All organisms contain one or more cells which are capable of carrying on the life activities needed by the organism. This idea is often referred to as the cell theory. The cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction.
Nature of Science:
1.1.NOS1: Looking for trends and discrepancies- although most organisms conform to cell theory, there are exceptions.
Objectives:
1.1.NOS1: Looking for trends and discrepancies- although most organisms conform to cell theory, there are exceptions.
Objectives:
- Define “trend” and “discrepancy.”
- Explain why “trends and discrepancies” are useful in scientific study.
- List features that would be considered a “trend” related to the cell theory.
- Discuss “discrepancies” to trends related to the cell theory.
Application:
1.1.A1: Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
Objectives:
1.1.A1: Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.
Objectives:
- Describe features of striated muscle fibers that make them an atypical example cell.
- Describe features of aseptate fungal hyphae that make them an atypical example cell.
- Describe features of giant algae that make them an atypical example cell.
Caveats to the Cell Theory
Certain types of cells/tissues do not conform to a standard notion of what constitutes a cell:
Certain types of cells/tissues do not conform to a standard notion of what constitutes a cell:
Striated muscle fibres:
- Muscle cells fuse to form fibres that may be very long (>300mm)
- Consequently, they have multiple nuclei despite being surrounded by a single, continuous plasma membrane
- Challenges the idea that cells always function as autonomous units
Aseptate fungal hyphae:
- Fungi may have filamentous structures called hyphae, which are separated into cells by internal walls called septa
- Some fungi are not partitioned by septa and hence have a continuous cytoplasm along the length of the hyphae
- Challenges the idea that living structures are composed of discrete cells
Giant Algae
- Certain species of unicellular algae may grow to very large sizes (e.g. Acetabularia may exceed 7 cm in length)
- Challenges the idea that larger organisms are always made of many microscopic cells