chapter 2 - Cell Structure And Microscopy Flashcards
Biological drawing checklist (10)
- sharp pencil
- take up at least half the page
- lines need to be clear and continuous (no shading/colouring)
- label lines in pencil
- label lines touch the actual part your labelling
- label lines don’t cross over each other
- ensure proportions are correct
- label all areas that you have shown
- no arrow heads
- LOW POWER TISSUE PLAN
Define magnification
How much bigger a sample appears to be under the microscope than in real life
Define resolution
The ability to distinguish between two points in an image - detail
Resolution of light microscope
200nm
What does it mean if something is closer together than 200nm on a light microscope
They will be seen as 1 object
Why is the magnification 200nm on a light microscope
Due to the magnitude of the wavelength of light
Resolution tends to be half the wavelength of the energy source being used
What is the resolution of human eye
100 micro meters
Maximum magnification of a light microscope
X1500
Type of samples for a light microscope
Thin, transparent samples
Living or dead
What stains DNA
Acetic Orcein
What colour does acetic orcein stain DNA
Dark red
Why may some samples be sectioned (embedded in wax)
To help preserve structure while cutting
How does a light microscope work
Has two convex glass lenses: objective (near specimen) and eyepiece lens.
Mirror/light source directs light through condenser (focuses light), diaphragm and through sample.
Image is magnified by the objective lens (usually 4x, 10x or 40x).
Pros of light microscopes
• Lens configuration allows for reduced Chromatic aberration
• Inexpensive to buy and operate
• Small and portable
• Sample preparation does not usually lead to distortion
• Vacuum not required
• Natural colour is seen – unless stained
• Specimens can be living or dead
Cons of light microscopes
• Lower magnification
• Lower resolution
• Bubbles in cover slips – artefacts
What are artefacts
damage caused in specimen preparation
Resolution of TEM
0.02-1nm
Resolution of SEM
0.2-10 nm
Resolution of LSCM
200nm
Magnification of SEM
X100,000
Magnification of TEM
X 500,000
Magnification of LSCM
X 20000
Types of samples SEM
- dead
- dries and coated with heavy metals
Types of samples TEM
- dead
- dries and coated with heavy metals
Why do electron microscope samples need to be coated with heavy metals
to increase the level of contrast in the final image.
Types of samples in LSCM
Different layers at different depths
Living or dead
How does TEM work
A beam of electrons is passed through a vacuum to ensure electrons are traveling in a straight line,
with a wavelength less than 1mm is transmitted through the specimen and focused to produce and image.
How does an SEM work
A beam of electrons is sent across the surface of a specimen and the reflected electrons are collected
Pros of a TEM
• High magnification
• High resolving power
Cons of a TEM
• Specimen must be fixed in plastic
• Must be dead
• Expensive
• Must be used in a carefully controlled environment
• Problem with artefacts – structures that are produced due to the preparation process
• Complex sample preparation
• Vacuum required
• Sample preparation often distorts image
• Black and white images produced – but can be coloured digitally
Pros of an SEM
• They can be used on thick or 3-D specimens
• They allow the external, 3-D structure of specimens to be observed•
Cons of an SEM
- Lower resolution than TEMS
- Samples must be dead
- They don’t produce a colour image
Diagram of a LSCM
How does an LSCM work
• Uses lasers
• Cells are stained with a fluorescent dye
• A thick section of tissue, or a living
organism, can then be scanned with a
laser beam which can be reflected by
the dyes
• The laser beam is scanned at different
depths
Advantages of LSCM
• The laser beam is focussed at a specific
depth, which eliminates blur caused by out
of focus tissue above the focal point
• Images are taken at successive depths and
then put together into a 3D picture by
computers
• Can be used to see living tissue (the eye)
or distribution of individual molecules
within cells
How do LSCM limit the focal plane
employ a pair of pinhole apertures to limit the specimen focal plane to a confined volume approximately a micron in size.
Relatively thick specimens can be imaged in successive volumes by acquiring a series of sections along the optical (z) axis of the microscope
Uses of LSCM
• A use in optometry
Eg. Looking at scratches in the cornea
What does the pinhole do in LSCM
Prevents scattered light from being detected - would blur the image
What type of microscope produced these
TEM
- Golgi apparatus and the mitochondria
What type of microscope produced these
SEM
What do the magnets do in an electron microscope
The condenser lenses are magnets which
can focus and direct the electron beam
Sample preparation for electron microscopes - list
- Chemical Fixation:
- Cryofixation
- Dehydration
- Embedding
- Sectioning
- Staining
- Mounting
Sample preparation for electron microscopes - in full
dry mount
- Solid specimens are viewed whole or cut into thin slices (sectioning).
- Specimen placed on centre of slide, cover slip onto
Examples of dry mount
Hai, pollen, dust, insect parts –whole, muscle tissue or plants – sectioned.
Wet mount
Specimens suspended in liquid (water or immersion oil). Cover slip placed at angle, aquatic samples and other living organisms viewed.
Squash slides
Wet mount prepared first, lens tissue used to gently press down cover slip.
Two microscope slides can be used to avoid coverslip damage.
Squash slides – soft samples. Root tip squashes used to look at cell division.
Smear slides
Edge of slide - smear sample, thin, even coating on slide. Cover slip on top. Eg. Blood sample.
Purpose of stains
help to better visualise components
under the microscope
What is differential staining
can distinguish between two types of organisms that would otherwise be hard to identify.
It can also differentiate between different organelles of a single organism within a tissue sample.
Types of standing techniques
Gram stain + acid fast technique
What is a prokaryotic cell
usually unicellular, small cells with no membrane-bound internal structures and circular
DNA.
Examples of prokaryotic cells
Bacteria, E. coli, Archaea
What is a eukaryotic cell
those cells that contain a nucleus and organelles enclosed by a plasma membrane.
Examples of eukaryotic cell
Plants and animal cell
Cell wall in eukaryotic cells
made of cellulose/lignin in plants and made of chitin in fungi
Cell wall in prokaryotic cells
Cell wall made of peptidoglycan and Murein
Size of eukaryotic cell
Up to 100 micrometers
Size of a prokaryotic cell
0.5-5 micrometres
How does a eukaryotic cell divided
Mitosis or meiosis
How does a prokaryotic cell divide
Binary fission
Where is dna found in eukaryotic and prokaryotic
Nucleus and cytoplasm
Size of ribosomes in eukaryotic and prokaryotic
Eukaryotic - Ribosomes structurally larger – 80 S
Prokaryotic- Ribosomes structurally smaller – 70 S
Organelles in plant cells
Golgi vesicles
Golgi apparatus
Ribosomes
Endoplasmic reticulum
Nucleus
Nucleolus
Vacuole
Amyloplast
Cell wall
Cell membrane
Mitochondria
Cytoplasm
Chloroplast
Organelle found in animal cells
Golgi vesicles
Golgi apparatus
Ribosomes
Endoplasmic reticulum
Nucleus
Nucleolus
Vacuole ?? - small
Cell membrane
Mitochondria
Centrosome
Lysosome
Cytoplasm
Which organelle are found in an animal cell but not plant cell
Centrosome
Lysosome
Centriole
• a component of the cytoskeleton
• present in most eukaryotic cells but flowering plants and fungi
• Hollow fibres made of microtubules in a 9 + 2 arrangement
• Two centrioles at right angles to each other form a centrosome
What does a Centrosome do
which organises the spindle fibres during cell division - anaphase
Mitochondria
• The site of aerobic respiration
• Surrounded by double-membrane with the inner membrane folded to form cristae
• Liquid compartment = Matrix
• The matrix contains enzymes
- contains DNA + ribosomes
Ribosome
- Functions as the site of protein synthesis
- Formed in the nucleolus
- Found freely in the cytoplasm or as part of the rough endoplasmic reticulum
Nucleus
- Contains chromatin
- relatively large
- Separated from the cytoplasm by a double membrane – nuclear envelope
- Contain nucleolus
What is Chromatin
(a complex of DNA and histone proteins)
Function of the nucleolus
Site of ribosome production
Golgi body
- Function is to modify/ finalise proteins and lipids before packaging them into Golgi vesicles
- Produces secretary vesicles
Lysosomes
- Function is to break down waste materials such as worn-out organelles
- Specialist form of vesicle
- Contains hydrolytic enzymes (break down)
- Used by the immune system and in apoptosis
Chloroplast
- site of photosynthesis
- Larger than mitochondria
- Surrounded by a double membrane
- Thylakoids containing chlorophyll stack to form grana – grana joined together by lamellae
- liquid part = stroma
Plasma membrane
- Functions as a partially permeable membrane that controls the exchange of materials between internal and external environment
- Diameter 10nm
- Formed from a phospholipid layer
Flagellum
• Found in specialised cells
• Similar in structure to cilia
- made from the plasma membrane + a bundle of 11 microtubules
• Contract to provide cell movement for example in sperm cells
Nuclear envelope / membrane
- Separates the nucleus from the cytoplasm
- Contains nuclear pores – allows mRNA and ribosomes to travel out of nucleus and allows enzymes and signalling molecules to travel in.
Rough endoplasmic reticulum
- Function is to process proteins made by the ribosomes
- Found in plant and animal cells
- Surface covered in ribosomes
- Formed from continuous folds of membrane with the nuclear envelope
Smooth endoplasmic reticulum
- Does not have ribosomes on surface
- Function is involved in the production, processing and storage of lipids, carbohydrates, and steroids
How is the flagella of a prokaryote different to flagella on eukaryotes?
Thinner
Doesn’t have the 9+2 arrangement
Rotary movement
energy comes from chemiosmosis (proton driven), not ATP
Eukaryotic vs prokaryotic table
Protein formation + transport diagram
Outline the role of the Golgi apparatus
D
B
C
Light microscope + Graticule
Differential staining - table
Differences between differential staining and simple staining - table
D
B
A
C
A
C
D
2nd part
C
D
B
C
A
B
C
What is the plasmodesmata
small channels that directly connect the cytoplasm of neighboring plant cells to each other, establishing living bridges between cells.
B
