Microscopy & Cells

March 19, 2023

A microscope is an optical instrument that uses lenses to magnify small objects, making them visible to the human eye. This allows scientists to observe cells and their internal structures, which are too small to be seen without magnification. Microscopes are crucial for studying biology, chemistry, and other fields where observing small details is essential.

Here's a more detailed explanation:

Key Concepts:

  • Magnification: The process of making an object appear larger than it is.

  • Resolution: The ability to distinguish between two separate points or details.

  • Light Microscopes: Use light and lenses to magnify specimens, allowing you to view cells and large subcellular structures.

  • Electron Microscopes: Use a beam of electrons instead of light, providing much higher magnification and resolution than light microscopes.

How Microscopes Work:

  1. Light or Electrons: Light microscopes use visible light, while electron microscopes use a beam of electrons.

  2. Lenses: Microscopes use lenses to bend and focus the light or electron beam.

  3. Magnification: The lenses magnify the image of the specimen, making it appear larger.

  4. Viewing: The magnified image is then projected for observation (e.g., through an eyepiece in light microscopes or on a screen in electron microscopes).

Types of Microscopes:

  • Light Microscopes:

    Used for studying living cells and have lower magnification and resolution, typically used for viewing cells and large organelles.

  • Electron Microscopes:

    Provide higher magnification and resolution but cannot be used to view living cells.

Importance in Biology:

Microscopes have revolutionized the field of biology, allowing scientists to: View cells and their internal structures, Study cellular processes, Identify and classify different types of cells, and Investigate diseases and develop treatments.

What is Magnification?

In biology, Magnification refers to how many times larger an image appears compared to the actual size of the object, typically when viewed through a microscope. It's essentially the process of enlarging the apparent size of something.

How is Magnification calculated?

 

Animal Cells

  • Eukaryotic cells have subcellular structures, each carrying out a particular function
  • Organelles are subcellular ‘compartments’ where specific processes take place within the cell
  • The main subcellular structures in animal cells are:
    • The nucleus
    • Cell membranes
    • Mitochondria
    • Ribosomes
    • Cytoplasm

structures-in-an-animal-cell-visible-under-a-light-microscope-and-an-electron-microscope-igcse-and-gcse-biology-revision-notes

 

Some cellular structures can only be seen when viewed with an electron microscope

                       Cell structures & Functions

 

Plant Cells

  • In addition to the subcellular parts found in animal cells, plant cells have:
    • A cell wall made of cellulose (algal cells also have this structural feature)
    • A permanent vacuole filled with cell sap
  • Plant cells found in the leaf and stem may also contain chloroplasts

 

 

The plant cell shown above contains chloroplasts, so it would be found in the leaves of a plant

     Plant cell structure & functions

Plant cell structure & function table, IGCSE & GCSE Biology revision notes

 

Eukaryotic cells

  • Plant and animal cells are both eukaryotic cells
  • They have the components listed in the table above (so a cell membrane, cytoplasm and ribosomes), as well as others
  • A defining feature of eukaryotic cells is that their genetic material (DNA) is enclosed within a nucleus
  • Eukaryotic cells vary in size, usually between 10 and 100 µm

typical-animal-and-plant-cells-igcse-and-gcse-biology-revision-notes

Animal and plant cells are both eukaryotic cells as their genetic material is packaged in a nucleus

 

Prokaryotic cells

  • Bacterial cells are a type of prokaryotic cell
  • A defining feature of prokaryotic cells is that their genetic material is not enclosed within a nucleus, it is found as a single loop of DNA within the cytoplasm
  • Additional smaller, circular pieces of DNA called plasmids may also be present
  • The cell membranes of all prokaryotic cells are surrounded by a cell wall (usually made from a substance called peptidoglycan)
  • Prokaryotic cells are much smaller in comparison to eukaryotic cells, with many measuring ~ 1 µm in size

a-typical-prokaryotic-cell-igcse-and-gcse-biology-revision-notes

 

 

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