Case Study
Passage with linked questions
Case Set 1
Case AnalysisPassage
During a biology laboratory session, students were asked to prepare temporary mounts of onion peel and human cheek cells. Under the microscope, they observed that the onion peel cells had a distinct outer boundary beyond the cell membrane, while the cheek cells lacked this additional layer. Inside both types of cells, a dense structure was visible that contained the hereditary material. The teacher explained that the presence or absence of certain structures distinguishes plant cells from animal cells, and that these differences have functional significance. Students were then asked to recall what they had learned about cell theory and its historical development. They noted that the first observation of a live cell was made centuries ago, and that the role of cells as the basic unit of life was formally established through the work of several scientists over many decades.
Question 1: Name the distinct outer boundary observed in onion peel cells but absent in cheek cells. What is its primary function?
- The distinct outer boundary is the cell wall, a non-living rigid structure present in plant cells but absent in animal cells.
- The cell wall gives shape to the cell and provides strong structural support, protecting it from mechanical damage and infection.
- It also helps in cell-to-cell interaction and provides a barrier to undesirable macromolecules entering the cell.
Question 2: Name the dense structure visible inside both onion peel and cheek cells. What does it contain and what is its role?
- The dense membrane-bound structure visible in both cell types is the nucleus.
- The nucleus contains chromosomes, which in turn carry the genetic material DNA, making it the hereditary and regulatory centre of the cell.
- The nucleus controls all cellular activities through gene expression and plays a major role in heredity and cell division.
Question 3: With reference to cell theory, identify the scientist who first saw a live cell and the scientist who completed the cell theory. Explain the specific contribution that completed the theory.
- Antonie Von Leeuwenhoek first saw and described a live cell using a simple microscope, and Robert Brown later discovered the nucleus within cells.
- Schleiden and Schwann together formulated the original cell theory, but it did not explain how new cells arise — a critical gap in the theory.
- Rudolf Virchow (1855) completed the cell theory by demonstrating that all cells arise from pre-existing cells, expressed as Omnis cellula-e cellula, ruling out spontaneous generation of cells and establishing cellular continuity as a fundamental biological principle.