Cell structure test revision Flashcards
Define Eukaryotic and Prokaryotic cells
Eukaryotic:DNA is contained in a nucleus, contains membrane-bound specialised organelles.
Prokaryotic:DNA is ‘free’ in cytoplasm, no organelles e.g bacteria and archaea
Describe the structure and function of cell-surface membrane
‘Fluid mosaic’ Phospholipid bilayer with extrinsic and intrinsic proteins embedded.
- Isolates cytoplasm from extra cellular enviroment.
- Selectively permeable to regulate transport of substances
- Involved in cell signalling/cell recognition
Explain the role of chloesterol, glycoproteins and glycolipids in the cell surface membrane.
Chloesterol: steriod molecule connects phospholipids and reduces fluidity
Glycoproteins: Cell signalling, cell recognition (antigens) and binding cells together.
Glycolipids Cell signalling and cell recognition.
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 and proteins assembles ribosomes
Describe the function of the nucleus
- Contains DNA coiled around chromatin into chromosomes
- Controls cellular processes:gene expression determines specialisation and site of mRNA transcription, mitosis, semi conservative replication.
Describe the structure of a mitrochondrion
- Surrounded by double membrane flolded inner membrane forms cristae:site of electron transport chain.
- Fluid Matrix: contains mitrochondrial DNA, respiratory enzymes, lipids, proteins
Describe how homogenisation and cell fractionation can be used to seperate cell organelles.
- Take sample of tissues containing cells intrested in
- homogenise tissue to break open cells and release organelles using a blender
- filter homogenate to remove debris
- separate organellse via differential centrifugation
- spin homogenate in centrifuge
- most dense organelles in the mixture form a pellet
- filter off the supernatant and spin at a higher speed
Desrcribe the structure of a chloroplast
- Vesicular plastid with a 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 mitrochondria and chloroplasts
Mitrochondira:site of aerobic respiration to produce ATP
Chloroplasts: Site of photosynthesis to convert solar energy to chemical energy
Describe the structure and function of the golgi apparatus
Planar stack of membrane-bound flatterned sacsis face aligns with rER
Molecules are processed in cisternae vesicles bud off trans face via exocytosis:
- modifies and packages proteins for export
- synthesises glycoproteins
Describe the structure and function of a lysosome
Sac surrounded by single membraine embedded H+ pump maintains acidic conditions.
contains digestive hydrolase enzymes.
glycoprotein coat protects interior
Digests contents of phagosome
exocytosis of digetsive enzymes
Describe the structure and function of a ribosome
Formed of protein and rRNA free in cytoplasm or attached to ER.
* Site of protein synthesis via translation:
* Large subunit joins amin acids
* Small subunit contains mRNA binding site
Describe the structure and function of the endoplasmic reticulum (ER)
Cisternae:Network of tubules and flatterned sacs extends from cell membrane through cytoplasm and conects to nucelur envelope
Rough ER:many ribosomes attached for protein synthesis and transport.
Smooth ER:lipid synthesis
Describe the Structure of the Cell wall
Bacteria:Made if the polysaccharide murein
Plants: made of cellulose microfibril. plasmodesmata allow molecules to pass between cells, middle lamella acts as a boundry between adjacent cell walls.
State the funcions of the cell wall
- Mechanical strength and support
- Physical barrier against pathogens
- Part of apoplast pathway (plants) to enable easy diffusion of water
Describe the structure and function of the cell vacuole in plants
Surrounded by single membrane: tonoplast. contains cell sap:mineral ions, water, enzymes and soluble pigments.
- controls turgor pressure
- absorbs and hydrolyses potentially harmful substance to detoxify cytoplasm
State role of plasmids in prokaryotes
- Small ring of DNA that carries non essential genes
- can be exchanged between bacterial cells via conjugation
State role of flagella in prokaryotes
- rotating tail propels organism (movement)
Compare Eukaryotic and Prokaryotuc cells
Both have: Cell membrane cytoplasms ribosomes
Prokaryotic: small cells always unicellular no membrane organelles and no nucleus. circular Dna…..
State the role of the capsule in Prokaryotes
- Prevents desiccation
- acts as food reserve
- sticks cells together
- provides mechanical protection against phagocytosis and external chemicals
Describe how optical microscopes work
- Lenses focus rays of light and magnify the view of a thin specimen
- different structures absorb differet amounts and wavelengths of light
- reflected light is transmitted to observer via objective lens and eyepiece
Outline how a student could prepare a temporary mount of tissue for a optical microscope
- Obtain thin section of tissue
- place plant tissue in a drop of water
- Stain tissue on a slide to make structure visible
- add coverslip using mounted needle avoid trapping air bubble
Suggest the advantages and limitations of using an optical microscope
+colour image
+can show living structures
+affordable apparatus
-2d image
-lower resolution than electron microscopes-cannot see ultrastructure
Describe how a transmission electron microscope TEM works
- 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 screeb or photographic plate using magnetic lense
Advantages and limitations of using a transmission electron microscope
+electrons have shorter wavelength than light=high resolution so ultrastructue visible
+high magnification (x500000)
-2D image
-requires a vaccuum cannot show living structures
-no colour image
Describe how a scanning electron microscope works
- Focus a beam of electrons on specimens surface using electromagentic lenses
- Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
Advantages and limitations of SEM
+3D image
+electrons have shorter wavelenghts than light=higher resolution
-requires vacum
-cannot show living specimens
-no colour image
-only shows outer surface
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 on another.
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
