Topic 3- Cells and Microscopes

By Tahmida Chowdhury

Microscopes

Why can light microscopes only distinguish between 2 objects if they are 0.2um apart?A: they have long wavelengthsIn 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 cellsWhy 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 objectDefine resolutionA: the minimum distance 2 objects can be until they are seen as separate objects

Electron Microscopes Name the two types of electron microscopesA: transmission electron microscope (TEM) & scanning electron microscope (SEM)What kind of radiation are used in electron microscopes?A: a beam of electronsWhat 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 vacuumWhat are the 2 advantages of using an TEM?A: it has short wavelengths and uses electron beams- greatest magnification and resolutionWhat are the 3 disadvantages of the TEM?A: images appear in black and whiteA: specimens pass through a vacuum therefore can’t be viewed liveA: the specimen has to very thin

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 belowWhich has greater resolution power?A: TEMIn what 3 ways is the SEM better than the TEM?A: it produced 3D imagesA: specimens need not be as thinA: specimens can be viewed live

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 enzymesWhy 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 pHWhat 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-membraneDescribe the 2 steps taken for centrifugation 1) The homogenate is spun in a centrifuge2) Organelles fall to the bottom (order depending on density) forming a pellet

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 nucleusA: 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

Mitochondria

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

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 materialsWhat does the SER do?A: synthesises, transport and processes proteins made at the ribosomes

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 GolgiWhat 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 synthesisWhere are ribosomes found?A: cytoplasm and RER What are the roles of vesicles?A: transport, digestion, secretion and storage