Cell Structure

Life, from the largest organisms to the most minuscule, is comprised of cells. Cells are the building blocks for life and provide the materials needed for life to exist.

While cells from all walks of life contain structures that are similar, such as DNA and protein, there are two different cell types based on how such structures are organized internally. Prokaryotic cells, those of bacteria and archaea, are simple in their organization. For example, while their genome is densely packed, it is not surrounded by a membrane. Eukaryotic cells, those making up animals, plants, and fungi are more complex. They compartmentalize their internal structures into organelles, membrane-bound structures that carry out specific functions. In contrast to prokaryotes, eukaryotic DNA is enclosed in a nuclear membrane. Other organelles include the endoplasmic reticulum, the mitochondrion, and the lysosome.

The first cells on earth appear in the fossil record from around 3.7 billion years ago and were thought to have been prokaryotic. Eukaryotic cells first appeared around 2.4 billion years ago when an amoeba like cell engulfed a bacterial cell and formed a stable coexistence. Over time, this cell within cell evolved to form structures such as the chloroplast and the mitochondrion.

Plants and animals also have diverse metabolic and structural needs, leading to further differences in their cells. Because plants need to make their own energy, plant cells contain chloroplasts that aid in photosynthesis. The plant cell also includes a large vacuole to store proteins, metabolites, and water. Lastly, plant cells also have a rigid cell wall, necessary for growth and water retention.

Since cells are so small, they can only be seen using microscopy. One of the simplest ways to view cells is through the bright field microscope. This microscope contains a light source, a condenser lens to focus the light, an ocular lens to view the specimen, and an objective lens for magnification. A microscope is not the only thing needed to visualize the invisible. The structures within the cells are transparent, so the cells must be stained with dyes. For example, safranin is used to stain cell nuclei red.

In this laboratory exercise, you will use a compound microscope to visualize cheek and plant cells.