Animal Cell

ZOO 11

Chrizta Margaret G. Asa Y-2L

2014-64386 August 22, 2017

Exercise 2a: Animal Cell

ABSTRACT

Background. In order to further study zoology, we must first understand the basic unit of life, the cell. This study deals with the basic components of the cell, with further understanding of the structure and function of the plasma membrane, the difference between diffusion and osmosis and the behavior of cell in different types of solution.

Methods. To look into the basic parts of the cell, human cheek cells were observed under the microscope. In explaining and understanding the structure and function of the plasma membrane, the interaction between oil and water, oil and egg albumin and the effect of heat in milk. To understand diffusion, a drop of ink was placed in a water nd observed through time. To explain osmosis, the displacement of egg albumin in a tube, with its end located at he round part of the egg while the water molecules move through the membrane of the egg. The last part of the experiment showed the cell in an isotonic, hypertonic and hypotonic solution.

Results. Found in these study is the images of the different set ups and the explanation of each set up.

Conclusion. I was able to observe and further understand the structure, properties and function of the cell, particularly the cell membrane. Despits the repitition of the other set ups, in the end I was able to complete and achieved the desired results.

INTRODUCTION

Zoology is the study of animals and its behavior, physiology, evolution and their interactions with each other and their environment. It is one of the vastest studies compared to other sciences since it deals with the colossal assortment of animals and the intricacy of processes happening inside them (Miller and Harley, 2001). If we look into the hierarchy of biological organization, the cell is the basic unit of life (Cain et al., 2014). Before we further study animals, we need to study first the cell. Cell is important in studying zoology like the atom is important in studying chemistry. According to Dr. Haifan Lin (2014), understanding how the cell works is the first part in uncovering biological mysteries.

The cell is has two type, prokaryotic and eukaryotic. Prokaryotic cells are found in bacterias and archaeans. The animals on the other hand are consists of eukaryotic cells. The main difference in the prokaryotic and eukaryotic is where the DNA is located. The DNA in eukaryotic cell is found in a membrane-bound organelle called nucleus, while the DNA of the prokaryotic cell is condensed in an area called the nucleoid which is not membrane-enclosed. Both the prokaryotic and eukaryotic cell is bound in a cell membrane called the plasma membrane (Cain et al., 2014). If we view a cell in a compound microscope, we can only see the nucleus (the dark stained part in the cell), the cytoplasm and the cell membrane (the outermost part of the cell).

In this study, I will focus on the outer membrane of a cell which is called the plasma membrane, particularly the plasma membrane of a eukaryotic cell since animals are composed of eukaryotic cells. It functions as a selective permeable barrier that act as an interface between the cytoplasm of the cell and the outer environment (Stubs and Suleyman, 2013). Scientists have used electron microscopy in order to know more about the plasma membrane. The plasma membrane is visible as two dark lines with approximately 3nm width, at each side of a light part. The width of the whole membrane is 8 to 10 nm. The image shows the phospholipid bilayer (Hickman et. Al., 2008).

Singer and Nicolson (1972) made the fluid-mosaic model to show the structure of the plasma membrane. The plasma membrane is a phospholipid bilayer. Phospholipid is a molecule with a polar and non-polar part. The tails of the phospholipid draw each other. These are the non-polar part of the phospholipid which are hydrophobic or water-dreading molecules. The phosphate portion of the phospholipid molecule are spherical in shape and are polar which are hydrophilic or water attracting. Another molecule present in the plasma membrane is cholesterol which are located on the inner part of the membrane. It makes the membrane less permeable to molecules that are soluble in water. It also helps in maintaining the relatively rigid structure of the membrane. Proteins are essential parts of the membrane. There are two kinds of membrane proteins: the peripheral proteins, which are located in the inner or outer membrane surface and the intrinsic proteins which are embedded in the membrane. There are different functions of the intrinsic proteins: some are links to sugar-protein markers on the surface of the cell while others serves as transportation for the ions and molecules across the membrane and others are attach at the membrane’s cytoskeleton, the cell’s inner scaffolding, or to other molecules outside the cell. There are two union of carbohydrates that are found in the plasma membrane: glycoproteins (carbohydrates joined with proteins) and the glycolipids (carbohydrates joined lipids), which are found in the surface of the plasma membrane. Carbohydrates, proteins and lipids found in the surface of the plasma membrane are components of the glycocalyx or the cell coat. The complicated arrangement and the distinct shape of the groups of sugar molecules of the glycocalyx serve as the molecular fingerprint for every cell type. This cell coat is important in cell-to-cell recognition and the behavior of cells (Miller and Harley, 2001).

The fluidity of the bilayer depends on the arrangement of the hydrocarbon interior. It can be ordered and rigid or disordered and fluid. The linear arrangement of saturated fatty acids makes the molecules of the bilayer closely packed thus it makes the bilayer rigid. While the kinks (where the cis double bond is located) in the hydrocarbon chain of an unsaturated fatty acids causes the plasma membrane to become more fluid. The cholesterol in the plasma membrane helps maintain the order and rigidity of the membrane. Temperature also affects the rigidity of the plasma membrane. With more heat, the rigid bilayers become less rigid and fluid bilayers become even more fluid. The more fluid a bilayer is it, the more possible a lateral motion of lipid molecules occur (Campbell and Farrell, 2009). In this experiment, I will observe the different properties of the plasma membrane through heating a small amount of milk in a beaker and observing the interaction between