#5. Plan diagrams of tissue and organ, prokaryotic and eukariotic cells

An organ usually contains many different types of cells. These are arranged in a particular pattern characteristic of the organ, with cells of a similar type found together, forming distinctive tissues.

A plan diagram shows the distribution of tissues in an organ, not individual cells.

A cross section of leaf, stem and root. 

Prokaryotes and Eukaryotes 

There are only 2 basic types of cells, primitive prokaryotes and the more complex eukaryotes.

• Prokaryotic cells (Pro=“before”, karyon = “nucleus”) are evolutionarily ancient. They were here first and for billions of years were the only form of life. Today most life is prokaryotic, and these cells are supremely successful. All bacteria and bacteria-like Archaea are prokaryotic organisms.

• Eukaryotes (Eu=“true”, karyon= “nucleus”) can be single celled or multi-cellular organisms. Eukaryotic cells are more complex, having evolved from a prokaryote-like predecessor. Most of the living things that we are typically familiar with are composed of eukaryotic cells: animals, plants, fungi and protists. 

Prokaryotic cells 

• much smaller  
• no membrane-bound nucleusor other membrane-bound organelles. The only membrane is the plasma membrane.
• the genetic material is naked within the cytoplasm
• ribosomes are the only type of organelle

Eukaryotic cells 

The main structure:

• a double membrane-bound nucleus separates the genetic material from the rest of the cell.
• an endomembrane system composed of different membrane-bound organelles that transport materials around the cell: the rough and smooth endoplasmic reticulum, Golgi apparatus and vesicles. 
• energy producing organelles: mitochondria and chloroplasts, involved in metabolism and energy conversion. 

Comparison of prokaryotic, animal and plant cells

Syllabus 2015 Characteristics of prokaryotic and eukaryotic cells (f) [PA] draw and label low power plan diagrams of tissues and organs (including a transverse section of stems, roots and leaves); (i) outline key structural features of typical prokaryotic cells (including: unicellular, 1-5μm diameter, peptidoglycan cell walls, lack of membrane-bound organelles, naked circular DNA, 70S ribosomes) and compare and contrast the structure of prokaryotic cells with eukaryotic cells (reference to mesosomes should not be included);

Syllabus 2016 - 2018 d) outline  key structural features of typical prokaryotic  cells as seen in a typical bacterium (including: unicellular, 1-5µm diameter, peptidoglycan cell walls, lack of organelles surrounded by double  membranes, naked  circular DNA, 70S ribosomes) e) compare and contrast the structure of typical prokaryotic  cells with typical eukaryotic cells (reference to mesosomes should not be included) f) outline  the key features of viruses as non-cellular structures (limited to protein  coat and DNA/RNA)