Cell Types & Structures: Skills (HL IB Biology)

• It is important to be able to recognise various organelles from light and electron microscope images
• When interpreting micrographs to identify and deduce the function of the cell it is important to:
  1. Identify whether it is a prokaryotic or eukaryotic cell - look to see if a nucleus is present or not
  2. Identify which type of eukaryotic cell it is (plant or animal) by looking for a cell wall or vacuole
  3. Identify the organelles present in the cells and consider their function

• You should be confident in identifying the following structures and organelles:
  • Nucleoid region in a prokaryotic cell
  • Prokaryotic cell wall
  • Nucleus
  • Mitochondria 
  • Chloroplast
  • Sap vacuole
  • Golgi apparatus
  • Rough and smooth endoplasmic reticulum
  • Chromosomes
  • Ribosomes
  • Plant cell wall
  • Plasma membrane
  • Microvilli 

• Some identifiable features of key organelles are:
  
  • Chloroplast
    • Has distinctive stacks of thylakoids
    • Double membrane
    • Has a roughly oval shape
    • Larger than mitochondria
    • Indicates the cell is a plant cell
  • Nucleus
    • Has a nuclear membrane and a dark nucleolus within
    • It has a roughly spherical shape
  • Vacuole
    • Occupies a large space within a cell
    • Often shows up as a very light shade (white) within an electron micrograph
    • Indicates the cell is a plant cell
  • Cell wall
    • Located around the perimeter of the cell
  • Mitochondria
    • Roughly oval-shaped
    • Double membrane
    • Sometimes observed with visible cristae (foldings of the inner membrane)

An interpretation of an electron micrograph of a cell

Electron micrograph of cell 1

• To identify this cell consider the following
  • The cell has a nucleus - therefore it is a eukaryotic cell
  • This cell does not have a cell wall or central vacuole - therefore it is an animal cell
  • The cell has a large u-shape nucleus - so it can manipulate itself through small pores
  • There are a large number of lysosomes in the cell - so it can digest substances found within the cell
  • There are a large number of mitochondria - this means it has sufficient energy for its many metabolic reactions
  • The deduction, therefore, is that this cell needs a lot of energy to break down substances that enter the cell and that it can move where it wants. This cell is a macrophage

An interpretation of an electron micrograph of a cell

Electron micrograph of cell 2

• To identify this cell consider the following
  • The cell has a nucleus - therefore it is a eukaryotic cell
  • This cell does not have a cell wall or central vacuole - therefore it is an animal cell
  • There are a large number of mitochondria - so it requires significant energy for many metabolic reactions
  • The cell has microvilli packed closely together (brush border) - so it needs to increase the surface area and prevent any substance from crossing into the cell
  • The deduction, therefore, is that this cell needs a lot of energy to control what enters or exits this cell and that the cell requires many of the substance to be absorbed. This cell is a ciliated epithelium of the small intestine