Cell Types & Structures: Skills (DP IB Biology) : Revision Note

Cell Types & Structures: Skills

• 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