion is the movement of molecules from an area of high concentration to an area of low concentration until the 'mixture' is even: this is known as equilibrium. Diffusion is faster in gases than in liquids, because particles in gases move faster than particles in liquids.
What is the difference between diffusion and osmosis brainly? ›Diffusion is the movement of gases from an area of higher concentration to lower concentration. It takes place in Oxygen and Carbon dioxide. Diffusion cannot be stopped or reversed. Osmosis is the movement of particles from higher water concentration to lower water concentration through a semi-permiable membrane.
What happens during diffusion? ›In the process of diffusion, a substance tends to move from an area of high concentration to an area of low concentration until its concentration becomes equal throughout a space.
What causes diffusion? ›The kinetic energy of the molecules results in random motion, causing diffusion. In simple diffusion, this process proceeds without the aid of a transport protein. It is the random motion of the molecules that causes them to move from an area of high concentration to an area with a lower concentration.
What is diffusion in short answer? ›Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration . Diffusion occurs in liquids and gases when their particles collide randomly and spread out. Diffusion is an important process for living things - it is how substances move in and out of cells.
What is the function of diffusion? ›Hint: Diffusion is the process of movement of solute or solvent molecules in accordance with the concentration gradient that is from the region of higher concentration to its region of lower concentration. It plays an essential role in respiration in plants and animals.
How do you explain simple diffusion? ›
In simple diffusion, small noncharged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration (they move down their concentration gradient).
What is the major difference between simple diffusion and osmosis? ›One big difference between osmosis and diffusion is that both solvent and solute particles are free to move in diffusion, but in osmosis, only the solvent molecules (water molecules) cross the membrane.
What is the difference between osmosis and diffusion and active transport? ›Diffusion and active transport involve the movement of dissolved solutes, such as sugars or mineral ions, whereas osmosis involves the transport of water only. In diffusion and osmosis, substances move down a concentration gradient. However, active transport moves substances against a concentration gradient.
What are the similarities and differences between diffusion and osmosis quizlet? ›What is the difference between osmosis and diffusion? Osmosis is the movement of water molecules through the cell. Diffusion is the movement of molecules, such as oxygen, in and out of a cell. The process by which water molecules are able to diffuse through the cell membrane.
What are 3 examples of osmosis? ›- Feeling thirsty after having salty food.
- Dialysis of kidney in the excretory system.
- Swelling of resins and other seeds when they are soaked in water.
- Movement of salt-water in the animal cell across our cell membrane.