Question

You are examining a cell from a crime scene using an electron microscope. It contains ribosomes, DNA, a plasma membrane, a cell wall, and mitochondria. What type of cell is it? a. lung cell b. plant cell c. prokaryotic cell d. cell from the surface of a human fingernail e. sperm cell

Short answer

The cell is a plant cell because it has ribosomes, DNA, a plasma membrane, a cell wall, and mitochondria.

Step-by-step solution

Identify Key Cell Structures

List the key structures found in the cell under examination: ribosomes, DNA, a plasma membrane, a cell wall, and mitochondria. Each of these components provide clues to the type of cell.

Distinguish Between Prokaryotic and Eukaryotic Cells

Note that the presence of mitochondria and a defined nucleus indicated by the presence of DNA imply that the cell is a eukaryotic cell, not a prokaryotic cell. Prokaryotic cells do not have a nucleus or mitochondria.

Eliminate Incorrect Eukaryotic Cell Types

Eliminate each option that does not fit with the structures identified. Lung cells (a), cells from the surface of a human fingernail (d), and sperm cells (e) are animal cells that do not have a cell wall. Therefore, these options are incorrect.

Identify the Correct Cell Type

Since the cell in question has a cell wall, mitochondria, and a plasma membrane, in addition to the ribosomes and DNA, it matches the description of a plant cell. Therefore, the correct answer is a plant cell.

Key concepts

Eukaryotic Cells

Understanding eukaryotic cells is fundamental to identifying various cell types. Eukaryotic cells are complex and characterized by the presence of a nucleus and other membrane-bound organelles. Unlike their prokaryotic counterparts, they have distinct compartments which allow for specific functions and more sophisticated control over cellular processes. Key organelles include the nucleus, which houses genetic material; mitochondria, often referred to as the 'powerhouses' of the cell due to their role in energy production; the endoplasmic reticulum and Golgi apparatus, which help in protein and lipid synthesis; and lysosomes, which are involved in waste breakdown.
In the context of the crime scene cell analysis, the presence of both DNA, which is contained in a nucleus, and mitochondria, indicates that we are indeed examining a eukaryotic cell.

Prokaryotic Cells

Prokaryotic cells are simpler and smaller than eukaryotic cells and are found in organisms such as bacteria and archaea. These cells lack a true nucleus; their genetic material is free-floating within the cell in an area called the nucleoid. Furthermore, prokaryotic cells do not contain membrane-bound organelles, such as mitochondria or a complex endomembrane system. They do, however, possess a cell wall, plasma membrane, and ribosomes for protein synthesis. When examining cell structures under a microscope, the absence of a nucleus and mitochondria would be indicative of a prokaryotic cell. As determined from the electron microscope imagery in our exercise, the presence of mitochondria rules out the possibility that the cell from the crime scene is prokaryotic.

Cell Structures

Cells are comprised of several structures, each fulfilling distinct functions. Ribosomes are responsible for protein synthesis and can be found in all cell types. The plasma membrane is a lipid bilayer that encases the cell, regulating the movement of substances in and out. In eukaryotes, the DNA is enclosed within the nucleus, whereas in prokaryotes, it is located in the nucleoid. Some cells also have a rigid cell wall, which provides additional support and protection. This feature is common in plant cells and certain prokaryotic cells but is not found in animal cells. The mitochondria are crucial for ATP production and are a hallmark of eukaryotic cells. By identifying and understanding these cell structures, we can determine the type of cell we are observing. In our exercise, the listed structures—ribosomes, DNA, a plasma membrane, a cell wall, and mitochondria—narrow down the possible types of cells significantly.

Plant Cell Characteristics

Plant cells exhibit unique features that distinguish them from other eukaryotic cells, such as those of animals. One of the most noticeable differences is the presence of a rigid cell wall composed of cellulose, which provides structure and protection for the plant cell. Additionally, plant cells contain chloroplasts for photosynthesis, although these structures were not mentioned in the problem we're analyzing. They also have a central vacuole, a large fluid-filled organelle that maintains cell pressure and stores nutrients. The crime scene cell's distinct combination of a cell wall and mitochondria hints at a plant cell, as animal cells do not have cell walls, and prokaryotic cells lack mitochondria. This aligns with our solution by indicating that option b, a plant cell, is indeed the correct identity of the cell in question.