2.1 Cell Theory

2.1.1 Outline the Cell Theory.

• Living organisms are composed of cells.

• Cells are the smallest unit of life.

• Cells come from pre-existing cells.

2.1.2 Discuss the evidence for the cell theory.

Microscopes:

• Microscopes have increased man's ability to visualise tiny objects

• All living things when viewed under a microscope have been found to be made of cells and cell products (e.g. hair)

• Note:  Certain types of cells do not conform to the standard notion of what constitutes a cell

  • Striated Muscles - long, multi-nucleated cells

  • Fungal Hyphae - some not partitioned and multi-nucleated

  

  • Sieve Element - no nuclei, few organelles, need surrounding

    cells to survive

  

  • Red Blood Cell - no nucleus/mitochondria, can’t replicate

  

Light vs Electron Microscopes

Experimental Evidence:

• Cells removed from tissues can survive independently for short periods of time

• Nothing smaller than a cell has been found to be able to live independently

• Experiments by Francesco Redi and Louis Pasteur have demonstrated that cells cannot grow in sealed and sterile conditions