Animal Cell

...

oil and water and oil and egg albumin.

As previously said, the plasma membrane is selectively permeable meaning the membrane is permeable to water yet selectively permeable or impermeable to solutes. There are types of transportation of molecules in the plasma membrane: diffusion and osmosis. Diffusion refers to the movement of molecules from a higher concentrated area to a lower concentrated area thus making the concentration on both areas of diffusion equal (Hickman et al., 2008). In this exercise, I will observe how diffusion works in a drop of ink spreading in water. In osmosis, water molecules moves to the more dilute to the more concentrated solution (Hickman et al., 2008). I will observed how osmosis works through a set-up of an egg submerged in water with the bottom membrane exposed.

To explain more about the permeability of a cell, scientists have observed the behavior of a cell in a solution. Tonicity refers to the ability of a solution to cause a cell to release or absorb water. Solute concentration and membrane permeability are two factors that can affect tonicity of a solution. If a solution is isotonic to a cell, no net movement of water molecules across its plasma membrane will be observed. The same rate of water movement will be observed to and from the cell and its surrounding solution. If a solution is hypertonic to a cell, the cell will release water and shrink. If a solution is hypotonic to a cell, the rate of the water entering the cell will be faster than the rate of the water leaving the cell which will caused the cell to swell and eventually burst (Cain et al., 2014). The red blood cell has the same solute concentration as 0.9% NaCl. I will observe this three types of tonicity in a red blood cell in a blood placed in distilled water, 0.9% NaCl and 10% NaCl.

This study aims to identify the different parts of the animal cell, to investigate the different processes by which the cell membrane transports molecules in and out of the cell, to differentiate diffusion and osmosis and to observe the behavior of a cell in a solution with different tonicity.

MATERIALS AND METHODS

Part 1: Structure of Animal Cells

Section 1: Human cheek cells

Section 2: Structure of the plasma membrane

Part 2: Diffusion and Osmosis

Section 1: Diffusion

Section 2: Osmosis

Section 3: Hemolysis and crenation of human red blood cells

RESULT

DISCUSSION

Human cheek cells are the easiest cell to study and was often used in school laboratory experiments. The cheek cells contain the basic parts of the cell and can easily be obtained by the simple scraping of the inner part of the cheek (Davidson, 2003). In Fig 1, the image shows the cheek cell viewed under HPO. It shows the basic parts of the cell: the dark spots in the middle of the cells is the nucleus, the outer lining of the cells is the plasma membrane, and the tainted part between the nucleus and the plasma membrane, the cytoplasm where the organelles are found.

Because of the difference in polarities of oil and water, it is impossible for them to mix completely even after vigorous shaking. In Fig 3, the image shows the thin lining between the oil and water parts of the oil and water mixture. This set-up shows how the cell membrane cannot easily allow entry of water and other water-soluble molecules into the cell because of its lipid components. Fig 4 shows the next set-up which is the heated milk. The formation of the membrane-like structure on top of the surface after heating of the milk and the absence of this part when heating is similar to the plasma membrane when affected by temperature. Just like the plasma membrane, the milk is composed of lipids (phospholipids and cholesterol) and proteins (Stubbs and Suleyman, 2013). With higher temperature, a rigid membrane will become less rigid (Campbell and Farrell, 2009). Fig 5 shows the next set-up which is the oil and egg albumin in a petri dish. Although the egg albumin was pricked with a toothpick, the membrane returned to its original form. This is similar to the ability of the animal cell membrane to repair itself when destroyed.

The next part of the experiment is the observation of the difference between diffusion and osmosis. I have observed in the experiment that the drop of ink placed in the water continuously spread out as time passes by. Fig 6 shows how the ink spread out equally in the petri dish. This set-up shows how diffusion works which is the movement of molecules from an area of higher (Hickman et al., 2008). On the next figure, Fig 7 shows the upward movement of the egg albumin. This was caused by the movement of the water toward the egg through the membrane of the round end of the egg. This shows the osmosis, or the movement of water molecules down a concentration gradient through a semipermeable membrane (Hickman et al., 2008). The egg is the area of higher concentration and the water outside the egg is the area with lower concentration, or in this case it is composed of pure water solvent.

Red blood cells have the same solute concentration with 0.9% NaCl solution and increasing and decreasing the concentration will caused the blood to either burst or shrink (McGill, 2005). Fig 8 shows the blood cells submerged in distilled water, a hypotonic solution, which causes water to enter the cell and making it swell and eventually burst. Fig 9 shows blood cells in 0.9% NaCl solution, which is isotonic. The next image, Fig 10, shows the blood cells submerged in 10% NaCl solution, a hypertonic media which causes the cells to release water making it shrink. 

CONCLUSION

Human cheek cells were observed under the microscope and the three basic components which are the nucleus, cytoplasm and the plasma membrane was clearly seen.

I was able to observe the different properties of the plasma membrane through the three different set ups. In the first set-up, the I was able to observe the impossibility of the mixing of oil and water, like the polar and

...