Cell Structure Flashcards
Define magnification
How much bigger an image is compared to a specimen
Define resolution
The ability to distinguish between two separate points
How detailed an image is
What is the maximum magnification of a light microscope
X1500
What is the maximum magnification of a TEM
X>1,000,000
What is the maximum magnification of a SEM
X<500,000
What is the maximum resolution of a light microscope
200nm/0.2um
What is the maximum resolution of a TEM
0.2nm/0.0002um
What is the maximum resolution of a SEM
20nm/0.002um
Advantages of light microscope
Relatively cheap
Can observe live specimens
Colour images
Disadvantages of light microscope
Low resolution (lower than electron microscopes)
Advantages of TEM
High resolution images to look at very small organelles eg ribosomes
Look at internal structures of organelles
Disadvantages of TEM
Specimens must be dead
Specimens must be thinly sliced
Images are black and white (colour can be added)
Produces 2D images
Advantages of SEM
Produces a 3D image
Shows the surface of an organism
Disadvantages of SEM
Specimens must be dead
Lower resolution than TEM
Images are black and white (colour can be added)
Advantages of scanning laser confocal
Pinhole prevents out of focus light reaching the detector so image is clearer
Can view thicker and living specimens at different depths
How does a light microscope work
Uses a number of lenses to produce an image that can be viewed directly at the eyepiece.
Light passes from a bulb under the stage, through a condenser lens and then through specimen.
This beam of light is passed through an objective lens (x4, x10, x40) and then the eyepiece lens (x10)
Looks at whole cells or tissues
How does a TEM work
Uses electromagnets to focus a beam of electrons, which is transmitted through the specimen.
Denser parts of the specimen absorb more electrons, which makes it look darker on the image, creating contrast
Produces 2D images
How does a SEM work
Scan a beam of electrons across the specimen
This knocks off the electrons across the specimen, which are gathered in a cathode ray tube to form an image
How are specimens treated before viewing with a SEM
Coated with a thin layer of gold particles
How are specimens treated before viewing with a LCSM
Tagged with fluorescent dye
What is the function of the pinhole in LSCM
Prevents out of focus light reaching the detector
What does methylene blue stain and it’s colour
DNA
Blue
What does giemsa stain and it’s colour
Blood cells
Red blood cells stain red
White blood cells stain purple
What does eosin stain and it’s colour
Cytoplasm
Pink
What does haemotoxylin stain and it’s colour
RNA purple
DNA blue
Why are specimens often stained before viewing under a light microscope
Organelles are often transparent so it prevents object from appearing white
How would you calculate actual size of a magnified object
Actual = image/ magnification
How does a LSCM work
Uses laser beams to scan a specimen, tagged with fluorescent dye
Laser beam is focused through a lens which is aimed at a beam splitter
Beam splits and some light is directed to specimen
When the laser hits dye it gives off fluorescent light
Light if focused through pinhole onto a detector
Detector is hooked to a computer which generates the image
How to prepare sample for use with electron microscopes
Treat it with heavy metals (like lead)
Metal ions scatter electrons foraged at the sample and give contrast between different structures
How to prepare a dry mount
Use a thinly sliced specimen
Use tweezers to place specimen in the middle of a clean slide
Place a cover slip on top
What can a dry mount be used for
Observing hairs,
Parts of insects
Pollen
Parts of a flower
How to prepare a wet mount
Pipette a small drop of water onto the slide
Use tweezers to place specimen on water droplet
Stand cover slip upright near water droplet
Carefully tilt and lower slip so it covers the specimen
Try to avoid air bubbles
Add a stain to edge of cover slip, drawing the stain across the specimen
What can a wet mount be used for
Living samples eg tiny aquatic organisms
How to use a light microscope
- Clip the slide containing the specimen onto the stage
- Select lowest powered objective lens
- Use coarse adjustment knob to bring stage up to just below objective lens
- Look down eyepiece, using coarse adjustment knob to move stage until image is in focus
- Adjust focus with fine adjustment knob until you get a clear image
- Swap to higher powered objective lens if required
What is an eyepiece graticule
It is fitted onto the eyepiece
Like a transparent ruler with numbers but no units
When you look through eyepiece you’ll see a scale
What is the stage micrometer
Placed on the stage
It is a microscope slide with an accurate scale (has units)
Used to work out value of divisions on the eyepiece graticule at a particular magnification
Why are a variety of stains used to stain samples
Different stains can be used to make different parts of cell show up
Structure and function of nucleus
Large organelles surrounded by nuclear envelope (double membrane)
Contains many pores
Contains chromatin (made of DNA and proteins)
Contains a nucleolus
Controls cells activities by controlling transcription of DNA
DNA contains instructions to make proteins
Pores allow substances to move between nucleus and cytoplasm
Nucleolus makes ribosomes
Structure and function of plasma membrane
Made of lipids and proteins
Regulates movement of substances in/out of cell
Has receptor molecules which allow it to respond to chemicals like hormones
Structure and function of cell wall
Rigid structure that surrounds plant cells
Made of cellulose
Supports plant cells
Structure and function of lysosome
Round organelle surrounded by a membrane with no clear internal structure
Contains digestive enzyme
To digest invading cells or break down worn out components
Transports hydrologic enzymes
Structure and function of rough ER
System of membranes enclosing a fluid filled space
Surface is covered with ribosomes
Folds and processes proteins made at the ribosomes
Structure and function of the smooth ER
System of membranes enclosing a fluid filled space
Synthesises and processes lipids and steroid hormones
Structure and function of a vesicle
Small fluid filled sac in the cytoplasm surrounded by a membrane
Transports substances in/out of cell via plasma membrane
Some are formed by Golgi apparatus or ER and some at the cell surface
Structure and function of Golgi apparatus
Group of fluid filled membrane bound flattened sacs
Vesicles at the edges of the sacs
Processes and packages new lipids and proteins
Makes lysosomes
Structure and function of mitochondrion
Double membrane
Inner membrane folded to form cristae
Inside is the matrix which contains enzymes for respiration
Site of aerobic respiration where ATP is produced
Found in large numbers in cells that are active and require a lot of energy
Structure and function of chloroplast
Small flattened structure found in plants
Surrounded by double membrane
Membranes inside called thylakoid membranes
Thylakoid are stacked up to form grana
Grana are linked together by lamellae - thin flat pieces of thylakoid membrane
Site of photosynthesis
Some photosynthesis happen in grana and other parts in the stroma (thick fluid in chloroplasts)
Structure and function of a centriole
Small hollow cylinders made of microtubules (tiny protein cylinders)
Found in animal cells but only some plant cells
Involved in separation of chromosomes during cell division
Structure and function of cilia
Small hair like structures found on the surface membrane of some animal cells
Cross section - outer membrane and a ring of 9 pairs of protein microtubules inside and a single pair in the middle
Microtubules allow cilia to move
Movement is used by the cell to move substances along the cell surface
Structure and function of flagellum
Flagella on eukaryotic cells are like cilia but longer
Stick out from the cell surface
Surrounded by plasma membrane
Two microtubules in centre and 9 pairs around the edge
Microtubules contract to make flagellum move
Flagella propel cells forward (eg when sperm swims to egg)
