Mod 1 Flashcards
(22 cards)
Cells
basic structural and functional unit of the diverse range of all living things.
Prokaryotic cells
primitive cells
no memebrane surrounding the genetic material and therefore no nucleus.
e.g. bacteria, archaea
Archaea
unicellular organisms found in extreme and harsh environments such as hydrothermal vents and hot springs.
Differences between eukaryotic and prokaryotic cells
much simpler structure
more prokaryotic cells on earth
membrane surrouding the genetic material
pili (singular: pilus)
hair-like structures on the surface of some cells that allow them to adhere to nearby substances.
Flagella (singular: flagellum)
whip-like tails that provide cell with locomotion.
Role of cell wall
protection
provides structural support
Eukaryotes
characterised by a membrane bound nucleus and organelles.
examples of unicellular eukaryotes
paramecium, Amoeba, euglena
Where is the term “cell” derived from?
Robert Hooke, in the 1660s, was able to view and draw the structure in cork that led to his use of the term ‘cella’, leading to our term ‘cell’
How can you see the magnified image of the specimen through the ocular lens?
a light source -> a condenser lens -> the thin specimen->the convex objective lens, where the image is magnified -> viewed through the ocular lens
total magnification
magnification = increase in size of the image
total magnification is calculated by multiplying the magnification of ocular lens by that of the objective lens.
Resolution
the ability to distinguish between two separate objects. It is the smallest distance between two objects where each can be observed as separate. (200nm)
A microscope similar to the light microscope
The flourescence microscopes
How does the fluorescence microscope work?
1) fluorescent substance attaches to the structures to observe.
2) The sample is illuminated with a high-intensity source of light that causes the fluorescent substance to emit light.
3) This fluorescent light is directed through filters that separate it from surrounding light 4) the viewer is able to see only those areas of the sample that are fluorescing
How does the electron microscope differ form light microscope? (Advantages)
uses an electron beam insted of light
=> gives much greater magnification
higher resolving power than light microscopes because electrons have a much shorter wavelength than light.
electromagnets instead of glass lenses.
The interaction between the electrons and the object forms a viewable image on a screen.
The electron microscope reveals structures at not only the cellular level, but also at the subcellular level.
Why can a living tissue not be seen under electorn microscopes?(Disadvantages of electon microscopes)
the specimen must be placed in a vacuum for viewing, because air would interfere with the flow of electrons. As a result, living tissue cannot be viewed.
Why are there 2 main types of electron microspoes?
(TEM) because
- the electrons are transmitted (pass through) the specimen.
- produces a two- dimensional image.
- The most common form of electron microscope.
-can magnify up to 1 500 000 times
-has a resolution of about 2 nm.
(SEM) because
- it bombards solid specimens with a beam of electrons, which causes secondary electrons to be emitted from the surface layers of the specimen.
-has poorer resolution (about 10 nm)
-gives excellent three-dimensional images of surfaces
Confocal laser scanning microscopes
use pinpoint laser beams to make images of many layers, which are then combined into a three-dimensional model
Scale
actual length / lengthof drawing
eg. 2micrometer/1cm
Therefore, a scale bar 1 cm in length would represent 2 µm
