Microscopes use wavelengths of light or electrons to visualize cells and organelles. Light microscopes can distinguish objects 0.2um apart while electron microscopes have much higher resolution down to 0.1nm. Specimens are cut thin and stained for contrast. Fractionation separates cell components through homogenization, centrifugation, and differential sedimentation based on density. Key organelles include the nucleus which houses DNA, mitochondria which perform aerobic respiration, the endoplasmic reticulum which modifies and transports proteins, and lysosomes which digest materials.

1. Topic 3- Cells and
Microscopes
By Tahmida Chowdhury

2. Microscopes
Why can light microscopes only distinguish between 2 objects if they are 0.2um apart?
A: they have long wavelengths
In light microscopes why are specimen cut into thin slices?
A: so the light can pass through. Also detail is clear when there is a single layer of cells
Why are specimen often stained?
A: to show contrast and pick out details and differentiate
What are the differences between an electron microscope and light microscope?
A: electron microscopes have shorter wavelengths, greater resolution and magnification and can
view smaller organelles
What is the equation to work out magnification?
A: image size of object/actual size of object
Define resolution
A: the minimum distance 2 objects can be until they are seen as separate objects

3. Electron Microscopes
Name the two types of electron microscopes
A: transmission electron microscope (TEM) & scanning electron microscope (SEM)
What kind of radiation are used in electron microscopes?
A: a beam of electrons
What is the maximum resolution power of TEM?
A: distinguish between two objects that as close as 0.1nm
How does an TEM work?
A: beam of electrons pass through a vacuum
What are the 2 advantages of using an TEM?
A: it has short wavelengths and uses electron beams- greatest magnification and resolution
What are the 3 disadvantages of the TEM?
A: images appear in black and white
A: specimens pass through a vacuum therefore can’t be viewed live
A: the specimen has to very thin

4. Electron Microscopes
What is the difference between SEM & TEM in terms of electrons?
A: SEM directs the beam of electrons onto the surface of the specimen
from above rather than TEM which absorbs the electrons from below
Which has greater resolution power?
A: TEM
In what 3 ways is the SEM better than the TEM?
A: it produced 3D images
A: specimens need not be as thin
A: specimens can be viewed live

5. Fractionation
The tissue is put in a cold, isotonic, buffered solution. Why does the solution have to be cold?
A: to prevent any unwanted chemical reactions by enzymes
Why does the solution have to be isotonic?
A: to prevent organelles shrinking or swelling due to osmosis
Why does the solution have to be buffered?
A: to prevent pH damage and maintain a constant pH
What is cell homogenation?
A: the breaking of a cell in order for the different organelles to separate out in a homogeniser. Then
filtered to remove any large cells or large pieces of cell-membrane
Describe the 2 steps taken for centrifugation
1) The homogenate is spun in a centrifuge
2) Organelles fall to the bottom (order depending on density) forming a pellet

6. Nucleus
What is the difference between a eukaryotic and prokaryotic cell?
A: eukaryotic have a distinct nucleus and membrane bound organelles
whereas prokaryotic don’t
Name the 4 features of the nucleus
A: nuclear pores, nuclear envelope, chromatin, nucleolus
What do the nuclear pores do?
A: allow the passage of mRNA
What is in the chromatin and what is the chromatins role?
A: proteins and the DNA. DNA replication
What is the role of the nucleolus?
A: to make the ribosomes and RNA

7. Mitochondria
What is the overall function of the mitochondria?
A: it is the site for aerobic respiration and produces ATP from energy or cells
How do cells without mitochondria produce ATP?
A: via anaerobic respiration
What 3 features are found in the mitochondria?
A: cristae, matrix, and a double membrane
What does the outer membrane do?
A: controls what enters and leaves the cell
What does the inner membrane (cristae) do?
A: it folds to provide a large surface area for the enzymes in respiration
What does the matrix do?
A: it contains the enzymes for respiration

8. Endoplasmic Reticulum
What is the endoplasmic reticulum?
A: a sheet-like membranes that spreads through the cytoplasm and continues off
with the nuclear membrane
What are the two types?
A: Rough-ER and Smooth-ER
Where are the ribosomes found on the RER?
A: on the surface of its membrane
What are the 2 roles of the rough endoplasmic reticulum?
A: to provide a large surface area for protein synthesis and it provides a passage for
the transport of materials
What does the SER do?
A: synthesises, transport and processes proteins made at the ribosomes

9. Cell Organelles
What is the function of the Golgi Apparatus?
A: to modify and package the proteins into vesicles which are then transported the plasma membrane
for secretion
What makes the lysosomes?
A: the Golgi
What do the lysosomes contain that help them carry out their role?
A: digestive and hydrolytic enzymes that digest worn out or invading cells
What does the lysosome’s membrane allow?
A: for it to be separated from the cytoplasm
What is the role of the ribosomes?
A: site of protein synthesis
Where are ribosomes found?
A: cytoplasm and RER
What are the roles of vesicles?
A: transport, digestion, secretion and storage