Cell structure Flashcards
(33 cards)
How can a student prepare a temporary mount of tissue for a light microscope?
- Obtain thin section of tissue e.g. using ultratome or by maceration.
- Place plant tissue in a drop of water.
- Stain tissue on a slide to make structures visible.
- Add coverslip using mounted needle at 45° to avoid trapping air bubbles.
How do light microscopes work?
- Lenses focus rays of light and magnify the view of a thin slice of specimen.
- Different structures absorb different amounts and wavelengths of light.
- Reflected light is transmitted to the observer via the objective lens and eyepiece.
How does a transmission electron microscope work?
- Pass a high energy beam of electrons through thin slice of specimen.
- More dense structures appear darker since they absorb more electrons.
- Focus image onto fluorescent screen or photographic plate using magnetic lenses.
How does a scanning electron microscope work?
- Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses.
- Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
How does a laser scanning confocal microscope work?
- Focus a laser beam onto a small area on a sample’s surface using objective lenses.
- Fluorophores in the sample emit photons.
- Photomultiplier tube amplifies the signal onto a detector. An image is produced pixel by pixel in the correct order.
How should the field view in microscopy be recorded?
Draw a diagram with a sharp pencil. Do not use sketchy lines or shading. Include a scale bar. Annotate visible structures.
What is the equation to calculate the actual size of a structure from microscopy?
Actual size = Image size / Magnification
Define magnification and resolution.
Magnification: factor by which the image is larger than the actual specimen.
Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another.
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. Differential staining: contrast between heavily & lightly stained areas distinguishes structures.
What are the magnification and resolution of a light microscope?
Magnification: x 1500
Resolution: 200 nm
What are the magnification and resolution of a transmission electron microscope?
Magnification: x 500 000
Resolution: 0.2 nm
What are the magnification and resolution of a scanning electron microscope?
Magnification: x 500 000
Resolution: 3-10 nm
How to use an eyepiece graticule and stage micrometer to measure the size of a structure?
- Place micrometer on stage to calibrate eyepiece graticule.
- Line up scales on graticule and micrometer. Count how many graticule divisions are in 100μm on the micrometer.
- Length of 1 eyepiece division = 100μm / number of divisions.
- Use calibrated values to calculate actual length of structures.
Describe the structure of the nucleus.
Surrounded by nuclear envelope, a semi-permeable double membrane.
Nuclear pores allow substances to enter/exit.
Dense nucleolus made of RNA & proteins assembles ribosomes.
Describe the function of the nucleus.
Contains DNA coiled around chromatin into chromosomes.
Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semiconservative replication.
Describe the structure and function of the endoplasmic reticulum.
Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear envelope:
Rough ER: many ribosomes attached for protein synthesis & transport.
Smooth ER: lipid synthesis.
Describe the structure and function of the Golgi apparatus.
Planar stack of membrane-bound, flattened sacs cis face aligns with rER. Molecules are processed in cisternae vesicles bud off trans face via exocytosis:
modifies & packages proteins for export
synthesises glycoproteins.
Describe the structure and function of ribosomes.
Formed of protein & rRNA.
Have large subunit which joins amino acids & small subunit with mRNA binding site.
Describe the relationship between the organelles involved in the production and secretion of proteins.
The ribosomes that synthesise proteins are attached to the rER. The Golgi apparatus, which modifies proteins for secretion, aligns with the rER.
Describe the structure of a mitochondrion.
Surrounded by double membrane folded inner membrane forms cristae: site of electron transport chain.
Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins.
Describe the structure and function of a chloroplast.
vesicular plastid with double membrane.
thylakoids: flattened discs stack form grana; contain photo systems with chlorophyll.
integrals lamellar: tubes attach thylakoids in adjacent grana.
stroma: fluid-filled matrix.
What are the functions of mitochondria and chloroplasts?
Mitochondria: site of aerobic respiration to produce ATP.
Chloroplasts: site of photosynthesis to convert solar energy to chemical energy.
Describe the structure and function of a lysosome.
Sac surrounded by single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enzymes glycoprotein coat protects cell interior:
digests contents of phagosome
exocytosis of digestive enzymes.
Describe the structure and function of a plant cell wall.
Made of cellulose microfibrils for mechanical support.
Plasmodesmata form part of apoplast pathway to allow molecules to pass between cells.
Middle lamella separates adjacent cell walls.
