2.1.1 Cell Structure Flashcards
Outline how a student could 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.
Describe how 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.
Describe how a transmission electron
microscope (TEM) works.
- Pass a high energy beam of electrons through
a 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.
Describe how a scanning electron
microscope (SEM) works.
- 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.
Describe how a laser scanning confocal
microscope works.
- 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 of 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.
State an 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.
State the magnification and resolution of
a compound light microscope.
magnification: x 2000
resolution: 200 nm
State the magnification and resolution of
a TEM.
magnification: x 500 000
resolution: 0.5 nm
State the magnification and resolution of
an SEM.
magnification: x 500 000
resolution: 3 - 10 nm
Explain 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 a nuclear envelope, a
semipermeable 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 (ER).
Describe the structure and function of the
endoplasmic reticulum (ER).
Cisternae: network of tubules & flattened sacs
extends from cell membrane & 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.
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.
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 of a chloroplast.
● Vesicular plastid with double membrane.
● Thylakoids: flattened discs stack to form
grana; contain photosystems with chlorophyll.
● Intergranal lamellae: tubes attach thylakoids in
adjacent grana.
● Stroma: fluid-filled matrix.
State the function 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.
What are bacterial and fungal cell walls
made of?
bacteria: peptidoglycan (murein)
fungi: chitin
Describe the structure and function of
centrioles.
● Spherical group of 9 microtubules
arranged in triples.
● Located in centrosomes.
● Migrate to opposite poles of cell during
prophase & spindle fibres form between
them.
Describe the structure and function of
the cell-surface plasma membrane.
Describe the structure and function of
the cell-surface plasma membrane.
Describe the structure and function of
the cell-surface plasma membrane.
● Cholesterol: steroid molecule connects
phospholipids & reduces fluidity.
● Glycoproteins: cell signalling, cell recognition
(antigens) & binding cells together.
● Glycolipids: cell signalling & cell recognition.
Describe the structure and function of
flagella.
● Hollow helical tube made of the protein
flagellin.
● Rotates to propel (usually unicellular)
organism.
Describe the structure and function of
cilia.
● Hairlike protrusions on eukaryotic cells. ● Move back and forth rhythmically to sweep foreign substances e.g. dust or pathogens away / to enable the cell to move.
Why is the cytoskeleton important?
● Provides mechanical strength.
● Aids transport within cells.
● Enables cell movement.
Compare eukaryotic and prokaryotic
cells.
Both have:
● cell membrane
● cytoplasm
● ribosomes
Contrast eukaryotic and prokaryotic
cells. PROKARYOTE
Prokaryotic:
- small cells and always unicellular
- no membrane bound organelles and no nucleus
- circular DNA not associated with proteins
- small ribosomes(70s)
- binary fission - always asexual reproduction
- cellulose wall (plants)/chitin (fungi)
- capsule, sometimes plasmid and cytoskeleton
Contrast eukaryotic and prokaryotic
cells. EUKARYOTE
Eukaryotic:
- larger cells and often multicellular
- always have organelles and nucleus
- linear chromosomes associated with histones
- larger ribosomes (80S)
- mitosis and meiosis - sexual and/or asexual
- murein cell walls
- no capsule, no plasmids, always cytoskeleton
