cell structure

• nucleus structure

  Largest organelle.

  Surrounded by the nuclear envelope;

  contains fluid nucleoplasm,

  nucleoli,

  chromatin,

  Nuclear pores
• Nucleus function

  contains genetic material

  direct synthesis of all proteins - enzymes - so controls metabolism
• Mitochondria structure

  double membrane

  inner mem folded to make cristae

  contains enzymes for membranes
• mitochondria function

  contains small amounts DNA.

  Energy stored in the bonds of molecules is made available to use by ATP.
• vesicles and lysosomes structure

  one membrane thin sacks with fluid inside

  lysosome - specialised form of vesicle that contain hydrolytic enzymes
• what are hydrolytic enzymes

  break down pathogens
• vesicles and lysosome function

  vesicles transport materials inside the cell

  lysosomes break down waste and pathogens
• cytoskeleton

  network of fibers for shape and stability and mechanical strength- made up of of three components

  microfilaments

  microtubules

  intermediate fibres
• intermediate fibers functions

  gives mechanical strength to cells
• microfilaments functions

  cytokinesis
• Centrioles structure

  paired cylindrical bodies, each composed of nine triplets of microtubules
• centrioles function

  organize DNA during cell division
• flagella and cillia structure

  both long cells. flagella and longer but cillia are present in greater numbers
• flagella and cillia function

  flagella - cell mobility sometimes to detect chemical changes

  cillia - stationary - on the surface for sensory detecting or

  - mobile that beat creating currents so things move
• ribosomes structure

  free floating or attached to an endoplasmic reticulum

  not surrounded by a membrane

  made of RNA in the nucleus of a cell
• ribosomes function and structure

  site if protein synthesis
• endoplasmic reticulum structure


  network of membranes and flattened sacs called cisterae connected to the outer membrane of the nucleus
• smooth endoplasmic reticulum function

  lipid and carbohydrate synthesis and storage
• rough endoplasmic reticulum

  has ribosomes bound to the surface

  synthesis and transport of proteins
• Golgi Apparatus structure

  flattened sack. compact and made of cisternae

  continuously changing

  no ribosomes
• Golgi Apparatus function

  modify proteins after receiving from the ER

  packages them into vesicles and processes proteins
• cellulose cell wall structure

  made of cellulose. freely permeable so substances can pass through it
• cellulose cell wall function


  makes the cell rigid and a defence mechanism against pathogens (in fungi it's made of chitin)
• vacuole structure


  membrane lined sacs containing cell sap and water

  the membrane is called tonoplast and it's selectively permeable so small molecules fit
• vacuole function

  keeps it rigid and turgid
• chloroplasts structure

  double membrane (envelope) with fluid - stroma

  internal network of membranes - thylakoids

  thylakoids stacked to make granum that contain chlorophyll

  grana joined by lamellae

  they also contain dna and ribosomes
• chloroplasts function


  photosynthesis

  found in green parts of plant

  make their own proteins
• is image produced 2D or 3D in TEM?

  2D - electrons pas through
• is image produced 2D or 3D in SEM

  3D - electrons bounce off
• thickness of specimen in TEM

  thin so electrons can pass through
• thickness of specimen in SEM

  can be thicker because electrons only scan the surface
• why must tissues be observed in a vacuum and why is this a disadvantage?

  because air absorbs electrons and because specimens have to be dead
• what is an artefact and give an example and why they are bad

  a structural detail that has appeared by the process of a sample - cracks or air bubbles - they could be confused with real structural details
• why does the light microscope have a limited resolution?

  visible light has a shorter wavelength
• laser scanning microscopes work by:

  adding fluorescent dye to a specimen (maybe lots of different colours), can produce 3d and see objects inside cells
• what is the magnification

  ratio of objects image size to actual size
• resolution


  measure of the clarity of the image or the smallest distance two objects can be apart while still appearing as two objects
• equation for magnification

  magnification = size of image/size of object
• why do we add stain to specimens

  to increase contrast to see organelles better
• lowest to highest magnification

  light, TEM, SEM