Cell Structure Flashcards
Outline how a student could prepare a temporary mount of tissue for a light microscope.
1) Obtain a thin section of tissue
2) Place plant tissue in a drop of water
3) Stain tissue on a slide to make structures visible
4) Add a coverslip using mounted needle at 45 degrees to avoid trapping air bubbles
Describe how light microscopes work.
1) Lenses focus rays of light and magnify the view of a thin slice of specimen
2) Different structures absorb different amounts and wavelengths of light
3) Reflected light is transmitted to the observer via the objective lens and eyepiece
Describe how a transmission electron microscope works.
1) Pass a high energy beam of electrons through a thin slice of specimen
2) More dense structures appear darker since they absorb more electrons
3) Focus image onto the florescent screen or photographic plate using a magnetic lens
Describe how a scanning electron microscope works.
1) Focus a beam of electrons onto a specimens surface using electromagnetic lenses
2) Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate
Describe how a laser scanning confocal microscope works.
1) Focus a laser beam onto a small area on a samples surface using objective lenses
2) Fluorophores in the sample emit photons
3) Photomultiplier tube amplifies the signal onto a detector. An image is produced pixel by pixel in the correct order
How should the field of view in microscopy be recorded?
Draw a diagram with a sharp pencil
include a scale bar
Annotate visible structures
Microscopy equation.
Magnification = Image/Actual
Define magnification.
Factor by which the image is larger than the actual specimen.
Define resolution.
Ability to distinguish between two objects.
Why do samples need to be stained for light microscopes?
- Coloured dye binds to the structures
- Facilitates absorption of wavelengths of light to produce image.
What is differential staining?
Contrast between heavily and lightly stained areas distinguishes structures
State the maximum magnification and resolution of a light microscope.
Magnification = x1500
Resolution = 200nm
State the magnification and resolution of a transmission electron microscope.
Magnification = x500,000
Resolution = 0.1 nm
State the magnification and resolution of a scanning electron microscope.
Magnification = x100,000
Resolution = 0.1 nm
Explain how to use an eyepiece graticule and stage micrometer to measure the size of a structure.
1) Place micrometer on stage to calibrate eyepiece graticule
2) Line up scales on graticule and micrometer. Count how many graticule divisions are in 100 micrometers on the micrometer
3) Length of 1 eyepiece division = 100 micrometers/ number of divisions
4) Use calibrated values to calculate actual length of structures.
Describe the structure of the nucleus.
Surrounded by a nuclear envelope( a semipermeable double membrane)
Nuclear pores allow substances to enter/exit
Dense nucleolus made of RNA and proteins assembles ribosomes
Describe the function of the nucleus.
Contains DNA coiled around chromatin into the chromosomes
Controls cellular processes: gene expression determines specialisation and site of mRNA transcription, mitosis, semiconservative replication.
Describe the structure and function of the endoplasmic reticulum.
Rough ER = many ribosomes attached for proteinsynthesis and transport
Smooth ER = lipid synthesis (no ribosomes)
Describe the structure and function of the Golgi apparatus.
Stack of membrane bound flattened sacs.
Modifies and packages proteins for export
Synthesises glycoproteins
Describe the structure and function of ribosomes.
Formed of protein and RNA
Proteinsynthesis
Describe the relationship between the organelles involved in the production and secretion of proteins
The ribosomes that synthesis proteins are attached to the rER. The Golgi apparatus which modifies proteins for secretion aligns with the rER.
Describe the structure of mitochondrion.
Surrounded by double membrane
Folded inner membrane forms cristae: site of electron transport chain.
Fluid matrix: contains mitochondrial DNA respiratory enzymes lipids and proteins.
Describe the structure of a chloroplast.
Double membrane
Thykaloids: flattened discs stack to form grana - contain photostems with chlorophyll
Intergranal lamellae: tubes attach thykaloids in adjacent grana.
Stroma: fluid-filled matrix
State the function of mitochondria and chloroplasts.
Mitochondria = site of aerobic respiration
Chloroplasts = site of photosynthesis to convert solar energy to chemical energy
