Lesson 3 Branches of biology: human biology and biology chemistry Warm up

LESSON 3
Branches of biology: human biology and biology chemistry


Warm up:

1. 
   What is a cell?
   
2. 
   Who discovered cells?
   
3. 
   Do plant cells differ from animal cells?
   

By the end of this text you should be able to:

● describe the main ideas of the cell theory
● compare the structures of animal and plant cells as seen with a light microscope.


Pre-reading
■ Read the given text and make your essential assignments:
Cells were discovered in 1665 by the English scientist and inventor Robert Hooke. Hooke designed his own compound light microscope to observe structures too small to be seen with the naked eye. Among the first structures he examined was a thin piece of cork (the outer surface of bark from a tree). Hooke described the cork as being made of hundreds of little boxes, giving it the appearance of a honeycomb. He called these little boxes cells. It soon became clear that virtually all living things are made of cells, and that these cells have certain features in common.
The cell theory
The concept that cells are the basic units of life became embodied in a theory called the cell theory, which embraces the following main ideas:

• 
  cells form the building blocks of living organisms
  

• 
  cells arise only by the division of existing cells
  
• 
  cells contain inherited information which controls their activities
  
• 
  the cell is the functioning unit of life; metabolism (the chemical reactions of life) takes place in cells
  
• 
  given suitable conditions, cells are capable of independent existence.
  

A typical animal cell
The structure of a typical animal cell:

• 
  the cell has a cell surface membrane which encloses the cell contents
  
• 
  the contents consist of a central ball-shaped nucleus surrounded by material called cytoplasm
  
• 
  the nucleus contains a fibrous material called chromatin
  
• 
  this condenses to form chromosomes during cell division
  
• 
  chromatin contains DNA, the material which controls the various activities inside the cell
  
• 
  scattered within the cytoplasm are mitochondria, small rod-like structures. They have been described as the “power-houses” of the cell because they supply
  
• 
  energy.
  
• 
  smaller dots within the cytoplasm are particles of stored food. Many consist of glycogen, which is a food storage polysaccharide.