A2.2 Cell Structure Flashcards
What is a cell?
Cells are the basic structural units of living organisms.
What does cell theory state?
Cell theory states that:
All living organisms are made up of one or more cells
Cells are the smallest units of life and are the basic functional unit in living organisms
New cells are produced from pre-existing cells
Why are stains used in microscopy when making temporary mounts?
Stains are used when making temporary mounts to provide colour contrast for cellular structures that might otherwise be transparent; this means that the structures can be seen under a microscope.
How is a coverslip used during preparation of a temporary mount of cells?
When making a temporary mount of cells a coverslip is gently lowered over a specimen after liquid and/or stain has been added.
Describe how a slide can be viewed using a light microscope.
A slide can be viewed using a light microscope as follows:
place slide onto microscope stage
lower the low power objective lens towards the stage as far as possible
use the coarse focus to locate the specimen
use the fine focus to bring the specimen into clear view
change the objective lens to increase magnification
repeat steps 3-5 as necessary
What is an eyepiece graticule?
An eyepiece graticule is a transparent scale mounted within the eyepiece lens of a light microscope.
How can an eyepiece graticule be used to determine the size of a specimen?
An eyepiece graticule can be used to determine the size of a specimen by calibrating the graticule using a stage micrometer. This process allows the actual length of each eyepiece graticule unit to be determined, and the eyepiece graticule can be used like a ruler to measure the length of a specimen.
What is the formula for calculating the actual size of a specimen?
The formula for calculating the actual size of a specimen is:
actual size = image size ÷ magnification
What is the formula for calculating magnification?
The formula for calculating magnification is:
magnification = image size ÷ actual size
Describe how a scale bar can be added to a biological drawing of a specimen viewed using a light microscope.
A scale bar can be added to a biological drawing as follows:
calibrate the eyepiece graticule and use it to measure the length of the specimen
calculate 20 % of the length of the specimen (or a similar percentage)
draw the specimen according to the rules of biological drawing
use a ruler to draw a line that is 20 % of the length of the drawing
write the actual length represented by the scale bar next to the bar; this should be a whole number
How do electron microscopes generate images?
Electron microscopes generate images by passing a beam of electrons through a specimen (TEM) or by bouncing electrons off the surface of a specimen (SEM).
What are the advantages of electron microscopes over light microscopes?
Advantages of electron microscopes over light microscopes are that they:
have higher resolving power
can magnify objects many more times (x500 000 compared to x2000)
can be used to show the details of internal cellular structures
How are specimens prepared using freeze fracture techniques?
Specimens can be prepared using freeze fracture methods as follows:
a specimen is rapidly frozen
the frozen tissue is broken apart, or fractured, exposing a surface that can be viewed
For what purpose is cryogenic electron microscopy used?
Cryogenic electron microscope is used for viewing the 3D structures of, e.g.:
proteins
viruses
cell membranes
How can fluorescent stains be used in microscopy?
Fluorescent stains are used in light microscopy; the dyes bind to specific target structures inside cells and then emit light when irradiated, showing where the structures are located within the cell.
What is immunofluorescence in microscopy?
Immunofluorescence uses antibodies with fluorescent dyes attached; the antibodies bind to specific target molecules and the dyes fluoresce when irradiated, showing whether or not, or where, the target molecules are present.
Which molecule makes up the genetic material of typical cells?
The genetic material of typical cells is made from DNA.
What is the role of DNA inside cells?
The role of DNA inside cells is to store the information needed to make proteins.
What is the role of cytoplasm within cells?
The role of cytoplasm within cells is to provide a medium in which the chemical reactions of cell metabolism can occur.