Unit 1 – Matter and Energy for Life

CELL THEORY AND MICROSCOPES

BIOGENESIS VS. ABIOGENESIS

• Biogenesis• Life is characterized

by the fact that living things come only from other living things

• Abiogenesis• The belief that living

things can arise from non-living things

SPONTANEOUS GENERATION

• Before the invention of the microscope, people believed that living things could be produced from non-living things• I.e. Spontaneous

Generation or Abiogenesis

• For example:• Maggots developing

on a piece of rotting meat

SPONTANEOUS GENERATION• The idea of abiogenesis was

not contested for 2000 years• Aristotle, the ancient Greek

philosopher, concluded that abiogenesis was a reasonable explanation for the origin of life

• No one challenged the idea because people could make daily observations that seems to support the idea • For example: during spring,

plants would start to grow where they hadn’t been before

PARADIGM SHIFT

• A change in the way we think of the world

• We start to challenge modern thinking because we’re critical of present day ideas

• For example:• The world is flat vs.

round• Abiogenesis vs.

Biogenesis

FRANCESCO REDI• Italian doctor who first

challenged the idea of spontaneous generation

• Conducted one of the first controlled experiments that supported biogenesis

• Used meat in jars, half covered with mesh and half open.

• Where were the maggots coming from?

ANTON VON LEEUWENHOEK• Was one of the first to make

and use microscopes • In 1675, he first observed

and described microorganisms (Bacteria)

• Working with solutions of broth, he discovered bacterial growth

• Suggested that the development of the microorganisms supported the arguments for abiogenesis (Life created from the non-living)

JOHN NEEDHAM• Performed experiments that

further supported abiogenesis

• Boiled meat broth to kill any microbes, sealed one container with a cork, another he left open

• Observed that microorganisms appeared in both containers

• He claimed that this proved that life can originate from the non-living

• Where did the microbes come from in the corked container?

LAZZARO SPALLANZANI• Investigated the work

done by Needham• He repeated Needham’s

experiment with two significant changes1. He boiled the broth

longer2. He sealed his containers

by melting the glass • The result was that

microorganisms did not grow in the sealed containers. Why? What was missing?

LOUIS PASTEUR

• Conducted experiments that finally disproved abiogenesis

• Used broth that was heated in flasks with an S-Shaped stem

• Demonstrated conclusively that microorganisms did/do not spontaneously generate

ROBERT HOOKE

• Used a compound microscope to investigate slices of cork

• He observed empty structures which he names “cells”

OTHER SCIENTISTS

• Robert Brown • Observed cells from a variety of organisms, noticed that each

had a dark region within them, later known as the nucleus• Matthias Schleiden

• Botanist who concluded that plants are also made of cells• Theodor Schwann

• Proposed that all organisms, both plants and animals, are made of cells

• Alexander Braun• Postulated that cells are the basic unit of life

• Robert Virchow• Concluded that cells must arise from other cells

WHY IS THIS IMPORTANT?What’s the big deal?

CELL THEORY

• Cell theory states:1. The cell is the basic

living unit of organization for all organisms

2. All organisms are made of cells or cell products

3. All cells come from other cells

• Watch this…• http://www.youtube.co

m/watch?v=4OpBylwH9DU

THE MICROSCOPEA SIGNIFICANT DISCOVERY

THE MICROSCOPE

• Revealed a whole new world to biologists

• Extended the limits of what could seen

• Changed the way scientists were able to study the world at a microscopic level

EARLY MICROSCOPES

• Often called Simple Microscopes

• Made of a single strongly curved lens

• Leeuwenhoek made simple microscopes that achieved magnifications as high as 400x

MODERN LIGHT MICROSCOPES

• Compound Microscopes• Made of a series of lenses

that allow you to magnify objects to about a max. magnification of 2000x

• Magnification is not enough to see all cells and certainly not all cellular organelles

• Resolution limited to about 0.2 µm

• Images appear upside down in the viewer

PARTS OF THE MICROSCOPE

Condenser lens

See page 16 in your textbook

MAGNIFICATION AND RESOLUTION• Magnification

• How many times larger an object appears to be, compared to its actual size

• For example: 400x• Resolution

• The ability of the eye, or other instrument, to distinguish between two objects that are close together

• I.e. Clarity • Measured in micrometers

(µm); 1000 µm = 1 mm

WHAT ABOUT GREATER DETAIL?

WHAT CAN WE USE?

ELECTRON MICROSCOPES

• They use a beam of electrons to magnify objects

• Use electromagnets to focus beams instead of lens

• Can achieve resolutions better than 50 pm and magnifications of up to 10,000,000x

TYPES OF ELECTRON MICROSCOPES

1. Transmission Electron Microscope

• Works on the same principle as the light microscope but uses electrons instead of light

• Magnifications up to 500,000x, Resolutions as low as 0.0002 µm

• First to observe cell structures

Mitochondrion

Rough ER – Notice the Ribosomes

TYPES OF ELECTRON MICROSCOPES

1. Transmission Electron Microscope

• Works on the same principle as the light microscope but uses electrons instead of light

• Magnifications up to 500,000x, Resolutions as low as 0.0002 µm

• First to observe cell structures

Mitochondrion

Rough ER – Notice the Ribosomes

ELECTRON MICROSCOPES

2. Scanning Electron Microscopes

• A narrow beam of electrons passes over the surface of a specimen

• Specimen is coated in a thin film of metal (Gold) which electrons scan to produce a 3D image

• Magnifications over 300,000x, Resolutions up to 0.005 µm

YOUR MICROSCOPESCOMPOUND LIGHT MICROSCOPES

HANDLE WITH CARE!

• One hand on the arm, the other supporting the base

• Keep lenses clean, do not touch them!• Do not adjust the focusing knobs until you’re ready

to use them• Always focus using the coarse adjustment knob first,

with the low-power objective in position• Do not use the coarse adjustment knob with the

medium-power or high-power lenses in place

TOTAL MAGNIFICATION

CALCULATING FIELD OF VIEW1. On low power, use a ruler and

place one dash of the millimeter side of the ruler to the far left edge of your field of view

2. On low power, the FOV is the distance read, in millimeters, on the ruler

3. Use the following equations to calculate the field of view for medium power and high power objective lenses (also in mm)

CALCULATING FIELD OF VIEWMedium Power FOV = Low Power FOV × Magnification of Low Power Magnification of Medium Power

High Power FOV = Low Power FOV × Magnification of Low Power Magnification of High Power

•Remember that FOV is originally measured in millimeters (mm). You will need to know how to covert the field of view to micrometers (μm)

•1 mm = 1000 μm or 1 μm = 0.001 mm

VIEWING A PREPARED SLIDE

1. Secure slide to stage with low power in place2. Adjust coarse adjustment3. Use fine adjustment to sharpen the focus4. Once in place, rotate to medium, make sure the

objective lens does not come in contact with slide5. Adjust the fine adjustment, NOT COARSE6. Rotate to high power, be careful of the slide7. Adjust fine adjustment8. When done, rotate back to low