3.5 Passive Transport

3.5 Passive Transport

• By the end of this section, you will be able to explain why and how passive transport occurs.
• Some substances are allowed but not others.
• The cell would no longer be able to sustain itself if they lost this selectivity.
• Some cells need more specific substances than others, and they need a way to get them from the extracellular fluids.
• As certain materials move back and forth, or as the cell has special mechanisms that ensure transport, this may happen passive.
• Most cells use most of their energy to create and maintain an even distribution of ion on the opposite side of their membranes.
• There are some problems with the structure of the plasma membrane.

• Passive forms of transport are the most direct.
• In passive transport, substances move from an area of higher concentration to an area of lower concentration.

• The asymmetric nature of the membranes means that the interior is not the same as the exterior.
• There are channels or pumps that work in one direction.
• Carbohydrates are found on the exterior surface of the cell.

• The cell uses these complexes to bind things in the fluid.
• It adds to the nature of the membranes.

• There are two regions in the plasma membranes.
• The characteristic helps the movement of certain materials and hinders the movement of others.
• The material can easily slip through the core.
• Substances such as the fat-soluble vitamins A, D, E, and K can be found in the body.
• Fat-soluble drugs are readily transported into the body's tissues and organs.
• Oxygen and carbon dioxide have no charge.

• Some polar molecules can connect with the outside of a cell, but they can't pass through the core of the cell.
• Small ion can easily slip through the spaces in the mosaic, but their charge prevents them from doing so.
• Ions such as sodium, potassium, calcium, and chloride must have special means of penetrating.
• Simple sugars need help with transport.

• When the concentration is equal across the space, a single substance tends to move from an area of high concentration to an area of low concentration.
• You are familiar with air movement.
• Imagine a person opening a bottle of perfume in a room filled with people.
• The perfume is at its highest concentration in the bottle and lowest at the edges of the room.
• As the perfume diffuses from the bottle, more and more people will smell the perfume as it spreads.
• The materials move within the cell's cytosol by diffusion.
• The different concentrations of materials in different areas are a form of potential energy that can be dissipated as materials move down their concentration gradients.

• A substance can be moved from an area of high concentration to one of low concentration with the help of a permeable membrane.

• The concentration of different substances in the same medium has their own concentration.
• The substance will diffuse according to the gradient.

• There are a number of factors that affect the rate of diffusion.

• The slower the rate of diffusion becomes, the closer the distribution of the material gets to equilibrium.

• The mass of the molecule diffuses more slowly if it is more difficult for them to move between the substance they are moving through.

• The movement of the molecule increases when the temperature is higher.

• The slower the molecule is, the harder it is to get through the denser medium.

• The substances that are transported through the air would not diffuse easily or quickly.
• The solution to moving polar substances and other substances is dependent on the proteins that span its surface.
• The material being transported is first attached to the surface of the cell.
• The material that is needed by the cell can be removed.
• The substances are passed through channels or pores that allow them to pass through the membranes.
• The transport proteins are either channels for the material or the carriers, and they are collectively referred to as transport proteins.

• Osmosis is a special case.
• Imagine a beaker with a semipermeable separator.
• If the volume of the water is the same, but the concentrations of solute are different, there are also different concentrations of water on either side of the membranes.

• Water always moves from an area of higher concentration to one of lower concentration.
• In this system, the solute cannot pass through a barrier.

• The principle of diffusion is that the Molecules will spread evenly throughout the Medium if they can move around.

• Only the material that can diffuse through it will do so.
• The water can diffuse the solute in this example.
• This system has a concentration of water.
• Water will diffuse to the side where it is less concentrated.
• The concentration of water in the air will continue until it goes to zero.
• In living systems, Osmosis proceeds constantly.

• There is a video that shows the difference between hot and cold solutions.

• Hypotonic, isotonic, and hypertonic are three terms used to describe the osmolarity of a cell.
• The cell has a lower concentration of water than the extracellular fluid.
• Water will enter the cell in this situation.
• This can cause an animal cell to burst.

• The fluid has a higher concentration of solutes than the cell's cytoplasm, so it contains less water.

• The water will leave the cell.
• The water is being drawn out of the cell by the solute.
• An animal cell may be damaged.

• There will be no net movement of water into or out of the cell if the concentration of solutes of the cell matches that of the extracellular fluid.
• The features of blood cells in hypotonic, isotonic, and hypertonic solutions are shown in Figure 3.22.

• Red blood cells in hypertonic, isotonic, and hypotonic solutions have their shape changed by osmotic pressure.

• A doctor injects a patient with a solution that isotonic.
• An autopsy shows that many red blood cells have been destroyed.

• Some organisms, such as plants, fungi,bacteria, and some protists, have cell walls that surround the plasma membrane and prevent cell lysis.
• The cell won't lyse because the cell can only expand to the limit of the wall.
• Water will always enter a cell if water is available, and the cytoplasm in plants is slightly hypertonic compared to the cellular environment.
• This influx of water stiffens the cell walls of the plant.
• Turgor pressure supports the plant in nonwoody plants.
• Water will leave the cell if it becomes hypertonic or if a plant is not watered adequately.
• Plants lose turgor pressure in this situation.

• Turgor pressure within a plant cell depends on the tonicity of the solution that it is bathed in.