Microscopes Cells &. What is a Microscope? Most microscopes consist of either a single lens (simple microscope) or multiple lenses (compound microscope)

Microscopes

Cells

&

What is a Microscope?

•Most microscopes consist of either a single lens (simple microscope) or multiple lenses (compound microscope) that allows us to magnify something to a size greater than we could see with the naked eye.

•Not all microscopes have lenses, the electron microscope uses a beam of electrons to create a detailed image of a specimen.

A Little Microscope History•It is difficult to trace the origins of the first lenses, but rock crystals found in northern Iraq in the 8th century B.C. may have been used as lenses.

•The word ‘microscope’ was first coined by members of the first “Academia dei Lincei” - which was a scientific society that included Galileo.

•The seventeenth century was a period of great interest in the microscope. But back then the microscope was not only engaged as a scientific tool, but also as a recreational toy used by upper-class citizens to look at things close up, such as the legs and wings of insects. Many of these citizens thought this was very interesting, but most could not imagine that a tool like this could make too many new scientific discoveries.

Early Microscopes•The first microscope was reported in use in 1590. It was invented by two Dutchmen named Hans and Janssen and had two ground lenses - this made it a compound microscope.

•In 1660 Marcello Malpighi used the microscope to see capillaries.

•The drawing below shows an early microscope used by Robert Hooke. The eye views from point A. The 3 lens system remains the standard configuration in microscopes today, except that each lens may be made out of a combination of close lenses.

Early Microscopes

• Robert Hooke was an English microscopist who made this microscope in 1665.

• The magnifying power was from about 10x to 40x.

• Can you pick the light source, condenser and eyepiece?

Early Microscopes

•In 1665 Hooke published his book of drawings - ‘Micrographia’ - where he showed micrographs of cork with small pockets of air.

•This reminded him of cells in a monastery and so the name “cell” was first used. Hooke didn’t understand though that these hollow spaces of air were once living.

Early Microscopes•By the 1670s Antoni van Leeuwenhoek started making drawings of bacteria and spermatozoa which he called “animalicules”. He also made detailed descriptions of the red blood cell.

•He used a microscope that he made himself at home (his actual profession was draper) that could magnify up to 200X compared to only 50X of the previously built microscopes. His trick was to use one very good quality lens that didn’t give a blurred image.

The lens of this simple microscope sat between two metal plates

•In 1827 Robert Brown was studying pollen down the microscope and noticed that it moved around in the water.

•He then looked at dust and found it did the same thing so he concluded that particles did not have to be alive to move.

•He could not explain this observation as Einstein had not yet published his work on kinetic energy - which would have provided the theory to do so.

•Browne called this phenomenon Brownian motion.

Brownian motion

Magnification & Resolution

•Magnification: the number of times larger an image is than the actual specimen. By adding stronger lenses a microscope can magnify an image many thousands of time, but resolution may be limited.

•Resolution: the degree of detail which can be achieved. An electron microscope has greater resolution than a light microscope.

All of these dots have the same magnification, but a different resolution

Early Microscopes

•In the USA, the first compound microscope appeared at Harvard College in 1732 - although simple microscopes would have been used before this.

•By 1831 there were about a dozen microscopes in the US. Instructors were using them by 1850 and some students by 1875.

•They were in general use in 1890.

Early Microscopes

Bonannus 1691

Light source Condenser

Specimen

Focus adjustment

Eye piece

The Light Microscope & Cells

•The most common microscope in use today is the light microscope.

•This is similar to the one we use in our laboratory at school.

•With the advent of the light microscope, scientists were able to study cells with the kind of detail never known before.

The Light Microscope

Eye piece

Arm

Rotating nose pieceHigh power

objective lens

StageDiaphrag

m

Low power objective lens

Condenser

Condenser knob

Stage adjustment

Stage clip

Mirror

Base

Coarse focus knob

Fine focus knob

Body tube

Cells - what can we see with the Light Microscope?

•Before we discuss cells in any detail, first we must consider a cell and the cell theory

•The cell theory states that:

•All living things are made up of one or more cells or of products of cells

•The cell is the simplest unit of life

•All cells are produced from existing cell


•Here are 3 light micrographs of onion skin (epidermis) at different magnifications

•You can just about make out the nucleus in the middle of the cell

•There is a rigid cell wall, which helps to identify it as a plant

•You could also label the cytoplasm

Nucleus

Rigid cell wall

Cytoplasm


Light micrograph of blood showing red blood cells (stained pink) and white blood cells (purple stained nucleus)

Light micrograph of plant cells with large vacuoles around the central nucleus


Human egg cell injected with a fine needle. The cell is held in place with the delicate suction from the pipette on the left.

Light micrograph of bacteria (bacillus) shown with a purple stain. Only the outline of the cells can be seen

The Phase Contrast Microscope

•The Phase contrast microscope looks like a light microscope but works on the principle of creating a type of shadow of the specimen.

•This sort of microscope has limited use for looking at specimens in great detail, but can be used in tissue culture where the general growth of cells is monitored.

•The beauty is that slides do not need to be prepared and specimens can be viewed actually in the dished they are growing in.

Cells - what can we see with the Phase Contrast Microscope?

This is an oocyte taken under a phase contrast microscope, again the detail is not as good as with an ordinary light microscope

Here we can see the bacteria similar to the bacteria under the light micrograph but with less detail

The Electron Microscope

•In the 1930s the electron microscope was developed. Instead of using light, it applied a beam of electrons to view the specimens at around 100,000x magnification.

•There are two kinds of electron microscopes in use today, the Scanning Electron Microscope (SEM) which gives an image of the surface of a specimen, and the Transmission Electron Microscope (TEM) which sends electrons through the specimen.

The Electron Microscope

Cells - what can we see with the Electron Microscope?

This EM micrograph shows the 3D state of these red blood cells (concave shape) and the single white blood cell. The photo has been colour enhanced as EM micrographs can be seen only in black and white.

These Electron micrographs show the surface of the female egg cell (oocyte). Compare the detail in these to the light and contrast photomicrographs!


All Cells

Prokaryotes:No true nucleus such

as in bacteria

Eukaryotes:True nucleus

Plant Cells:Cell wall

Chloroplasts

Large centralvacuole

Animal Cells:No cell wall

No Chloroplast

Small vaculoes

Electron Microscopes allowed Scientists to identify new and different structures within cells. This enabled them to classify cells into three basic types.


Prokaryotic cell - Bacteria

•Much greater detail is evident on the surface of this bacteria.

•Two cell membranes can be seen.


Prokaryotic cell - Bacteria


Eukaryotic cell - Animal cell

•As with the bacteria, the electron microscope can pick up much greater detail.

•Here we can even see some of the organelles inside the cell.

•Let’s have a closer look...



Nucleus

Nucleolus

Mitochondria

Cell membran

e

Cytoplasm

Golgi bodyGolgi vesicles

Smooth endoplasmic

reticulum -SER

Rough endoplasmic reticulum - RER

Ribosome

Centrioles

Microtubules

Lysosome

Pinocytosis vesicle



Mitochondria

Golgi body

Nucleus

Nucleolus

Nuclear pore

Rough ER

Mitochondria

Cell Membrane

•Here is a 3D diagram of a plant cell with all its membrane bound organelles.

•See how many of these you can recognise...


Eukaryotic cell - Rough ER

Nucleus

Rough ER with many ribosomes


Eukaryotic cell - Mitochondria

Mitochondria

Inner folded membrane

Outer membrane


Eukaryotic cell - Mitochondria


Eukaryotic cell - Golgi Body

Golgi body

Golgi vesicle


Eukaryotic cell - Centrioles

Centrioles

RER Nucleus


Eukaryotic cell - Plant cell

•What other structures can you identify in a plant cell?

•Can you find the cell wall, the chloroplasts and the large vacuoles?



Nucleus

Nucleolus

Rough ER

Smooth ER

Ribosomes

Golgi body

Golgi vesiclesCell membrane

Mitochondria

Cytoplasm

Vacuole

Vacuole membrane

Cell wall

Chloroplast

Starch granule



•This is the 3D view of a typical plant cell; note the rigid shape that is typical of plant cells

•Can you recognise the typical plant cell organelles?

VacuoleChloroplast

Cell wall


Eukaryotic cell - Plant cell - Chloroplast

Grana stacks

Thylakoid membrane

Cells - what can we see with the ELectron Microscope?

Eukaryotic cell - Plant cell - Chloroplast

The End

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Microscopes Cells &. What is a Microscope? Most microscopes consist of either a single lens (simple microscope) or multiple lenses (compound microscope)