Topic 1: Cell Theory
1.1 Introduction to Cells
Cell Theory
Understanding: According to the cell theory, living organisms are composed of cells
Principles of the Cell Theory:
- Cells are the smallest units of life
- All living organisms are composed of cells
- All cells comes from pre-existing cells
Application: Questioning the cell theory using examples of exceptions
Exceptions to the cell theory:
Striated Muscle Fibres: (Skeletal Muscle)
- Very Long (>300 mm)
- Contain hundreds of Nuclei
Challenges the idea that cells always function as autonomous units
Giant Algae: Ex. Acetabularia
- Some unicellulars can grow into large sizes
- Only contain 1 nucleus
Challenges the idea that larger organisms are always made of many microscopic cells
Aseptate Fungi:
- Hyphae not divided up into sub-units containing a single nucleus
- Long undivided sections of hypha which contain many nuclei
Challenges the idea that living structures are composed of discrete cells
Functions of Life
Understanding: Organisms consisting of only one cell carry out all functions of life in that cell
Unicellular = Smallest organisms capable of independent life
Characteristics of Life:
- Metabolism (undertake essential chemical reactions)
- Response (responsive to internal and external stimuli)
- Homeostasis (maintain a stable internal environment)
- Growth (move and change shape or size)
- Reproduction (produce offspring, either sexually or asexually)
- Excretion (exhibit the removal of waste products)
- Nutrition (exchange materials and gases with the environment)
Application: Investigate the functions of life in Paramecium and one named photosynthetic unicellular organism
Unicellular = One cell must carry out all the characteristics of life
Paramecium (heterotroph):