Seminar B5 The cell: Organelles

What is a Cell?
A cell is the basic unit of life
All organisms are made of cells
In the hierarchy of biological organization, the cell is the simplest collection of matter that can be alive
Many forms of life exist as single-celled organisms
More complex organisms, including plants and animals, are multicellular
Multicellular organisms are cooperatives of many kinds of specialized cells that could not survive for long on their own. However, the cell remains the organism’s basic unit of structure and function

What do we call the study of cells?
Cytology
But… How can we study
cells?
The most obvious way is by
observing them
How can we observe cells?

Microscopy!!!
What types of microscopy do you know?

Microscopy Terms
Magnification is the increase in an object’s image size compared with its actual size.
Resolution is a measure of the clarity of an image. It is the ability of an instrument to show two nearby objects as separate.

The Discovery
The progress in cell discovery is associated with the evolution of microscopy.
Larger cells were spotted first while smaller organisms had to wait for the technology to be developed.

Major events in cell biology & imaging

Frog egg
Paramecium
Human egg
Most plant and
animal cells
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosome
Proteins
Lipids
Small
molecules
Atoms
Light microscope
Electron microscope
1 mm
100 nm
10 nm
1 nm
0.1 nm
100 μm
10 μm
1 μm

Microscopes reveal the world of the cell
In a light microscope (LM), visible light passes through a specimen, then through glass lenses, and finally is projected into the viewer’s eye.
The first microscopes were light microscopes.

What can we see with an LM?
Plant cell (non-leaf)
Red blood cells
Plant cell (leaf)

Electron microscopes
Beginning in the 1930s, scientists started using a very powerful microscope called the electron microscope (EM) to view the ultrastructure of cells.
Instead of light, EM uses a beam of electrons.
Electron microscopes can
resolve biological structures as small as 0.2 nm
magnify up to 1,000,000 times.

What do they look like?
Scanning Electron Microscope
Transmission Electron Microscope

Electron Microscopy
Electron microscopes use a beam of electrons to view very small objects. The beam acts in different ways:
It will either scan the surface or pass through the samples.

Scanning Electron Microscope
Transmission Electron Microscope
SEMs vs TEMs

SEMs vs TEMs
Scanning electron microscopes (SEMs) show the detailed architecture of cell surfaces.
Transmission electron microscopes (TEMs) show the details of internal cell structure.
Scanning electron micrograph of Paramecium
Transmission electron micrograph of Toxoplasma

Your Task
You are going to be given a set of cards with pictures of 8 organelles.
There are 6-8 pictures for each organelle.
For each organelle:
Collect the micrographs showing that organelle
Identify the drawing that shows the organelle
Choose the correct description
Hint: you can spy on other groups to confirm your ideas.

Let’s check your conclusions!!

Nucleus

RER

SER

Golgi Body

Mitochondria

Chloroplast

Lysosomes

Centrioles/Flagella

Would you be able to tell which photomicrographs are from…
Light microscope?

Which photomicrographs are SEM?