Cell Types & Structures: Skills (DP IB Biology: HL): 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) - these increase the surface area for absorption of substances 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 an epithelial cell of the small intestine