Cell Theory (HL IB Biology)

• Cells are the basic structural unit of all living organisms
• Until microscopes became powerful enough to view individual cells, no-one knew for certain what living organisms were made from
• A scientist called Robert Hooke came up with the term "cells" in the 1660's after examining the structure of cork
• Matthias Schleiden and Theodor Schwann were two scientists who studied animal and plant cells
  • In 1837, they came up with the idea that all living organisms are made of cells
  • This idea is known as ‘cell theory’
  • The cell theory is a unifying concept in biology (meaning it is universally accepted)
• The cell theory includes three main ideas:
• 1. All living organisms are made up of one or more cells
  2. Cells are the basic functional unit (i.e. the basic unit of structure and organisation) in living organisms
  3. New cells are produced from pre-existing cells
• Although cells vary in size and shape they all
  • Are surrounded by a membrane
  • Contain genetic material
  • Have chemical reactions occurring within the cell that are catalysed by enzymes

NOS: Deductive reasoning can be used to generate predictions from theories. Based on cell theory, a newly discovered organism can be predicted to consist of one or more cells.

• Deductive reasoning is an approach where one progresses from general ideas to hypothesis testing to specific conclusions
  
  • This is in contrast with inductive reasoning where one starts with specific observations and then develops theories
• Cytology, the branch of biology which focuses on cell theory, can be used to demonstrate deductive reasoning
  
  • Cell theory states that all living organisms are made of at least one cell
  • We can hypothesise that any newly discovered living organisms on Earth will also be made up of at least one cell
  • We can observe living organisms to test this hypothesis

Deductive reasoning flow diagram

Deductive reasoning can be used to develop specific hypothesis from existing theories