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Life Sciences
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Lab Report
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English (U.S.)
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Topic:

Osmosis (Lab Report Sample)

Instructions:

This is a lab report on Osmosis. The report aimed at observing the change of osmosis rate in three materials; onions, potatoes, and an egg.

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Content:

Osmosis
Presented by
Instructions
Introduction
The fact that atoms and molecules contain kinetic energy and are always in motion introduces many aspects experienced in the life of a cell. The kinetic energy contained in cells makes molecules bang into one other and moves in different new directions. This process is referred to as the diffusion. In order to understand the concept of osmosis, it is essential to understand diffusion. Diffusion is the movement of particles from an area of higher particle concentration to an area of lower particle concentration. The movement occurs randomly. Osmosis forms a special case of diffusion where water moves through selected permeable membranes. A permeable membrane is the one allowing diffusion of water and specific solutes. According to Borg (2003), in osmosis particles move from regions of higher water potential to regions of lower water potential. Osmosis is a significant mechanical process that allows exchange of water and specific solutes through body cells. The process accounts for the movement of fluids from major animal and plant cells.
Mechanism of osmosis
When two solutions bear the same concentration of solutes, they are referred to as isotonic solutions. When a selectively permeable membrane separates two solutes, water moves between the solutions with no significant change in the amount of water in either solution. If the concentration of solutes in each solution differs, the solution with more concentration (hypertonic) draws water from the solution with the lower concentration (hypotonic). The process occurs because the hypertonic solution has more solute and thus less water concentration. Due to the differences in the standard osmotic pressure between the two solutions, the net movement of water occurs from the hypotonic solution to the hypertonic solution. His process constitutes mechanism of osmosis. Figure 1 shows the following mechanism with the use of a sugar solution (Borg, 2003).
Figure 1: The mechanism of osmosis using sugar molecules
A potato cell placed inside a solution with pure water and another solution of salt water lead to loss of mass. The potato in pure water gains more mass than the potato in salt water because of the difference in osmotic pressure between the two solutions. A chicken egg is another substance used to demonstrate the mechanism of osmosis. With the use of vinegar or sugar syrup, the egg gains or losses mass depending on the type of solution. The egg is used to test Endosmosis and Exosmosis. Exosmosis refers to the passage fluid through a selective semipermeable membrane into a solution of lower concentration. On the other hand, endosmosis refers to the inward movement of a fluid through a selective semipermeable membrane into cells with a greater concentration. The most common fluid used in most experiments is water. Figure 2 below illustrates Endosmosis and Exosmosis.
Figure 2: Endosmosis and Exosmosis processes
Name of the experiment
To study osmosis using onion cells, potato, and egg.
Aim of the experiment
The following experiment aimed at observing the change of osmosis rate in three materials; onions, potatoes, and an egg.
Objectives
1 To learn the effects of osmosis on plant and animal cells
2 To observe changes in the onion cell
3 To study Endosmosis and Exosmosis using a chicken egg
4 To determine changes that a potato undergoes after adding high and low concentrated solute.
Materials used
The experiment involved three parts. The first part made use of a boiled and raw potato; the second stage used an onion, while the last stage used an egg.
Part A: Test using a potato
Materials
* Potato (boiled and un-boiled)
* Potato peeler
* Salt
* Two Petri dishes
* Water
* Two flags
Procedure
* The potatoes was first cut into half, a 1 centimeter strip was removed from the base of each potato.
* A hollow was made on the boarder side of each potato half using a peeler. See figure 3.
Figure 3: Half potato with hollow
* Equal amounts of water were poured into each Petri dish, one with salt and the other without salt.
* Each base of the peeled potato half was dipped into the Petri dish
* Salt was then added in the hollow of the half dipped in water only, and water added in the hollow of the other half dipped in salty water.
* The experiment was left for one hour after which the results were recorded.
Part B: Study of Endosmosis and Exosmosis
Materials
* Plastic cup or a bottle
* White vinegar
* Sugar syrup
* Water
Procedure
* Firstly, an egg was soaked in a bottle of vinegar and water in order to make the shell soft for easier removal. The egg was soaked for a period of two days
* The egg was rapped with a paper until the shell fell off and became almost transparent. The egg also became bigger in size because it was submerged in water for the whole period.
* After the shell was removed, the egg was soaked in syrup of water and sugar in order to restore its original size.
* The egg was then removed in syrup and placed in water, and changes observed.
* The observed changes were recorded on the observation sheet
Part C: Study of osmosis in onion cells
Material
* Microscope
* Slide and cover slip
* 15-% Sodium Chloride (NaCl) water
* Coloring (Stain)
* Onion
* A knife
Procedure
* A fresh onion was used because it was easier to peel a single layer of cells. The section of the tissue from the epidermis (skin) of the onion on the purple side was removed. An epidermis is thin and almost transparent.
* The strip was placed on a slide and covered with a drop or two of distilled water. The cover strip was then added.
* Another strip was taken and this time, 2 to 3 drops of 15-% NaCl solution was added under the cover slip.
* A stain was then added in each strip in order to see the onion cells under a microscope
* The onion cell was observed with the help of a microscope on a 10X and 40 X resolutions.
* An examination was made through a microscope and a comparison made between cells to those mounted with distilled water.
Precautions
1 A lab coat during the experiment for protection
2 Care was taken while using sharp objects such as a knife to avoid injuries
3 Any accessory was removed from the lap
4 Gloves were used to protect hands from any harm from acids
Overview
From the first experiment using boiled and un-boiled potatoes to test osmosis, major differences between the two potatoes were observed. In the first two minutes, no observable difference was noticed in the two sets of hollow potatoes. After the second minute, the salt filled hollow half was seen to start gaining some water and eventually within ten minutes, the amount of water in a Petri dish had reduced. On the other hand, the potato filled with pure water started losing water into a Petri dish and after about ten minutes, the hollow was left without water. The hollow potato half filled with salt was observed to contain more water that the hollow half filled with water. No significant change was observed in the boiled potato. The second experiment to test endosmosis and exosmosis also recorded some differences as seen in figure 4.
Figure 4: Egg osmosis results
The final experiment made use of the onion cell. Several changes in the onion cells were observed using the microscope. In the beginning, the cell was whitish in color because it contained glucose and starch. In the final stage, the cell that contained NaCl solution changed color to black because of the movement of NaCl molecules into the onion cells. The cells tested with distilled water showed no color change an indication that there was no movement of molecules from or into the onion cell. In addition, some movements of solvent molecules were observed in the microscope as the solution diffused through the onion membrane until a balance between the molecules and solution molecules was...
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