Lab 5 - Transport Across Membranes - Study Notes: 110 total terms / 31 key items from class

Hypotonic solution is when?

The solute concentration in the solution is less than the solute concentration inside the cell.

Solutions consist of two components?

The solvent which is the dissolving medium and solute which is the substance dissolved in the solvent. An example would be salt (solute) put into water (the universal solvent).

Concentration gradient in class analogy?

Greater the hill = greater the concentration.

Crenated in animal cells occurs in what ______ solution?

Hypertonic

Hemolysis in animal cells occurs in what ______ solution?

Hypertonic

Was the 20% NaCl solution hypertonic, isotonic, or hypotonic in relationship to the cytoplasm?

Hypertonic because it shrunk in one solid mass in result of water leaving the cell.

Which of the concentrations most closely approximates the solute concentration in an erythrocyte? What makes you choose this concentration?

0.9%, because the solute concentration has an equal ratio; which mimics the isotopic conditions of the cell having equal inside and outside solute concentration.

Which of the slides held cells in an isotonic state? Describe the shape of these cells?

0.9%; The cells were equal inside and outside.

While diffusion will go forward in the presence of a concentration gradient of a substance, several factors affect the rate of diffusion?

1) Extent of the concentration gradient: The greater the difference in concentration, the more rapid the diffusion. The closer the distribution of the material gets to equilibrium, the slower the rate of diffusion becomes. Mass of the molecules diffusing: Heavier molecules move more slowly; therefore, they diffuse more slowly. The reverse is true for lighter molecules. 2) 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. 3) Solvent density: As the density of a solvent increases, the rate of diffusion decreases. The molecules slow down because they have a more difficult time getting through the denser medium. If the medium is less dense, diffusion increases. Because cells primarily use diffusion to move materials within the cytoplasm, any increase in the cytoplasm's density will inhibit the movement of the materials. An example of this is a person experiencing dehydration. As the body's cells lose water, the rate of diffusion decreases in the cytoplasm, and the cells' functions deteriorate. Neurons tend to be very sensitive to this effect. Dehydration frequently leads to unconsciousness and possibly coma because of the decrease in diffusion rate within the cells. 4) Solubility: As discussed earlier, nonpolar or lipid-soluble materials pass through plasma membranes more easily than polar materials, allowing a faster rate of diffusion. Surface area and thickness of the plasma membrane: Increased surface area increases the rate of diffusion, whereas a thicker membrane reduces it. 5) Distance travelled: The greater the distance that a substance must travel, the slower the rate of diffusion. This places an upper limitation on cell size. A large, spherical cell will die because nutrients or waste cannot reach or leave the center of the cell. Therefore, cells must either be small in size, as in the case of many prokaryotes, or be flattened, as with many single-celled eukaryotes.

Which of the slides held cells in a hypertonic state? Describe the shape of these cells?

10%; The cells were shrunken and looked like "raisins".

Cytolysis, or osmotic lysis, occurs when?

A cell bursts due to an osmotic imbalance that has caused excess water to move into the cell.

A living cell is encased within a __________ that allows interactions with the ​environment?

A living cell is encased within a lipid membrane that allows interactions with the ​environment.

Lab Part II. Examining Osmotic Behavior in Plant and Animal Cells

A. Examine osmotic behavior in plant cells: Plant cells, unlike animal cells, are surrounded by a rigid cell wall composed primarily of cellulose. Plant cells also have a large central vacuole that is surrounded by a selectively permeable membrane. Water may move in and out, but the solutes inside the vacuole remain there. You will examine Elodea, a water plant that normally has a higher solute content in its vacuole than is present in the water surrounding the plant. In this case, water moves into the vacuole and creates turgor pressure. The incoming water pushes against the membrane, but the pressure is restrained by the cell wall and the cell does not burst. Rather, it becomes turgid. Nonwoody plants like beans rely on turgor pressure to remain upright.

What would be the consequence to an animal cell that has water moving into it like the plant cell?

Animal cells do not have cell walls. In hypotonic solutions (Turgid:when cells take in water, swells and burst. Dilute solutes outside) , animal cells swell up and explode as they cannot become turgid because there is no cell wall to prevent the cell from bursting. When the cell is in danger of bursting, organelles called contractile vacuoles will pump water out of the cell to prevent this. In hypertonic solutions, water diffuses out of the cell due to osmosis and the cell shrinks. Thus, the animal cell has always to be surrounded by an isotonic solution. In the human body, the kidneys provide the necessary regulatory mechanism for the blood plasma and the concentration of water and salt removed from the blood by the kidneys is controlled by a part of the brain called the hypothalamus.

At which of the concentrations of NaCl was lysis the fastest?

At the 0% was the fastest. Cells placed in a hypotonic solution will burst, especially when the solution concentration is more water than anything else; hence 0% of NaCl means the water will move rapidly to more space or less concentrated areas i.e inside the cell.

Substances diffuse according to their?

Concentration gradient; within a system, different substances in the medium will each diffuse at different rates according to their individual gradients.

Materials move within the cell's cytosol by diffusion, and certain materials move through the plasma membrane by diffusion.

Diffusion expends no energy. On the contrary, concentration gradients are a form of potential energy, dissipated as the gradient is eliminated.

When solute concentrations are equal inside and outside cell then it is?

Isotonic. Equilibrium: When the ratio of substrate to product is exact or balance from product back to substrate, substrate back to producing product.

Plant cells also have what versus animal cells?

Large Central vacuole that surrounds a selectively permeable membrane. Note: Water may move in and out but the solutes inside the vacuole remains. For example, elodea has a higher solute content in its vacuole and creates turgor pressure.

Kinetic molecular theory means what?

Matter has molecules that occupy space that has kinetic energy.

Osmosis is a?

Osmosis is a form of diffusion but specially involves the movement of water across a selectively permeable membrane. By definition: osmosis is the movement of water across a selectively permeable membrane from an area of high water concentration (potential) to an area of low water concentration (potential). This also means that water will go to the highest solute concentration.

Which direction did osmosis occur - From the water into the bag or bag into the water?

Osmosis pressure was most active from the water into the dialysis tubing.

Diffusion is a process of?

Passive transport in which molecules move from an area of higher concentration to one of lower concentration.

Section B of the lab, we examined the effect of the three types of solutions on living red blood cells or erthrocytes. • Label seven test tubes 1-7 with a wax pencil. • Fill them as directed in the following table. Use one pipet for dH2O and the second one exclusively for NaCl. *how fast the tube became clear enough to see through, i.e you used the lab worksheet words to see when the tube was clear or burst (hemolysis) to where you could see the writing.

Remember you worked with Parker and the tube that goes over more than 6 minutes the timer was ignored.

Plant cells unlike animal cells are surrounded by what?

Rigid cell wall composed of cellulose.

If the solute molecules are in equal suspension with the solvent, then it is a?

Saturated solution.

H2O, O2, and CO2 easily does what?

Small molecules like H2O, O2, and CO2 can easily diffuses across the membrane.

Very large molecules cannot pass through?

The cell membrane easily.

What happened to the central vacuole in the leaf in the 20% NaCl solution?

The central vacuoles shrunk and the plasma membrane shrunk into the middle due to the 20% NaCl solution.

Describe how the mass changed in the bags over time?

The dialysis tubing increased in mass overtime with temperature because the water diffuse into the dialysis tubing pores.

Make a prediction about the relationship between temperature and the rate of osmosis?

The extreme increase or decrease of temperature will effect the rate of osmosis, because the greater the temperature, the greater the energy.

Briefly describe the relationship between temperature and the rate of osmosis?

The higher the temperature, the greater the effects of osmosis taking place. The fluidity also increases with increase temperature.

What do you observe about this leaf?

The leaf became plasmolyzed because of the 20% NaCl solution.

Make a prediction about the relationship between solute concentration and the rate of osmosis?

The rate of osmosis will increase with the changes of tonicity. Note: When considering tonicity, think in terms of the solute concentration. Movement naturally moves from crowed areas to more space.

Hypertonic solution is when?

The solute concentration in the solution is greater than the solute concentration inside the cell.

Turgor pressure refers to?

The water pressure inside plant cells is called turgor pressure, and it is maintained by a process called osmosis. Technically speaking, osmosis is the movement of water across a differentially permeable membrane from a place where water concentration is higher to one where the concentration is lower. Hypotonic - when cells take in water, swells and burst. Dilute solutes outside.

When a hypotonic and a hypertonic solution are separated by a selectively permeable membrane, which direction will the water move?

The water will moves from the hypotonic solution to the hypertonic solution because water travels from higher concentration to lower.

Tonicity is often used to refer to what?

This term is often used when referring to the solute concentration inside the cell versus the outside of the cell.

When a solution can dissolve more solute, it is?.

Unsaturated.

Plasmolyzed refers to?

When cells become Hypertonic, the cell body shrinks and puts away from the cell wall, wilting.

Flaccid referes to?

When cells become isotonic. Occurs when the solute concentration is at an equal ratio.

What is a supersaturated solution?

When the amount of solute exceeds the saturated point, it will remain undissolved in the bottom of the container. In this situation, tonicity (osmosis pressure) refers to the concentration of the solute in the solution surrounding the cell. Note: When considering tonicity, think in terms of the solute concentration.

Lab section B: Examine osmotic behavior in animal cells: Most plant cells do best in a slightly hypotonic solution because when water enters the cell, it swells outward against the cell wall. The cell wall keeps the cell from bursting. The turgor the cell experiences aids the plant in standing upright. However, animal cells, not having a rigid cell wall, react differently from plants in hypotonic, isotonic, and hypertonic solutions. Cells that are placed in a hypotonic solution will?

Will burst (blood cells undergo hemolysis) and those placed in a hypertonic solutions will shrink, becoming crenated.

Did you prove or disprove your prediction? Discuss your answer?

Yes; The increase in temperature surrounding the dialysis tubing mimic the pressures a cell would be position into versus tonicity because the rate of diffusion also increases with the rate of extreme temperature differential

Which of the slides held cells in a hypotonic state? Describe the shape of these cells?

dH2O; The cells looked like a blob of pink.

Part 1 of Lab - Observing the effect of temperature on the rate of osmosis - procedures

• Soak 3 sections of dialysis tubing in distilled water until it is soft and pliable. The tubing acts as a selectively permeable membrane. • Fill 3 beakers with water. Make one into an ice bath, place one on a hot plate (do not bring to boil) and leave one setting on the table at room temperature. • Make 3 bags of 40% sucrose. o Tie one end of dialysis tubing securely with string. o Using a small beaker and/or funnel, pour the sucrose solution in the opening of the tubing. (Do not overfill-allow enough space for the bag to expand.) o Tie the other end of the tubing with a string forming a secure bag. o Rinse bag in distilled water to remove any sugar solution of the outside. • Measure the mass of the tubes full of sucrose using the electronic scale. Record the initial mass in Table 1. • Place one tube containing the sucrose in the hot beaker, one in the cold beaker, and one tube in the room temperature beaker. • Allow osmosis to take place for 5 minutes. • Remove the tubing, blot on a paper towel, and weigh the tube. Record the new mass in Table 1. • Repeat this procedure every 5 minute for 20 minutes, recording the mass each time in Table 1. *Data measured in grams.

Section B of Lab - Observing the Effect of Concentration on the Rate of Osmosis

• Soak 5 sections of dialysis tubing in distilled water until it is soft and pliable. The tubing acts as a selectively permeable membrane. • Tie off one end of each piece with the string provided. • Pour ~20mL of each of the following sucrose solutions into separate tubing bags. o 0% sucrose - bag 1 o 1% sucrose - bag 2 o 10% sucrose - bag 3 o 20% sucrose - bag 4 o 40% sucrose - bag 5 • Tie off the top end of the tubes and rinse bag in distilled water to remove any sugar solution of the outside. • Measure the mass of the sucrose tubes using the electronic scale and record the initial mass in Table 3. • Place the sucrose tubes in one of 5 beakers filled with 200 mL of room temperature distilled water. • Allow osmosis to take place for 5 minutes. • Remove the tubing, blot on a paper towel, and weigh the tube. Record in Table 3. • Repeat the previous steps at 5 minute intervals for 20 minutes, recording the mass each time in the table.