2.1.1 Cell structure Flashcards
What is a light microscope?
-uses light that passes through thin specimen to reflect an image in the objective lens
- to look at whole cells and tissues
What is the magnification and resolution of a light microscope?
magnification: 1500x
resolution: 200nm (0/2micromtr)
What is the magnification and resolution of a transmission electron microscope?
magnification: 500,000x
resolution: 0.05nm
What is the magnification and resolution of a scanning electron microscope?
magnification: 100,000x
resolution: 0.20nm
How does an TEM work?
- passes beam of electrons through specimen
- specimen must be thin to prevent deflection of electrons
- denser parts of specimen absorb more electrons = appear darker = produces contrast
Why are TEM used?
to look at organelle detail
Why do TEM images appear different from each other?
The images have been cut along different planes/angles
How do SEM work?
- the beam of electrons scan the surface of specimen
- the beam is bounced off the surface and the electrons are detected
- forming a 3D image = surface of specimens
Why are SEM used?
to look at cell surface
What are laser scanning confocal microscopes?
- specimen needs to be treated with fluorescent dye
- laser beam is reflected by the fluorescent dyes
Why are laser scanning confocal microscopes used?
to look at an object at a certain depth within the cell
What are the advantages of TEM?
high resolution images = more detail
internal structures to be seen e.g vesicles
What are the disadvantages for TEM?
-only be viewed with very thin specimens
-cannot be used to observe live specimens (vacuum)
- length treatment to prepare = artefacts
- doesnt produced coloured image
What are the advantages of light microscopes?
- see whole cells and tissues
- use live specimen
- view coloured image
What are the disadvantages of light microscopes?
- low magnification
- low resolution
What are the strengths of SEM?
- produce 3D image
- used on thick specimens
What are the disadvantages of SEM?
- lower resolution than TEM
- cannot observe live specimens
- no colour image
What are the advantages of light microscopes?
- used on thick specimens
- high resolution = observe cytoskeleton
What are the disadvantages of laser scanning confocal microscope?
- slow process; takes a long time to obtain image
- laser has potential to cause photodamage to cells
How do you prepare for light microscopes?
staining;
specimen becomes more visible e.g to see certain (named) organelles;
to improve contrast
What does acetic orcein stain?
DNA - dark red
What does Eosin stain?
cytoplasm - pink
What does Sudan black stain?
membranes and other lipids - black
What type of specimen needs to be prepared for a light microscope?
thin specimen,
thin sections allow light to pass through;
artefacts may occur
What is magnification?
the number of times larger the image is in in comparison to the object
What is resolution?
the ability to distinguish between very small structures that are close together; in detail;
Draw the units diagram?
cm
/10 mm x10
/1000 µm x 1000
/1000 nm x 1000
What is found in the eyepeice?
eye piece graticule;
used in calibration
What is used to calibrate the eye piece graticule?
a stage micrometer
What is the formula for magnification?
I/AM
What is the function of the nucleus?
contains the cells DNA (chromatin)
What is the function of nuclear pores?
- allows mRNA and ribosomes to travel out
- allowing enzymes e.g DNA polymerase and signalling molecules to travel in
What is the nucleolus?
dense part of nucleus = site of ribosome production
What is the function of the nuclear envelope?
separates the nucleus from the cytoplasm
What is the function of the rough endoplasmic reticulum?
flattened sacs of cisternae continuous from the nuclear envelope
surface covered in ribosomes
where protein synthesis occurs
What is the function of the smooth endoplasmic reticulum?
dont have ribosomes on its surface
lipid and hormone production occurs here
What is the function of the golgi apparatus?
- stack of membrane bound flattened sacs
- modifies, packages proteins into vesicles
What is the function of a ribosome?
site of protein synthesis
What is the function of the mitochondria?
produces ATP;
made during aerobic respiration
What is the function of lysosomes?
contain powerful digestive enzymes which are used to break down materials
What is the function of a chloroplast?
site of photosynthesis
What is the function of the cell surface membrane?
made out of phospholipid bilayer
controls what enters and leaves the cells
What is the function of centrioles?
take part in mitosis to form spindle fibres
Where are centrioles not found?
in flowering plants and fungi
What is the function of a cell wall?
provides structural support to cell
What is the cell wall made of in plants?
celluose
What is the cell wall made of in bacteria?
peptidoglycon
What is the function of the flagella?
whole cell movement
made of long microtubules;
they contract
What is the function of cillia?
hair like projections made from microtubules
allow movement of substances over the cell surface
How do organelles work together to produce proteins?
- nucleus produces mRNA
- mRNA leaves nucleus via nuclear pores
- mRNA attaches to ribosome in the cytoplasm/RER
- once protein has been made by proteinsynthesis
- proteins travels in vesicle and transported to golgi apparatus
- protein is modified and packaged in vesicle (addition of carbohydrate)
- moved towards cells surface membrane
- released via exocytosis
also; other organelle
- mitochondria: provides ATP = needed for the cytoskeleton to contract
and move vesicle
What is the importance of the cytoskeleton?
whole cell support;
movement of cilia and flagella;
changing cell shape;
moving organelles;
movement of chromosomes;
What type of ribosomes are found in prokaryotes?
70s
What is the function of plasmids?
circular DNA; can be passed to bacteria to exchange genetic info - through pili to surrounding bacteria
What type of DNA is found in prokaryotes?
circular
What is the role of the flagella in prokaryotes?
used in movement of cell
requires ATP
What is the role of the mesosome?
ATP is produces at the infolded regions of cells membrane
